Regulated recruitment of SRGAP1 modulates RhoA signaling for contractility during epithelial junction maturation.

Adherens junctions in epithelia are contractile structures, where coupling of adhesion to the actomyosin cytoskeleton generates mechanical tension for morphogenesis and homeostasis. In established monolayers, junctional contractility is supported by the interplay between cell signals and scaffolding proteins. However, less is known about how contractile junctions develop, especially during the establishment of epithelial monolayers. Here, we show that junctional tension increases concomitant with accumulation of actomyosin networks as Caco-2 epithelia become confluent. This is associated with development of a zone of RhoA signaling at junctions. Further, we find that the low levels of RhoA signaling and contractility found in subconfluent cultures reflect a mechanism for their active suppression. Specifically, the RhoA antagonist, SRGAP1, is present at subconfluent junctions to a greater extent than in confluent cultures and SRGAP1 RNAi restores RhoA signaling and contractility in subconfluent cultures to levels seen in confluent cells. Overall, these observations suggest that regulated changes in junctional contractility mediated by modulation of RhoA signaling occur as epithelial monolayers mature.