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Three different calcium wave pacemakers in ascidian eggs

Rémi Dumollard and Christian Sardet

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

Distribution of the endoplasmic reticulum (labeled with DiIC16) observed in tangential confocal sections of an unfertilized egg along the animal-vegetal axis (animal pole on top). The cursor indicates the level of section (from 1 mm to 15 mm below the cell surface) (see Fig. 1g,h). (see also http://www.obs-vlfr.fr/%7Ebiocell/Biomarcell/biomarcell.html).

Distribution of cytosol observed (with CG dextran) in tangential confocal sections (from 1 mm to 15 mm below the cell surface) of an unfertilized egg oriented along the animal-vegetal axis (animal pole on top) (see also http://www.obs-vlfr.fr/%7Ebiocell/Biomarcell/biomarcell.html).

Confocal ratio imaging of [Ca2+]c in a Phallusia mammillata egg. Three calcium waves triggered by the moving pacemaker PM1. The calcium wave displayed in Fig. 2Ba is the second one of the sequence (see also http://www.obs-vlfr.fr/%7Ebiocell/Biomarcell/biomarcell.html).

Two calcium waves triggered by pacemaker PM2. The calcium wave displayed in Fig. 2Bc is the second one of the sequence (see also http://www.obs-vlfr.fr/%7Ebiocell/Biomarcell/biomarcell.html).

Uncaging cIP3 in activated eggs produces calcium waves. The three first calcium waves correspond to Fig. 3Aa,b,c and are due to three localised UV flashes. The last wave triggered by a global UV flash (Fig. 3Ad) initiates from pacemaker PM3 in the animal pole of the zygote where the first polar body can be observed (top left) (see also http://www.obs-vlfr.fr/%7Ebiocell/Biomarcell/biomarcell.html).

Pacemaker PM3 can be induced by global elevations of intracellular IP3 while pacemaker PM2 is functioning. A first wave is emitted by pacemaker PM2 (Fig. 4a) in the vegetal contraction pole (bottom). A second wave induced by a global UV flash starts from pacemaker PM3 in the opposite pole (top) (Fig. 4uv1). A third wave emanates again from PM2 (Fig. 4b). A second UV flash induces a wave initiating in the vegetal hemisphere (Fig. 4uv2), whereas a third UV flash induces a wave that starts at both poles of the zygote (last wave of the sequence) (Fig. 4uv3) (see also http://www.obs-vlfr.fr/%7Ebiocell/Biomarcell/biomarcell.html).

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