Development, Vol 121, Issue 10 3457-3466, Copyright © 1995 by Company of Biologists

JOURNAL ARTICLES

The sperm entry point defines the orientation of the calcium-induced contraction wave that directs the first phase of cytoplasmic reorganization in the ascidian egg

F Roegiers, A McDougall and C Sardet
URA 671 Biologie Cellulaire Marine, CNRS, Universite P. et M. Curie, Villefranche-sur-Mer, France.

Ascidians eggs are spawned with their cytoskeleton and organelles organized along a preexisting animal-vegetal axis. Fertilization triggers a spectacular microfilament-dependant cortical contraction that causes the relocalization of preexisting cytoplasmic domains and the creation of new domains in the lower part of the vegetal hemisphere. We have investigated the relationship between fertilization, the cortical contraction and the localization of cytoplasmic domains in eggs of the ascidian Phallusia mammillata. We have also examined the link between this first phase of ooplasmic segregation and the site of gastrulation. The cortical contraction was found to be initiated on the side of the egg where intracellular calcium is first released either by the entering sperm or by photolysis of caged InsP3. The cortical contraction carries the sperm nucleus towards the vegetal hemisphere along with a subcortical mitochondria-rich domain (the myoplasm). If the sperm enters close to the animal or vegetal poles the cortical contraction is symmetrical, travelling along the animal-vegetal axis. If the sperm enters closer to the equator, the contraction is asymmetrical and its direction does not coincide with the animal-vegetal axis. The direction of contraction defines an axis along which preexisting (such as the myoplasm) or newly created cytoplasmic domains are relocalized. Two microfilament-rich surface constrictions, the 'contraction pole' and the 'vegetal button' (which forms 20 minutes later), appear along that axis approximately opposite the site where the contraction is initiated. The contraction pole can be situated as much as 55 degrees from the vegetal pole, and its location predicts the site of gastrulation. It thus appears that in ascidian eggs, the organization of the egg before fertilization defines a 110 degrees cone centered around the vegetal pole in which the future site of gastrulation of the embryo will lie. The calcium wave and cortical contraction triggered by the entering sperm adjust the location of cytoplasmic domains along an axis within that permissive zone. We discuss the relation between that axis and the establishment of the dorsoventral axis in the ascidian embryo.
CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?

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]

				C. R. Cowan and A. A. Hyman Acto-myosin reorganization and PAR polarity in C. elegans Development, March 15, 2007; 134(6): 1035 - 1043. [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]

				H. Parry, A. McDougall, and M. Whitaker Microdomains bounded by endoplasmic reticulum segregate cell cycle calcium transients in syncytial Drosophila embryos J. Cell Biol., October 10, 2005; 171(1): 47 - 59. [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]

				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]

				C. Sardet, H. Nishida, F. Prodon, and K. Sawada Maternal mRNAs of PEM and macho 1, the ascidian muscle determinant, associate and move with a rough endoplasmic reticulum network in the egg cortex Development, December 1, 2003; 130(23): 5839 - 5849. [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]

				G. FitzHarris, P. Marangos, and J. Carroll Cell Cycle-dependent Regulation of Structure of Endoplasmic Reticulum and Inositol 1,4,5-Trisphosphate-induced Ca2+ Release in Mouse Oocytes and Embryos Mol. Biol. Cell, January 1, 2003; 14(1): 288 - 301. [Abstract] [Full Text]

				R. Dumollard and C. Sardet Three different calcium wave pacemakers in ascidian eggs J. Cell Sci., January 7, 2001; 114(13): 2471 - 2481. [Abstract] [Full Text] [PDF]

				A McDougall, M Levasseur, A. O'Sullivan, and K. Jones Cell cycle-dependent repetitive Ca(2+ )waves induced by a cytosolic sperm extract in mature ascidian eggs mimic those observed at fertilization J. Cell Sci., January 10, 2000; 113(19): 3453 - 3462. [Abstract] [PDF]

				C. Garello, H. Baker, J. Rai, S. Montgomery, P. Wilson, C.R. Kennedy, and G.M. Hartshorne Pronuclear orientation, polar body placement, and embryo quality after intracytoplasmic sperm injection and in-vitro fertilization: further evidence for polarity in human oocytes? Hum. Reprod., October 1, 1999; 14(10): 2588 - 2595. [Abstract] [Full Text] [PDF]

				F Roegiers, C Djediat, R Dumollard, C Rouviere, and C Sardet Phases of cytoplasmic and cortical reorganizations of the ascidian zygote between fertilization and first division Development, January 6, 1999; 126(14): 3101 - 3117. [Abstract] [PDF]

				L Alessa and D. Kropf F-actin marks the rhizoid pole in living Pelvetia compressa zygotes Development, January 1, 1999; 126(1): 201 - 209. [Abstract] [PDF]

				A McDougall and M Levasseur Sperm-triggered calcium oscillations during meiosis in ascidian oocytes first pause, restart, then stop: correlations with cell cycle kinase activity Development, January 11, 1998; 125(22): 4451 - 4459. [Abstract] [PDF]

				K Kyozuka, R Deguchi, T Mohri, and S Miyazaki Injection of sperm extract mimics spatiotemporal dynamics of Ca2+ responses and progression of meiosis at fertilization of ascidian oocytes Development, January 10, 1998; 125(20): 4099 - 4105. [Abstract] [PDF]