Injection of a sperm extract triggers egg activation in the newt Cynops pyrrhogaster

Unfertilized eggs of the newt Cynops pyrrhogaster are arrested at the secon d meiotic metaphase. The primary signal for egg activation is a transient i ncrease in [Ca2+](i), which is triggered by the fertilizing sperm and propa gates over the egg cortex as a Ca2+ wave. We injected an extract of Cynops sperm (SE) into unfertilized eggs and induced a wave-like [Ca2+](i) increas e which resulted in activation and resumption of meiosis. The SE-injected e ggs showed degradation of cyclin B1 and DNA replication. When SE was boiled or treated with proteinase K before injection, it was unable to cause egg activation. Preinjection of Ca2+-chelator BAPTA before SE injection inhibit ed egg activation. These results indicate that a heat-labile and proteinace ous factor in the sperm cytoplasm induces a transient increase in [Ca2+](i) which is required for egg activation. Injection of IF, into unfertilized e ggs caused an increase in [Ca2+](i) and egg activation, but injection of cA DP-ribose did not. These results support the hypothesis that Ca2+ release a t fertilization occurs via IF, receptors. (C) 2001 Academic Press.