The Ca2+ 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 Ca2+ signaling events impact long-term development, in particular development to term, is unknown. Using fertilized eggs that have undergone the first few Ca2+ oscillations, we developed procedures that result either in inhibiting or stimulating the natural pattern of Ca2+ 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 Ca2+ oscillations is precociously interrupted, the incidence of implantation is compromised whereas hyper-stimulation of Ca2+ 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 approximately 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 Ca2+ signaling events following fertilization (an excess or reduction) has long-term effects on both gene expression and development to term.

Although the dynamics of oscillations of cytosolic Ca2+ concentration ([Ca2+]cyt) play important roles in early mammalian development, the impact of the duration when [Ca2+]cyt is elevated is not known. To determine the sensitivity of fertilization-associated responses [i.e., cortical granule exocytosis, resumption of the cell cycle, Ca2+/calmodulin-dependent protein kinase II (CaMKII) activity, recruitment of maternal mRNAs] and developmental competence of the parthenotes to the duration of a [Ca2+]cyt transient, unfertilized mouse eggs were subjected to a prolonged [Ca2+]cyt change for 15, 25, or 50 min by means of repetitive Ca2+ electropermeabilization at 2-min intervals. The initiation and completion of fertilization-associated responses are correlated with the duration of time in which the [Ca2+]cyt is elevated, with the exception that autonomous CaMKII activity is down-regulated with prolonged elevated [Ca2+]cyt. Activated eggs from 25- or 50-min treatments readily develop to the blastocyst stage with no sign of apoptosis or necrosis and some implant. Ca2+ influx into unfertilized eggs causes neither Ca2+ release from intracellular stores nor rapid removal of cytosolic Ca2+. Thus, the total Ca2+ signal input appears to be an important regulatory parameter that ensures completion of fertilization-associated events and oocytes have a surprising degree of tolerance for a prolonged change in [Ca2+]cyt.

No abstract

In mammals fertilization triggers a series of Ca2+ oscillations that not only are essential for events of egg activation but also stimulate oxidative phosphorylation. Little is known, however, about the relationship between quantitative changes in egg metabolism and specific long-term effects in offspring. This study assessed whether post-natal growth is modulated by early transient changes in NAD(P)H and FAD2+ in zygotes. We report that experimentally manipulating the redox potential of fertilized eggs during the pronuclear (PN) stage affects post-natal body weight. Exogenous pyruvate induces NAD(P)H oxidation and stimulates mitochondrial activity with resulting offspring that are persistently and significantly smaller than controls. Exogenous lactate stimulates NAD+ reduction and impairs mitochondrial activity, and produces offspring that are smaller than controls at weaning but catch up after weaning. Cytosolic alkalization increases NAD(P)+ reduction and offspring of normal birth-weight become significantly and persistently larger than controls. These results constitute the first report that post-natal growth rate is ultimately linked to modulation of NAD(P)H and FAD2+ concentration as early as the PN stage.