Microinjection of Ca2+ store-enriched microsome fractions to dividing newt eggs induces extra-cleavage furrows via inositol 1,4,5-trisphosphate- induced Ca2+ release

Abstract

The cleavage signal transferred to the future cleavage cortex during anaphase has been proposed as 'cleavage stimulus,' but no signal has proved to induce cleavage furrows. The local Ca2+ transient along the cleavage furrow has been reported, but the Ca2+ source has remained unknown. To address these questions, we studied functions of Ca2+ stores in dividing newt eggs and found that microinjection of the Ca2+ store-enriched microsome fraction to the dividing newt egg induced a local extra-cleavage furrow at the injection site in 64-67% of the injected newt eggs while coinjection with inositol 1,4,5-trisphosphate receptor (IP3R) antagonists heparin or anti-type 1-IP3R antibody clearly suppressed this induction (5 and 11% in induction rates, respectively). Injection of cerebellar microsomes from the type 1-IP3R-deficient mice induced extracleavage furrows albeit at a low rate (19%). Our observations strongly suggest that Ca2+ stores with IP3R induce and position a cleavage furrow via IP3-induced Ca2+ release (IICR) as Ca2+-releasing machinery and putative cleavage stimulus itself.