Epithelial polarity requires septin coupling of vesicle transport to polyglutamylated microtubules

Abstract

In epithelial cells, polarized growth and maintenance of apical and basolateral plasma membrane domains depend on protein sorting from the trans-Golgi network (TGN) and vesicle delivery to the plasma membrane. Septins are filamentous GTPases required for polarized membrane growth in budding yeast, but whether they function in epithelial polarity is unknown. Here, we show that in epithelial cells septin 2 (SEPT2) fibers colocalize with a subset of microtubule tracks composed of polyglutamylated (polyGlu) tubulin, and that vesicles containing apical or basolateral proteins exit the TGN along these SEPT2/polyGlu microtubule tracks. Tubulin-associated SEPT2 facilitates vesicle transport by maintaining polyGlu microtubule tracks and impeding tubulin binding of microtubule-associated protein 4 (MAP4). Significantly, this regulatory step is required for polarized, columnar-shaped epithelia biogenesis; upon SEPT2 depletion, cells become short and fibroblast-shaped due to intracellular accumulation of apical and basolateral membrane proteins, and loss of vertically oriented polyGlu microtubules. We suggest that septin coupling of the microtubule cytoskeleton to post-Golgi vesicle transport is required for the morphogenesis of polarized epithelia.

Tubulin detyrosination promotes monolayer formation and apical trafficking in epithelial cells

“…Cytoskeletal tracks can further be characterized by the alignment with small GTP-binding septins. Spiliotis et al have shown that septin-2 coupling of polyglutamylated microtubules to post-Golgi vesicle transport is required for the morphogenesis of polarized MDCK cells (Spiliotis et al, 2008).…”

Shaping microtubules into diverse patterns: Molecular connections for setting up both ends

“…The septin tracks also facilitate post-Golgi vesicle transport by antagonizing MAP4, which has an inhibitory role in vesicle transport. This regulatory step is required for columnar-shaped epithelial morphogenesis [Spiliotis et al, 2008].…”

sept7b is essential for pronephric function and development of left–right asymmetry in zebrafish embryogenesis

“…Septins were originally discovered in a screen for temperature-sensitive cell division mutants in yeast (Hartwell, 1971). There are 14 septin genes in humans (Hall et al, 2005;Peterson et al, 2007), which play roles in mitosis (Spiliotis et al, 2005), vesicle trafficking (Beites et al, 1999;Spiliotis et al, 2008) and membrane compartmentalization in specialized structures -such as the primary cilium (Hu et al, 2010;Kim et al, 2010).…”