Satellite cells originate from the lateral plate mesoderm in Xenopus laevis

Xenopus laevis tadpoles possess high regenerative ability of amputated tails, except during the ‘refractory period’ when regenerative ability is transiently lost. We recently reported that treatment with an immunosuppressant (FK506) restores the regenerative ability, suggesting that immune responses act to impair regenerative ability during the refractory period. An expression analysis of immune-related genes suggested that immature cytotoxic T cells infiltrate regenerating tail tissues during the refractory period, which eventually impairs the regenerative ability. To identify the molecular processes affected by the immune response, we screened for genes whose expression in the tail stumps was altered by FK506 treatment during the refractory period, and identified three candidate gene fragments. Expression of these three candidate genes was significantly increased after tail amputation during the refractory period. Expression of two of the genes was downregulated by FK506 treatment, whereas expression of the third gene was upregulated. These findings suggest that the two genes downregulated by FK506 treatment are involved in immune responses that impair regenerative ability during the refractory period. Alternatively, these genes might encode autoantigens that are expressed in regenerating tail tissues and targeted by the immune system. The candidate gene that was upregulated by FK506 treatment might be involved in the regenerative processes, which are restored by FK506 treatment.