Fertilisation calcium signals in the ascidian egg.
The egg of ascidians (urochordate), as virtually all animal and plant species, displays Ca2+ signals upon fertilisation. These Ca2+ signals are repetitive Ca2+ waves that initiate in the cortex of the egg and spread through the whole egg interior. Two series of Ca2+ waves triggered from two distinct Ca2+ wave pacemakers entrain the two meiotic divisions preceding entry into the first interphase. The second messenger inositol (1,4,5) trisphosphate (IP3) is the main mediator of these global Ca2+ waves. Other Ca2+ signalling pathways (RyR and NAADPR) are functional in the egg but they mediate localised cortical Ca2+ signals whose physiological significance remains unclear. The meiosis I Ca2+ wave pacemaker is mobile and relies on intracellular Ca2+ release from the endoplasmic reticulum (ER) induced by a large production of IP3 at the sperm aster site. The meiosis II Ca2+ wave pacemaker is stably localised in a vegetal protrusion called the contraction pole. It is probable that a local production of IP3 in the contraction pole determines the site of this second pacemaker while functional interactions between ER and mitochondria regulate its activity. Finally, a third ectopic pacemaker can be induced by a global increase in IP3, making the ascidian egg a unique system where three different Ca2+ wave pacemakers coexist in the same cell.
Dumollard
Rémi
R
Department of Physiology, University College London, Gower Street, London, WC1E 6BT, UK. r.dumollard@ucl.ac.uk
McDougall
Alex
A
Rouvière
Christian
C
Sardet
Christian
C
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D005260:Female; D005306:Fertilization / Q000502:physiology*; D010063:Ovum / Q000378:metabolism*; D014561:Urochordata / Q000378:metabolism*
D002118:Calcium