It is widely believed that stimulation of the phosphoinositide pathway and production of 1,4,5-inositol trisphosphate (IP3) underlies the oscillatory changes in the concentration of intracellular free calcium ions ([Ca2 ]i) seen during mammalian fertilization. IP3 promotes Ca2 release in eggs by binding to its receptor, the type-1 IP3 receptor (IP3R-1, also known as ITPR1), a ligand-gated Ca2 channel located in the membrane of the endoplasmic reticulum, the main Ca2 store of the cell. While IP3R-1 has been shown to mediate all Ca2 release during mouse fertilization, whether or not it plays such an essential role in fertilization-induced Ca2 release in large domestic species such as bovine and porcine is presently not known. Accordingly, we have generated metaphase II bovine eggs with a ∼70%–80% reduction in the number of intact IP3R-1 by inducing receptor down-regulation during oocyte maturation. We did so by injecting the nonhydrolyzable IP3 analogue, adenophostin A. Functional Ca2 release analysis revealed that IP3R-1 is the predominant Ca2 release channel in bovine eggs, requiring as little as 20% of total intact receptor to mount persistent [Ca2 ]i oscillations in response to fertilization, expression of PLCζ (also known as PLCZ1), and adenophostin A. However, lower concentrations of IP3 and near-physiological concentrations of porcine sperm extract were unable to trigger [Ca2 ]i oscillations in this reduced IP3R-1 model. Furthermore, we present evidence that the sensitivity of bovine IP3R-1 is impaired at the first embryonic interphase. Together, these results demonstrate the essential role of IP3R-1-mediated Ca2 release during fertilization in bovine eggs, and identify cell cycle regulatory mechanisms of [Ca2 ]i oscillations at the level of IP3R-1.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.