Research Group of Dr Mickey Marks, University of Pennsylvania School of Medicine

Research Group of Dr Mickey Marks, University of Pennsylvania School of Medicine

Mickey Marks is an Associate Professor in the Department of Pathology and Lab Medicine and the Chair of the Graduate program in Cell Biology and Physiology at the University of Pennsylvania School of Medicine. Mickey’s laboratory is interested in understanding how proteins are delivered to endosomal compartments within cells and how specialized sorting and delivery mechanisms are utilized to generate tissue-specific endosomal organelles.

The central vacuolar system of eukaryotic cells is compartmentalized into distinct membrane-bound organelles and vesicular structures, each with its own characteristic function and set of protein constituents. Work in the Marks laboratory is focused on understanding how integral membrane protein complexes are assembled and sorted to the appropriate compartments within the late secretory and endocytic pathways, and how sorting and assembly contributes to the biogenesis of specific organelles.

Their primary focus is on melanosomes of pigmented cells. Melanosomes are unique lysosome-related organelles present only in cells that make melanin, the major synthesized pigment in mammals. Melanosomes are among a number of tissue-specific lysosome-related organelles that are disrupted in a group of rare heritable disorders, including Hermansky-Pudlak and Chediak-Higashi syndromes, and pigment cell-specific proteins that localize to melanosomes are targets for the immune system in patients with melanoma. In an effort to understand the molecular basis of these diseases and of presentation of melanosomal proteins to the immune system, they are trying to understand how different stage melanosomes are formed and integrated with the endosomal pathway. They use biochemical and morphological approaches to follow the fates of melanosome-specific and ubiquitous endosomal and lysosomal proteins within pigment cells from normal individuals/ mice and disease models.

Mickey received his bachelor’s degree in Biological Sciences from Cornell University , Ithaca NY and his PhD in Immunology/ Microbiology at Duke University , Durham , NC where he worked on the cell biology of antigen processing/ presentation by major histocompatibility complex (MHC) class II molecules under the direction of Peter Cresswell. He did his first postdoctoral fellowship at the National Instiitutes of Health (NIH), National Inst. of Child Health and Human Development (NICHD), Bethesda, MD in the laboratory of Keiko Ozato where he worked on transcription factors regulating MHC class I genes, and discovered that one of them - RXRbeta - was a cofactor for many nuclear hormone receptors. His second postdoctoral research fellowship was also done at the NIH, NICHD in the laboratory of Juan Bonifacino where he returned to the cell biology of antigen processing/ presentation, with more of a focus on endosomal trafficking within the MHC class II pathway. In 1995 he came to the Department of Pathology and Laboratory Medicine at University of Pennsylvania School of Medicine as an Assistant Professor. He was promoted to Associate Professor in 2003, and is currently the Chair of the Graduate program in Cell Biology and Physiology within the cell and Molecular Biology Graduate Group.

The lab uses Openlab to capture images from an inverted microscope, and processes images using either Openlab or Volocity. Their interest is in intracellular protein localization, so they compare the distribution of different markers at the subcellular level. They find that deconvolving a z-series with Volocity Restoration provides better, more representative and more highly resolved images than what they get from a conventional confocal microscope. They use both Volocity Quantitation and the Openlab Morphology bundle to measure the degree of overlap of multiple markers. In addition they also measure the intensity levels on compressed, deconvolved z-series stacks. They plan to use Volocity in the future to improve their live-cell imaging studies of intracellular transport (with GFP/RFP/CFP/YFP-tagged markers).

Mickey writes: "The image deconvolution packages in Openlab and Volocity have given us the tools to distinguish intracellular compartments in melanocytes that are very closely apposed in 3-dimensional space and that could not have otherwise been distinguished - and in a format that even the most inexperienced in my lab can use. We look forward to making more use of the new software upgrade capabilities in dissecting membrane dynamics in real-time to better appreciate membrane transfer between these compartments."

For more information about research in the Marks lab please click here to visit his website.

Immunofluorescence/ light microscopy image of primary melanocytes derived from the skins of newborn C57BL/6J mice.  It shows labeling for a component of the melanosome limiting membrane, Tyrp1, relative to that of a component largely limited to late endosomes/ lysosomes, LAMP-1 (using unlabeled primary antibodies and Alexaflour-conjugated secondary antibodies).  Also shown is a brightfield image, emphasizing the pigmented melanosomes in these cells.  In the insets, the melanosomes are pseudocolored blue to emphasize their colocalization with Tyrp1 and lack thereof with LAMP-1.