Reinitiation of meiosis in starfish oocytes requires an increase in nuclear ca²⁺

Here we report that an increase in nuclear Ca²⁺ is hormonally regulated and is required for reinitiation of meiosis in starfish oocytes. We have shown in Asteria pectirtifera that a Ca²⁺ transient and a baseline increase of Ca²⁺ occur both in the cytoplasm and in the nucleus. These increases are in response to 1-methyladenine (1-MA), the hormone responsible for the induction of meiotic maturation. The Ca²⁺ transients are not necessary for the reinitiation of meiosis. However, blocking the baseline increase in nuclear Ca²⁺ blocks both the nuclear envelope breakdown (NEBD) and the continuation of meiosis.