Book Description

Embryos have a striking ability to heal wounds rapidly and without scarring. Embryonic wound repair is a conserved process, driven by polarization of cell-cell junctions and the actomyosin cytoskeleton in the cells around the wound to coordinate cell movements. However, the mechanisms of junctional and cytoskeletal polarization during embryonic wound repair are unclear. To investigate the upstream signals that mediate cell polarization around wounds, I used quantitative in vivo microscopy in Drosophila embryos to show that the endocytic machinery localizes to the wound margin, in a process dependent on calcium and actomyosin contractility. Blocking endocytosis with pharmacological or genetic approaches disrupted wound repair, E- cadherin trafficking, and actomyosin polarization. E-cadherin overexpression also resulted in reduced actin accumulation around wounds and slower wound closure. Reducing E-cadherin levels in embryos in which endocytosis was blocked rescued actin localization to the wound margin. Together, these results demonstrate a central role for endocytosis in wound healing and indicate that polarized E-cadherin endocytosis is necessary for actomyosin remodeling during embryonic wound repair. I next identified reactive oxygen species (ROS) as a critical signal that promotes polarized junctional rearrangements around wounds in Drosophila and zebrafish embryos. Blocking ROS production significantly inhibited wound healing, and severely impaired junctional trafficking and actomyosin accumulation around the wound. ROS can post-translationally modify proteins by oxidizing electron-rich cysteine residues. The Drosophila ortholog of Src kinase, Src42A, contains several putative redox-sensitive cysteines, and has been implicated in E-cadherin trafficking during morphogenesis. I found that embryos mutant for Src42A[C471], a conserved cysteine that is oxidized in zebrafish leukocytes upon wounding, displayed impaired wound healing and myosin polarization, indicating that oxidation of Src42A[C471] is required for efficient tissue repair. Together, my results detail mechanisms by which polarization of junctions and the cytoskeleton are regulated during the coordinated cell movements that drive wound healing in vivo.