Store-operated Ca(2+) entry is not required for fertilization-induced Ca(2+) signaling in mouse eggs.

Abstract Repetitive oscillations in cytoplasmic Ca 2+ due to periodic Ca 2+ release from the endoplasmic reticulum (ER) drive mammalian embryo development following fertilization. Influx of extracellular Ca 2+ to support the refilling of ER stores is required for sustained Ca 2+ oscillations, but the mechanisms underlying this Ca 2+ influx are controversial. Although store-operated Ca 2+ entry (SOCE) is an appealing candidate mechanism, several groups have arrived at contradictory conclusions regarding the importance of SOCE in oocytes and eggs. To definitively address this question, Ca 2+ influx was assessed in oocytes and eggs lacking the major components of SOCE, the ER Ca 2+ sensor STIM proteins, and the plasma membrane Ca 2+ channel ORAI1. We generated oocyte-specific conditional knockout (cKO) mice for Stim1 and Stim2, and also generated Stim1/2 double cKO mice. Females lacking one or both STIM proteins were fertile and their ovulated eggs displayed normal patterns of Ca 2+ oscillations following fertilization. In addition, no impairment was observed in ER Ca 2+ stores or Ca 2+ influx following store depletion. Similar studies were performed on eggs from mice globally lacking ORAI1; no abnormalities were observed. Furthermore, spontaneous Ca 2+ influx was normal in oocytes from Stim1/2 cKO and ORAI1-null mice. Finally, we tested if TRPM7-like channels could support spontaneous Ca 2+ influx, and found that it was largely prevented by NS8593, a TRPM7-specific inhibitor. Fertilization-induced Ca 2+ oscillations were also impaired by NS8593. Combined, these data robustly show that SOCE is not required to support appropriate Ca 2+ signaling in mouse oocytes and eggs, and that TRPM7-like channels may contribute to Ca 2+ influx that was previously attributed to SOCE.