Laboratory of Reproductive Developmental Biology and Developmental Cell Biology, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yamaguchi, Japan.
Reproduction. 2022 May 23;164(1):F29-F37. doi: 10.1530/REP-21-0480.
Mature amphibian eggs arrested at meiotic metaphase II must undergo activation to initiate embryonic development soon after fertilization. Fertilizing sperm provide eggs with a signal that induces egg activation, and an increase in intracellular Ca2+ concentration in the egg cytoplasm (a Ca2+ rise) is the most important signal for this initiation. The sperm transmits the signal for the Ca2+ rise, known as the sperm factor, which is divergent between anurans and urodeles. In monospermic anurans, the sperm transmits the signal through a receptor on the egg membrane, causing a single rapid Ca2+ rise. Sperm matrix metalloproteinase-2 is a potential candidate for the receptor-mediated sperm factor in anurans. In physiologically polyspermic urodeles, multiple slower Ca2+ rises are caused by a soluble sperm factor (sperm-specific citrate synthase) which is transferred to the egg cytoplasm after sperm-egg fusion. We discuss the molecular mechanisms of egg activation in amphibian fertilization, focusing on recent progress in characterizing these sperm factors and their divergence during the evolution of tetrapod vertebrates.
成熟的两栖类卵子在减数分裂中期被阻止，必须在受精后立即进行激活，以启动胚胎发育。受精的精子为卵子提供了一个诱导卵子激活的信号，而卵子细胞质中细胞内钙离子浓度的增加（钙离子上升）是这一启动的最重要信号。精子传递钙离子上升的信号，称为精子因子，在无尾两栖动物和有尾两栖动物之间存在差异。在单精入卵的无尾两栖动物中，精子通过卵子膜上的受体传递信号，导致单个快速的钙离子上升。精子基质金属蛋白酶-2是无尾两栖动物中受体介导的精子因子的潜在候选者。在生理上多精入卵的有尾两栖动物中，多个较慢的钙离子上升是由可溶性精子因子（精子特异性柠檬酸合酶）引起的，该因子在精子-卵子融合后被转移到卵子细胞质中。我们讨论了两栖类受精中卵子激活的分子机制，重点是最近在描述这些精子因子及其在四足脊椎动物进化过程中的差异方面的进展。
