Increased sensitivity and clustering of elementary Ca2+ release events during oocyte maturation.
The universal signal for egg activation at fertilization is a rise in cytoplasmic Ca(2+) with defined spatial and temporal kinetics. Mammalian and amphibian eggs acquire the ability to produce such Ca(2+) signals during a maturation period that precedes fertilization and encompasses resumption of meiosis and progression to metaphase II. In Xenopus, immature oocytes produce fast, saltatory Ca(2+) waves that can be oscillatory in nature in response to IP(3). In contrast, mature eggs produce a single continuous, sweeping Ca(2+) wave in response to IP(3) or sperm fusion. The mechanisms mediating the differentiation of Ca(2+) signaling during oocyte maturation are not well understood. Here, I characterized elementary Ca(2+) release events (Ca(2+) puffs) in oocytes and eggs and show that the sensitivity of IP(3)-dependent Ca(2+) release is greatly enhanced during oocyte maturation. Furthermore, Ca(2+) puffs in eggs have a larger spatial fingerprint, yet are short lived compared to oocyte puffs. Most interestingly, Ca(2+) puffs cluster during oocyte maturation resulting in a continuum of Ca(2+) release sites over space in eggs. These changes in the spatial distribution of elementary Ca(2+) release events during oocyte maturation explain the continuous nature and slower speed of the fertilization Ca(2+) wave.
Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA. kamachaca@uams.edu
Khaled
K
Machaca
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D005260:Female; D053496:Inositol 1,4,5-Trisphosphate Receptors; D007700:Kinetics; D009865:Oocytes / Q000378:metabolism*; D010063:Ovum / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D013997:Time Factors; D014981:Xenopus
D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D002118:Calcium