• campus:  a to z index
• map
• directory
• calendar

Search:

Mark Metzstein

Assistant Professor of Human genetics

B.A. University of Cambridge

Ph.D. Massachusetts Institute of Technology

Research

References

markm@genetics.utah.edu

 

Research

We are interested in the mechanisms by which cells form their shapes to build tissues and organs.  To address this question, we are studying the development of the Drosophila tracheal system, an interconnected network of epithelial tubes through which oxygen is delivered to internal tissues.  The branching and tubulogenesis processes in one tracheal cell type, terminal cells, is of particular interest.  These cells show considerable morphological complexity:  each cell forms dozens of fine subcellular branches by a process that involves cytoplasmic extension and bifurcation, and each branch forms an intracellular lumen through which air flows.  This complexity at the single cell level combined with the genetic and molecular tools available in Drosophila represent an excellent opportunity to ask and answer questions important to the understanding of cellular morphogenesis.

To identify genes involved in terminal cell morphogenesis, we performed a large scale genetic screen, using a genetic mosaic approach, to identify mutations affecting terminal cell development.  Mutant cells are identified and examined using GFP to observe cell and branch morphology and bright-field microscopy to observe the subcellular lumen.  In this screen we identified 32 mutations that affect diverse aspects of tracheal terminal cell development, including branch outgrowth, lumen formation and branch/lumen morphogenesis.  Ongoing genetic and molecular analysis of these mutants is uncovering the mechanisms that control cell morphogenesis.

For example, analysis of one of our mutants has revealed a role for vesicle trafficking in formation of the terminal cell intracellular lumen.  We found the gene out of gas (oog), so called because terminal cells mutant for this gene have essentially normal branch outgrowth but do not form lumens, encodes the Drosophila homolog of mammalian Rabconnectin, a protein that was isolated by its ability to bind the GAP and GEF for the small GTP binding protein Rab3.  Rab proteins have diverse functions associated with intracellular vesicle trafficking and function, at least in part, to direct the movement of vesicles to target membranes.  This suggests a model in which oog directs the movement of a specific vesicle population to deliver membrane to the center of the tracheal terminal branches to form the intracellular lumen.  Continuing genetic, molecular, and ultrastructural studies are revealing how oog is involved in directing this targeting.

Genetic analysis of nonsense mediated mRNA decay
In addition to mutants with tracheal defects, the screen identified six mutants in which GFP reporter expression is greatly increased.  We have found that these mutations are in the Drosophila homologs of three components of the nonsense mediated decay (NMD) pathway:  Upf1, Upf2, and Smg1.  The NMD pathway monitors mRNAs to identify transcripts that contain premature stop codons and to target these RNAs for rapid destruction.  Ours are the first Drosophila mutants identified that affect this pathway and we are interested in using these mutations to understand the roles that NMD plays in normal development and to identify the cis acting signals that define which transcripts are to be targeted for degradation.

 

Morphology of a single Drosophila tracheal terminal cell.  Left:  cytoplasmically localized GFP expressed in the terminal cell shows numerous subcellular branches generated by the cell.  Right:  brightfield microscopy of the same cell reveals an air-filled luminal tube running within each branche.

References