Expression analysis of XPhyH-like during development and tail regeneration in Xenopus tadpoles: possible role of XPhyH-like expressing immune cells in impaired tail regenerative ability.

Xenopus tadpoles have high regenerative ability of amputated tails except during the 'refractory period', when the ability is transiently lost. We previously demonstrated that distinct immune responses occur in tail stumps between the refractory and pre/post-refractory regeneration periods. Furthermore, treatment with an immunosuppressant, FK506, restores the tail regenerative ability during the refractory period. Based on these findings, we previously proposed that autoreactive immune cells infiltrate the tail stumps to attack blastema cells as 'non-self' during the refractory period, resulting in the impaired regenerative ability. The immune cells that attack the blastema cells, however, remained unclear. Here we screened for genes whose expression in the tail stumps was altered by FK506 treatment during the refractory period and identified a Xenopus homolog of phytanoyl-CoA dioxygenase (PhyH)-like. XPhyH-like expression transiently increased in tail stumps after amputation during the refractory period, and was reduced by FK506 treatment. XPhyH-like expression in the whole tadpole body specifically increased during the refractory period and was enriched in the blood cell fraction. These findings suggest that XPhyH-like is expressed in autoreactive immune cells that are distributed in the whole body during the refractory period and transiently infiltrate the tail stumps to attack the blastema cells as 'non-self'.