Ueno Tomoyo, Ohgami Takehiro, Harada Yuichirou, Ueno Shuichi, Iwao Yasuhiro
Laboratory of Molecular Developmental Biology, Department of Applied Molecular Biosciences, Graduate School of Medicine, Yamaguchi University, 753-8512 Yamaguchi, Japan.
Int J Dev Biol. 2014;58(5):315-23. doi: 10.1387/ijdb.130333yi.
The egg of the polyspermic newt is activated by Ca(2+) waves induced by several sperm at fertilization. A major component of the sperm factor for egg activation is the sperm-specific citrate synthase (CS), which is introduced into the egg cytoplasm after sperm-egg fusion. We tried to clarify the mechanism for sperm-specific CS to induce [Ca(2+)]i increase in egg cytoplasm. The injection of the sperm factor into the unfertilized egg induces a [Ca(2+)]i increase that propagates over the whole egg surface as a Ca(2+) wave. The propagation of the Ca(2+) wave is inhibited by depolymerization of microtubules in the egg cytoplasm. The sperm-specific CS is highly phosphorylated and binds the component containing microtubules and the IP3 receptor. The sperm CS localized in the midpiece region was dispersed in the egg cytoplasm, but most of the CS accumulates at the sperm entry site and is distributed in association with the microtubules around the midpiece region and the nucleus. Phospholipase C (PLC) γ in egg cytoplasm also accumulates around the midpiece region in association with the sperm CS. Thus, CS at the initiation site of the Ca(2+) wave forms a complex of microtubules and endoplasmic reticulum (ER) with the IP3 receptor, in addition to PLCγ, indicating close involvement of those complexes in Ca(2+) releases from the ER by the sperm factor.
多精蝾螈的卵在受精时由多个精子诱导的Ca(2+)波激活。卵子激活的精子因子的一个主要成分是精子特异性柠檬酸合酶（CS），它在精卵融合后被引入卵细胞质中。我们试图阐明精子特异性CS诱导卵细胞质中[Ca(2+)]i增加的机制。将精子因子注入未受精卵会诱导[Ca(2+)]i增加，并作为Ca(2+)波在整个卵表面传播。卵细胞质中微管的解聚会抑制Ca(2+)波的传播。精子特异性CS高度磷酸化，并与包含微管和IP3受体的成分结合。位于中段区域的精子CS分散在卵细胞质中，但大部分CS聚集在精子进入位点，并与中段区域和细胞核周围的微管相关分布。卵细胞质中的磷脂酶C（PLC）γ也与精子CS相关，聚集在中段区域周围。因此，Ca(2+)波起始位点的CS除了与PLCγ一起，还与IP3受体形成微管和内质网（ER）的复合物，表明这些复合物密切参与了精子因子从内质网释放Ca(2+)的过程。
