Academic Appointments

  • Basic Life Science Research Associate, Biology

All Publications

  • Separable mechanisms drive local and global polarity establishment in the C. elegans intestinal epithelium. Development (Cambridge, England) Pickett, M. A., Sallee, M. D., Cote, L., Naturale, V. F., Akpinaroglu, D., Lee, J., Shen, K., Feldman, J. L. 2022


    Apico-basolateral polarization is essential for epithelial cells to function as selective barriers and transporters, and to provide mechanical resiliency to organs. Epithelial polarity is established locally, within individual cells to establish distinct apical, junctional, and basolateral domains, and globally, within a tissue where cells coordinately orient their apico-basolateral axes. Using live imaging of endogenously tagged proteins and tissue specific protein depletion in the C. elegans embryonic intestine, we found that local and global polarity establishment are temporally and genetically separable. Local polarity is initiated prior to global polarity and is robust to perturbation. PAR-3 is required for global polarization across the intestine but is not required for establishment of local polarity as small groups of cells are able to establish polarized domains in PAR-3 depleted intestines in an HMR-1/E-cadherin dependent manner. Despite the role of PAR-3 in localizing PKC-3 to the apical surface, we additionally find that PAR-3 and PKC-3/aPKC have distinct roles in the establishment and maintenance of local and global polarity. Together, our results indicate that different mechanisms are required for local and global polarity establishment in vivo.

    View details for DOI 10.1242/dev.200325

    View details for PubMedID 36264257

  • Apical PAR complex proteins protect against programmed epithelial assaults to create a continuous and functional intestinal lumen. eLife Sallee, M. D., Pickett, M. A., Feldman, J. L. 2021; 10


    Sustained polarity and adhesion of epithelial cells is essential for the protection of our organs and bodies, and this epithelial integrity emerges during organ development amidst numerous programmed morphogenetic assaults. Using the developing C. elegans intestine as an in vivo model, we investigated how epithelia maintain their integrity through cell division and elongation to build a functional tube. Live-imaging revealed that apical PAR complex proteins PAR-6/Par6 and PKC-3/aPkc remained apical during mitosis while apical microtubules and microtubule-organizing center (MTOC) proteins were transiently removed. Intestine-specific depletion of PAR-6, PKC-3, and the aPkc regulator CDC-42/Cdc42 caused persistent gaps in the apical MTOC as well as in other apical and junctional proteins after cell division and in non-dividing cells that elongated. Upon hatching, gaps coincided with luminal constrictions that blocked food, and larvae arrested and died. Thus, the apical PAR complex maintains apical and junctional continuity to construct a functional intestinal tube.

    View details for DOI 10.7554/eLife.64437

    View details for PubMedID 34137371

  • Microtubule organization across cell types and states. Current biology : CB Sallee, M. D., Feldman, J. L. 2021; 31 (10): R506-R511


    Encircling and traversing the cell are architectural struts and dynamic intracellular highways made of cylindrical polymers called microtubules. Built from structurally asymmetric subunits of alphabeta-tubulin heterodimers, microtubules have an inherent structural polarity with a slow-growing minus end and a comparatively dynamic plus end that grows and shrinks. Thus, a key feature of microtubules is that each polymer is polarized, allowing for the execution of cellular tasks that are directional in nature. For example, microtubules build polarized highways allowing directional intracellular transport, generate directional force such as in chromosome alignment and segregation, provide structural support for cell shape, and assemble into highly ordered polar structures like centrioles and cilia. The output of these microtubule-based functions is the performance of different tasks, including establishment and maintenance of cellular polarity, secretion and absorption, cell-cell communication, migration, mechanical resiliency, and mitosis. Different cells accomplish these functions by using distinct sites within the cell called microtubule-organizing centers (MTOCs) to build cell-specific microtubule arrangements. While the specific requirement for microtubules in many in vivo cell types is unknown, disrupting even a subset of microtubule-supported functions is often lethal and is associated with many diseases (e.g., cancer and neuropathies), suggesting that specific patterns of microtubule organization are likely important for cellular function in vivo. This Primer focuses on how differentiated animal and plant cells use distinct MTOCs to generate specific microtubule arrangements, how those arrangements support cellular functions, and how cells rearrange their microtubules to accommodate changing cellular tasks.

    View details for DOI 10.1016/j.cub.2021.01.042

    View details for PubMedID 34033781

  • Microtubule organization across cell types and states CURRENT BIOLOGY Sallee, M. D., Feldman, J. L. 2021; 31 (10): R506-R511
  • Visualizing the metazoan proliferation-quiescence decision in vivo. eLife Adikes, R. C., Kohrman, A. Q., Martinez, M. A., Palmisano, N. J., Smith, J. J., Medwig-Kinney, T. N., Min, M., Sallee, M. D., Ahmed, O. B., Kim, N., Liu, S., Morabito, R. D., Weeks, N., Zhao, Q., Zhang, W., Feldman, J. L., Barkoulas, M., Pani, A. M., Spencer, S. L., Martin, B. L., Matus, D. Q. 2020; 9


    Cell proliferation and quiescence are intimately coordinated during metazoan development. Here, we adapt a cyclin-dependent kinase (CDK) sensor to uncouple these key events of the cell cycle in C. elegans and zebrafish through live-cell imaging. The CDK sensor consists of a fluorescently tagged CDK substrate that steadily translocates from the nucleus to the cytoplasm in response to increasing CDK activity and consequent sensor phosphorylation. We show that the CDK sensor can distinguish cycling cells in G1 from quiescent cells in G0, revealing a possible commitment point and a cryptic stochasticity in an otherwise invariant C. elegans cell lineage. Finally, we derive a predictive model of future proliferation behavior in C. elegans based on a snapshot of CDK activity in newly born cells. Thus, we introduce a live-cell imaging tool to facilitate in vivo studies of cell cycle control in a wide-range of developmental contexts.

    View details for DOI 10.7554/eLife.63265

    View details for PubMedID 33350383

  • Visualizing the metazoan proliferation-quiescence decision in vivo ELIFE Adikes, R. C., Kohrman, A. Q., Martinez, M. Q., Palmisano, N. J., Smith, J. J., Medwig-Kinney, T. N., Min, M., Sallee, M. D., Ahmed, O. B., Kim, N., Liu, S., Morabito, R. D., Weeks, N., Zhao, Q., Zhang, W., Feldman, J. L., Barkoulas, M., Pani, A. M., Spencer, S. L., Martin, B. L., Matus, D. Q. 2020; 9
  • 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

  • Tissue-specific degradation of essential centrosome components reveals distinct microtubule populations at microtubule organizing centers. PLoS biology Sallee, M. D., Zonka, J. C., Skokan, T. D., Raftrey, B. C., Feldman, J. L. 2018; 16 (8): e2005189


    Non-centrosomal microtubule organizing centers (ncMTOCs) are found in most differentiated cells, but how these structures regulate microtubule organization and dynamics is largely unknown. We optimized a tissue-specific degradation system to test the role of the essential centrosomal microtubule nucleators gamma-tubulin ring complex (gamma-TuRC) and AIR-1/Aurora A at the apical ncMTOC, where they both localize in Caenorhabditis elegans embryonic intestinal epithelial cells. As at the centrosome, the core gamma-TuRC component GIP-1/GCP3 is required to recruit other gamma-TuRC components to the apical ncMTOC, including MZT-1/MZT1, characterized here for the first time in animal development. In contrast, AIR-1 and MZT-1 were specifically required to recruit gamma-TuRC to the centrosome, but not to centrioles or to the apical ncMTOC. Surprisingly, microtubules remain robustly organized at the apical ncMTOC upon gamma-TuRC and AIR-1 co-depletion, and upon depletion of other known microtubule regulators, including TPXL-1/TPX2, ZYG-9/ch-TOG, PTRN-1/CAMSAP, and NOCA-1/Ninein. However, loss of GIP-1 removed a subset of dynamic EBP-2/EB1-marked microtubules, and the remaining dynamic microtubules grew faster. Together, these results suggest that different microtubule organizing centers (MTOCs) use discrete proteins for their function, and that the apical ncMTOC is composed of distinct populations of gamma-TuRC-dependent and -independent microtubules that compete for a limited pool of resources.

    View details for PubMedID 30080857

  • Tissue-specific degradation of essential centrosome components reveals distinct microtubule populations at microtubule organizing centers PLOS BIOLOGY Sallee, M. D., Zonka, J. C., Skokan, T. D., Raftrey, B. C., Feldman, J. L. 2018; 16 (8)
  • Flipping the switch: regulating MTOC location. Cell cycle (Georgetown, Tex.) Sallee, M. D., Feldman, J. L. 2015; 14 (22): 3519-20

    View details for DOI 10.1080/15384101.2015.1093450

    View details for PubMedID 26375186

    View details for PubMedCentralID PMC4825708