PH Domain-Arf G Protein Interactions Localize the Arf-GEF Steppke for Cleavage Furrow Regulation in XXXX .

@entity1 @entity3007 @entity73307 @entity154 @entity73304 @entity73305 @entity3006 @entity73306 @entity3689 @entity238
UNASSIGNED: The recruitment of @entity3006 / @entity3007 exchange factors (GEFs) to specific subcellular sites dictates where they activate small G proteins for the regulation of various cellular processes. Cytohesins are a conserved family of plasma membrane GEFs for Arf small G proteins that regulate endocytosis. Analyses of @entity1 cytohesins have identified a number of recruitment mechanisms for these multi-domain proteins, but the conservation and developmental roles for these mechanisms are unclear. Here, we report how the pleckstrin homology (PH) domain of the @entity238 cytohesin Steppke affects its localization and activity at cleavage furrows of the early embryo. We found that the PH domain is necessary for Steppke furrow localization, and for it to regulate furrow structure. However, the PH domain was not sufficient for the localization. Next, we examined the role of conserved PH domain @entity3689 residues that are required for @entity1 cytohesins to bind PIP3 or @entity3007 -bound Arf G proteins. We confirmed that the Steppke PH domain preferentially binds PIP3 in vitro through a conserved mechanism. However, disruption of residues for PIP3 binding had no apparent effect on GFP-Steppke localization and effects. Rather, residues for binding to @entity3007 -bound Arf G proteins made major contributions to this Steppke localization and activity. By analyzing GFP-tagged Arf and Arf-like small G proteins, we found that @entity73304 -GFP, @entity73305 -GFP and @entity73306 -GFP, but not @entity73307 -GFP, localized to furrows. However, analyses of embryos depleted of @entity73304 , @entity73305 or @entity73306 revealed either @entity154 than occur in embryos depleted of Steppke, or no detectable @entity154 , possibly because of redundancies, and thus it was difficult to assess how individual Arf small G proteins affect Steppke. Nonetheless, our data show that the Steppke PH domain and its conserved residues for binding to @entity3007 -bound Arf G proteins have substantial effects on Steppke localization and activity in early @entity238 embryos.
