Conserved Genes in Highly Regenerative Metazoans Are Associated with Planarian Regeneration.

Metazoan species depict a wide spectrum of regeneration ability which calls into question the evolutionary origins of the underlying processes. Since species with high regeneration ability are widely distributed throughout metazoans, there is a possibility that the metazoan ancestor had an underlying common molecular mechanism. Early metazoans like sponges possess high regenerative ability, but, due to the large differences they have with Cnidaria and Bilateria regarding symmetry and neuronal systems it can be inferred that this regenerative ability is different. We hypothesized that the last common ancestor of Cnidaria and Bilateria possessed remarkable regenerative ability which was lost during evolution. We separated Cnidaria and Bilateria into three classes possessing Whole-body regenerating (WBR), High regenerative ability (HRA) and Low regenerative ability (LRA). Using a multiway blast and gene phylogeny approach we identified genes conserved in WBR species and lost in LRA species and labeled them Cnidaria and Bilaterian regeneration (CBR) genes. Through transcription factor analysis we identified that CBR genes were associated with an overabundance of homeodomain regulatory elements. RNA interference of CBR genes resulted in loss of regeneration phenotype for HRJDa, HRJDb, DUF21, DISP3 and ARMR genes. We observed that DUF21 knockdown was highly lethal in the early stages of regeneration indicating a potential role in wound response. Also, HRJDa, HRJDb, DISP3 and ARMR knockdown showed loss of regeneration phenotype after second amputation. The results strongly correlate with their respective RNA-Seq profiles. We propose that CBR genes play a major role in regeneration across highly regenerative Cnidaria and Bilateria.