Analysis of Ca~(2+) oscillations and Ca~(2+) influx in mouse eggs

摘要

In mammalian eggs, repetitive transients in intracellular concentration of Ca~(2+) ([Ca~(2+)]_i,), called Ca~(2+) oscillations are induced by the sperm at fertilization. Little is known about how spermatozoon activates the egg. One strong hypothesisis that a sperm protein called sperm factor that the sperm introduces into the egg causes Ca~(2+) oscillations. Microinjecting sperm extracts (SE) from several species into eggs in the same or different species induce Ca~(2+) oscillations as observed atfertilization. The Ca~(2+) oscillations are due to intracellular Ca~(2+) release from the endoplasmic reticulum (ER) mainly through InsP_3 receptor/Ca~(2+) channels because micro injecting a functional monoclonal antibody against Type 1 lnsP_3 receptor,18A10 blocks Ca~(2+) oscillations at fertilization as well as Ca~(2+) transient (Ca~(2+) release) induced by micro inject ion of InsP_3 or CaCl_2. Furthermore, Ca~(2+) influx is required for maintaining the Ca~(2+) oscillations because Ca~(2+) oscillationsat fertilization are abolished by deprivation of external Ca~(2+). The Ca~(2+) influx is thought to be store-operated (or capacitative) Ca~(2+) entry. However, the precise mechanism of Ca~(2+) oscillations or Ca~(2+) influx is not clear. Therefore, it is very important to study the mechanisms of Ca~(2+) oscillations and Ca~(2+) influx toward clarifying the mechanism of mammalian fertilization.