Urbisz Anna Z, Chajec Łukasz, Świątek Piotr
Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007 Katowice, Poland.
PLoS One. 2015 May 22;10(5):e0126173. doi: 10.1371/journal.pone.0126173. eCollection 2015.
Recent studies on the ovary organization and oogenesis in Tubificinae have revealed that their ovaries are small polarized structures that are composed of germ cells in subsequent stages of oogenesis that are associated with somatic cells. In syncytial cysts, as a rule, each germ cell is connected to the central cytoplasmic mass, the cytophore, via only one stable intercellular bridge (ring canal). In this paper we present detailed data about the composition of germ-line cysts in Tubifex tubifex with special emphasis on the occurrence and distribution of the cytoskeletal elements. Using fixed material and live cell imaging techniques, we found that the entire ovary of T. tubifex is composed of only one, huge multicellular germ-line cyst, which may contain up to 2,600 cells. Its architecture is broadly similar to the cysts that are found in other clitellate annelids, i.e. a common, anuclear cytoplasmic mass in the center of the cyst and germ cells that are connected to it via intercellular bridges. The cytophore in the T. tubifex cyst extends along the long axis of the ovary in the form of elongated and branched cytoplasmic strands. Rhodamine-coupled phalloidin staining revealed that the prominent strands of actin filaments occur inside the cytophore. Similar to the cytophore, F-actin strands are branched and they are especially well developed in the middle and outermost parts of the ovary. Microfilaments are also present in the ring canals that connect the germ cells with the cytophore in the narrow end of the ovary. Using TubulinTracker, we found that the microtubules form a prominent network of loosely and evenly distributed tubules inside the cytophore as well as in every germ cell. The well-developed cytoskeletal elements in T. tubifex ovary seem to ensure the integrity of such a huge germ-line cyst of complex (germ cells-ring canals-cytophore) organization. A comparison between the cysts that are described here and other well-known female germ-line cysts is also made.
近期对颤蚓科卵巢组织和卵子发生的研究表明，它们的卵巢是小型极化结构，由卵子发生后续阶段的生殖细胞与体细胞组成。在合胞体囊肿中，通常每个生殖细胞仅通过一条稳定的细胞间桥（环管）与中央细胞质团（细胞滋养体）相连。在本文中，我们提供了关于颤蚓生殖系囊肿组成的详细数据，特别强调了细胞骨架成分的出现和分布。通过使用固定材料和活细胞成像技术，我们发现颤蚓的整个卵巢仅由一个巨大的多细胞生殖系囊肿组成，其中可能包含多达2600个细胞。其结构与其他寡毛纲环节动物中发现的囊肿大致相似，即囊肿中央有一个共同的无核细胞质团，生殖细胞通过细胞间桥与之相连。颤蚓囊肿中的细胞滋养体以细长且分支的细胞质链形式沿卵巢长轴延伸。罗丹明偶联鬼笔环肽染色显示，肌动蛋白丝的突出链出现在细胞滋养体内。与细胞滋养体类似，F-肌动蛋白丝也是分支状的，并且在卵巢中部和最外层特别发达。微丝也存在于连接生殖细胞与卵巢窄端细胞滋养体的环管中。使用微管蛋白追踪剂，我们发现微管在细胞滋养体内部以及每个生殖细胞中形成了一个由松散且均匀分布的小管组成的突出网络。颤蚓卵巢中发育良好的细胞骨架成分似乎确保了这种具有复杂（生殖细胞 - 环管 - 细胞滋养体）组织结构的巨大生殖系囊肿的完整性。本文还对这里描述的囊肿与其他知名的雌性生殖系囊肿进行了比较。
