Faculté des Sciences de Tunis, LR18ES41 Ecologie, Biologie et Physiologie des organismes aquatiques, Université de Tunis El Manar, 2092, Tunis, Tunisia.
Faculty of Natural Sciences, Institute of Biology, Biotechnology and Environmental Protection, University of Silesia in Katowice, Bankowa, 9, 40-007, Katowice, Poland.
Protoplasma. 2021 Jan;258(1):191-207. doi: 10.1007/s00709-020-01560-7. Epub 2020 Oct 9.
This study reveals the ovary micromorphology and the course of oogenesis in the leech Batracobdella algira (Glossiphoniidae). Using light, fluorescence, and electron microscopies, the paired ovaries were analyzed. At the beginning of the breeding season, the ovaries were small, but as oogenesis progressed, they increased in size significantly, broadened, and elongated. A single convoluted ovary cord was located inside each ovary. The ovary cord was composed of numerous germ cells gathered into syncytial groups, which are called germ-line cysts. During oogenesis, the clustering germ cells differentiated into two functional categories, i.e., nurse cells and oocytes, and therefore, this oogenesis was recognized as being meroistic. As a rule, each clustering germ cell had one connection in the form of a broad cytoplasmic channel (intercellular bridge) that connected it to the cytophore. There was a synchrony in the development of the clustering germ cells in the whole ovary cord. In the immature leeches, the ovary cords contained undifferentiated germ cells exclusively, from which, previtellogenic oocytes and nurse cells differentiated as the breeding season progressed. Only the oocytes grew considerably, gathered nutritive material, and protruded at the ovary cord surface. The vitellogenic oocytes subsequently detached from the cord and filled tightly the ovary sac, while the nurse cells and the cytophore degenerated. Ripe eggs were finally deposited into the cocoons. A comparison of the ovary structure and oogenesis revealed that almost all of the features that are described in the studied species were similar to those that are known from other representatives of Glossiphoniidae, which indicates their evolutionary conservatism within this family.
本研究揭示了蛭形蚓目 Batracobdella algira 的卵巢微观结构和卵子发生过程。使用光镜、荧光显微镜和电子显微镜对成对的卵巢进行了分析。在繁殖季节开始时，卵巢很小，但随着卵子发生的进行，卵巢显著增大、变宽和伸长。每个卵巢内都有一条单独的卷曲卵巢索。卵巢索由聚集在一起的许多生殖细胞组成，这些细胞被称为生殖细胞囊。在卵子发生过程中，聚集的生殖细胞分化为两个功能类别，即滋养细胞和卵母细胞，因此，这种卵子发生被认为是有丝分裂的。通常，每个聚集的生殖细胞只有一个宽细胞质通道（细胞间桥）的连接，将其与细胞体连接。整个卵巢索中聚集的生殖细胞的发育具有同步性。在未成熟的蛭形蚓中，卵巢索仅含有未分化的生殖细胞，随着繁殖季节的进行，这些生殖细胞分化为卵原细胞和滋养细胞。只有卵母细胞显著生长，聚集营养物质，并在卵巢索表面突出。随后，卵黄生成的卵母细胞从索状组织上脱落，紧紧填充卵巢囊，而滋养细胞和细胞体则退化。成熟的卵子最终被沉积到茧中。卵巢结构和卵子发生的比较表明，在所研究的物种中描述的几乎所有特征都与其他蛭形蚓目代表物种中的特征相似，这表明它们在该科内具有进化保守性。
