Urbisz Anna Z, Chajec Łukasz, Brąszewska-Zalewska Agnieszka, Kubrakiewicz Janusz, Świątek Piotr
Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007 Katowice, Poland.
Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007 Katowice, Poland.
Dev Biol. 2017 Jun 1;426(1):28-42. doi: 10.1016/j.ydbio.2017.04.009. Epub 2017 Apr 19.
The paired ovaries of E. albidus are like a bunch of grapes and are composed of clearly separated units, syncytial germ cysts (clusters), which are surrounded by a thin layer of somatic cells. Each cyst maintains the connection with the ovary by an extended stalk that is composed of somatic cells. The spatial architecture of the germ-line cysts found in E. albidus is the same as in other clitellate annelids that have been studied to date. As a rule, germ cells are located at the cyst periphery and each has only one ring canal that connects it to the common and centrally located cytoplasmic mass, the cytophore. Here we present data about the F-actin and microtubular cytoskeleton and some molecular components of the germ-line cysts. We show that the ring canals have an inner rim that is enriched with microfilaments and proteins that contain phosphotyrosine. The microtubules form a loose network in the cytoplasm of the oocyte and nurse cells; moreover, some of them pass through the ring canals to the cytophore. Numerous microtubules are also located in the somatic cells. The germ-line cysts in E. albidus ovaries consist of 16 cells, which is the lowest known number of interconnected germ cells within clitellate annelids. During oogenesis, the fate of interconnected germ cells differentiates and only one cell develops as the future egg, while the other 15 become nurse cells. This differentiation means ovary meroism. The nurse cells gather cell organelles and storage material that then pass through the ring canals and cytophore moving towards the growing oocyte. At the end of oogenesis, the vitellogenic oocyte surrounds the siblings' cells together with the cytophore and engulfs their remnants into the ooplasm. No morphological or molecular markers of the apoptosis of the nurse cells were found. Moreover, the nurse cells did not undergo polyploidisation. The measured DNA level was 4C, which indicates that these cells are not highly-specialised.
白线蚓的成对卵巢像一串葡萄，由明显分开的单元即合胞体生殖囊肿（簇）组成，这些囊肿被一层薄薄的体细胞包围。每个囊肿通过由体细胞组成的延长柄与卵巢保持连接。在白线蚓中发现的生殖系囊肿的空间结构与迄今为止研究过的其他寡毛纲环节动物相同。通常，生殖细胞位于囊肿周边，每个生殖细胞只有一个环形通道将其连接到共同的、位于中央的细胞质团即细胞团。在这里，我们展示了关于F-肌动蛋白和微管细胞骨架以及生殖系囊肿的一些分子成分的数据。我们表明，环形通道有一个富含微丝和含磷酸酪氨酸蛋白质的内边缘。微管在卵母细胞和滋养细胞的细胞质中形成一个松散的网络；此外，其中一些微管穿过环形通道到达细胞团。许多微管也位于体细胞中。白线蚓卵巢中的生殖系囊肿由16个细胞组成，这是寡毛纲环节动物中已知的相互连接的生殖细胞的最低数量。在卵子发生过程中，相互连接的生殖细胞的命运发生分化，只有一个细胞发育为未来的卵子，而其他15个细胞成为滋养细胞。这种分化意味着卵巢异律分节。滋养细胞收集细胞器和储存物质，然后这些物质通过环形通道和细胞团向生长中的卵母细胞移动。在卵子发生结束时，卵黄生成的卵母细胞将同胞细胞与细胞团一起包围，并将它们的残余物吞噬到卵质中。未发现滋养细胞凋亡的形态学或分子标记。此外，滋养细胞没有经历多倍体化。测得的DNA水平为4C，这表明这些细胞不是高度特化的。
