Fertilization and Inositol 1,4,5-Trisphosphate (IP3)-Induced Calcium Release in Type-1 Inositol 1,4,5-Trisphosphate Receptor Down-Regulated Bovine Eggs1

Abstract

It is widely believed that stimulation of the phosphoinositide pathway and production of 1,4,5-inositol trisphosphate (IP(3)) underlies the oscillatory changes in the concentration of intracellular free calcium ions ([Ca(2+)](i)) seen during mammalian fertilization. IP(3) promotes Ca(2+) release in eggs by binding to its receptor, the type-1 IP(3) receptor (IP(3)R-1, also known as ITPR1), a ligand-gated Ca(2+) channel located in the membrane of the endoplasmic reticulum, the main Ca(2+) store of the cell. While IP(3)R-1 has been shown to mediate all Ca(2+) release during mouse fertilization, whether or not it plays such an essential role in fertilization-induced Ca(2+) release in large domestic species such as bovine and porcine is presently not known. Accordingly, we have generated metaphase II bovine eggs with a approximately 70%-80% reduction in the number of intact IP(3)R-1 by inducing receptor down-regulation during oocyte maturation. We did so by injecting the nonhydrolyzable IP(3) analogue, adenophostin A. Functional Ca(2+) release analysis revealed that IP(3)R-1 is the predominant Ca(2+) release channel in bovine eggs, requiring as little as 20% of total intact receptor to mount persistent [Ca(2+)](i) oscillations in response to fertilization, expression of PLCzeta (also known as PLCZ1), and adenophostin A. However, lower concentrations of IP(3) and near-physiological concentrations of porcine sperm extract were unable to trigger [Ca(2+)](i) oscillations in this reduced IP(3)R-1 model. Furthermore, we present evidence that the sensitivity of bovine IP(3)R-1 is impaired at the first embryonic interphase. Together, these results demonstrate the essential role of IP(3)R-1-mediated Ca(2+) release during fertilization in bovine eggs, and identify cell cycle regulatory mechanisms of [Ca(2+)](i) oscillations at the level of IP(3)R-1.

Single Ca2+ transients vs oscillatory Ca2+ signaling for assisted oocyte activation: limitations and benefits

“…The frequency of Ca 2+ oscillations depends in part on the IP3 concentration (Mehlmann et al 1996, Malcuit et al 2005; hence, it is not unexpected that the oscillation frequency is also dependent on PLCζ concentration. As a result, PLCζ concentrations are correlated with sperm activation potential (Heytens et al 2009, Nomikos et al 2014b.…”

Ca2+ Signaling During Mammalian Fertilization: Requirements, Players, and Adaptations

“…Data in the latter study and in follow up reports provided strong evidence to support the concept that PLCz is the pivotal, and possibly exclusive, initiator of [Ca 2þ ] i oscillations in mammals. Specifically, injection of recombinant PLCz (Fujimoto et al 2004;Kouchi et al 2004) or PLCz cRNA evoked spermlike oscillations in mouse (Saunders et al 2002), rat (Ito et al 2008b), human (Rogers et al 2004), bovine (Malcuit et al 2005;Ross et al 2008), porcine (Yoneda et al 2006), and equine (Bedford-Guaus et al 2008) eggs. In vitro PLC assays, using recombinant PLCz confirmed the enzyme's high sensitivity to Ca 2þ , which render it nearly fully active at basal [Ca 2þ ] i concentrations ).…”

Phospho-Signaling at Oocyte Maturation and Fertilization: Set Up for Embryogenesis and Beyond Part II. Kinase Regulators and Substrates

“…IP3R is dynamically regulated during meiotic maturation and is required for fertilization induced Ca 2+ release in Xenopus (Kume et al 1997;Runft et al 1999). Developmentally regulated type 1 IP3R is upregulated in oocytes at fertilization and down-regulated after fertilization and this downregulation is mediated by degradation in proteasome pathway in mouse (Fissore et al 1999;Jellerette et al 2000;Parrington et al 1998;Wakai et al 2011) and bovine (Malcuit et al 2005). IP3R1 is phosphorylated during both maturation and the first cell cycle mediated by M-phase kinases e.g.…”