QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

This Article Figures Only Full Text Full Text (PDF) Movies Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Dumollard, R. Articles by Sardet, C. Search for Related Content PubMed PubMed Citation Articles by Dumollard, R. Articles by Sardet, C.

Three different calcium wave pacemakers in ascidian eggs

Bio Mar Cell, Unité de Biologie du Développement UMR 7009 CNRS/Paris VI, Observatoire, Station Zoologique, Villefranche sur Mer, 06230 France

*Author for correspondence (e-mail: sardet{at}obs-vlfr.fr)

Accepted April 12, 2001

Calcium wave pacemakers in fertilized eggs of ascidians and mouse are associated with accumulations of cortical endoplasmic reticulum in the vegetal hemisphere. In ascidians, two distinct pacemakers (PM1 and PM2) generate two series of calcium waves necessary to drive meiosis I and II. Pacemaker PM2 is stably localized in a cortical ER accumulation situated in the vegetal contraction pole. We now find that pacemaker PM1 is situated in a cortical ER-rich domain that forms around the sperm aster and moves with it during the calcium-dependant cortical contraction triggered by the fertilizing sperm.

Global elevations of inositol (1,4,5)-trisphosphate (Ins(1,4,5)P₃) levels produced by caged Ins(1,4,5)P₃ or caged glycero-myo-PtdIns(4,5)P₂ photolysis reveal that the cortex of the animal hemisphere, also rich in ER-clusters, is the cellular region most sensitive to Ins(1,4,5)P₃ and acts as a third type of pacemaker (PM3). Surprisingly, the artificial pacemaker PM3 predominates over the natural pacemaker PM2, located at the opposite pole. Microtubule depolymerization does not alter the activity nor the location of the three pacemakers. By contrast, blocking the acto-myosin driven cortical contraction with cytochalasin B prevents PM1 migration and inhibits PM2 activity. PM3, however, is insensitive to cytochalasin B.

Our experiments suggest that the three distinct calcium wave pacemakers are probably regulated by different spatiotemporal variations in Ins(1,4,5)P₃ concentration. In particular, the activity of the natural calcium wave pacemakers PM1 and PM2 depends on the apposition of a cortical ER-rich domain to a source of Ins(1,4,5)P₃ production in the cortex.

Movies available on-line

Key words: Calcium waves, Fertilization, inositol (1,4,5)-trisphosphate, Cortex, Endoplasmic reticulum, Pacemaker, Eggs, Ascidians

This article has been cited by other articles:

				M. Levasseur, M. Carroll, K. T. Jones, and A. McDougall A novel mechanism controls the Ca2+ oscillations triggered by activation of ascidian eggs and has an absolute requirement for Cdk1 activity J. Cell Sci., May 15, 2007; 120(10): 1763 - 1771. [Abstract] [Full Text] [PDF]

				M. Whitaker Calcium at Fertilization and in Early Development Physiol Rev, January 1, 2006; 86(1): 25 - 88. [Abstract] [Full Text] [PDF]

				F. Prodon, P. Dru, F. Roegiers, and C. Sardet Polarity of the ascidian egg cortex and relocalization of cER and mRNAs in the early embryo J. Cell Sci., June 1, 2005; 118(11): 2393 - 2404. [Abstract] [Full Text] [PDF]

				G. Dupont and R. Dumollard Simulation of calcium waves in ascidian eggs: insights into the origin of the pacemaker sites and the possible nature of the sperm factor J. Cell Sci., August 15, 2004; 117(18): 4313 - 4323. [Abstract] [Full Text] [PDF]

				M. Carroll, M. Levasseur, C. Wood, M. Whitaker, K. T. Jones, and A. McDougall Exploring the mechanism of action of the sperm-triggered calcium-wave pacemaker in ascidian zygotes J. Cell Sci., December 15, 2003; 116(24): 4997 - 5004. [Abstract] [Full Text] [PDF]

				S. A. Stricker and T. L. Smythe Endoplasmic reticulum reorganizations and Ca2+ signaling in maturing and fertilized oocytes of marine protostome worms: the roles of MAPKs and MPF Development, July 1, 2003; 130(13): 2867 - 2879. [Abstract] [Full Text] [PDF]

				R. Dumollard, K. Hammar, M. Porterfield, P. J. Smith, C. Cibert, C. Rouviere, and C. Sardet Mitochondrial respiration and Ca2+ waves are linked during fertilization and meiosis completion Development, February 15, 2003; 130(4): 683 - 692. [Abstract] [Full Text] [PDF]

				R. Dumollard, J. Carroll, G. Dupont, and C. Sardet Calcium wave pacemakers in eggs J. Cell Sci., September 15, 2002; 115(18): 3557 - 3564. [Abstract] [Full Text] [PDF]