Abstract
Calcium is a universal messenger that mediates egg activation at fertilization in all sexually reproducing species studied. However, signaling pathways leading to calcium generation and the mechanisms of calcium-induced exit from meiotic arrest vary substantially among species. Here, we review the pathways of calcium signaling and the mechanisms of meiotic exit at fertilization in the eggs of the established developmental model, African clawed frog, Xenopus laevis. We also discuss calcium involvement in the early fertilization-induced events in Xenopus egg, such as membrane depolarization, the increase in intracellular pH, cortical granule exocytosis, cortical contraction, contraction wave, cortical rotation, reformation of the nuclear envelope, sperm chromatin decondensation and sister chromatid segregation.
Highlights
Molecular mechanisms of sperm-egg interaction differ greatly among sexually reproducing biological species
This review summarizes in a concise form our current knowledge about different aspects of calcium signaling at fertilization in the eggs of African clawed frog Xenopus laevis
The findings obtained using Xenopus egg extracts demonstrate that PP2A-B55 phosphatase, suppressed in metaphase II by the high activity of Greatwall kinase (Gwl) kinase, becomes activated when Cdk1 is inactivated and the cytostatic factor (CSF)-arrested extracts are released into interphase [27,87]
Summary
Molecular mechanisms of sperm-egg interaction differ greatly among sexually reproducing biological species. Some events of fertilization-induced egg activation are highly conserved. The calcium signal represents a main early event of fertilization-induced egg activation observed in all species studied. It is a prerequisite for subsequent fertilization events, such as the block to polyspermy, exit from meiotic arrest, nuclear reformation, etc. This review summarizes in a concise form our current knowledge about different aspects of calcium signaling at fertilization in the eggs of African clawed frog Xenopus laevis. Frog oocytes and eggs have been widely used in studies of meiotic progression and fertilization. Many of the control mechanisms that operate in maturing oocytes, fertilized eggs and early embryos have been first established in the frog model. We refer occasionally to other biological species; a comprehensive discussion of calcium signaling at fertilization in different species is outside the scope of this paper
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