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doi: 10.1242/10.1242/jcs.00056

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Calcium wave pacemakers in eggs

¹ Bio Mar Cell, Unité de Biologie du Développement UMR 7009 CNRS/Paris VI, Observatoire, Station Zoologique, Villefranche sur Mer, 06230 France
² Department of Physiology, University College London, Gower Street, London, WC1E 6BT, UK
³ Unité de Chronobiologie Théorique, Faculté des Sciences, Université Libre de Bruxelles, Brussels, Belgium

View larger version (28K): [in a new window]   Fig. 1. Cortical Ca2+ wave pacemakers in the ascidian and mouse egg. (A) Sperm-triggered Ca2+ waves in ascidians: the meiotic Ca2+ waves, composed of a fertilization wave (F) followed by repetitive Ca2+ waves, are initiated by two pacemakers (MI PMasc and MII PMasc). (B) An artificial pacemaker (artPMasc, red arrowhead) can be induced in the animal pole of the egg (a) by global UV photorelease of cgPtdIns(4,5)P2. The Ca2+ waves emitted by this pacemaker are preceded by a pacemaker Ca2+ rise (red asterisks). (C) The mouse egg is fertilized at metaphase II and thus possesses only a MII pacemaker (MII PMmouse). After the fertilization wave (F) starting from the point of sperm entry, repetitive calcium waves emanate from the vegetal cortex of the egg. Each calcium wave is preceded by a pacemaker calcium rise (red asterisks). (D) The drawings represent schematically the organization in the ascidian (MI, MII and artPMasc) and mouse egg (MII PMmouse) of the ER network (in red) and mitochondria (in green). Red arrows indicate the direction of the waves, whereas the postulated sites of Ins(1,4,5)P3 production are symbolized as purple dots. sa: sperm aster; cp: contraction pole. (E) Postulated temporal variations of [Ins(1,4,5)P3]c, which may underlie the activity of the meiotic Ca2+ wave pacemakers. Two possibilities remain for the ascidian and mouse MII pacemakers: a sustained Ins(1,4,5)P3 production (pink trace) or oscillatory Ins(1,4,5)P3 production (purple trace).

View larger version (62K): [in a new window]   Fig. 2. Ca2+ wave pacemakers in eggs. (A) A sequence showing a Ca2+ wave initiated by the meiosis II pacemaker (MII PM) in the vegetal pole (v) of a mouse egg injected with sperm extracts. The second polar body is visible in the animal pole (a). (B) A sequence showing two examples of fertilized ascidian eggs displaying Ca2+ waves initiated by the MII calcium wave pacemaker located in the vegetal contraction pole (MII PM). (C) Two examples of a UV flash releasing cgPtdIns(4,5)P2 applied between two waves, the fertilized ascidian eggs respond by eliciting a wave from the animal pole of the egg (artPM). (D) The distribution of ER and mitochondria in the contraction pole (cp). A layer of cortical ER in the cortical most layer can be seen (in red) juxtaposed to the mitochondria-rich sub-cortical region (in green). (E) Schematic representation of the contraction pole showing the microvillated plasma membrane, microfilaments (in blue), as well as the ER-rich domains in the cortex (red) and the mitochondria-rich subcortical domain (green). (F) Calcium Green/Texas Red ratiometric image of [Ca2+]c, showing the initiation of a Ca2+ wave elicited by the MII pacemaker in the contraction pole.

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