Mitochondria Required for Second Calcium Waves

Science's STKE  14 Jan 2003:
Vol. 2003, Issue 165, pp. tw27-TW27
DOI: 10.1126/stke.2003.165.tw27

Ascidian oocytes are a model system used to study the signaling events associated with fertilization and completion of meiosis. The sperm triggers a first set of calcium oscillations by the first pacemaker (PM1) upon fertilization, and then the polar body is released. A second set of calcium waves is initiated by pacemaker 2 (PM2) from the region in the vegetal pole where there is a dense network of endoplasmic reticulum (ER) and mitochondria. Pacemakers are defined as the site of the source of the calcium oscillation. Dumollard et al. showed that during the calcium oscillations, mitochondrial respiration was increased. Treatment of the eggs with mitochondrial respiration inhibitors or uncouplers showed that PM2 activity required adenosine-triphosphate (ATP)-generating mitochondria that could accumulate calcium. The PM2-initiated calcium waves could be partially restored by release of caged ATP to restore ATP levels when the mitochondria were inhibited. The authors propose that there is an intimate connection physically and biochemically between the ER and mitochondria in ascidian eggs that controls the calcium oscillations produced by PM2.

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