Caspase-9 has a non-apoptotic function in Xenopus embryonic primitive blood formation

Abstract

Caspases constitute a family of cysteine proteases centrally involved in programmed cell death, which is an integral part of normal embryonic and fetal development. However, it has become clear that specific caspases also have functions independent of cell death. In order to identify novel apoptotic and non-apoptotic developmental caspase functions we designed and transgenically integrated novel fluorescent caspase-reporter constructs in developing Xenopus embryos and tadpoles. This model organism has an external development, hence allowing direct and continuous monitoring. These studies uncovered a non-apoptotic role for the initiator caspase-9 in primitive blood formation. Functional experiments further corroborated that caspase-9, but possibly not the executioner caspases-3 and -7, are required for primitive erythropoiesis in the early embryo. These data revealed a novel non-apoptotic function for the initiator caspase-9, and for the first time implicates non-apoptotic caspase activity in primitive blood formation.