Telomerase and Alternative Lengthening of Telomeres coexist in the regenerating zebrafish caudal fins

Telomeres are essential for chromosome protection and genomic stability, and telomerase function is critical to organ homeostasis. Zebrafish has become a useful vertebrate model for understanding the cellular and molecular mechanisms of regeneration. The regeneration capacity of the caudal fin of wild-type zebrafish is not affected by repetitive amputation, but the behavior of telomeres during this process has not yet been studied. In this study, the regeneration process was characterized in a telomerase deficient zebrafish model. Moreover, the regenerative capacity after repetitive amputations and at different ages was studied. Regenerative efficiency decreases with aging in all genotypes and surprisingly, telomere length is maintained even in telomerase deficient genotypes. Our results suggest that telomere length can be maintained by the regenerating cells through the recombination-mediated Alternative Lengthening of Telomeres (ALT) pathway, which is likely to support high rates of cell proliferation during the tailfin regeneration process. As far as we know, this is the first animal model to study ALT mechanism in regeneration, which opens a wealth of possibilities to study new treatments of ALT dependent processes.