Outside-in calcium signaling is required for mouse egg activation

Monday, October 24, 2011 — Poster Session I
Noon – 2:00 p.m.	Natcher Conference Center	NIEHS	DEV-7

Authors

• YL Miao
• P Stein
• CJ Williams

Abstract

Mammalian fertilization is accompanied by oscillations in egg cytoplasmic calcium (Ca2+) concentrations that are critical for completion of egg activation. We hypothesized that Ca2+ influx across the plasma membrane was a requisite component of egg activation signaling, and not simply a Ca2+ source for store repletion. We found that Ca2+ influx was not required to initiate resumption of meiosis II. However, even if multiple oscillations in intracellular Ca2+ occurred, in the absence of Ca2+ influx the fertilized eggs remained arrested in anaphase. Additional experiments using BAPTA/AM, demonstrated that Ca2+ influx is sufficient to support pronucleus formation after only a single Ca2+ transient, whereas BAPTA/AM-treated ICSI eggs cultured in Ca2+-free medium remained arrested in metaphase II. Inhibition of SOCE had no effect on ICSI-induced egg activation. Ca2+ influx appears to be upstream of CaMKIIγ activity because eggs can be parthenogenetically activated with a constitutively active form of CaMKIIγ whether or not they are cultured in the presence of extracellular Ca2+. These results suggest that eggs can resume meiosis after ICSI without Ca2+ influx; however, Ca2+ influx at fertilization not only maintains Ca2+ oscillations by replenishing Ca2+ stores, but also activates critical signaling pathways that are required for completion of meiosis.

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