Serine Proteolytic Pathway Activation Reveals an Expanded Ensemble of Wound Response Genes in Drosophila

Abstract

After injury to the animal epidermis, a variety of genes are transcriptionally activated in nearby cells to regenerate the missing cells and facilitate barrier repair. The range and types of diffusible wound signals that are produced by damaged epidermis and function to activate repair genes during epidermal regeneration remains a subject of very active study in many animals. In Drosophila embryos, we have discovered that serine protease function is locally activated around wound sites, and is also required for localized activation of epidermal repair genes. The serine protease trypsin is sufficient to induce a striking global epidermal wound response without inflicting cell death or compromising the integrity of the epithelial barrier. We developed a trypsin wounding treatment as an amplification tool to more fully understand the changes in the Drosophila transcriptome that occur after epidermal injury. By comparing our array results with similar results on mammalian skin wounding we can see which evolutionarily conserved pathways are activated after epidermal wounding in very diverse animals. Our innovative serine protease-mediated wounding protocol allowed us to identify 8 additional genes that are activated in epidermal cells in the immediate vicinity of puncture wounds, and the functions of many of these genes suggest novel genetic pathways that may control epidermal wound repair. Additionally, our data augments the evidence that clean puncture wounding can mount a powerful innate immune transcriptional response, with different innate immune genes being activated in an interesting variety of ways. These include puncture-induced activation only in epidermal cells in the immediate vicinity of wounds, or in all epidermal cells, or specifically in the fat body, or in multiple tissues.

Spatiotemporal regulation of cell fusion by JNK and JAK/STAT signaling during Drosophila wound healing

“…Our results and those of others highlight that, not only the induction of wound healing responses, but also the confinement of the responses to wound vicinity is under strict genetic control in flies (Juarez et al, 2011;Patterson et al, 2013). While cell fusion, in combination with cell growth, is critically required for epidermal wound closure (Losick et al, 2013), whether too much cell fusion is harmful to proper wound healing is unclear.…”

Toll pathway is required for wound-induced expression of barrier repair genes in the Drosophila epidermis

“…Surprisingly, in this context, spz function was not required (19). Other studies in late stage embryos revealed that clean puncture wounding results in the transcriptional activation of the dorsal and spz genes in epidermal cells adjacent to wounds (20), suggesting their involvement in epidermal wound healing, perhaps in an autoregulatory circuit involved in wound repair.…”

“…Our previous research showed that serine protease function is required and sufficient to activate certain epidermal barrier repair genes after puncture wounding of late stage embryos (20). The activation of epidermal barrier repair genes has been shown to require different combinations of transcription factors (11,12); however, the entire range of signaling pathways genetically required for proper barrier regeneration is still unknown.…”

“…We have not identified the endogenous protease that activates pro-Spz in the context of wound gene activation, so we tested the epistatic relationship of protease activation and spz by treating spz mutant embryos with a concentration of trypsin in the perivitelline space that is sufficient to activate wound repair genes without breaching the epidermal barrier (20).…”

Persephone/Spätzle Pathogen Sensors Mediate the Activation of Toll Receptor Signaling in Response to Endogenous Danger Signals in Apoptosis-deficient Drosophila

“…Our findings extend this theory by showing that Psh is responsible for endogenous DAMP-mediated systemic activation of Toll signaling. The activation of innate immunity-regulated genes including Drs and Mtk was previously observed following serine protease activation in response to wound stimulation (56). Serine protease(s) released from necrotic cells may act to initiate the Psh-dependent Toll signaling pathway.…”