Developmental regulation of epithelial polarization by pre-mRNA splicing

Abstract
The apical membrane of epithelial cells in the intestine play critical roles in physiology and homeostasis. Many
specialized functions of intestinal epithelial cells, such as nutrient absorption, depend on faithfully sorting proteins
to the apical membrane during biosynthetic delivery. However, the cellular mechanisms driving apical membrane
protein sorting and how it matures during development are poorly defined. Also unknown is what controls the
onset of apical endocytosis in Lysosome Rich Enterocytes (LREs). To discover mechanisms of apical membrane
polarization in vivo, we performed a forward genetics screen for factors required for sorting of a model apical
cargo (O-glycan-GFP, Og-GFP) in the zebrafish intestine. We isolated distinct classes of mutants affecting apical
Og-GFP sorting. Our preliminary data has uncovered a pH-dependent mechanism for sorting membrane proteins
in subapical endosomes either to the degradative pathway or to the apical membrane. We also discovered a role
for regulated pre-mRNA intron splicing in activating apical membrane transport pathways crucial for polarized
protein delivery in enterocytes and for apical endocytosis in LREs of the developing intestine. Our studies will
uncover genetic and cellular mechanisms crucial for the maturation of a fully polarized and physiologically active
epithelium in the vertebrate gut.

Grant Number: 5R01DK132120-04
NIH Institute/Center: NIH
Principal Investigator: Michel Bagnat