Starting a new life: sperm PLC-zeta mobilizes the Ca2+ signal that induces egg activation and embryo development: an essential phospholipase C with implications for male infertility.
ABSTRACT We have discovered that a single sperm protein, phospholipase C-zeta (PLCζ), can stimulate intracellular Ca(2+) signalling in the unfertilized oocyte ('egg') culminating in the initiation of embryonic development. Upon fertilization by a spermatozoon, the earliest observed signalling event in the dormant egg is a large, transient increase in free Ca(2+) concentration. The fertilized egg responds to the intracellular Ca(2+) rise by completing meiosis. In mammalian eggs, the Ca(2+) signal is delivered as a train of long-lasting cytoplasmic Ca(2+) oscillations that begin soon after gamete fusion and persist beyond the completion of meiosis. Sperm PLCζ effects Ca(2+) release from egg intracellular stores by hydrolyzing the membrane lipid PIP(2) and consequent stimulation of the inositol 1,4,5-trisphosphate (InsP(3) ) receptor Ca(2+) -signalling pathway, leading to egg activation and early embryogenesis. Recent advances have refined our understanding of how PLCζ induces Ca(2+) oscillations in the egg and also suggest its potential dysfunction as a cause of male infertility.
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ABSTRACT: When intracytoplasmic sperm injection (ICSI) is performed in mice, isolation of sperm heads is usually performed prior to injections in order to increase the efficiency of the procedure. Consequently, the isolated sperm heads undergo an inevitable incubation in vitro. However, little is known about the effects of this incubation step on fertilization and embryo development following ICSI. When we incubated sperm heads at 37 °C, there was a significant time-dependent decrease in fertilization and blastocyst formation. Moreover, the DNA integrity of the sperm heads was maintained over 12 h incubation. Using assisted oocyte activation, these defects in fertilization and embryo development were rescued. Taken together, incubation of sperm heads following isolation can affect the oocyte-activating capacity of sperm thereby compromising fertilization and embryo development associated with ICSI.Biotechnology Letters 07/2013; · 1.85 Impact Factor
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ABSTRACT: Egg activation is the final transition that an oocyte goes through to become a developmentally competent egg. This transition is usually triggered by a calcium-based signal that is often, but not always, initiated by fertilization. Activation encompasses a number of changes within the egg. These include changes to the egg's membranes and outer coverings to prevent polyspermy and to support the developing embryo, as well as resumption and completion of the meiotic cell cycle, mRNA polyadenylation, translation of new proteins, and the degradation of specific maternal mRNAs and proteins. The transition from an arrested, highly differentiated cell, the oocyte, to a developmentally active, totipotent cell, the activated egg or embryo, represents a complete change in cellular state. This is accomplished by altering ion concentrations and by widespread changes in both the proteome and the suite of mRNAs present in the cell. Here, we review the role of calcium and zinc in the events of egg activation, and the importance of macromolecular changes during this transition. The latter include the degradation and translation of proteins, protein posttranslational regulation through phosphorylation, and the degradation, of maternal mRNAs.Current Topics in Developmental Biology 01/2013; 102:267-92. · 6.91 Impact Factor
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ABSTRACT: Metaphase-I-arrested eggs of marine protostome worms in the phylum Nemertea generate a series of point-source calcium waves during fertilization. Such calcium oscillations depend on inositol-1,4,5-trisphosphate-mediated calcium release from endoplasmic reticulum (ER) stores that undergo structural reorganizations prior to and after fertilization. This article reviews fertilization-induced calcium transients and ER dynamics in nemertean eggs and compares these topics to what has been reported for other animals in order to identify unifying characteristics and distinguishing features of calcium responses during fertilization across the animal kingdom.Biochemical and Biophysical Research Communications 04/2014; · 2.28 Impact Factor