The tyrosine kinase Stitcher activates Grainy head and epidermal wound healing in Drosophila

Abstract

Epidermal injury initiates a cascade of inflammation, epithelial remodelling and integument repair at wound sites. The regeneration of the extracellular barrier and damaged tissue repair rely on the precise orchestration of epithelial responses triggered by the injury. Grainy head (Grh) transcription factors induce gene expression to crosslink the extracellular barrier in wounded flies and mice. However, the activation mechanisms and functions of Grh factors in re-epithelialization remain unknown. Here we identify stitcher (stit), a new Grh target in Drosophila melanogaster. stit encodes a Ret-family receptor tyrosine kinase required for efficient epidermal wound healing. Live imaging analysis reveals that Stit promotes actin cable assembly during wound re-epithelialization. Stit activation also induces extracellular signal-regulated kinase (ERK) phosphorylation along with the Grh-dependent expression of stit and barrier repair genes at the wound sites. The transcriptional stimulation of stit on injury triggers a positive feedback loop increasing the magnitude of epithelial responses. Thus, Stit activation upon wounding coordinates cytoskeletal rearrangements and the level of Grh-mediated transcriptional wound responses.

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

“…In addition, receptor tyrosine kinase signaling is influenced by receptor trafficking, both positively and negatively (Miaczynska et al, 2004;Sadowski et al, 2009). At least two receptor tyrosine kinases, Stitcher and the EGF receptor, participate in Drosophila embryonic wound closure and are therefore potentially important targets of endocytosis (Wang et al, 2009;Geiger et al, 2011).…”

“…Using this system, some of the upstream signals that trigger wound edge actin assembly have been identified. For example, the kinases Stitcher and Src are required for wound edge actin assembly, and the GTPases Rho and Cdc42 regulate formation of the actin cable and protrusions, respectively (Wood et al, 2002;Wang et al, 2009;Tsarouhas et al, 2014). However, the identity of the actin regulators that drive actin assembly at wound edges downstream of these signaling proteins remains largely unknown.…”

Phosphorylation of Grainy head by ERK is essential for wound-dependent regeneration but not for development of an epidermal barrier

“…Mammalian cell culture studies suggest that receptor tyrosine kinases (RTK) are responsible for the wounddependent activation of ERK (32). In Drosophila, stitcher (stit) encodes a Ret-family tyrosine kinase that contributes to transmission of an epidermal wound signal, because null mutations in stit result in a partial inhibition of wound-induced ERK phosphorylation, and reduced activation of wound enhancers in embryonic epidermal cells (33) RTK(s) are responsible for the activation of ERK after epidermal wounding observed in stit null mutant embryos. The PVR RTK is a good candidate because its function has been shown to be required for wound healing in larval epidermal tissue (34).…”

A Targeted UAS-RNAi Screen in Drosophila Larvae Identifies Wound Closure Genes Regulating Distinct Cellular Processes

“…However, because this is the first systematic in vivo approach for screening for postembryonic wound closure defects, it holds great promise for identifying the set of evolutionarily conserved genes required tissue autonomously for wound closure. This is especially the case given the numerous recent studies (Li et al 2003;Galko and Krasnow 2004;Mace et al 2005;Pujol et al 2008;Tong et al 2009;Wang et al 2009;Wu et al 2009) that point to a deep evolutionary conservation in epidermal wound healing responses. Figure 4D).…”