Synaptotagmin-like proteins control the formation of a single apical membrane domain in epithelial cells.

The formation of epithelial tissues requires both the generation of apical-basal polarity and the coordination of this polarity between neighbouring cells to form a central lumen. During de novo lumen formation, vectorial membrane transport contributes to the formation of a singular apical membrane, resulting in the contribution of each cell to only a single lumen. Here, from a functional screen for genes required for three-dimensional epithelial architecture, we identify key roles for synaptotagmin-like proteins 2-a and 4-a (Slp2-a/4-a) in the generation of a single apical surface per cell. Slp2-a localizes to the luminal membrane in a PtdIns(4,5)P(2)-dependent manner, where it targets Rab27-loaded vesicles to initiate a single lumen. Vesicle tethering and fusion is controlled by Slp4-a, in conjunction with Rab27/Rab3/Rab8 and the SNARE syntaxin-3. Together, Slp2-a/4-a coordinate the spatiotemporal organization of vectorial apical transport to ensure that only a single apical surface, and thus the formation of a single lumen, occurs per cell.

p120 catenin is required for normal renal tubulogenesis and glomerulogenesis.

Defects in the development or maintenance of tubule diameter correlate with polycystic kidney disease. Here, we report that absence of the cadherin regulator p120 catenin (p120ctn) from the renal mesenchyme prior to tubule formation leads to decreased cadherin levels with abnormal morphologies of early tubule structures and developing glomeruli. In addition, mutant mice develop cystic kidney disease, with markedly increased tubule diameter and cellular proliferation, and detached luminal cells only in proximal tubules. The p120ctn homolog Arvcf is specifically absent from embryonic proximal tubules, consistent with the specificity of the proximal tubular phenotype. p120ctn knockdown in renal epithelial cells in 3D culture results in a similar cystic phenotype with reduced levels of E-cadherin and active RhoA. We find that E-cadherin knockdown, but not RhoA inhibition, phenocopies p120ctn knockdown. Taken together, our data show that p120ctn is required for early tubule and glomerular morphogenesis, as well as control of luminal diameter, probably through regulation of cadherins.