Multiple transcription factor codes activate epidermal wound–response genes in Drosophila

Abstract

Wounds in Drosophila and mouse embryos induce similar genetic pathways to repair epidermal barriers. However, the transcription factors that transduce wound signals to repair epidermal barriers are largely unknown. We characterize the transcriptional regulatory enhancers of 4 genes— Ddc , ple , msn , and kkv —that are rapidly activated in epidermal cells surrounding wounds in late Drosophila embryos and early larvae. These epidermal wound enhancers all contain evolutionarily conserved sequences matching binding sites for JUN/FOS and GRH transcription factors, but vary widely in trans - and cis -requirements for these inputs and their binding sites. We propose that the combination of GRH and FOS is part of an ancient wound–response pathway still used in vertebrates and invertebrates, but that other mechanisms have evolved that result in similar transcriptional output. A common, but largely untested assumption of bioinformatic analyses of gene regulatory networks is that transcription units activated in the same spatial and temporal patterns will require the same cis -regulatory codes. Our results indicate that this is an overly simplistic view.

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

“…One gene that is partially required upstream of JNK activation in wound closure is Ced-12, which performs a similar role in thorax closure (Ishimaru et al 2004 RNAi expression also support redundancy. Finally, our results, as do other recent studies (Campos et al 2009;Pearson et al 2009), indicate the importance of DJun-and DFos-mediated transcription following wounding. In our study, differences in morphology, msn-lacZ activation, survival, and fragility of the cuticle (not shown) also suggest that DJun and DFos may not act together but rather serve distinct functions in wound closure.…”

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

“…Because GRH 2E expression did not constitutively activate transcription of GRH target genes in both developmental and wound response contexts, the phosphorylation of GRH alone is not likely to be sufficient for triggering activation of the wound response genes. Given that both GRH and FOS-D are required for the induction of Ddc and msn (26), and that FOS function can be also activated by ERK phosphorylation (30), we believe that wound-induced signaling input through FOS or other transcription factors is also necessary for the transcription of these wound response genes along with the phosphorylation of GRH. Therefore, the ERK-dependent phosphorylation of both GRH and FOS upon injury may activate both transcription factors to synergistically induce many target genes that facilitate epidermal barrier regeneration.…”

“…Immunostaining was done as described (4). Images of wounded embryos were obtained with a Leica SP2 laser-scanning upright confocal microscope, choosing representative embryos as described (26).…”

“…GRH target genes such as Ddc and misshapen (msn) are rapidly transcribed around epidermal wounds where ERK is activated (4,26). Because ERK is also activated in cells surrounding wound sites (4), we hypothesized that phosphorylation of GRH by ERK might be required for activation of epidermal wound response genes.…”

“…We have shown that GRH induces expression of another wound responsive gene msn (26). To monitor GRH activity in wounded epidermal cells, we used a Msn in vivo wound response reporter after epidermal wounding.…”