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Duke Medical Center

Michel Bagnat, PhD
BS, UAM, Madrid, Spain
PhD, EMBL, Heidelberg, Germany/UAM

Assistant Professor, Cell Biology


Bagnat

Cellular mechanisms of tube formation

Our laboratory is interested in studying how basic cellular processes define the shape and size of complex multicellular structures such as organs. Most internal organs are networks of interconnected tubes that transport fluids and cells. Tubes are composed of polarized epithelial cells that serve as barriers between different compartments. Transport of ions, water and various types of substances across body compartments depends on the ability of epithelial cells to develop and maintain a polarized distribution of channels, pores and transporters. During development, physiological functions such as fluid secretion and flow also contribute to organogenesis and epithelial biology. It is therefore important to analyze tissue and organ morphogenesis in a physiologically relevant context using an in vivo model that provides direct experimental access. Using zebrafish as a model system our laboratory studies tube formation in the gut. Our work is aimed at understanding how biological tubes are assembled and maintained as physiologically active systems. We study three main interralated questions.
Email
m.bagnat@cellbio.duke.edu

333B Nanaline Duke Bldg., Box 3709, Duke University Medical Center, Durham, NC 27710

Telephone 919-681-9268
Fax 919-684-5481		 Zebrafish Gut
Confocal image of a 5dpf transgenic
zebrafish larva in cross section.

A
Single Lumen

B
mutant for transcription factor

Single lumen formation is genetically controlled. A) Mutants for the transcription factor tcf2 fail to form a single lumen in the gut. B) tcf2 regulates single lumen formation through a Cldn15 and Na/K-ATPase-dependent fluid accumulation process.

 

 

1) Cellular processes regulating single lumen specification:

Biological tubes are assembled through very diverse developmental processes that generate structures of different shapes and sizes suited for the specific physiological function they perform in organs. However, all biological tubes invariably possess one single lumen. We have recently shown that single lumen formation in the zebrafish gut tube is genetically controlled and involves the colaescence of multiple small lumens into one. This process is driven, at least in part, by the accumulation of fluid. We have characterized the role of two genes involved in fluid accumulation and lumen expansion.  We want to explore the role of ion and water channels in single lumen formation. Single lumen formation must also involve other cellular processes including complex cell-cell interactions and contact rearrangements. We have mutants that fail to form a single lumen. Characterization of these mutants indicates that the affected genes regulate tissue remodelling. Using genomics and reverse genetics we want to define and study new celullar and molecular mechanisms involved in single lumen formation.

 
 

2) Fluid secretion and tube size control:

Following a froward genetic screen we identified several mutants in which the gut accumulates fluid and enlarges dramatically. Fluid accumulation is caused by the de-regulation of an ion channel. Characterization of these mutants and the cellular process they elicit will help uncover  how the physiological output of the gut epithelium (fluid secretion) contributes to the morphogenesis of the gut tube and will also identify molecular mechanisms regulation ion channel function in vivo.

3) Apical membrane biogenesis in vivo:

The apical surface of tube-forming epithelial cells develops a specialized coat of glycans that provides mechanical cohesion and protection against luminal contents. Interestingly, glycosylation also serves as a sorting determinant for many apical membrane proteins, including ion channels, and lipids. In spite of its biological relevance little is known about the mechanism of glycan-mediated sorting. The zebrafish gut provides an excellent model to investigate apical membrane biogenesis. It is generated from a solid rod of mesenchimal cells that differentiate into an epithelium in situ and all epithelial specific proteins are necessarily made de novo. We use forward and reverse genetics and transgenic zebrafish lines to uncover molecular proceses involved in apical membrane biogenesis and tube formation in vivo.
 
   

Selected Publications
Bagnat, M., Cheung I.D, Mostov, K.E., and Stainier D.Y. (2007) Genetic control of single lumen formation in the zebrafish gut. Nat Cell Biol. 9:954-60.

Proszynski T.J., Simons K., and Bagnat M. (2004) O-Glycosylation functions as a sorting determinant for cell surface delivery in Saccharomyces cerevisiae. Mol. Biol. Cell 15,1533-43.

Bagnat M. & Simons K. (2002) Cell surface polarization during yeast mating. Proc Natl Acad Sci USA, 99,14183-14188.

Bagnat M., Chang A., and Simons K. (2001) Plasma membrane proton ATPase Pma1p requires raft association for surface delivery in yeast. Mol. Biol. Cell. 12,4129-38.

Bagnat M., Keranen S., Shevchenko A, Shevchenko A, andSimons K. (2000) Lipid rafts function in biosynthetic delivery of proteins to the cell surface. Proc Natl Acad Sci USA  97,3254-3259.


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