Fic, W. | bioRxiv Science

bioRxiv2020

RhoGAP19D inhibits Cdc42 laterally to control epithelial cell shape and prevent invasion

Cdc42-GTP is required for apical domain formation in epithelial cells where it recruits and activates the Par-6/aPKC polarity complex, but how the activity of Cdc42 itself is restricted apically unclear. We used sequence analysis and 3D structure modelling to determine which Drosophila GTPase Activating Proteins (GAPs) are likely to interact with Cdc42 and identified RhoGAP19D as the sole Cdc42GAP required for polarity in the follicle cell epithelium. RhoGAP19D is recruited by -catenin to lateral E-cadherin adhesion complexes, resulting in exclusion of active Cdc42 from the lateral domain. rhogap19d mutants therefore lead to lateral Cdc42 activity, which expands the apical domain through increased Par-6/aPKC activity and stimulates lateral contractility through the myosin light chain kinase, Genghis khan (MRCK). This causes buckling of the epithelium and invasion into the adjacent tissue, a phenotype resembling that of pre-cancerous breast lesions. Thus, RhoGAP19D couples lateral Cadherin adhesion to the apical localisation of active Cdc42, thereby suppressing epithelial invasion.

cell biology↗

bioRxiv2018

Drosophila IMP regulates Kuzbanian to control the timing of Notch signalling in the follicle cells

The timing of Drosophila egg chamber development is controlled by a germline Delta signal that activates Notch in the follicle cells to induce them to cease proliferation and differentiate. Here we report that follicle cells lacking the RNA-binding protein IMP go through one extra division due to a delay in the Delta-dependent S2 cleavage of Notch. The timing of Notch activation has previously been shown to be controlled by cis-inhibition by Delta in the follicle cells, which is relieved when the miRNA pathway represses Delta expression. imp mutants are epistatic to Delta mutants and give an additive phenotype with belle and dicer mutants, indicating that IMP functions independently of both cis-inhibition and the miRNA pathway. We find that the imp phenotype is rescued by over-expression of Kuzbanian, the metalloprotease that mediates the Notch S2 cleavage. Furthermore, Kuzbanian is not enriched at the apical membrane in imp mutants, accumulating instead in late endosomes. Thus, IMP regulates Notch signalling by controlling the localisation of Kuzbanian to the apical domain, where Notch cleavage occurs, revealing a novel regulatory step in the Notch pathway.\n\nSummaryIMP regulates Notch signalling in follicle cells by controlling Kuzbanian localisation to the apical domain, where Notch cleavage occurs, revealing a novel regulatory step in the Notch pathway.

developmental biology↗