Mouse strain-dependent egg factors regulate calcium signals at fertilization.

Calcium (Ca2+ ) signals triggered at fertilization initiate resumption of the cell cycle and initial steps of embryonic development. In mammals, the sperm factor phospholipase Cζ triggers the release of Ca2+ from the endoplasmic reticulum (ER), initiating an oscillatory pattern of Ca2+ transients that is modulated by egg factors including Ca2+ influx channels, Ca2+ transporters, and phosphoinositide-regulating enzymes. Here we compared characteristics of Ca2+ oscillations following in vitro fertilization (IVF) and ER Ca2+ stores among nine common laboratory mouse strains: CF1, C57BL6, SJL, CD1, DBA, FVB, 129X1, BALBc, 129S1, and the F1 hybrid B6129SF1. Sperm from B6SJLF1/J males was used for all IVF experiments. There were significant differences among the strains with respect to duration and maximum amplitude of the first Ca2+ transient, frequency of oscillations, and ER Ca2+ stores. With male strain held constant, the differences in Ca2+ oscillation patterns observed result from variation in egg factors across different mouse strains. Our results support the importance of egg-intrinsic properties in determining Ca2+ oscillation patterns and have important implications for the interpretation and comparison of studies on Ca2+ dynamics at fertilization.