RhoA and microtubule dynamics control cell–basement membrane interaction in EMT during gastrulation

Abstract

Molecular and cellular mechanisms of epithelial-mesenchymal transition (EMT), crucial in development and pathogenesis, are still poorly understood. Here we provide evidence that distinct cellular steps of EMT occur sequentially during gastrulation. Basement membrane (BM) breakdown is the first recognizable step and is controlled by loss of basally localized RhoA activity and its activator neuroepithelial-transforming-protein-1 (Net1). Failure of RhoA downregulation during EMT leads to BM retention and reduction of its activity in normal epithelium leads to BM breakdown. We also show that this is in part mediated by RhoA-regulated basal microtubule stability. Microtubule disruption causes BM breakdown and its stabilization results in BM retention. We propose that loss of Net1 before EMT reduces basal RhoA activity and destabilizes basal microtubules, causing disruption of epithelial cell-BM interaction and subsequently, breakdown of the BM.

Timing and kinetics of E‐ to N‐cadherin switch during neurulation in the avian embryo

“…1A, B), immunostaining for Ecadherin was strong on the whole surface of all superficial epithelial cells both in the nascent neural plate and in the non-induced epiblast. No Ecadherin was found in the mesoderm, but, as shown previously (Nakaya et al, 2008;Hardy et al, 2011), it was detectable in the primitive streak, in both ingressing and early migrating mesodermal cells. N-cadherin exhibited a reciprocal pattern to E-cadherin, with a strong expression in the mesoderm and a complete exclusion from the neural plate and the epiblast.…”

“…The slow replacement of E-cadherin by N-cadherin in the neural plate contrasts strikingly with the situation found in the primitive streak, where ingressing mesodermal cells express Snail-2 and Brachyury and immediately execute a complete EMT program with breakdown of the basement membrane, loss of cell polarity, and a rapid E-to N-cadherin switch (Sefton et al, 1998;Nakaya et al, 2008;Acloque et al, 2011). Beside Snail-1, Snail-2 is considered as the prototype of EMT inducers.…”

“…In particular, the switch between E-and N-cadherin has been found to play a key role in early morphogenesis and in pathological situations, by promoting the process of epithelium-to-mesenchyme transition (EMT; Wheelock et al, 2008;Thiery et al, 2009). During gastrulation, for example, N-cadherin is up-regulated at the expense of E-cadherin on the surface of nascent mesodermal cells ingressing from the superficial ectoderm into the primitive streak (Ohta et al, 2007;Nakaya et al, 2008;Hardy et al, 2011). Similarly, dissemination of carcinoma cells from primary epithelial tumors is often associated with E-cadherin loss combined with N-cadherin expression, and inappropriate N-cadherin up-regulation in tumor epithelial cells has been shown to promote motility and invasion (Thiery et al, 2009).…”

Zyxin Mediates Actin Fiber Reorganization in Epithelial–Mesenchymal Transition and Contributes to Endocardial Morphogenesis

“…The picture emerging from diverse EMT-related studies suggests that precise molecular and cellular control of EMT is complex and context-dependent (Nakaya et al, 2008). An example of developmentally regulated EMT occurs during the initial stages of cardiac morphogenesis.…”

The guanine nucleotide exchange factor Net1 facilitates the specification of dorsal cell fates in zebrafish embryos by promoting maternal β-catenin activation

“…In Xenopus, Net1 associates with Dishevelled and activates RhoA to regulate gastrulation [38]. In chick gastrulation-stage embryos, reducing Net1 or RhoA expression in epiblast cells prior to the epithelial-to-mesenchymal transition (EMT) leads to ingression and migration defects [39]. In mouse embryos, net1-deficient mammary glands exhibit decreased RhoA-mediated phosphorylation of the regulatory subunits of myosin light chain and myosin light-chain phosphatase, which results in reduced and disorganized ductal branching [40].…”