Egg activation is the result of calcium signal summation in the mouse

Oscillatory Ca2+ dynamics and cell cycle resumption at fertilization in mammals: a modelling approach

“…This is in agreement with the fact that the 6 spikes-30 min protocol is at the border between success and failure in activation and experimentally leads to egg activation in about half the cases. In fact, with these parameter values, the model can successfully reproduce all the protocols tested by Toth et al (2006). The model can thus be viewed as a satisfactory phenomenological description of the Ca 2+ -related activatory events occurring at fertilization in mice, although the set of parameter values leading to this agreement is certainly not unique.…”

“…6B). In Toth et al (2006), 6 Ca 2+ spikes, each separated by a 30 min interval were shown to activate the egg in about half the cases. The notion of 'rate of successful activation' cannot be immediately transposed in our simulations.…”

“…Parameters appearing in the minimal model for the cell cycle (eqs (3)- (5)), listed in Table 2, were chosen to get oscillations with a period of ~15 h in the absence of CSF and Ca 2+ , which roughly corresponds to the time delay between successive cell divisions in mice (Kubiak et al, 2008). The others, characterizing the effect of CaMKII on APC activation, were fixed (1) by the assumption that the pathway implying direct APC activation is much faster than the one leading to CSF degradation, and (2) by constraining the model to reproduce the results obtained by Toth et al (2006) on the rate of activation of mouse eggs submitted to various artificial patterns of Ca 2+ stimulation. Thus, the parameter values involved in the pathway between CaMKII activation and CSF degradation (V Ai 's and V Di 's in equ.…”

“…The existence of the latter pathway is required to account for the possibility of a metaphase III (MIII) arrest, a pathological state of the egg that results from an insufficient activation by Ca 2+ (Kubiak et al, 1992). The model can also account for the experimental results of Toth et al (2006), where mouse eggs were artificially activated by different Ca 2+ stimulatory protocols of different frequencies, durations and amplitudes. We then used the model in the context of 'assisted oocyte activation (AOA)' and discuss the molecular mechanism underlying the observation that the best rates of successful activation are obtained when eggs are submitted to two applications of Ca 2+ ionophores (Heytens et al, 2008a).…”

Nuclear reprogramming: what has been done and potential avenues for improvements

“…This fundamental step in skipped in SCNT, therefore the activation stimulus must be artificially applied to the oocyte. There has been a plethora of studies addressing this issue since the era of embryonic blastomere cloning, therefore, the reader is directed to the many reviews published [86]. The activation protocol varies with the species, therefore the cloner must check the reliability of a date activation method, before applying it to SCNT [87].…”