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Reproduction, Fertility and Development Reproduction, Fertility and Development Society
Vertebrate reproductive science and technology
RESEARCH ARTICLE

010. Coordinating the transition from egg to embryo in mammals

J. Carroll

Reproduction, Fertility and Development 16(supplement) 10 - 10
Published: 26 August 2004

Abstract

At fertilization of mammalian oocytes, the sperm induces a series of increases in the concentration of intracellular Ca2+. These Ca2+ oscillations trigger all the events of egg activation, including cortical granule exocytosis, completion of meiosis and entry into the first mitotic division. Thus, intracellular Ca2+ plays a pivotal role in coordinating the transition from egg to embryo. Our work is focussed on understanding how the oocyte prepares for fertilisation, how the Ca2+ oscillations are controlled and how Ca2+ stimulates signalling pathways that lead to optimal early embryonic development. In this lecture I will focus on the downstream pathways of Ca2+ signalling at fertilisation. Conventional Protein Kinase C (cPKC) is the major downstream target of Ca2+ in many cell functions. Using PKC-GFP fusion proteins we have found that cPKC is recruited to the membrane in a manner that is dependent on the frequency and amplitude of the Ca2+ oscillations. Recruitment of cPKC appears to promote the Ca2+ influx necessary to sustain the generation of long lasting Ca2+ oscillations. In other cell types cytosolic Ca2+ increases are known to stimulate mitochondrial respiration. We have found that maintenance of resting Ca2+ levels and sperm-induced Ca2+ oscillations are critically dependent on mitochondrial ATP production: a feature not shared by many cell types. Since Ca2+ release increases ATP consumption we investigated whether the Ca2+ transients increase mitochondrial activity so as to meet this increase in demand. Monitoring autofluorescence from NADH and flavoproteins reveals that Ca2+ transients stimulate a change in redox state of mitochondria, presumably by activating Ca2+-sensitive dehydrogenases of the TCA cycle. Thus, through activation of downstream pathways, including PKC, cyclin B degradation and mitochondrial activity, intracellular Ca2+ provides a signal that orchestrates the activation of early mammalian development.

https://doi.org/10.1071/SRB04Abs010

© CSIRO 2004

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