Activators of protein kinase C trigger cortical granule exocytosis, cortical contraction, and cleavage furrow formation in Xenopus laevis oocytes and eggs.

Abstract

Abstract. Prophase I oocytes, free of follicle cells, and metaphase II eggs of the amphibian Xenopus laevis were subjected to transient treatments with the protein kinase C activators, phorbol 12-myristate 13-acetate (PMA), phorbol 12,13-didecanoate, and 1-olyeoyl-2-acetyl-sn-glycerol. In both oocytes and eggs, these treatments triggered early events of amphibian development: cortical granule exocytosis, cortical contraction, and cleavage furrow formation. Surprisingly, activation of oocytes occurred in the absence of meiotic resumption, resulting in cells with an oocytelike nucleus and interior cytoplasm, but with a zygotelike cortex. PMA-induced activation of oocytes and eggs did not require external calcium, a prerequisite for normal activation of eggs. PMA-induced activation of eggs was inhibited by retinoic acid, a known inhibitor of protein kinase C. In addition, pretreatment of eggs with retinoic acid prevented activation by mechanical stimulation and inhibited activation by calcium ionophore A23187. The results suggest that protein kinase C activation is an integral component of the Xenopus fertilization pathway.T HE program of fertilization in frog eggs is similar to that of sea urchin eggs (20, 49), fish eggs (24, 25), and mammalian eggs (17,40) in that it involves a wavelike increase in intracellular free calcium (7, 36), which precedes a wave of cortical granule exocytosis (26, 36). Cortical granule exocytosis in the frog Xenopus laevis is followed by contraction of the cortex and later, the formation of the first cleavage furrow (for a table of postfertilization events, see reference 55). Cortical granule exocytosis, cortical contraction, and cleavage furrow formation are the morphological hallmarks of frog egg activation, and provide convenient markers for use in the dissection of the activation process (21, 28).The discovery that inositol-l,4,5-trisphosphate (IPa),* an intermediate of the polyphosphoinositide pathway, triggered the intracellular wave of calcium and activated Xenopus eggs led to the suggestion that polyphosphoinositide turnover mediates the activation of Xenopus eggs (8, 44). Added support for this hypothesis is derived from studies of fertilization in sea urchins, mammals, and fish which indicate that IP3 formation triggers the wave of increase in intracellular free calcium (16,39,43,52,54). More recently, this hypothesis has been further strengthened by the finding that stimulation of receptors that trigger IP3 formation induces activation of Xenopus eggs (35).1. Abbreviations used in this paper: IP3, inositol-l,4,5-triphosphate; PD, phorbol 12,13-didecanoate; PDD, 4 ct-phorbol 12,13-didecanoate; PKC, protein kinase C; PMA, phorbol 12-myristate 13-acetate; OAG, 1-olyeolyl-2-acetyl-sn-glycerol.IP3 is one of two intermediates produced by the activity of phospholipase C in the polyphosphoinositide pathway. This bifurcating signal pathway results in the formation of IP3 with the stoichiometric production of diacylglycerol (for reviews, see reference 4 and 42) and the latter activates...

sn-1,2-diacylglycerol and choline increase after fertilization in Xenopus laevis.

“…Phosphorylation studies suggest that PKC inhibits cleavage furrow formation (Satterwhite et al, 1992) and a phorbol ester has been found to inhibit cleavage in mouse oocytes (Niemierko and Komar, 1985). Because phorbol esters rapidly down-regulate at least one PKC isozyme in Xenopus (Sahara et al, 1992), phorbol ester may induce cleavage furrow formation in Xenopus [for review, Bement and Capco (1989, 1990, 1991a Significance of the DAG Changes The timing of the PKC activation is crucial because events such as cortical granule breakdown and cleavage may be due to PKC (see review by Bement, 1992). In Xenopus, the initial increases in DAG and PKC activation are after the peaks of [Ca2+]i (Busa et al, 1985b) or IP3 (Stith et al, 1993(Stith et al, , 1994.…”

“…DAG, the other second messenger, may also play a role in fertilization. By acting as an activator of protein kinase C (PKC; Nishizuka, 1992), DAG may induce DAG, sn-1,2-diacylglycerol; IP3, inositol 1,4,5-trisphosphate; MBS, modified Barth's solution; PA, phosphatidic acid; PC, phosphatidylcholine; PIP2, phosphatidylinositol 4,5-bisphosphate; PKC, protein kinase C. resumption of endocytosis (Vasilets et al, 1990;Khan et al, 1991), cortical contraction, cortical granule exocytosis, chromosome decondensation, nuclear envelope and Golgi reformation, and cleavage furrow formation in Xenopus laevis (Bement and Capco, 1989, 1990, 1991a. PKC may be responsible for elevation of intracellular pH in sea urchin fertilization (Shen and Buck, 1990).…”

The effect of protein kinase C activator and nitric oxide donor on oocyte activation and cortical granule exocytosis in porcine eggs

“…Several studies have demonstrated the possible involvement of PKC in the oocyte activation process (Colonna et al, 1997;Green et al, 1999;Sedmíková et al, 2006) and the exocytosis of CGs (Bement and Capco, 1989;Fan et al, 2002). PKC belongs to the serine/threonine kinase, and 12 isoforms are known, being classified into three groups.…”

PKC Regulation of Gametogenesis and Early Development

“…Conventional, resin-embedded transmission electron microscopy has been utilized by investigators as a powerful tool to interrogate the ultrastructural changes that accompany www.intechopen.com fertilization (Bement and Capco, 1989;Gallicano et al, 1991Gallicano et al, , 1994. However, mammalian eggs and embryos do not afford high contrast images in resin-embedded, ultrathin sections (silver to gold interference patterns corresponding to 60-70 nm).…”