Faculty of Bioresources, Mie University, 1577 Kurimamachiya, Tsu, Mie, 514-8507, Japan.
Dev Genes Evol. 2010 Nov;220(5-6):139-49. doi: 10.1007/s00427-010-0335-3. Epub 2010 Aug 20.
In bivalve, the distribution of primordial germ cells can be traced from early embryogenesis to the veliger larva by the expression of the vasa ortholog. However, the distribution of germ cells from metamorphosis to maturation in bivalves has not been examined extensively. In this study, we used in situ hybridization to observe expression of the Mytilus galloprovincialis vasa-like gene (Myvlg). The distribution of germ cells was clarified in immature mussels. We observed germ cells in adult mussels during the non-reproductive and reproductive seasons. Myvlg was specifically expressed in germ cells. Gametogenesis occurs in acini surrounded by connective tissue. Myvlg expression was detected in spermatogonia, spermatocytes, oogonia, and oocytes. In the non-reproductive season, gametes were not observed in the acini, but Myvlg was expressed in germinal stem cells along the acini. The expression intensity in the non-reproductive season, however, was much weaker than that in the reproductive season. Myvlg-positive cells proliferated during the non-reproductive season. In immature mussels, a pair of germ cell clumps was distributed laterally in the connective tissue between the nephric tubules and posterior byssal retractor muscle. Germ cells were also observed along pericardium. When immature mussels grew, a pair of germ cell clumps migrated anteriorly in the connective tissue along the outer epithelium at the dorsal region of the mantle base between the mantle and gill. The number of germ cells increased significantly as the mussels grew. This is the first report to observe the proliferation and migration of germ cells in immature mussels.
在双壳类动物中，通过 vasa 同源基因的表达，可以从早期胚胎发生追踪到原生殖细胞在面盘幼虫中的分布。然而，双壳类动物从变态到成熟过程中生殖细胞的分布尚未被广泛研究。在本研究中，我们使用原位杂交技术观察了贻贝 Mytilus galloprovincialis vasa 样基因（Myvlg）的表达。在未成熟贻贝中，明确了生殖细胞的分布。我们在非繁殖和繁殖季节观察了成年贻贝中的生殖细胞。Myvlg 特异性表达于生殖细胞中。生殖细胞发生于被结缔组织包围的腺泡中。Myvlg 在精原细胞、精母细胞、卵原细胞和卵母细胞中均有表达。在非繁殖季节，腺泡中未观察到配子，但在腺泡周围的生殖干细胞中检测到了 Myvlg 的表达。然而，非繁殖季节的表达强度远低于繁殖季节。在非繁殖季节，Myvlg 阳性细胞增殖。在未成熟贻贝中，一对生殖细胞团块位于靠近肾管和后闭壳肌的结缔组织中。在心脏周围也观察到了生殖细胞。当未成熟贻贝生长时，一对生殖细胞团块在结缔组织中沿着外套膜基部背部外套膜和鳃之间的外上皮向前迁移。随着贻贝的生长，生殖细胞的数量显著增加。这是首次观察到未成熟贻贝中生殖细胞的增殖和迁移。
