Regenerative capacity differs greatly across organisms and the ability to regenerate declines as morphological complexity increases. Within the chordate phylum, vertebrate animals exhibits a very limited regenerative potential, however, the sea squirt Botrylloides leachi is a chordate with a remarkable ability to undergo whole body regeneration (WBR). A fully functional adult organism (zooid) can regenerate from a minuscule piece of vascular tissue within only 8 days. In order to compare the molecular mechanisms underlying WBR in a chordate to the regeneration process in other animals, we have analysed the transcriptome of B. leachi at each stage of regeneration, in addition to sequencing the genome.
Genomic analysis identified signaling factor families that had expanded in the colonial sea squirt lineage but not solitary sea squirts, which have a limited ability to regenerate. Following de novo transcriptome assembly (6 transcriptomes in total), differential expression analysis was performed to identify genes up or/and down-regulated during WBR. Differential gene expression analysis indicates that both wound healing and an immune response are activated during early steps of regeneration in B. leachi WBR. These processes are also key to regeneration in response to injury in vertebrate models of regeneration such as the limb regeneation in salamanders. This suggests that chordate animals may employ a homologous series of molecular events during regeneration events wheather it be WBR or tissue regeneration.