The RhoGEF Cysts couples apical polarity proteins to Rho and myosin activity at adherens junctions

Abstract

The spatio-temporal regulation of small Rho GTPases is crucial for the dynamic stability of epithelial tissues. However, how RhoGTPase activity is controlled during development remains largely unknown. To explore the regulation of Rho GTPases in vivo we analyzed the Rho GTPase guanine nucleotide exchange factor (RhoGEF) Cysts, the Drosophila orthologue of mammalian p114RhoGEF, GEF-H1, p190RhoGEF, and AKAP-13. Loss of Cysts causes a phenotype that closely resemble the mutant phenotype of the apical polarity regulator Crumbs.This phenotype can be suppressed by the loss of basolateral polarity proteins suggesting that Cysts in an integral component of the apical polarity protein network. Cysts activates Rho at adherens junctions to promote junctional enrichment of myosin II, which requires the RhoGEF domain and the coiled-coil domain containing C-terminal region of Cysts. Cysts recruitment to the apico-lateral cortex depends on Crumbs and Bazooka/Par3 and requires multiple domains within Cysts including the C-terminal region. Together, our findings indicate that Cysts links apical polarity proteins to Rho1 and myosin activation at adherens junctions to support junctional and epithelial integrity in the Drosophila ectoderm.

aPKC regulates apical constriction to prevent tissue rupture in the Drosophila follicular epithelium

“…45 Alternatively, aPKC may target other actomyosin regulators or function through other apical polarity proteins implicated in the regulation of apical actomyosin contractility, such as Crumbs and Lulu2/Yurt. 24,41,[45][46][47][48] In line with recent work showing aPKC prevents apical constriction by repressing apical Yurt accumulation, 36 we observed Yurt apical enrichment after optogenetic inactivation of aPKC .…”

“…aPKC is essential for apical-basal polarity and thereby provides spatial cues that position the actomyosin network apically. Other apical polarity proteins can also act as positive regulators of apical constriction, such as Crumbs associated with Yurt 36 or Cysts, 41 and Cdc42, which activates MyoII through MRCK. 24,42 Thus, it is anticipated that whenever a genetic perturbation of aPKC disrupts apical-basal polarity, it would also prevent apical constriction.…”

Apical constriction induces tissue rupture in a proliferative epithelium

“…Phosphorylation of ROCK by aPKC induces its cortical dissociation to downregulate junctional contractility in mammalian cells [26], but aPKC does not regulate equivalent sites in Drosophila Rok [58]. Alternatively, aPKC may target other actomyosin regulators or function through other apical polarity proteins implicated in the regulation of apical contractility, such as Crumbs and Lulu2/Yurt [34,[59][60][61][62][63].…”

“…Rok [58]. Alternatively, aPKC may target other actomyosin regulators or function through other apical polarity proteins implicated in the regulation of apical contractility, such as Crumbs and Lulu2/Yurt [34,[59][60][61][62][63].…”