Resumen de Molecular and mechanical control of single lumen formation during epithelial morphogenesis by Synaptotagmin-like proteins
Most epithelial organs are made of branching tubules that exert critical functions for the correct functioning of the living organisms. These tubules usually show a complex architecture that consists in a central cavity or lumen surrounded of polarized cells. To reach this geometry, it is necessary the coordination of different cues that come from the surrounding tissues, the extracellular matrix and the cell-cell interaction within the epithelial tissue itself. These cues promote a series of changes in the cells including the activation of transcriptional programs, deep rearrangements of the cytoskeleton, the activation of intracellular membrane trafficking pathways and the remodeling of the cell-cell junctions. How the cells can coordinate all these changes together with the others cells within the tissue it has been largely unknown, and only in the last few years we were beginning to understand this process. Based in changes in the transcriptional program we have developed a functional screening for the identification of previously unknown regulators of epithelial morphogenesis by means of organotypic cultures of MDCKII cells. Moreover, it has been functional and mechanistically characterized the role of one of the regulators in epithelial lumen formation, the protein of the Synaptotagmin-like protein family (Slp), Slp2-a. Together with Slp2-a, other member of the Slp family, Slp4-a, the Rab-GTPases Rab27/3/8 and the SNARE Syntaxin-3 constitute a new trafficking pathway ensures the apical markers are correctly targeted to the nascent apical membranes at early stages of lumen formation. To summarize, Slp2-a coordinate the trafficking of Rab27 positive vesicles to phosphatidylinositol- 4, 5-bisphosphate enriched membrane domains, whereas, Slp4-a controls the fusion of these vesicles through its interaction with Syntaxin-3. Furthermore, this study has been focused in the role these proteins develop in vivo in the zebrafish model. In the zebrafish embryos Slp2 and Slp4 are specifically expressed in the pronephric duct, the developing kidney. More specifically, the silencing of Slp4 by morpholinos impaired renal function in the larvae and causes the abnormal dilation of the distal part of the pronephric duct. Moreover, we have found that Slp4 silencing leads to the decrease of Claudin-2 in MDCKII cells and of Claudin-15a and F in the zebrafish pronephros. We hypothesize that the loss of claudins is responsible of the impaired renal function and the enlargement of the tubule diameter. Summarizing, the present work shows Synaptotagmin-like proteins are important for epithelial morphogenesis, homeostasis and function in both, organotypic cultures and vertebrate developing kidney
