Par3/Bazooka and phosphoinositides regulate actin protrusion formation during Drosophila dorsal closure and wound healing

Abstract

SUMMARYEffective wound closure mechanisms are essential for maintenance of epithelial structure and function. The repair of wounded epithelia is primarily driven by the cells bordering the wound, which become motile after wounding, forming dynamic actin protrusions along the wound edge. The molecular mechanisms that trigger wound edge cells to become motile following tissue damage are not well understood. Using wound healing and dorsal closure in Drosophila, we identify a direct molecular link between changes in cell-cell adhesion at epithelial edges and induction of actin protrusion formation. We find that the scaffolding protein Par3/Bazooka and the lipid phosphatase Pten are specifically lost from cell-cell junctions at epithelial edges. This results in a localized accumulation of phosphatidylinositol 3,4,5-trisphosphate (PIP3), which promotes the formation of actin protrusions along the epithelial edge. Depleting PIP3 results in defective epithelial closure during both dorsal closure and wound healing. These data reveal a novel mechanism that directly couples loss of epithelial integrity to activation of epithelial closure.

Pvr receptor tyrosine kinase promotes tissue closure by coordinating corpse removal and epidermal zippering

“…tGPH encodes GFP fused to a PIP3-binding PH domain, which relocates to the plasma membrane in response to PIP3 production, reflecting a bias in the opposing enzymatic activities of PI3K and the phosphatase Pten (Britton et al, 2002). During dorsal closure, PIP3 distribution is polarized at the LE interface, driving actin-based protrusive activity to facilitate midline zippering (Pickering et al, 2013). We confirmed this localization and quantified tGPH fluorescence at the LE junctions versus lateral membranes in live wild-type or Pvr mutant embryos.…”

“…In this light, the planar polarized distribution of Pvr at the LE is noteworthy and could differentially impact PI3K signaling components. The effects of Pvr on the magnitude of membrane-associated PIP3 appear distinct, however, from that of Bazooka and Pten phosphatase, which are required to polarize PIP3 distribution in LE cells (Pickering et al, 2013). Altogether, the cumulative defects in hemocyte function, slowing removal of the AS in Pvr mutants, coupled with submaximal PIP3-dependent protrusive activity of the epidermal LE, result in compromised midline zippering, leaving debris-filled dorsal holes and causing cardia bifida.…”

“…Live tGPH-expressing stage 14 embryos were imaged at 40× using identical settings for all genotypes. Projected z-stacks of four slices were quantified in ImageJ with a Profile plot of gray values (Pickering et al, 2013). Fold change was calculated by dividing maximum mean pixel intensity for control and experimental genotypes by mean lateral membrane intensity to control for different background intensities.…”

Endocytosis-dependent coordination of multiple actin regulators is required for wound healing

“…The AJs along the wound edge undergo changes in composition and appearance after wounding, and this remodeling has been proposed to be important in triggering wound responses (Pickering et al, 2013;Carvalho et al, 2014;Tsarouhas et al, 2014;Zulueta-Coarasa The ability to heal wounds efficiently is essential for life. After wounding of an epithelium, the cells bordering the wound form dynamic actin protrusions and/or a contractile actomyosin cable, and these actin structures drive wound closure.…”

Automated multidimensional image analysis reveals a role for Abl in embryonic wound repair

“…Drosophila has emerged as a model to investigate embryonic wound repair (Abreu-Blanco et al, 2012FernandezGonzalez and Zallen, 2013;Kiehart et al, 2000;Pickering et al, 2013;Wood et al, 2002). The genetic tractability of Drosophila allows the use of genetic screening to identify novel molecules implicated in embryonic wound healing (Campos et al, 2010;Juarez et al, 2011).…”