Title:
Molecular regulation of the basement membrane integrity during EMT in chick gastrulation

Yukiko Nakaya (RIKEN Center for Developmental Biology)

Abstract:
Epithelial-mesenchymal transition (EMT) is a critical process in embryonic development and in many diseases. An important aspect of EMT is the loss of epithelial cell/basement membrane (BM) adhesion accompanied by BM degradation, of which the regulation mechanisms remain unclear. Using chicken gastrulation as an in vivo EMT model, we have previously found that basal microtubules (MTs) in epiblast are required to control cell-BM interaction during EMT.ll- vivo EMTmicrotubule-stabilizing proteins that can mediate the interaction between distal microtubule ends and the cell cortex. Here, we demonstrate that over-expression of CLASP in epiblast leads to BM retention and downregulation of CLASP activity causes ectopic BM breakdown during EMT. These effects are mediated through the CLASP-binding partner, LL5s. Live-imaging using EB1-eGFP revealed that reducing CLASP and LL5 levels in epiblast destabilizes basal MTs. We also show that the transmembrane glycoprotein Dystroglycan’s expression and its functions are tightly correlated with the regulation of BM/basal membrane interaction. Finally, we show that CLASP plays a role in the basal localization of Dystroglycan and these two proteins can bind to each other at the basal cell cortex before cells undergo EMT. Based on these results, we propose that CLASP-mediated anchoring of MTs to the basal side controls basal dystroglycan expression, contributing to the maintenance of BM integrity; disruption of this mechanism leads to BM breakdown during EMT. Furthermore, our recent ongoing studies that highlight the role of the matrix metalloproteinase in BM degradation during EMT will be discussed.