The challenges of abundance: epithelial junctions and small GTPase signalling

Xenopus δ-catenin is essential in early embryogenesis and is functionally linked to cadherins and small GTPases

“…As the appropriate forms of exogenous RhoA or Rac1 could rescue -catenin-knockdown phenotypes, small GTPases are further likely to be involved in producing the depletion effects. As others have indicated, one possibility is that these small GTPases reside downstream of cadherin (Charrasse et al, 2007;Charrasse et al, 2002;Fukuyama et al, 2006;Goodwin et al, 2003;Johnson et al, 2004;Lampugnani et al, 2002;Nakagawa et al, 2001;Nelson and Chen, 2003;Semina et al, 2009;Yap and Kovacs, 2003), such that their reintroduction restores needed downstream signals, possibly even allowing for cadherin function to be likewise rescued (positive feedback) (Braga, 2002;Braga and Yap, 2005). In all cases, the gross effects we observe following -catenin depletion in Xenopus point to its essential role in embryogenesis.…”

Involvement of Rab13 and JRAB/MICAL-L2 in epithelial cell scattering

“…In the case of cell locomotion, the polarized membrane insertion actively drives the cell motility (Bretscher, 1996). RhoA, Rac1 and Cdc42 are principal regulators for the remodeling of actin cytoskeletons and their activation/ inactivation cycles are strictly regulated at AJCs (Braga and Yap, 2005). RhoA is downregulated in confluent epithelial cells, and the decreased RhoA activity is associated with the inactivation of the RhoA guanine nucleotide exchange factor, guanine nucleotide exchange factor (GEF)-H1/Lfc, through binding to the TJ plaque protein cingulin (Aijaz et al, 2005).…”

The catenin family at a glance

“…Small-GTPase actions are often complex, which is due in part to crosstalk between members, and they are context dependent (e.g. effects vary according to cell type) (Braga and Yap, 2005). Even so, RhoA activation is frequently associated with Rhokinase activation, and thereby the promotion of stress-fiber formation and contractility in sessile cells.…”