The Group-I Paks participate in a regulatory network controlling actomyosin contractility in the Drosophila follicular epithelium

Epithelial morphogenesis takes place in response to F-actin modulation, which is regulated by signaling cues from the Rho family of small GTPases and their downstream effectors such as the Group-I p21-activated kinases, Pak and Pak3. The basal F-actin fibres of the Drosophila ovarian follicular epithelium (FE) form parallel bundles that contribute to egg chamber elongation. Pak has been demonstrated to modulate the levels of phosphorylated myosin light chain (pMLC) in the FE, but little is known about Pak3. Here, I present evidence that Pak3 is a major MLC kinase and is repressed by Pak in the elongating FE. In addition, actomyosin contractility promoted by Pak and the Rho1 pathway drives Pak3 expression through the MAL-SRF transcriptional regulatory complex, to ensure there is sufficient active myosin to provide contractility. The more Factin in the FE, the greater the activity of MAL-SRF and consequently the higher the levels of Pak3 and pMLC.