Molecular characterization of the immediate wound response of the regenerative solitary ascidian Polycarpa mytiligera

The early stages of injury response create the environment that will promote either regeneration or scarring. Yet, analyses of transcriptional changes after injury were performed only on a handful of regenerative organisms. In this study, on the injury response of the highly regenerative ascidian Polycarpa mytiligera, an emerging model organism, we used the siphon for studying transcriptional changes following injury in regenerating and non-regenerating tissues, and identified a robust gene expression program that is activated at the initial 24 hours post-amputation (hpa). We detected the upregulation of conserved genes, such as BMP1, GHSR and a serine protease inhibitor (PI), expression of which was sustained only in non-regenerating tissue fragments by 24 hpa. We optimized fluorescent in situ hybridization protocol, and detected the majority of BMP1+ cells in the ECM-like tunic covering the animal. Analysis of injuries in other body regions suggested BMP1 may be part of a common wound response program. Our results suggest that initially injury-induced programs are similar across organs, however, distinct genetic profiles are observed between the regenerating and the necroting fragments. Ascidians are the closest relatives of vertebrates, making them an important system for studies of regeneration, and P. mytiligera is the only known solitary ascidian capable of regenerating every body part. The finding that highly conserved genes, found also in vertebrates, are involved in scar-free injury response highlights the importance of studying diverse regenerating and non-regenerating tissues to regeneration, which is essential for identifying targets for inducing tissue regeneration in non-regenerating animals.