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| Michel Bagnat, PhD
BS,
UAM, Madrid, Spain
PhD,
EMBL, Heidelberg, Germany/UAM
Assistant
Professor, Cell Biology
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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 follows and integrated approach combing forward and reverse genetics and genomics to study tube formation in the gut. Then we use 3D cell culture we translate our findings into the mammalian system.
Our work is aimed at understanding how biological tubes are assembled and maintained as physiologically active systems. We study three main, interrelated questions:
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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
Bagnat Lab Website |
Confocal image of a 5dpf transgenic
zebrafish larva in cross section. |
A
B
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.
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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 shown that single lumen formation in the zebrafish gut tube is genetically controlled and involves the coalescence 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. However, single lumen formation must also involve other cellular processes including complex cell-cell interactions and contact rearrangements. We have identified mutants that fail to form a single lumen. Characterization of these mutants indicates that the affected genes regulate tissue remodeling. Using genomics and reverse genetics we want to define and study new cellular and molecular mechanisms involved in single lumen formation.
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2) Fluid secretion and tube size control: uncovering CFTR regulators
Following a forward genetic screen we identified several mutants in which the gut accumulates fluid and enlarges dramatically. Fluid accumulation is caused by the de-regulation of the CFTR channel. Characterization of these mutants and the cellular process they elicit will help elucidate how the physiological output of the gut epithelium (fluid secretion) contributes to the morphogenesis of the gut tube and will also identify molecular mechanisms regulating the CFTR channel in vivo. We have recently isolated one gene, baobab, that functions as a negative regulator of the CFTR channel and are currently cloning several loci.
3) Apical membrane biogenesis:
The apical surface of tube-forming epithelial cells develops a specialized coat of glycans, the glycocalyx) 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. The gut tube is generated from a solid rod of mesenchymal 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 processes involved in apical membrane biogenesis and tube formation in vivo. |
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Selected
Publications
 Kathryn Ellis, Jennifer Bagwell, Michel Bagnat. (2013). Notochord vacuoles are lysosome-related organelles that function in axis and spine morphogenesis. J. Cell Biol. 200(5):667-679. -PDF-. This article is featured in:
In Focus: Notochord vacuoles make a rod for the vertebrate back. J Cell Biol. 200(5):553 -PDF- and:
-SCIENCENOW: http://news.sciencemag.org/sciencenow/2013/03/video-giant-bubbles-protect-fish.html and:
-Science in the Clouds:
http://scienceintheclouds.blogspot.com/2013/03/giant-bubbles-protect-fish-from_14.html
Navis, A., Marjoram, L. and Bagnat, M. cftr controls lumen expansion and function of Kupffer’s vesicle in zebrafish. Development (In press) (2013).
Bagnat M., Navis A., Herbstreith S., Brand-Arzamendi K., Curado S., Gabriel S., Mostov K., Huisken J., Stainier D.Y. (2010) Cse1l is a negative regulator of CFTR-dependent fluid secretion. Curr. Bio. 20:1840-5.
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.
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