Calcineurin inhibitors block dorsal-side signaling that affect late-stage development of the heart, kidney, liver, gut and somitic tissue during Xenopus embryogenesis.

Calcineurin, a calcium/calmodulin-dependent serine/threonine protein phosphatase, is a key constituent of signaling pathways involved in antigen-dependent T-cell activation and development of the mammalian heart. In addition, calcineurin constitutes a part of the Wnt/calcium-signaling pathway that regulates early stages of dorsoventral axis formation in Xenopus embryos. Although some of the Wnt family members are involved in organ formation at relatively late stages of Xenopus development, the involvement of calcineurin in the development of those organs remains unclear. In the present study, we demonstrate that calcineurin inhibitors (cyclosporine A, FK506, and FK520), but not non-calcineurin inhibitors (rapamycin and GPI1046) that bind the same intracellular receptor as that for FK506, induce edema and gut coiling disruption and exhibit teratogenesis in the kidney, heart, gut, liver, and somitic tissue during Xenopus development. The same effects were observed by injecting the calcineurin inhibitors into the dorsal side, but not ventral side, of blastomeres at the 4-cell stage, although the inhibitors did not affect dorsoventral axis formation. These results suggest that calcineurin is involved in dorsal-side signaling that leads to the formation of the heart, kidney, liver, gut and somitic tissue during Xenopus embryogenesis.