Ca2+ is a highly versatile intracellular signal that operates over a wide temporal range to regulate many different cellular processes. An extensive Ca2+-signalling toolkit is used to assemble signalling systems with very different spatial and temporal dynamics. Rapid highly localized Ca2+ spikes regulate fast responses, whereas slower responses are controlled by repetitive global Ca2+ transients or intracellular Ca2+ waves. Ca2+ has a direct role in controlling the expression patterns of its signalling systems that are constantly being remodelled in both health and disease.

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Calcium signalling: dynamics, homeostasis and remodelling

Comparative Biology of Calcium Signaling during Fertilization and Egg Activation in Animals

We have developed a method to produce live somatic clones in the rabbit, one of the mammalian species considered up to now as difficult to clone. To do so, we have modified current cloning protocols proven successful in other species by taking into account both the rapid kinetics of the cell cycle of rabbit embryos and the narrow window of time for their implantation after transfer into foster recipients. Although our method still has a low level of efficiency, it has produced several clones now proven to be fertile. Our work indicates that cloning can probably be carried out successfully in any mammalian species by taking into account physiological features of their oocytes and embryos. Our results will contribute to extending the use of rabbit models for biomedical research.

https://www.researchgate.net/profile/Laurent_Boulanger/publication/11441131_Cloned_rabbits_produced_by_nuclear_transfer_from_adult_somatic_cells/links/0f317537b76fddab04000000.pdf

Cloned rabbits produced by nuclear transfer from adult somatic cells.

Mitochondrial function in the human oocyte and embryo and their role in developmental competence.

Fertilization calcium waves are introduced, and the evidence from which we can infer general mechanisms of these waves is presented. The two main classes of hypotheses put forward to explain the ge...

/pdf/calcium-at-fertilization-and-in-early-development-4f8xabt5ha.pdf

Calcium at fertilization and in early development.

Egg-to-embryo transition is driven by differential responses to Ca(2+) oscillation number.

Freshly ovulated rabbit oocytes were activated parthenogenetically by periodically repeated calcium stimuli generated by electric field pulses applied onto the plasma membrane. Electric field pulses of 1.8 kV cm-1 were delivered every 4 min for 1 h 30 min (22 double pulses) in a specially designed chamber. Before each pulse, the culture medium was replaced by an isotonic glucose solution containing 10 microM Ca2+. The effects of modulating the ionic stimuli (by changing the duration of EF pulse) on a postactivation reaction, and/or on the pre- and postimplantation development, were studied. The rate of activation increased progressively as the pulse duration lengthened. For 22 pulses of 200 microseconds, 13% of oocytes were activated versus 100% for 1200 microseconds. The uniformity of the parthenogenetic response was obtained when oocytes were exposed to a series of pulses within which the reduction of pulse duration followed a negative exponential law. The influence of such activating treatment on the preimplantation development was tested using two treatments of 22 pulses with a total pulse duration equal to 14,868 and 11,228 microseconds, respectively. For the weaker treatment, a lower proportion of embryos underwent compaction and those that compacted were irregular. In contrast, the majority of embryos resulting from the stronger treatment compacted and developed into blastocysts. The most significant result that emerges from this study is that the level of stimulation affects in vitro developmental potency after the third cleavage division. The postimplantation viability of parthenogenetic eggs was tested and the results showed that parthenogenetic rabbit embryos died at a similar stage of development to the parathenogenetic mouse embryos. But, in the present series, high implantation rates and embryonic development (66%) till day 10-11 of pregnancy were obtained after the appropriate pulsatile EF treatment of oocytes. The parthenogenetic fetuses were of smaller size than the controls, but the development of the trophoblast tissue was proportional to the development of the fetuses. Anomalies of fetuses were also observed. This study reveals that activation is not a time-limited event and that the type of activating treatment has a marked effect on the ability of the resulting parthenogenetic embryos to develop to the early postimplantation stages. The sustained alteration of the cytoplasmic activity provides a useful tool to study the function of embryonic or somatic nuclei introduced during the earliest stages of activation.

The parthenogenetic development of rabbit oocytes after repetitive pulsatile electrical stimulation

Publisher Summary At fertilization in mammals, the incoming sperm makes two essential contributions to the development of the new organism. One contribution is the DNA and all its associated genes, which enables a diploid organism to develop to full term. The other is the message that triggers egg development. Without this message, delivering the DNA is pointless. In all animal species studied, the message that the sperm delivers is written in the language of cell Ca2+ changes. This chapter focuses on the way that changes of intracellular Ca2+ are generated in mammalian eggs, and describes how these Ca2+ changes affect the subsequent development of the embryo. It is shown that the Ca2+ dynamics at fertilization in mammalian eggs are more complex than in nonmammalian systems. One of the main points that is emphasized is that mammalian eggs are different from other eggs in that they undergo Ca2+ oscillations, or repetitive Ca2+ spikes, during activation at fertilization. One of the central problems to be solved is the triggering mechanism for the oscillations at fertilization. Ca2+o scillations have been described in a vast range of somatic cell types.

Dynamics of the calcium signal that triggers mammalian egg activation.

Postfertilization manipulation of mammalian embryos results in various developmental alterations. To determine whether the manipulation of the Ca2+ regime causing oocyte activation is a valuable experimental means in helping understand the biological process by which embryos integrate signals from outside and later regulate gene expression, we linked Ca2+ signal parameters i.e. amplitude, number and frequency, with the efficiency and quality of postimplantation development. Freshly ovulated rabbit oocytes were subjected to repetitive and modulated Ca2+ influx. The results provide three major pieces of information. Firstly, the Ca2+ stimulus is the most efficient signal activating mammalian eggs when it is applied in a repetitive manner, the amplitude being the crucial factor. Secondly, the dynamics of early cleavage does not appear to be determined by either the frequency or the amplitude of modulation of the Ca2+ signal that activates the oocyte. Thirdly, amplitude and temporal modulation of the Ca2+ signal in the early minutes influences the developmental performance and the morphology of the rabbit parthenogenetic conceptus at day 11.5 of pregnancy. The results demonstrate the importance of epigenetic events during postfertilization as well as the possible uses of Ca2+ modulation in studying long term developmental effects.

Jean-Pierre Ozil

Papers

Egg-to-embryo transition is driven by differential responses to Ca(2+) oscillation number.

The parthenogenetic development of rabbit oocytes after repetitive pulsatile electrical stimulation

Dynamics of the calcium signal that triggers mammalian egg activation.

Activation of rabbit oocytes: the impact of the Ca2+ signal regime on development.

Ca2+ oscillatory pattern in fertilized mouse eggs affects gene expression and development to term.