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Science China Life Sciences

, Volume 54, Issue 8, pp 733–743

First Online: 24 July 2011Received: 10 June 2011Accepted: 20 June 2011

Abstract

Since the first demonstration of sperm entry into the fertilized eggs of Mediterranean sea urchin Paracentrotus lividus by Hertwig 1876, enormous progress and insights have been made on this topic. However, the precise molecular mechanisms underlying fertilization are largely unknown. The two most dramatic changes taking place in the zygote immediately after fertilization are: i a sharp increase of intracellular Ca that initiates at the sperm interaction site and traverses the egg cytoplasm as a wave, and ii the concomitant dynamic rearrangement of the actin cytoskeleton. Traditionally, this has been studied most extensively in the sea urchin eggs, but another echinoderm, starfish, whose eggs are much bigger and transparent, has facilitated experimental approaches using microinjection and fluorescent imaging methodologies. Thus in starfish, it has been shown that the sperm-induced Ca increase in the fertilized egg can be recapitulated by several Ca-evoking second messengers, namely inositol 1,4,5-trisphosphate InsP3, cyclic ADP-ribose cADPr and nicotinic acid adenine dinucleotide phosphate NAADP, which may play distinct roles in the generation and propagation of the Ca waves. Interestingly, it has also been found that the dynamic rearrangement of the actin cytoskeleton in the fertilized eggs plays pivotal roles in guiding monospermic sperm entry and in the fine modulation of the intracellular Ca signaling. As it is well known that Ca regulates the structure of the actin cytoskeleton, our finding that Ca signaling can be reciprocally affected by the state of the actin cytoskeleton raises an intriguing possibility that actin and Ca signaling may form a ‘positive feedback loop’ that accelerates the downstream events of fertilization. Perturbation of the cortical actin networks also inhibits cortical granules exocytosis. Polymerizing actin bundles also compose the ‘acrosome process,’ a tubular structure protruding from the head of fertilizing sperm. Hence, actin, which is one of the most strictly conserved proteins in eukaryotes, modulates almost all major aspects of fertilization.

Keywordsstarfish calcium egg maturation fertilization PIP2 actin cytoskeleton cofilin This article is published with open access at Springerlink.com

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Autor: Luigia Santella - Jong T. Chun

Fuente: https://link.springer.com/article/10.1007/s11427-011-4202-x



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