Mouse strain‐dependent egg factors regulate calcium signals at fertilization

Abstract

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.

Age-related alterations in fertilization-induced Ca2+ oscillations depend on the genetic background of mouse oocytes†

“…Moreover, embryos originating from oocytes of different mouse strains display distinct epigenetic modifications not only in maternal but also paternal genome [ 63–65 ] and may differ in the protein expression levels [ 66 ]. Interestingly, it has been reported recently that oocytes from young females of various genetic origins accumulate different amounts of Ca 2+ and display different patterns of fertilization-induced Ca 2+ oscillations [ 36 ], which accords well with the results presented here.…”

“…Changes in the Oregon Green BAPTA fluorescence were analyzed as described for the imaging of Ca 2+ oscillations. The amplitude of the Ca 2+ transient (a difference between the maximum fluorescence intensity and the fluorescence intensity at the beginning of the Ca 2+ increase) and the area under the curve (AUC) of the Ca 2+ transient (calculated for the first 10 min following the onset of Ca 2+ increase relative to baseline using the trapezoidal method; modified from [ 36 ]) were measured. All oocytes included in the analysis were viable at the end of the imaging period.…”