A cytostatic factor in amphibian oocytes: Its extraction and partial characterization

Abstract

In mature unfertilized Rana pipiens oocytes a cytoplasmic substance exists that arrests mitosis at metaphase when injected into blastomeres. This is called “cytostatic factor (CSF)”. CSF is found to be inactive in fertilized eggs. CSF is extractable in a stable form with an extraction medium containing Ca⁺⁺. In the absence of Ca⁺⁺ it is inactivated during storage. CSF is not dialyzable and precipitates in ammonium sulfate solution between 20 and 30% saturation. Heat treatment at 55°C for 30 min inactivates CSF. RNAase treatment inactivates CSF, but protease treatment does not. Roles of CSF and Ca⁺⁺ in oocyte activation at the time of fertilization are discussed.