- Clinical Pathology
- Molecular Pathology
- Clinical Laboratory Techniques
Medical Director, Clinical Virology Laboratory (2010 - Present)
Medical Director, Point of Care Testing, Surgery Center at Byers Eye Institute (2012 - Present)
Boards, Advisory Committees, Professional Organizations
Microbiology Resource Committee, College of American Pathologists (2012 - Present)
Training and Education Committee, Association for Molecular Pathology (2013 - Present)
Councilor, Pan American Society for Clinical Virology (2014 - Present)
Residency:Stanford Hospital and Clinics (2010) CA
Medical Education:University of Washington School of Medicine (2007) WA
Board Certification, American Board of Pathology, Clinical Pathology (2012)
Fellowship, Stanford Hospital & Clinics, Molecular Pathology (2010)
Ph.D., University of Washington Medical Scientist Training Program-Fred Hutchinson Cancer Research Center, Molecular and Cellular Biology (2005)
Current Research and Scholarly Interests
Development and application of molecular assays for the diagnosis and management of infectious diseases.
Diagnosis of Febrile Illness in Nigeria
Dengue Virus Detection among Febrile Children Clinically Diagnosed with a non-Dengue Illness
Multiplex Molecular Diagnostics for Undifferentiated Febrile Illness in Brazil
Rio de Janeiro, Brazil
Multiplex Molecular Diagnostics for Undifferentiated Febrile Illness in Sri Lanka
Colombo, Sri Lanka
Multiplex Molecular Diagnostics for Undifferentiated Febrile Illness in Zimbabwe
- Independent Studies (5)
- Sensitive Real-Time PCR Detection of Pathogenic Leptospira spp. and a Comparison of Nucleic Acid Amplification Methods for the Diagnosis of Leptospirosis PLOS ONE 2014; 9 (11)
Improved detection of emerging drug-resistant mutant cytomegalovirus subpopulations by deep sequencing.
Antimicrobial agents and chemotherapy
2014; 58 (8): 4697-4702
In immunosuppressed hosts, the development of multidrug resistance complicates the treatment of cytomegalovirus (CMV) infection. Improved genotypic detection of impending drug resistance may follow from recent technical advances. A severely T-cell-depleted patient with chronic lymphocytic leukemia developed CMV pneumonia and high plasma viral loads that were poorly responsive to antiviral therapy. Serial plasma specimens were analyzed for mutant viral populations by conventional and high-throughput deep-sequencing methods. Uncharacterized mutations were phenotyped for drug resistance using recombinant viruses. Conventional genotyping detected viruses with the UL97 kinase substitution C607Y after ganciclovir treatment, a transient subpopulation of UL54 polymerase L773V mutants first detected 8 weeks after foscarnet was started, and a subpopulation of a mutant with deletion of UL54 codons 981 and 982 2 months after the addition of cidofovir. Deep sequencing of the same serial specimens revealed the same UL54 mutants sooner, along with a more complex evolution of known and newly recognized mutant subpopulations missed by conventional sequencing. The UL54 exonuclease substitutions D413N, K513R, and C539G were newly shown to confer ganciclovir-cidofovir resistance, while L773V was shown to confer foscarnet resistance and add to the ganciclovir resistance conferred by UL97 C607Y. Increased sequencing depth provided a more timely and detailed diagnosis of mutant viral subpopulations that evolved with changing anti-CMV therapy.
View details for DOI 10.1128/AAC.03214-14
View details for PubMedID 24890586
Multiplex Nucleic Acid Amplification Test for Diagnosis of Dengue Fever, Malaria, and Leptospirosis
JOURNAL OF CLINICAL MICROBIOLOGY
2014; 52 (6): 2011-2018
Dengue, leptospirosis, and malaria are among the most common etiologies of systemic undifferentiated febrile illness (UFI) among travelers to the developing world, and these pathogens all have the potential to cause life-threatening illness in returned travelers. The current study describes the development of an internally controlled multiplex nucleic acid amplification test for the detection of dengue virus (DENV) and Leptospira and Plasmodium species, with a specific callout for Plasmodium falciparum (referred to as the UFI assay). During analytical evaluation, the UFI assay displayed a wide dynamic range and a sensitive limit of detection for each target, including all four DENV serotypes. In a clinical evaluation including 210 previously tested samples, the sensitivities of the UFI assay were 98% for DENV (58/59 samples detected) and 100% for Leptospira and malaria (65/65 and 20/20 samples, respectively). Malaria samples included all five Plasmodium species known to cause human disease. The specificity of the UFI assay was 100% when evaluated with a panel of 66 negative clinical samples. Furthermore, no amplification was observed when extracted nucleic acids from related pathogens were tested. Compared with whole-blood samples, the UFI assay remained positive for Plasmodium in 11 plasma samples from patients with malaria (parasitemia levels of 0.0037 to 3.4%). The syndrome-based design of the UFI assay, combined with the sensitivities of the component tests, represents a significant improvement over the individual diagnostic tests available for these pathogens.
View details for DOI 10.1128/JCM.00341-14
View details for Web of Science ID 000337919500028
View details for PubMedID 24671788
Detection of Cytomegalovirus Drug Resistance Mutations by Next-Generation Sequencing
JOURNAL OF CLINICAL MICROBIOLOGY
2013; 51 (11): 3700-3710
Antiviral therapy for cytomegalovirus (CMV) plays an important role in the clinical management of solid organ and hematopoietic stem cell transplant recipients. However, CMV antiviral therapy can be complicated by drug resistance associated with mutations in the phosphotransferase UL97 and the DNA polymerase UL54. We have developed an amplicon-based high-throughput sequencing strategy for detecting CMV drug resistance mutations in clinical plasma specimens using a microfluidics PCR platform for multiplexed library preparation and a benchtop next-generation sequencing instrument. Plasmid clones of the UL97 and UL54 genes were used to demonstrate the low overall empirical error rate of the assay (0.189%) and to develop a statistical algorithm for identifying authentic low-abundance variants. The ability of the assay to detect resistance mutations was tested with mixes of wild-type and mutant plasmids, as well as clinical CMV isolates and plasma samples that were known to contain mutations that confer resistance. Finally, 48 clinical plasma specimens with a range of viral loads (394 to 2,191,011 copies/ml plasma) were sequenced using multiplexing of up to 24 specimens per run. This led to the identification of seven resistance mutations, three of which were present in <20% of the sequenced population. Thus, this assay offers more sensitive detection of minor variants and a higher multiplexing capacity than current methods for the genotypic detection of CMV drug resistance mutations.
View details for DOI 10.1128/JCM.01605-13
View details for Web of Science ID 000325812200035
View details for PubMedID 23985916
Comparison of the FDA-Approved CDC DENV-1-4 Real-Time Reverse Transcription-PCR with a Laboratory-Developed Assay for Dengue Virus Detection and Serotyping
JOURNAL OF CLINICAL MICROBIOLOGY
2013; 51 (10): 3418-3420
Dengue virus (DENV) is the agent of the most common vector-borne disease worldwide. Using 199 clinical samples collected from Nicaragua and Sri Lanka, a laboratory-developed DENV multiplex real-time reverse transcription-PCR (rRT-PCR) proved more clinically sensitive than the FDA-approved CDC assay for DENV serotypes 1 to 4 when measured against a composite reference standard, with sensitivities of 97.4% versus 87.1%, respectively.
View details for DOI 10.1128/JCM.01359-13
View details for Web of Science ID 000324624300039
View details for PubMedID 23903549
Development of an Internally Controlled Real-Time Reverse Transcriptase PCR Assay for Pan-Dengue Virus Detection and Comparison of Four Molecular Dengue Virus Detection Assays
JOURNAL OF CLINICAL MICROBIOLOGY
2013; 51 (7): 2172-2181
A number of diagnostic tests are available for dengue virus (DENV) detection, including a variety of nucleic-acid amplification tests (NAATs). However, reports describing the direct comparison of different NAATs are limited. In this study, we report the design of an internally-controlled, real-time reverse-transcriptase PCR (rRT-PCR) that detects all four DENV serotypes but does not distinguish between them (the pan-DENV assay). Two-hundred clinical samples were then tested using four different DENV RT-PCR assays: the pan-DENV assay; a commercially-produced, internally-controlled DENV rRT-PCR (the Altona assay); a widely-used hemi-nested RT-PCR; and a serotype-specific, multiplex rRT-PCR assay. The pan-DENV assay had a linear range extending from 7.0 to 1.0 log10 complimentary DNA (cDNA) equivalents/μL and a lower limit of 95% detection ranging from 1.7 to 7.6 cDNA equivalents/μL depending on the serotype. When measured against a composite reference standard, the pan-DENV assay proved more clinically sensitive than either the Altona or hemi-nested assays, with a sensitivity of 98.0% compared to 72.3% and 78.8%, respectively (p≤0.0001 for both comparisons). The pan-DENV assay detected DENV in significantly more samples collected on or after day five of illness and in a subgroup of patients with detectable anti-DENV IgM at presentation. No significant difference in sensitivity was observed between the pan-DENV assay and the multiplex rRT-PCR, despite the presence of an internal control in the former. The detection of DENV RNA late in the course of clinical illness should serve to lengthen the period during which a confirmed, molecular diagnosis of DENV infection can be provided.
View details for DOI 10.1128/JCM.00548-13
View details for Web of Science ID 000320595800024
View details for PubMedID 23637298
- Single-Reaction, Multiplex, Real-Time RT-PCR for the Detection, Quantitation, and Serotyping of Dengue Viruses PLOS NEGLECTED TROPICAL DISEASES 2013; 7 (4)
Single-reaction, multiplex, real-time rt-PCR for the detection, quantitation, and serotyping of dengue viruses.
PLoS neglected tropical diseases
2013; 7 (4)
Dengue fever results from infection with one or more of four different serotypes of dengue virus (DENV). Despite the widespread nature of this infection, available molecular diagnostics have significant limitations. The aim of this study was to develop a multiplex, real-time, reverse transcriptase-PCR (rRT-PCR) for the detection, quantitation, and serotyping of dengue viruses in a single reaction.An rRT-PCR assay targeting the 5' untranslated region and capsid gene of the DENV genome was designed using molecular beacons to provide serotype specificity. Using reference DENV strains, the assay was linear from 7.0 to 1.0 log₁₀ cDNA equivalents/µL for each serotype. The lower limit of detection using genomic RNA was 0.3, 13.8, 0.8, and 12.4 cDNA equivalents/µL for serotypes 1-4, respectively, which was 6- to 275-fold more analytically sensitive than a widely used hemi-nested RT-PCR. Using samples from Nicaragua collected within the first five days of illness, the multiplex rRT-PCR was positive in 100% (69/69) of specimens that were positive by the hemi-nested assay, with full serotype agreement. Furthermore, the multiplex rRT-PCR detected DENV RNA in 97.2% (35/36) of specimens from Sri Lanka positive for anti-DENV IgM antibodies compared to just 44.4% (16/36) by the hemi-nested RT-PCR. No amplification was observed in 80 clinical samples sent for routine quantitative hepatitis C virus testing or when genomic RNA from other flaviviruses was tested.This single-reaction, quantitative, multiplex rRT-PCR for DENV serotyping demonstrates superior analytical and clinical performance, as well as simpler workflow compared to the hemi-nested RT-PCR reference. In particular, this multiplex rRT-PCR detects viral RNA and provides serotype information in specimens collected more than five days after fever onset and from patients who had already developed anti-DENV IgM antibodies. The implementation of this assay in dengue-endemic areas has the potential to improve both dengue diagnosis and epidemiologic surveillance.
View details for DOI 10.1371/journal.pntd.0002116
View details for PubMedID 23638191
Improved serotype-specific dengue virus detection in Trinidad and Tobago using a multiplex, real-time RT-PCR.
Diagnostic microbiology and infectious disease
2015; 81 (2): 105-106
Dengue virus (DENV) transmission occurs throughout the Caribbean, though laboratory confirmation and epidemiologic surveillance are limited by the availability of serotype-specific molecular diagnostics. In this study, we show that a serotype-specific DENV multiplex, real-time reverse transcriptase-PCR (RT-PCR) detected DENV RNA in significantly more samples (82/182) than a reference hemi-nested RT-PCR (57/182; P=0.01).
View details for DOI 10.1016/j.diagmicrobio.2014.10.001
View details for PubMedID 25533614
- Commutability of the Epstein-Barr Virus WHO International Standard across Two Quantitative PCR Methods JOURNAL OF CLINICAL MICROBIOLOGY 2014; 52 (10): 3802-3804
Encephalitis caused by chikungunya virus in a traveler from the kingdom of tonga.
Journal of clinical microbiology
2014; 52 (9): 3459-3461
Febrile travelers from countries with unique endemic pathogens pose a significant diagnostic challenge. In this report, we describe the case of a Tongan man presenting with fever, rash, and altered mental status. The diagnosis of Chikungunya encephalitis was made using a laboratory-developed real-time RT-PCR and serologic testing.
View details for DOI 10.1128/JCM.01288-14
View details for PubMedID 24958800
- Reply to "Inconclusive reverse transcription-PCR assay comparison for dengue virus detection and serotyping". Journal of clinical microbiology 2014; 52 (5): 1801-1802
Evaluation of serial urine viral cultures for the diagnosis of cytomegalovirus infection in neonates and infants.
Pediatric and developmental pathology
2014; 17 (3): 176-180
Cytomegalovirus (CMV) is the most common cause of congenital infection worldwide. Urine viral culture is the standard for CMV diagnosis in neonates and infants. The objectives of this study were to compare the performance of serial paired rapid shell vial cultures (SVC) and routine viral cultures (RVC), and to determine the optimal number of cultures needed to detect positive cases. From 2001 to 2011, all paired CMV SVC and RVC performed on neonates and infants less than 100 days of age were recorded. Testing episodes were defined as sets of cultures performed within 7 days of one another. A total of 1264 neonates and infants underwent 1478 testing episodes; 68 (5.4%) had at least one episode with a positive CMV culture. In episodes where CMV was detected before day 21 of life, the first specimen was positive in 100% (16/16) of cases. When testing occurred after 21 days of life, the first specimen was positive in 82.7% (43/52) of cases, requiring three cultures to reach 100% detection. The SVC was more prone to assay failure than RVC. Overall, when RVC was compared to SVC, there was 86.0% positive agreement and 99.9% negative agreement. In conclusion, three serial urine samples are necessary for detection of CMV in specimens collected between day of life 22 and 99, while one sample may be sufficient on or before day of life 21. Though SVC was more sensitive than RVC, the risk of SVC failure supports the use of multimodality testing to optimize detection.
View details for DOI 10.2350/14-01-1432-OA.1
View details for PubMedID 24617645
- Profound plasmacytosis in a patient with dengue. International journal of hematology 2013; 98 (5): 518-519
Diagnosis of Congenital CMV Using PCR Performed on Formalin-fixed, Paraffin-embedded Placental Tissue
AMERICAN JOURNAL OF SURGICAL PATHOLOGY
2013; 37 (9): 1413-1420
Congenital cytomegalovirus (CMV) infection may be asymptomatic until hearing loss manifests in childhood. Because diagnosis of congenital CMV requires viral detection within an infant's first 21 days of life, CMV polymerase chain reaction (PCR) on formalin-fixed, paraffin-embedded (FFPE) placental tissue provides a unique opportunity to identify congenital exposure in cases in which CMV is not initially suspected. To assess the utility of this approach, a database of all CMV cultures performed from July 2001 to March 2012 was used to identify infants in whom urine CMV cultures were obtained within 100 days of life. Corresponding placentas were then identified through the pathology database. The database was also queried to identify placentas in which CMV immunohistochemical analysis had been performed. CMV PCR was positive in FFPE placental tissue from 100% (5/5) of cases in which the first urine culture collected before the first 21 days of life was positive. Placentas from 20 infants with negative CMV urine cultures were CMV PCR negative. Interestingly, CMV was detected in 12.5% (1/8) of placentas in which the first CMV-positive urine culture was collected after the first 21 days of life. Furthermore, 4% (1/26) of placentas with chronic villitis by histology (no urine cultures available) were CMV PCR positive. In the 10 CMV PCR-positive placentas, including 3 cases of fetal demise, CMV immunohistochemistry was positive in just 6 cases. These results suggest that the confirmation of CMV exposure in utero by PCR of FFPE placental tissue provides a useful adjunct to histologic evaluation and may identify infants requiring close clinical follow-up.
View details for Web of Science ID 000330429800016
A Comparison of CMV Detection in Gastrointestinal Mucosal Biopsies Using Immunohistochemistry and PCR Performed on Formalin-fixed, Paraffin-embedded Tissue
AMERICAN JOURNAL OF SURGICAL PATHOLOGY
2013; 37 (7): 995-1000
Cytomegalovirus (CMV) can precipitate and exacerbate gastrointestinal (GI) mucosal injury. The gold standard for CMV detection in formalin-fixed, paraffin-embedded (FFPE) tissue is immunohistochemistry (IHC). Although CMV polymerase chain reaction (PCR) on fresh tissue may be a valuable adjunct to IHC, its utility is unknown for FFPE tissues. We therefore evaluated quantitative, real-time CMV PCR in a total of 102 FFPE GI biopsy specimens from 74 patients with a history of hematopoietic stem cell or solid organ transplant, inflammatory bowel disease, human immunodeficiency virus infection, or unspecified colitis. CMV DNA was detected by PCR in 90.9% (30/33) of IHC-positive, 14.5% (8/55) of IHC-negative, and 20.0% (1/5) of IHC-equivocal FFPE tissues. Quantitation of CMV DNA copies normalized to β-globin demonstrated a wide range of values (median 0.276; range, 0.0004 to 144.50). Importantly, 93.3% (14/15) of patients with IHC-positive, active colitis showed no evidence of CMV in matched concurrent, histologically normal biopsies tested by PCR. These results suggest that CMV PCR on FFPE GI biopsies complements IHC and has the potential to identify additional patients who may benefit from anti-CMV therapy.
View details for Web of Science ID 000330377200007
View details for PubMedID 23648457
p16 Is Superior to ProEx C in Identifying High-grade Squamous Intraepithelial Lesions (HSIL) of the Anal Canal
AMERICAN JOURNAL OF SURGICAL PATHOLOGY
2013; 37 (5): 659-668
Although the incidence of human papillomavirus (HPV)-associated anal neoplasia is increasing, interobserver and intraobserver reproducibility in the grading of biopsy specimens from this area remains unacceptably low. Attempts to produce a more reproducible grading scheme have led to the use of biomarkers for the detection of high-risk HPV (HR-HPV). We evaluated the performance of standard morphology and biomarkers p16, ProEx C, and Ki-67 in a set of 75 lesions [17 nondysplastic lesions, 23 low-grade squamous intraepithelial lesions (LSIL)/condyloma, 20 high-grade squamous intraepithelial lesions (HSIL), 15 invasive squamous cell carcinomas] from the anal and perianal region in 65 patients and correlated these findings with HPV subtype on the basis of a type-specific multiplex real-time polymerase chain reaction assay designed to detect HR-HPV. A subset of cases with amplifiable HPV DNA was also sequenced. HSIL was typically flat (15/20), and only a minority (4/20) had koilocytes. In contrast, only 1 LSIL was flat (1/23), and the remainder were exophytic. The majority of LSIL had areas of koilocytic change (20/23). HR-HPV DNA was detected in the majority (89%) of invasive carcinomas and HSIL biopsies, 86% and 97% of which were accurately labeled by strong and diffuse block-positive p16 and ProEx C, respectively. LSIL cases, however, only infrequently harbored HR-HPV (13%); most harbored low-risk HPV (LR-HPV) types 6 and 11. Within the LSIL group, p16 outperformed ProEx C, resulting in fewer false-positive cases (5% vs. 75%). Ki-67 was also increased in HR-HPV-positive lesions, although biopsies with increased inflammation and reactive changes also showed higher Ki-67 indices. These data suggest that strong and diffuse block-positive nuclear and cytoplasmic labeling with p16 is a highly specific biomarker for the presence of HR-HPV in anal biopsies and that this finding correlates with high-grade lesions.
View details for DOI 10.1097/PAS.0b013e31828706c0
View details for Web of Science ID 000317663100005
View details for PubMedID 23552383
An International Collaboration to Harmonize the Quantitative Plasma Epstein-Barr Virus DNA Assay for Future Biomarker-Guided Trials in Nasopharyngeal Carcinoma
CLINICAL CANCER RESEARCH
2013; 19 (8): 2208-2215
Persistently elevated posttreatment plasma EBV DNA is a robust predictor of relapse in nasopharyngeal carcinoma (NPC). However, assay standardization is necessary for use in biomarker-driven trials. We conducted a study to harmonize the method between four centers with expertise in EBV DNA quantitation.Plasma samples of 40 patients with NPC were distributed to four centers. DNA was extracted and EBV DNA copy number was determined by real-time quantitative PCR (BamHI-W primer/probe). Centers used the same protocol but generated their own calibrators. A harmonization study was then conducted using the same calibrators and PCR master mix and validated with ten pooled samples.The initial intraclass correlations (ICC) for the first 40 samples between each center and the index center were 0.62 [95% confidence interval (CI): 0.39-0.78], 0.70 (0.50-0.83), and 0.59 (0.35-0.76). The largest variability was the use of different PCR master mixes and calibrators. Standardization improved ICC to 0.83 (0.5-0.95), 0.95 (0.83-0.99) and 0.96 (0.86-0.99), respectively, for ten archival frozen samples. For fresh plasma with spiked-in EBV DNA, correlations were more than 0.99 between the centers. At 5 EBV DNA copies per reaction or above, the coefficient of variance (CV) was less than 10% for the cycle threshold (Ct) among all centers, suggesting this concentration can be reliably used as a cutoff for defining the presence of detectable EBV DNA.Quantitative PCR assays, even when conducted in experienced clinical labs, can yield large variability in plasma EBV DNA copy numbers without harmonization. The use of common calibrators and PCR master mix can help to reduce variability.
View details for DOI 10.1158/1078-0432.CCR-12-3702
View details for Web of Science ID 000317597500029
CMV antigenemia and quantitative viral load assessments in hematopoietic stem cell transplant recipients
JOURNAL OF CLINICAL VIROLOGY
2013; 56 (2): 108-112
Sensitive and reliable diagnostic tests are essential for the prevention of cytomegalovirus (CMV) disease after hematopoietic stem cell transplantation (HSCT). pp65 antigenemia and polymerase chain reaction (PCR) assays are commonly used to monitor CMV in HSCT recipients. However, there is considerable intra- and inter-laboratory variability in the results, which impact comparability and clinical practice. OBJECTIVES/STUDY DESIGN: Using 380 samples from 135 HSCT recipients, we compared the new FDA approved quantitative PCR assay, COBAS(®) AmpliPrep/COBAS(®) TaqMan(®) CMV test (CAP/CTM CMV test) developed and standardized using the 1st WHO International Standard for CMV with pp65 antigenemia and COBAS(®) AMPLICOR MONITOR CMV tests.The median time between transplantation and testing samples was 57 days (range, 0-207 days). The median CMV load (log(10)) was 3.17 IU/mL (3.21 copies/mL). Among samples with detectable CMV load, 52% were negative by pp65 antigenemia. CMV loads were higher in pp65 antigenemia-positive than in negative samples. One pp65-antigenemia-positive cell per 100,000 leukocytes corresponded to a median CMV load of 1200 IU/mL. CMV loads determined by the CAP/CTM CMV test were slightly lower than the ones by the AMPLICOR MONITOR CMV test (-0.15 [95% CI, -0.18 to -0.13] copies/mL), but slope differences indicated only limited co-linearity.The CAP/CTM CMV test is more sensitive than pp65 antigenemia and the AMPLICOR MONITOR CMV test in HSCT recipients. The lower limit of quantification and co-linearity with the international WHO standard renders the CAP/CTM CMV test suitable for future clinical trials defining viral load thresholds of CMV therapy.
View details for DOI 10.1016/j.jcv.2012.10.001
View details for Web of Science ID 000313565100004
View details for PubMedID 23146665
An International Multicenter Performance Analysis of Cytomegalovirus Load Tests
CLINICAL INFECTIOUS DISEASES
2013; 56 (3): 367-373
Quantification of cytomegalovirus (CMV) load is central to the management of CMV infections in immunocompromised patients, but quantitative results currently differ significantly across methods and laboratories.The COBAS AmpliPrep/COBAS TaqMan CMV Test (CAP/CTM CMV test), developed using the first World Health Organization CMV standard in the calibration process, was compared to local assays used by 5 laboratories at transplant centers in the United States and Europe. Blinded plasma panels (n = 90) spiked with 2.18-6.7 log(10) copies/mL and clinical plasma samples from immunocompromised patients (n = 660) were tested.Observed mean panel member concentrations by site and 95% confidence intervals (CIs) of the data combined across sites were narrower for CAP/CTM CMV test compared with local assays. The 95% CI in log(10) copies/mL of the combined data per panel member for CAP/CTM CMV test vs comparator assays was .17 vs 1.5 at 2.18 log(10) copies/mL; .14 vs .52 at 2.74 log(10) copies/mL; .16 vs .6 at 3.3 log(10) copies/mL; .2 vs 1.11 at 4.3 log(10) copies/mL; .21 vs 1.13 at 4.7 log(10) copies/mL; and .18 vs 1.4 at 6.7 log(10) copies/mL. In clinical specimens, constant and variable quantification differences between the CAP/CTM CMV test and comparator assays were observed.High interlaboratory agreement and precision of CAP/CTM CMV test results across 5 different laboratories over 4 orders of magnitude suggest that this assay could be valuable in prospective studies identifying clinical viral load thresholds for CMV treatment.
View details for DOI 10.1093/cid/cis900
View details for Web of Science ID 000313617400014
View details for PubMedID 23097587
Severe Hepatitis Associated with an Echovirus 18 Infection in an Immune-Compromised Adult
JOURNAL OF CLINICAL MICROBIOLOGY
2013; 51 (2): 684-687
Enteroviruses are recognized as important pathogens in pediatric patients; however, they are often overlooked as etiologic agents of disease in adults. Here, we report a case of echovirus 18-associated severe systemic infection and acute liver failure in an adult hematopoietic stem cell transplant recipient. Additionally, we illustrate the utility of molecular methods for the detection and typing of enteroviral infections.
View details for DOI 10.1128/JCM.02405-12
View details for Web of Science ID 000314108000055
View details for PubMedID 23175267
Laboratory-Developed L1 Sequencing and Type-Specific, Real-Time Polymerase Chain Reaction for the Detection and Typing of Human Papillomaviruses in Formalin-Fixed, Paraffin-Embedded Tissues
ARCHIVES OF PATHOLOGY & LABORATORY MEDICINE
2013; 137 (1): 50-54
The detection and typing of high-risk and low-risk human papillomavirus (HPV) in archival formalin-fixed, paraffin-embedded tissues by nucleic acid amplification testing is an important adjunct to immunohistochemical staining in evaluation of squamous cell proliferations of the oropharynx, larynx, and anal canal.To evaluate semiautomated, xylene-free extraction from formalin-fixed, paraffin-embedded tissues combined with laboratory-developed HPV L1 sequencing and type-specific HPV 6, 11, 16, and 18 real-time polymerase chain reaction for identification and typing of HPV in the clinical laboratory.We evaluated the adequacy of extraction using β-globin amplification and compared L1 sequencing and real-time polymerase chain reaction methods for typing accuracy using 68 formalin-fixed, paraffin-embedded tissues, including 56 anorectal biopsy or surgical resection specimens and 12 laryngeal papilloma specimens from patients with recurrent respiratory papillomatosis.Adequate DNA was obtained from 68 of 68 specimens analyzed and all were HPV positive. In 47 cases where L1 sequencing demonstrated that the predominant HPV type was 6, 11, 16, or 18, type-specific, real-time polymerase chain reaction provided concordant results. Sequencing revealed additional low-risk (HPV 40) and high-risk HPV types (HPV 31, 33, 56, and 58) in anorectal specimens, whereas HPV 6 or 11 were the types found in laryngeal papillomas.Both L1 sequencing and type-specific, real-time polymerase chain reaction are suitable methods for routine HPV testing of formalin-fixed, paraffin-embedded tissues in a clinical laboratory setting.
View details for DOI 10.5858/arpa.2011-0392-OA
View details for Web of Science ID 000313625100009
View details for PubMedID 23276174
Comparison of Xpert Flu rapid nucleic acid testing with rapid antigen testing for the diagnosis of influenza A and B
JOURNAL OF VIROLOGICAL METHODS
2012; 186 (1-2): 137-140
Influenza infections are associated with thousands of hospital admissions and deaths each year. Rapid detection of influenza is important for prompt initiation of antiviral therapy and appropriate patient triage. In this study the Cepheid Xpert Flu assay was compared with two rapid antigen tests, BinaxNOW Influenza A & B and BD Directigen EZ Flu A+B, as well as direct fluorescent antibody testing for the rapid detection of influenza A and B. Using real-time, hydrolysis probe-based, reverse transcriptase PCR as the reference method, influenza A sensitivity was 97.3% for Xpert Flu, 95.9% for direct fluorescent antibody testing, 62.2% for BinaxNOW, and 71.6% for BD Directigen. Influenza B sensitivity was 100% for Xpert Flu and direct fluorescent antibody testing, 54.5% for BinaxNOW, and 48.5% for BD Directigen. Specificity for influenza A was 100% for Xpert Flu, BinaxNOW, and BD Directigen, and 99.2% for direct fluorescent antibody testing. All methods demonstrated 100% specificity for influenza B. These findings support the use of the Xpert Flu assay in settings requiring urgent diagnosis of influenza A and B.
View details for DOI 10.1016/j.jviromet.2012.07.023
View details for Web of Science ID 000312763600024
View details for PubMedID 22841669
Clinical Significance of Low Cytomegalovirus DNA Levels in Human Plasma
JOURNAL OF CLINICAL MICROBIOLOGY
2012; 50 (7): 2378-2383
The clinical significance of the detection of low copy numbers of cytomegalovirus (CMV) DNA in immune-suppressed patients remains unclear. In this study, we compared the artus CMV Rotor-Gene PCR, utilizing an automated nucleic acid extraction and assay setup (the artus CMV protocol), with the COBAS Amplicor CMV Monitor test (our reference protocol). We then analyzed the results of all CMV PCR tests ordered following the implementation of the artus CMV protocol at our institution and followed 91 adult patients with positive test results. The artus CMV protocol had a linear range extending from 2.0 to 7.0 log(10) copies/ml and had a lower limit of 95% detection of 57 copies/ml. With archived plasma samples, this protocol demonstrated 100% sensitivity and 94% specificity for the detection of CMV DNA. Following implementation of the artus CMV protocol, 320 of 1,403 (22.8%) plasma samples tested positive (compared with 323/3,579 [9.0%] samples in the preceding 6 months), and 227 (16.2%) samples had copy numbers of <400/ml. Ninety-one adult patients had at least one positive test. The data were analyzed using a threshold of 200 copies/ml, and in 22 episodes, the viral load increased from <200 copies/ml to ? 200 copies/ml on sequential tests. In 21 of these 22 episodes, either the viral load continued to increase or antiviral treatment was initiated in response to the repeat value. In summary, we evaluate the performance characteristics of a protocol utilizing the artus CMV PCR and identify clinically meaningful changes in CMV DNA copy numbers even when they are initially detected at a low level.
View details for DOI 10.1128/JCM.06800-11
View details for Web of Science ID 000307360800033
View details for PubMedID 22518866
Quantitation of Human Papillomavirus DNA in Plasma of Oropharyngeal Carcinoma Patients
INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS
2012; 82 (3): E351-E358
To determine whether human papillomavirus (HPV) DNA can be detected in the plasma of patients with HPV-positive oropharyngeal carcinoma (OPC) and to monitor its temporal change during radiotherapy.We used polymerase chain reaction to detect HPV DNA in the culture media of HPV-positive SCC90 and VU147T cells and the plasma of SCC90 and HeLa tumor-bearing mice, non-tumor-bearing controls, and those with HPV-negative tumors. We used real-time quantitative polymerase chain reaction to quantify the plasma HPV DNA in 40 HPV-positive OPC, 24 HPV-negative head-and-neck cancer patients and 10 non-cancer volunteers. The tumor HPV status was confirmed by p16(INK4a) staining and HPV16/18 polymerase chain reaction or HPV in situ hybridization. A total of 14 patients had serial plasma samples for HPV DNA quantification during radiotherapy.HPV DNA was detectable in the plasma samples of SCC90- and HeLa-bearing mice but not in the controls. It was detected in 65% of the pretreatment plasma samples from HPV-positive OPC patients using E6/7 quantitative polymerase chain reaction. None of the HPV-negative head-and-neck cancer patients or non-cancer controls had detectable HPV DNA. The pretreatment plasma HPV DNA copy number correlated significantly with the nodal metabolic tumor volume (assessed using (18)F-deoxyglucose positron emission tomography). The serial measurements in 14 patients showed a rapid decline in HPV DNA that had become undetectable at radiotherapy completion. In 3 patients, the HPV DNA level had increased to a discernable level at metastasis.Xenograft studies indicated that plasma HPV DNA is released from HPV-positive tumors. Circulating HPV DNA was detectable in most HPV-positive OPC patients. Thus, plasma HPV DNA might be a valuable tool for identifying relapse.
View details for DOI 10.1016/j.ijrobp.2011.05.061
View details for Web of Science ID 000300423500003
View details for PubMedID 21985946
- A Synonymous Change in the Influenza A Virus Neuraminidase Gene Interferes with PCR-Based Subtyping and Oseltamivir Resistance Mutation Detection JOURNAL OF CLINICAL MICROBIOLOGY 2011; 49 (8): 3101-3102
Ultrasensitive Detection of Drug-Resistant Pandemic 2009 (H1N1) Influenza A Virus by Rare-Variant-Sensitive High-Resolution Melting-Curve Analysis
JOURNAL OF CLINICAL MICROBIOLOGY
2011; 49 (7): 2602-2609
Oseltamivir (Tamiflu), an oral neuraminidase inhibitor, has been widely used to treat pandemic 2009 (H1N1) influenza A. Although a majority of 2009 (H1N1) influenza A virus remains oseltamivir susceptible, the threat of resistance due to the His275Tyr mutation is highlighted by the limitations of alternative therapies and the potential for rapid, global fixation of this mutation in the circulating influenza A virus population. In order to better understand the emergence of resistance, we developed a rare-variant-sensitive high-resolution melting-curve analysis method (RVS-HRM) that is able to detect the His275Tyr oseltamivir resistance mutation to 0.5% in a background of susceptible virus. We applied RVS-HRM to clinical specimens from patients who developed oseltamivir resistance and demonstrated the ultrasensitive detection of influenza A virus N1 neuraminidase quasispecies. Interestingly, we were unable to detect the oseltamivir resistance mutation in pretreatment samples, suggesting that resistant virus does not reach even this very low detection threshold until exposed to selective drug pressure. Thus, patients naive to oseltamivir are most likely to be susceptible when this drug is used as a first-line treatment modality.
View details for DOI 10.1128/JCM.00277-11
View details for Web of Science ID 000292276200035
View details for PubMedID 21543559
Long-term Shedding of Influenza A Virus in Stool of Immunocompromised Child
EMERGING INFECTIOUS DISEASES
2010; 16 (7): 1165-1167
In immunocompromised patients, influenza infection may progress to prolonged viral shedding from the respiratory tract despite antiviral therapy. We describe chronic influenza A virus infection in an immunocompromised child who had prolonged shedding of culturable influenza virus in stool.
View details for DOI 10.3201/eid1607.091248
View details for Web of Science ID 000279522200024
View details for PubMedID 20587197
Real-Time PCR Testing for mecA Reduces Vancomycin Usage and Length of Hospitalization for Patients Infected with Methicillin-Sensitive Staphylococci
JOURNAL OF CLINICAL MICROBIOLOGY
2010; 48 (3): 785-790
Nucleic acid amplification tests (NAATs) have revolutionized infectious disease diagnosis, allowing for the rapid and sensitive identification of pathogens in clinical specimens. Real-time PCR testing for the mecA gene (mecA PCR), which confers methicillin resistance in staphylococci, has the added potential to reduce antibiotic usage, improve clinical outcomes, lower health care costs, and avoid emergence of drug resistance. A retrospective study was performed to identify patients infected with methicillin-sensitive staphylococcal isolates who were receiving vancomycin treatment when susceptibility results became available. Vancomycin treatment and length of hospitalization were compared in these patients for a 6-month period before and after implementation of mecA PCR. Among 65 and 94 patients identified before and after mecA PCR, respectively, vancomycin usage (measured in days on therapy) declined from a median of 3 days (range, 1 to 44 days) in the pre-PCR period to 1 day (range, 0 to 18 days) in the post-PCR period (P < 0.0001). In total, 38.5% (25/65) of patients were switched to beta-lactam therapy in the pre-PCR period, compared to 61.7% (58/94) in the post-PCR period (P = 0.004). Patient hospitalization days also declined from a median of 8 days (range, 1 to 47 days) in the pre-PCR period to 5 days (range, 0 to 42 days) in the post-PCR period (P = 0.03). Real-time PCR testing for mecA is an effective tool for reducing vancomycin usage and length of stay of hospitalized patients infected with methicillin-sensitive staphylococci. In the face of ever-rising health care expenditures in the United States, these findings have important implications for improving outcomes and decreasing costs.
View details for DOI 10.1128/JCM.02150-09
View details for Web of Science ID 000274996200016
View details for PubMedID 20071556
Preferential Lower Respiratory Tract Infection in Swine-Origin 2009 A(H1N1) Influenza
CLINICAL INFECTIOUS DISEASES
2010; 50 (3): 391-394
We report a case of 2009 influenza A(H1N1) virus infection in which virus was detected predominantly in specimens from the lower respiratory tract but was absent or at very low levels in nasopharyngeal swab samples. This presentation suggests that, in certain hosts or for particular variants of 2009 A(H1N1) virus, the lower respiratory tract may be the preferred site of infection.
View details for DOI 10.1086/649875
View details for Web of Science ID 000273500300014
View details for PubMedID 20047483
First documentation of isoniazid reversion in Mycobacterium tuberculosis
INTERNATIONAL JOURNAL OF TUBERCULOSIS AND LUNG DISEASE
2009; 13 (11): 1347-1354
Drug-resistant strains of Mycobacterium tuberculosis are increasing worldwide and pose a major threat to global health. However, it remains unsettled whether drug-resistant mutants are fixed in the bacterial population or if they would revert in the absence of drug pressure.To document the occurrence of isoniazid (INH) reversion in a patient with multidrug-resistant tuberculosis (TB) and investigate its association with fitness cost.Genotypic and phenotypic assays were used to characterize the reversion of INH resistance in isolates from a patient with pulmonary TB. The pre-reversion katG mutation was reconstructed in a pan-susceptible laboratory strain (H37Rv DeltakatG::katG W300G) and tested for susceptibility to INH and oxidative stress.Genotyping and drug susceptibility testing showed that an isogenic strain of M. tuberculosis reverted from an INH-resistant to a susceptible phenotype in the absence of INH therapy. The genotypic basis of this reversion was mapped to the katG codon 300 which reverted from GGG (glycine, G) to a wild-type codon, TGG (tryptophan, W). The H37Rv DeltakatG::katG W300G mutant was resistant to INH, but also showed a deficiency in coping with oxidative stress.This study confirms that, in the absence of INH pressure, some INH-resistant mutants will revert to a drug-susceptible phenotype. This finding may have broader implications for INH-resistant strains and for the clinically useful lifespan of INH.
View details for Web of Science ID 000271883400007
View details for PubMedID 19861005
Comparison of Real-Time PCR and Conventional Biochemical Methods for Identification of Staphylococcus lugdunensis
JOURNAL OF CLINICAL MICROBIOLOGY
2009; 47 (11): 3472-3477
Staphylococcus lugdunensis is an aggressive, virulent member of the coagulase-negative staphylococci (CoNS) that is responsible for severe, rapidly progressive skin and soft tissue infections and native valve endocarditis. To facilitate prompt identification and appropriate therapy, we describe here a rapid and robust multiplex real-time PCR assay that is able to definitively distinguish S. lugdunensis from other staphylococci. Using melting curve analysis, the assay also identifies Staphylococcus aureus and CoNS other than S. lugdunensis and determines MecA-dependent resistance to methicillin (meticillin). When applied to a panel of well-characterized staphylococcal reference strains, as well as 165 clinical isolates previously identified by conventional methods, the assay was both sensitive and specific for S. lugdunensis, correctly identifying the reference strain and all 47 S. lugdunensis isolates without inappropriate amplification of other staphylococci. Furthermore, rapid biochemical identification using the WEE-TAB system to detect ornithine decarboxylase activity was found to be unsuitable as an alternative to PCR identification, displaying just 31% sensitivity and 77% specificity when tested on a subset (90 isolates) of the clinical strains. We therefore propose that this simple, accurate PCR approach will allow for the routine and timely identification of S. lugdunensis in the clinical microbiology laboratory.
View details for DOI 10.1128/JCM.00342-09
View details for Web of Science ID 000271373000013
View details for PubMedID 19741081
Protein Phosphatase 1 Regulates Exit from the Spindle Checkpoint in Budding Yeast
2009; 19 (14): 1182-1187
Accurate chromosome segregation depends on sister kinetochores coming under tension when they make bioriented attachments to microtubules from opposite poles. The spindle checkpoint halts the cell cycle in response to defects in generating proper attachments or tension on kinetochores, although the precise signal that triggers the checkpoint is unclear because tension and attachment are coupled. The target of the checkpoint is the Cdc20 protein, which initiates the anaphase-promoting complex (APC)-dependent degradation of the anaphase inhibitor Pds1/securin. Although the molecular details of spindle checkpoint activation are still being elucidated, phosphorylation by at least four kinases is a crucial requirement. However, less is known about the mechanisms that silence the checkpoint after kinetochores biorient. Here, we show that the catalytic subunit of the budding yeast protein phosphatase 1 (PP1) homolog, Glc7, regulates exit from the checkpoint. Glc7 overexpression prevents spindle checkpoint activation in response to both tension and attachment defects. Although glc7 mutant cells are able to efficiently release from a non-checkpoint-mediated metaphase arrest, they are uniquely sensitive to transient spindle checkpoint activation as a result of a failure in spindle checkpoint exit. We therefore propose that PP1 activity silences the checkpoint by reversing key phosphorylation events.
View details for DOI 10.1016/j.cub.2009.06.043
View details for Web of Science ID 000268530200024
View details for PubMedID 19592248
Hair Sheep Blood, Citrated or Defibrinated, Fulfills All Requirements of Blood Agar for Diagnostic Microbiology Laboratory Tests
2009; 4 (7)
Blood agar is used for the identification and antibiotic susceptibility testing of many bacterial pathogens. In the developing world, microbiologists use human blood agar because of the high cost and inhospitable conditions for raising wool sheep or horses to supply blood. Many pathogens either fail to grow entirely or exhibit morphologies and hemolytic patterns on human blood agar that confound colony recognition. Furthermore, human blood can be hazardous to handle due to HIV and hepatitis. This study investigated whether blood from hair sheep, a hardy, low-maintenance variety of sheep adapted for hot climates, was suitable for routine clinical microbiology studies.Hair sheep blood obtained by jugular venipuncture was anticoagulated by either manual defibrination or collection in human blood bank bags containing citrate-phosphate-dextrose. Trypticase soy 5% blood agar was made from both forms of hair sheep blood and commercial defibrinated wool sheep blood. Growth characteristics, colony morphologies, and hemolytic patterns of selected human pathogens, including several streptococcal species, were evaluated. Specialized identification tests, including CAMP test, reverse CAMP test, and satellite colony formation with Haemophilus influenzae and Abiotrophia defectiva were also performed. Mueller-Hinton blood agar plates prepared from the three blood types were compared in antibiotic susceptibility tests by disk diffusion and E-test.The results of all studies showed that blood agar prepared from citrated hair sheep blood is suitable for microbiological tests used in routine identification and susceptibility profiling of human pathogens. The validation of citrated hair sheep blood eliminates the labor-intensive and equipment-requiring process of manual defibrination. Use of hair sheep blood, in lieu of human blood currently used by many developing world laboratories and as an alternative to cost-prohibitive commercial sheep blood, offers the opportunity to dramatically improve the safety and accuracy of laboratory diagnosis of pathogenic bacteria in resource-poor countries.
View details for DOI 10.1371/journal.pone.0006141
View details for Web of Science ID 000267806300010
View details for PubMedID 19578541
Bartholin's abscess caused by hypermucoviscous Klebsiella pneumoniae
JOURNAL OF MEDICAL MICROBIOLOGY
2009; 58 (5): 671-673
Klebsiella pneumoniae serogroups displaying the hypermucoviscosity phenotype are associated with a distinct clinical syndrome characterized by liver abscesses, bacteraemia and metastatic lesions. We describe here what we believe to be the first reported case of hypermucoviscous K. pneumoniae causing a superficial Bartholin's abscess in the absence of systemic involvement.
View details for DOI 10.1099/jmm.0.006734-0
View details for Web of Science ID 000266018900019
View details for PubMedID 19369531
Multiplex real-time PCR assay for rapid identification of Mycobacterium tuberculosis complex members to the species level
JOURNAL OF CLINICAL MICROBIOLOGY
2008; 46 (7): 2241-2246
The species identification of members of the Mycobacterium tuberculosis complex is critical to the timely initiation of both appropriate antibiotic therapy and proper public health control measures. However, the current commercially available molecular assays identify mycobacteria only to the complex level and are unable to differentiate M. tuberculosis from the closely related M. bovis and M. bovis BCG. We describe here a rapid and robust two-step, multiplex, real-time PCR assay based on genomic deletions to definitively identify M. tuberculosis, M. bovis, M. bovis BCG, and other members of the complex. When tested against a panel of well-characterized mycobacterial reference strains, the assay was both sensitive and specific, correctly identifying all strains. We applied this assay to 60 clinical isolates previously identified as M. tuberculosis complex and found 57 M. tuberculosis isolates and 3 M. bovis BCG isolates from patients who had received intravesical BCG. Furthermore, analysis of 15 clinical specimens previously identified as M. bovis by spoligotyping revealed an isolate of M. tuberculosis that had been misidentified. We propose that this assay will allow the routine identification of M. tuberculosis complex members in the clinical laboratory.
View details for DOI 10.1128/JCM.00347-08
View details for Web of Science ID 000258906800016
View details for PubMedID 18508937
Glc7/protein phosphatase 1 regulatory subunits can oppose the Ipl1/aurora protein kinase by redistributing Glc7
MOLECULAR AND CELLULAR BIOLOGY
2006; 26 (7): 2648-2660
Faithful chromosome segregation depends on the opposing activities of the budding yeast Glc7/PP1 protein phosphatase and Ipl1/Aurora protein kinase. We explored the relationship between Glc7 and Ipl1 and found that the phosphorylation of the Ipl1 substrate, Dam1, was altered by decreased Glc7 activity, whereas Ipl1 levels, localization, and kinase activity were not. These data strongly suggest that Glc7 ensures accurate chromosome segregation by dephosphorylating Ipl1 targets rather than regulating the Ipl1 kinase. To identify potential Glc7 and Ipl1 substrates, we isolated ipl1-321 dosage suppressors. Seven genes (SDS22, BUD14, GIP3, GIP4, SOL1, SOL2, and PEX31) encode newly identified ipl1 dosage suppressors, and all 10 suppressors encode proteins that physically interact with Glc7. The overexpression of the Gip3 and Gip4 suppressors altered Glc7 localization, indicating they are previously unidentified Glc7 regulatory subunits. In addition, the overexpression of Gip3 and Gip4 from the galactose promoter restored Dam1 phosphorylation in ipl1-321 mutant cells and caused wild-type cells to arrest in metaphase with unsegregated chromosomes, suggesting that Gip3 and Gip4 overexpression impairs Glc7's mitotic functions. We therefore propose that the overexpression of Glc7 regulatory subunits can titrate Glc7 away from relevant Ipl1 targets and thereby suppress ipl1-321 cells by restoring the balance of phosphatase/kinase activity.
View details for DOI 10.1128/MCB.26.7.2648-2660.2006
View details for Web of Science ID 000236312200017
View details for PubMedID 16537909
The Ipl1-Aurora protein kinase activates the spindle checkpoint by creating unattached kinetochores
NATURE CELL BIOLOGY
2006; 8 (1): 78-U28
The spindle checkpoint ensures accurate chromosome segregation by delaying cell-cycle progression until all sister kinetochores capture microtubules from opposite poles and come under tension (for reviews, see refs 1, 2). Although the checkpoint is activated by either the lack of kinetochore-microtubule attachments or defects in the tension exerted by microtubule-generated forces, it is not clear whether these signals are linked. We investigated the connection between tension and attachment by studying the conserved budding yeast Ipl1Aurora protein kinase that is required for checkpoint activation in the absence of tension but not attachment. Here, we show that spindle-checkpoint activation in kinetochore mutants that seem to have unattached kinetochores depends on Ipl1 activity. When Ipl1 function was impaired in these kinetochore mutants, the attachments were restored and the checkpoint was turned off. These data indicate that Ipl1 activates the checkpoint in response to tension defects by creating unattached kinetochores. Moreover, although the Dam1 kinetochore complex has been implicated as a key downstream target, we found the existence of unidentified Ipl1 sites on Dam1 or additional important substrates that regulate both microtuble detachment and the checkpoint.
View details for DOI 10.1038/ncb1341
View details for Web of Science ID 000234651500015
View details for PubMedID 16327780
The spindle checkpoint: tension versus attachment
TRENDS IN CELL BIOLOGY
2005; 15 (9): 486-493
The spindle checkpoint ensures the fidelity of chromosome segregation by preventing cell-cycle progression until all the chromosomes make proper bipolar attachments to the mitotic spindle and come under tension. Despite significant advances in our understanding of spindle checkpoint function, the primary signal that activates the spindle checkpoint remains unclear. Whereas some experiments indicate that the checkpoint recognizes the lack of microtubule attachment to the kinetochore, others indicate that the checkpoint senses the absence of tension generated on the kinetochore by microtubules. The interdependence between tension and microtubule attachment make it difficult to determine whether these signals are separable. In this article (which is part of the Chromosome Segregation and Aneuploidy series), we consider recent evidence that supports and opposes the hypothesis that defects in tension act as the primary checkpoint signal.
View details for DOI 10.1016/j.tcb.2005.07.005
View details for Web of Science ID 000232333700006
View details for PubMedID 16084093
An Mtw1 complex promotes kinetochore biorientation that is monitored by the lpl1/Aurora protein kinase
2003; 5 (5): 735-745
Chromosome segregation depends on kinetochore biorientation so that sister kinetochores attach to microtubules from opposite poles and come under tension. The budding yeast Ipl1/Aurora protein kinase allows the absence of tension to activate the spindle checkpoint. We found that checkpoint activation in the mtw1-1 kinetochore mutant requires Ipl1p, suggesting that Mtw1p promotes tension. We isolated mtw1-1 dosage suppressors and identified Dsn1, a kinetochore protein that immunoprecipitates with the Mif2/CENP-C and Cse4/CENP-A proteins, as well as the Mtw1, Nnf1, and Nsl1 kinetochore proteins. mtw1 and dsn1 mutant strains exhibit similar phenotypes, suggesting that Mtw1p and Dsn1p act together. Although mtw1 mutant cells contained unattached chromosomes, attachment was restored by impairing Ipl1p function. These results suggest that mtw1 mutant kinetochores are competent to bind microtubules but Ipl1p generates unattached chromosomes. We therefore propose that an Mtw1 complex is required for kinetochore biorientation that is monitored by the Ipl1p kinase.
View details for Web of Science ID 000186544400011
View details for PubMedID 14602074
Top-SUMO wrestles centromeric cohesion
2002; 3 (1): 4-6
Sister chromatid cohesion at the centromere is distinct from cohesion at the chromosome arms. In the June issue of Molecular Cell, Bachant et al. have shown that centromeric cohesion in budding yeast is specifically regulated by SUMO-1 modification of Topoisomerase II.
View details for Web of Science ID 000176769500003
View details for PubMedID 12110161
Nlk is a murine protein kinase related to Erk/MAP kinases and localized in the nucleus
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1998; 95 (3): 963-968
Extracellular-signal regulated kinases/microtubule-associated protein kinases (Erk/MAPKs) and cyclin-directed kinases (Cdks) are key regulators of many aspects of cell growth and division, as well as apoptosis. We have cloned a kinase, Nlk, that is a murine homolog of the Drosophila nemo (nmo) gene. The Nlk amino acid sequence is 54. 5% similar and 41.7% identical to murine Erk-2, and 49.6% similar and 38.4% identical to human Cdc2. It possesses an extended amino-terminal domain that is very rich in glutamine, alanine, proline, and histidine. This region bears similarity to repetitive regions found in many transcription factors. Nlk is expressed as a 4. 0-kb transcript at high levels in adult mouse brain tissue, with low levels in other tissues examined, including lung, where two smaller transcripts of 1.0 and 1.5 kb are expressed as well. A 4.0-kb Nlk message is also present during embryogenesis, detectable at day E10. 5, reaching maximal steady state levels at day E12.5, and then decreasing. Nlk transiently expressed in COS7 cells is a 60-kDa kinase detectable by its ability to autophosphorylate. Mutation of the ATP-binding Lys-155 to methionine abolishes its ability to autophosphorylate, as does mutation of a putative activating threonine in kinase domain VIII, to valine, aspartic, or glutamic acid. Subcellular fractionation indicates that 60-70% of Nlk is localized to the nucleus, whereas 30-40% of Nlk is cytoplasmic. Immunofluorescence microscopy confirms that Nlk resides predominantly in the nucleus. Nlk and Nmo may be the first members of a family of kinases with homology to both Erk/MAPKs and Cdks.
View details for Web of Science ID 000071878500031
View details for PubMedID 9448268