Increased sensitivity and clustering of elementary Ca super(2+) release events during oocyte maturation

• Published in: Developmental biology 2004-11, Vol.275 (1), p.170-182
• Main Author: Machaca, K
• Format: Article
• Language: English
• Subjects: Freshwater; Xenopus
• ISSN: 0012-1606
• DOI: 10.1016/j.ydbio.2004.08.004

The universal signal for egg activation at fertilization is a rise in cytoplasmic Ca super(2+) with defined spatial and temporal kinetics. Mammalian and amphibian eggs acquire the ability to produce such Ca super(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 super(2+) waves that can be oscillatory in nature in response to IP sub(3). In contrast, mature eggs produce a single continuous, sweeping Ca super(2+) wave in response to IP sub(3) or sperm fusion. The mechanisms mediating the differentiation of Ca super(2+) signaling during oocyte maturation are not well understood. Here, I characterized elementary Ca super(2+) release events (Ca super(2+) puffs) in oocytes and eggs and show that the sensitivity of IP sub(3)-dependent Ca super(2+) release is greatly enhanced during oocyte maturation. Furthermore, Ca super(2+) puffs in eggs have a larger spatial fingerprint, yet are short lived compared to oocyte puffs. Most interestingly, Ca super(2+) puffs cluster during oocyte maturation resulting in a continuum of Ca super(2+) release sites over space in eggs. These changes in the spatial distribution of elementary Ca super(2+) release events during oocyte maturation explain the continuous nature and slower speed of the fertilization Ca super(2+) wave.