Impaired caudal fin‐fold regeneration in zebrafish deficient for the tumor suppressor Pten

Zebrafish are able to completely regrow their caudal fin‐folds after amputation. Following injury, wound healing occurs, followed by the formation of a blastema, which produces cells to replace the lost tissue in the final phase of regenerative outgrowth. Here we show that, surprisingly, the phosphatase and tumor suppressor Pten, an antagonist of phosphoinositide‐3‐kinase (PI3K) signaling, is required for zebrafish caudal fin‐fold regeneration. We found that homozygous knock‐out mutant (ptena(−/−)ptenb(−/−)) zebrafish embryos, lacking functional Pten, did not regenerate their caudal fin‐folds. AKT phosphorylation was enhanced, which is consistent with the function of Pten. Reexpression of Pten, but not catalytically inactive mutant Pten‐C124S, rescued regeneration, as did pharmacological inhibition of PI3K. Blastema formation, determined by in situ hybridization for the blastema marker junbb, appeared normal upon caudal fin‐fold amputation of ptena(−/−)ptenb(−/−) zebrafish embryos. Whole‐mount immunohistochemistry using specific markers indicated that proliferation was arrested in embryos lacking functional Pten, and that apoptosis was enhanced. Together, these results suggest a critical role for Pten by limiting PI3K signaling during the regenerative outgrowth phase of zebrafish caudal fin‐fold regeneration.