Matthew Buechner

Regulation of cell shape in nematode tubule formation.

Why are capillaries narrower than an aorta? What regulates the diameter of the various segments of the long nephrons, Schwann cells, and all the other tubes in our bodies?  Our research studies the mechanisms used by epithelial cells to form and regulate the diameter of very narrow tubules.  We use the tiny roundworm Caenorhabditis elegans to look at a series of genes whose function is required to prevent tubules from swelling into fluid-filled cysts.  This roundworm grows quickly on a bacterial lawn on Petri plates, and is clear, so we can watch the development and growth of its renal tubules (called the excretory canals) in living creatures.

We have discovered and cloned a large series of genes named exc that normally maintain the hollow excretory canals as narrow tubules.  These genes encode proteins that surround the hollow (apical) surface of the canals, through which liquid flows.  These proteins include major filaments that make up the structure of cells (cytoskeleton), proteins that regulate flow of ions excreted by this cell (ion channels), and proteins that regulate the movement of small compartments (endosomes) within the cell.  Intriguingly, mutations of the genes result in tubules defective at the apical surface to cause large fluid-filled cysts; but when the proteins are present in very high amounts (i.e. too much of a good thing), the tubules have defects at the outside (basal) surface that cause them to be too short.  We are now using CRISPR gene editing, fluorescence microscopy, and molecular genetics to determine how these components work together to regulate simultaneously the growth, structure, and function of the hollow excretory canals.  Interestingly, the human version of several of these genes are implicated in human developmental diseases, including Charcot-Marie-Tooth Syndrome Type 4H (a Schwann cell disease causing muscular dystrophy) and colon cancer.