Michael (Mickey) Marks


Department of Pathology & Laboratory Medicine, CHOP

Departments of Pathology & Laboratory Medicine and of Physiology, Penn


816G Abramson Research Center

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Eukaryotic cells are 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, how sorting and assembly contribute to the formation of cell type-specific “lysosome-related organelles” (LROs), how these processes impact biological function in the pigmentary, blood clotting, and immune systems, and how they are thwarted by generally rare genetic diseases.


Our main focus is on the biogenesis of melanosomes, the pigment organelles of skin melanocytes and eye pigment epithelia, and understanding the function of genes that are defective in various forms of oculocutaneous albinism. Some of these include genes that impact the formation of other LROs in platelets, dendritic cells, and lung epithelia, among others, and we are trying to understand the similarities and differences in the biogenesis of these organelles.

Marks Image.jpg

Immunofluorescence and bright field microscopy analysis of a fixed pigmented immortalized mouse melanocyte labeled for two components of the melanosome limiting membrane (Tyrosinase, green; TYRP1, red). Pigment granules, visualized by bright field microscopy, are pseudocolored blue. The image was captured by Yueyao Zhu using spinning disk microscopy with a BioVision Yokogawa system on a Leica DMi8 stand, a 100X PlanApo objective, and a Orca Flash 4 CMOS digital camera. Courtesy of Yueyao Zhu, Marks lab.

Image stream of an immortalized mouse melanocyte that has been transduced to express the enhanced green fluorescent protein (EGFP) conjugated to a SNARE fusion protein, VAMP7, and a red fluorescent protein (mCherry) conjugated to another SNARE protein, syntaxin 13 (STX13). STX13 is an early endosomal SNARE, and mCherry-STX13 labels the entire early endosomal network – particularly recycling endosomes. In melanocytes, tubular endosomes that emerge from early endosomal vacuoles ferry transmembrane protein cargoes, such as melanogenic enzymes, to maturing melanosomes. VAMP7 is required for transient fusion of these tubules with melanosomes, and when overexpressed EGFP-VAMP7 resides on melanosomes at steady state. The image stream – captured by spinning disk microscopy with a BioVision Yokogawa system on a Leica DMi8 stand, a 100X PlanApo objective, and a Orca Flash 4 DualView CMOS digital camera at 1 sec intervals between frames – shows an endosomal tubule (red) making transient contacts (note in the middle of the tubule at the center of the field) with VAMP7-containing melanosomes (green for VAMP7; pigment, visualized by bright field microscopy, is pseudocolored blue). Courtesy of Yueyao Zhu, Marks lab.