Academic Appointments

  • Basic Life Research Scientist, Biology

Current Research and Scholarly Interests

Mechanism of MT polarity establishment during PVD neuron dendrite outgrowing in C. elegans.

All Publications

  • Endoplasmic Reticulum Exit Sites scale with somato-dendritic size in neurons. Molecular biology of the cell Land, R., Fetter, R., Liang, X., Tzeng, C. P., Taylor, C. A., Shen, K. 2023: mbcE23030090


    Nervous systems exhibit dramatic diversity in cell morphology and size. How neurons regulate their biosynthetic and secretory machinery to support such diversity is not well understood. Endoplasmic reticulum exit sites (ERESs) are essential for maintaining secretory flux, and are required for normal dendrite development, but how neurons of different size regulate secretory capacity remains unknown. In C. elegans, we find that the ERES number is strongly correlated with the size of a neuron's dendritic arbor. The elaborately branched sensory neuron, PVD, has especially high ERES numbers. Asymmetric cell division provides PVD with a large initial cell size critical for rapid establishment of PVD's high ERES number before neurite outgrowth, and these ERESs are maintained throughout development. Maintenance of ERES number requires the cell fate transcription factor MEC-3, C. elegans TOR (ceTOR/let-363), and nutrient availability, with mec-3 and ceTOR/let-363 mutant PVDs both displaying reductions in ERES number, soma size, and dendrite size. Notably, mec-3 mutant animals exhibit reduced expression of a ceTOR/let-363 reporter in PVD, and starvation reduces ERES number and somato-dendritic size in a manner genetically redundant with ceTOR/let-363 perturbation. Our data suggest that both asymmetric cell division and nutrient sensing pathways regulate secretory capacities to support elaborate dendritic arbors.

    View details for DOI 10.1091/mbc.E23-03-0090

    View details for PubMedID 37556208

  • Proximity labeling reveals non-centrosomal microtubule-organizing center components required for microtubule growth and localization. Current biology : CB Sanchez, A. D., Branon, T. C., Cote, L. E., Papagiannakis, A., Liang, X., Pickett, M. A., Shen, K., Jacobs-Wagner, C., Ting, A. Y., Feldman, J. L. 2021


    Microtubules are polarized intracellular polymers that play key roles in the cell, including in transport, polarity, and cell division. Across eukaryotic cell types, microtubules adopt diverse intracellular organization to accommodate these distinct functions coordinated by specific cellular sites called microtubule-organizing centers (MTOCs). Over 50 years of research on MTOC biology has focused mainly on the centrosome; however, most differentiated cells employ non-centrosomal MTOCs (ncMTOCs) to organize their microtubules into diverse arrays, which are critical to cell function. To identify essential ncMTOC components, we developed the biotin ligase-based, proximity-labeling approach TurboID for use in C.elegans. We identified proteins proximal to the microtubule minus end protein PTRN-1/Patronin at the apical ncMTOC of intestinal epithelial cells, focusing on two conserved proteins: spectraplakin protein VAB-10B/MACF1 and WDR-62, a protein we identify as homologous to vertebrate primary microcephaly disease protein WDR62. VAB-10B and WDR-62 do not associate with the centrosome and instead specifically regulate non-centrosomal microtubules and the apical targeting of microtubule minus-end proteins. Depletion of VAB-10B resulted in microtubule mislocalization and delayed localization of a microtubule nucleation complex ɣ-tubulin ring complex (gamma-TuRC), while loss of WDR-62 decreased the number of dynamic microtubules and abolished gamma-TuRC localization. This regulation occurs downstream of cell polarity and in conjunction with actin. As this is the first report for non-centrosomal roles of WDR62 family proteins, we expand the basic cell biological roles of this important disease protein. Our studies identify essential ncMTOC components and suggest a division of labor where microtubule growth and localization are distinctly regulated.

    View details for DOI 10.1016/j.cub.2021.06.021

    View details for PubMedID 34242576

  • Growth cone-localized microtubule organizing center establishes microtubule orientation in dendrites. eLife Liang, X., Kokes, M., Fetter, R. D., Sallee, M. D., Moore, A. W., Feldman, J. L., Shen, K. 2020; 9


    A polarized arrangement of neuronal microtubule arrays is the foundation of membrane trafficking and subcellular compartmentalization. Conserved among both invertebrates and vertebrates, axons contain exclusively 'plus-end-out' microtubules while dendrites contain a high percentage of 'minus-end-out' microtubules, the origins of which have been a mystery. Here we show that in Caenorhabditis elegans the dendritic growth cone contains a non-centrosomal microtubule organizing center, which generates minus-end-out microtubules along outgrowing dendrites and plus-end-out microtubules in the growth cone. RAB-11-positive endosomes accumulate in this region and co-migrate with the microtubule nucleation complex gamma-TuRC. The MTOC tracks the extending growth cone by kinesin-1/UNC-116-mediated endosome movements on distal plus-end-out microtubules and dynein clusters this advancing MTOC. Critically, perturbation of the function or localization of the MTOC causes reversed microtubule polarity in dendrites. These findings unveil the endosome-localized dendritic MTOC as a critical organelle for establishing axon-dendrite polarity.

    View details for DOI 10.7554/eLife.56547

    View details for PubMedID 32657271

  • The THO Complex Coordinates Transcripts for Synapse Development and Dopamine Neuron Survival. Cell Maeder, C. I., Kim, J., Liang, X., Kaganovsky, K., Shen, A., Li, Q., Li, Z., Wang, S., Xu, X. Z., Li, J. B., Xiang, Y. K., Ding, J. B., Shen, K. 2018


    Synaptic vesicle and active zone proteins are required for synaptogenesis. The molecular mechanisms for coordinated synthesis of these proteins are not understood. Using forward genetic screens, we identified the conserved THO nuclear export complex (THOC) as an important regulator of presynapse development in C.elegans dopaminergic neurons. In THOC mutants, synaptic messenger RNAs are retained in the nucleus, resulting in dramatic decrease of synaptic protein expression, near complete loss of synapses, and compromised dopamine function. CRE binding protein (CREB) interacts with THOC to mark synaptic transcripts for efficient nuclear export. Deletion of Thoc5, a THOC subunit, in mouse dopaminergic neurons causes severe defects in synapse maintenance and subsequent neuronal death in the substantia nigra compacta. These cellular defects lead to abrogated dopamine release, ataxia, and animal death. Together, our results argue that nuclear export mechanisms can select specific mRNAs and be a rate-limiting step for neuronal differentiation and survival.

    View details for PubMedID 30146163

  • A Dendritic Guidance Receptor Complex Brings Together Distinct Actin Regulators to Drive Efficient F-Actin Assembly and Branching DEVELOPMENTAL CELL Zou, W., Dong, X., Broederdorf, T. R., Shen, A., Kramer, D. A., Shi, R., Liang, X., Miller, D. M., Xiang, Y. K., Yasuda, R., Chen, B., Shen, K. 2018; 45 (3): 362-+


    Proper morphogenesis of dendrites plays a fundamental role in the establishment of neural circuits. The molecular mechanism by which dendrites grow highly complex branches is not well understood. Here, using the Caenorhabditis elegans PVD neuron, we demonstrate that high-order dendritic branching requires actin polymerization driven by coordinated interactions between two membrane proteins, DMA-1 and HPO-30, with their cytoplasmic interactors, the RacGEF TIAM-1 and the actin nucleation promotion factor WAVE regulatory complex (WRC). The dendrite branching receptor DMA-1 directly binds to the PDZ domain of TIAM-1, while the claudin-like protein HPO-30 directly interacts with the WRC. On dendrites, DMA-1 and HPO-30 form a receptor-associated signaling complex to bring TIAM-1 and the WRC to close proximity, leading to elevated assembly of F-actin needed to drive high-order dendrite branching. The synergistic activation of F-actin assembly by scaffolding distinct actin regulators might represent a general mechanism in promoting complex dendrite arborization.

    View details for PubMedID 29738713

  • Dynein and EFF-1 control dendrite morphology by regulating the localization pattern of SAX-7 in epidermal cells JOURNAL OF CELL SCIENCE Zhu, T., Liang, X., Wang, X., Shen, K. 2017; 130 (23): 4063–71


    Our previous work showed that the cell adhesion molecule SAX-7 forms an elaborate pattern in Caenorhabditis elegans epidermal cells, which instructs PVD dendrite branching. However, the molecular mechanism forming the SAX-7 pattern in the epidermis is not fully understood. Here, we report that the dynein light intermediate chain DLI-1 and the fusogen EFF-1 are required in epidermal cells to pattern SAX-7. While previous reports suggest that these two molecules act cell-autonomously in the PVD, our results show that the disorganized PVD dendritic arbors in these mutants are due to the abnormal SAX-7 localization patterns in epidermal cells. Three lines of evidence support this notion. First, the epidermal SAX-7 pattern was severely affected in dli-1 and eff-1 mutants. Second, the abnormal SAX-7 pattern was predictive of the ectopic PVD dendrites. Third, expression of DLI-1 or EFF-1 in the epidermis rescued both the SAX-7 pattern and the disorganized PVD dendrite phenotypes, whereas expression of these molecules in the PVD did not. We also show that DLI-1 functions cell-autonomously in the PVD to promote distal branch formation. These results demonstrate the unexpected roles of DLI-1 and EFF-1 in the epidermis in the control of PVD dendrite morphogenesis.

    View details for PubMedID 29074578

    View details for PubMedCentralID PMC5769588

  • Sarcomeres Pattern Proprioceptive Sensory Dendritic Endings through UNC-52/Perlecan in C. elegans DEVELOPMENTAL CELL Liang, X., Dong, X., Moerman, D. G., Shen, K., Wang, X. 2015; 33 (4): 388-400


    Sensory dendrites innervate peripheral tissues through cell-cell interactions that are poorly understood. The proprioceptive neuron PVD in C. elegans extends regular terminal dendritic branches between muscle and hypodermis. We found that the PVD branch pattern was instructed by adhesion molecule SAX-7/L1CAM, which formed regularly spaced stripes on the hypodermal cell. The regularity of the SAX-7 pattern originated from the repeated and regularly spaced dense body of the sarcomeres in the muscle. The extracellular proteoglycan UNC-52/Perlecan linked the dense body to the hemidesmosome on the hypodermal cells, which in turn instructed the SAX-7 stripes and PVD dendrites. Both UNC-52 and hemidesmosome components exhibited highly regular stripes that interdigitated with the SAX-7 stripe and PVD dendrites, reflecting the striking precision of subcellular patterning between muscle, hypodermis, and dendrites. Hence, the muscular contractile apparatus provides the instructive cues to pattern proprioceptive dendrites.

    View details for DOI 10.1016/j.devcel.2015.03.010

    View details for Web of Science ID 000355151900005

    View details for PubMedID 25982673

  • Conditional targeted genome editing using somatically expressed TALENs in C. elegans. Nature biotechnology Cheng, Z., Yi, P., Wang, X., Chai, Y., Feng, G., Yang, Y., Liang, X., Zhu, Z., Li, W., Ou, G. 2013; 31 (10): 934-7


    We have developed a method for the generation of conditional knockouts in Caenorhabditis elegans by expressing transcription activator-like effector nucleases (TALENs) in somatic cells. Using germline transformation with plasmids encoding TALENs under the control of an inducible or tissue-specific promoter, we observed effective gene modifications and resulting phenotypes in specific developmental stages and tissues. We further used this method to bypass the embryonic requirement of cor-1, which encodes the homolog of human severe combined immunodeficiency (SCID) protein coronin, and we determined its essential role in cell migration in larval Q-cell lineages. Our results show that TALENs expressed in the somatic cells of model organisms provide a versatile tool for functional genomics.

    View details for DOI 10.1038/nbt.2674

    View details for PubMedID 23955274