Ca2+ release and the development of Ca2+ release mechanisms during oocyte maturation: a prelude to fertilization

Abstract

Oogenesis involves the production of an oocyte that can undergo fertilization and support early development. The stimulus that initiates embryogenesis is an increase in the concentration of intracellular Ca2+ in the cytoplasm of the oocyte at the time of fertilization. The development of the ability of the oocyte to release Ca2+ in response to the fertilizing spermatozoon is an essential step in the process of oogenesis. Mammalian oocytes are particularly useful for studying the development of Ca2+ signalling systems, owing to the series of Ca2+ oscillations generated at fertilization, compared with the monotonic Ca2+ increase seen in nonmammalian species. Recent evidence has revealed that Ca2+ release mechanisms are modified during oogenesis. The maximal sensitivity of Ca2+ release is reached in the final stages of oocyte maturation, just before the optimal time for fertilization. In this review, we consider the mechanism underlying Ca2+ release in mammalian oocytes and discuss how the release mechanisms are modified during oocyte maturation. The tight co-ordination of the differentiation of the Ca2+ signalling system with the development of the oocyte provides a means of ensuring successful activation at the time of fertilization. Finally, we consider the consequences for embryo development in circumstances in which the co-ordination is lost.

Control of Spontaneous Activation of Rat Oocytes by Regulating Plasma Membrane Na+/Ca2+ Exchanger Activities

“…It is known that the regulation of cytoplasmic free Ca 2+ concentration is a key factor for the maintenance of the viability of cells, including oocytes [61], and that increases (oscillations) in intracellular free Ca 2+ occur during oocyte meiotic maturation and fertilization [62,63]. Furthermore, the poor embryo development in mouse oocytes aged in vitro was found to be associated with impaired Ca 2+ homeostasis [64].…”

Dynamic Changes to the Inositol 1,4,5-Trisphosphate and Ryanodine Receptors during Maturation of Bovine Oocytes

“…In addition, the RyR was observed and apparently undergoes dynamic changes during maturation as observed by immunocytochemistry (Yue et al, 1998, and the present study) implying that the RyR may function and appear during maturation of bovine oocytes and leading to a hypothesis that a stagespecific expression of RyR may occur in bovine oocytes. One potential explanation for this change in RyR function is that post-translational modification or rearrangement of the RyR may occur and render the RyR more reactive in the late stages of maturation as in the mouse oocyte (Carroll et al, 1994(Carroll et al, , 1996. An additional explanation could be that receptor synthesis occurs during maturation and leads to increased responsiveness.…”

Artificial oocyte activation with calcium ionophore A23187 in intracytoplasmic sperm injection cycles using surgically retrieved spermatozoa

“…In mammalian oocytes, an intracellular calcium rise is the signal responsible for the resumption of meiosis and the beginning of embryo development, thus playing an important role during fertilization (22)(23)(24). It has been suggested that sperm provide a soluble factor that is released into the egg upon sperm-egg fusion (25).…”