Ca 2+ oscillatory pattern in fertilized mouse eggs affects gene expression and development to term

Abstract

The Ca 2+ oscillations initiated by the fertilizing sperm (but terminating concomitant with pronucleus formation) apparently ensure that the events constituting egg activation occur in the correct temporal order; early events (e.g., cortical granule exocytosis) require fewer oscillations than later events (e.g., recruitment of maternal mRNA). Whether the Ca 2+ signaling events impact long-term development, in particular development to term, is unknown. Using fertilized eggs that have undergone the first few Ca 2+ oscillations, we developed procedures that result either in inhibiting or stimulating the natural pattern of Ca 2+ signaling of inseminated eggs. Although the incidence of development to the blastocyst stage is unaltered by these procedures, fewer offspring are born following embryo transfer, indicating that developmental competence of the blastocysts is reduced. Interestingly, embryo transfer experiments reveal that when the natural regime of Ca 2+ oscillations is precociously interrupted, the incidence of implantation is compromised whereas hyper-stimulation of Ca 2+ signaling events compromises post-implantation development. Moreover, although there was no major difference in the overall growth rates of the offspring, those obtained following hyper-stimulation exhibited a far greater variability in their weight. Analysis of global patterns of gene expression by microarray analysis revealed that ∼ 20% of the transcripts are mis-regulated when too few oscillations are experienced by the embryo and EASE analysis indicates that genes preferentially involved in RNA processing and polymerase II transcription are differentially affected. In addition, a set of genes involved in cell adhesion is also mis-expressed and could thus be mechanistically linked to the observed reduced implantation. Only about 3% of the transcripts were mis-regulated following hyper-stimulation, and EASE analysis indicates that genes preferentially involved in metabolism are differentially affected. In toto, these results indicate that a range Ca 2+ signaling events following fertilization (an excess or reduction) has long-term effects on both gene expression and development to term.