Świątek Piotr, de Wit Pierre, Jarosz Natalia, Chajec Łukasz, Urbisz Anna Z
Department of Animal Histology and Embryology, Faculty of Biology and Environmental Protection, University of Silesia in Katowice, Bankowa 9, 40-007 Katowice, Poland.
Department of Marine Sciences, The Sven Lovén Centre for Marine Infrastructure at Tjärnö, University of Gothenburg, SE-45296 Strömstad, Sweden.
Zoology (Jena). 2018 Feb;126:119-127. doi: 10.1016/j.zool.2017.11.004. Epub 2017 Nov 14.
The genus Grania comprises over 70 species of exclusively marine clitellate annelids belonging to the family Enchytraeidae. Morphologically, this genus is well separated from other enchytraeids, with thick cuticles, anterior segments I-IV fused into a "head", chaetal bundles consisting only of one stout chaeta, and reduction of circular musculature. The aim of the present study is to describe the ovary organization and the course of oogenesis in Grania postclitellochaeta, and to compare it with other known systems of ovary organization and oogenesis in clitellate annelids, especially in enchytraeids. Generally, oogenesis in G. postclitellochaeta can be divided into two phases: (i) early stages of oogenesis, occurring within the paired ovaries - each ovary is similar to a bunch of grapes, where each 'lobe' is a germ-line cyst enveloped by flat somatic cells, and (ii) oogenesis proper, which takes place within the body lumen where each growing oocyte is accompanied by its own group of nurse cells. Germ cells are interconnected by cytoplasmic channels (intercellular bridges, ring canals) and form syncytial cysts. As in other clitellate annelids, the cyst center contains a common cytoplasm (cytophore) to which each cell is connected by one ring canal only. Initially, within the ovary, all interconnected cells develop synchronously and are morphologically similar. At the time when the cysts detach from the ovary, one of the interconnected cells begins to gather nutrients, grows and becomes an oocyte, whereas the rest of the cells (nurse cells) do not continue meiosis and instead seem to provide the oocyte with macromolecules and cell organelles. Analysis of serial sections reveals that cysts are always composed of 16 cells - one oocyte and fifteen nurse cells. A comparative analysis showed that almost all features of oogenesis in G. postclitellochaeta are similar to that in other representatives of Enchytraeidae (mainly Enchytraeus albidus), suggesting evolutionary conservation of the process across this family.
格拉尼亚属包含70多种仅生活在海洋中的寡毛纲环节动物，属于线蚓科。从形态学上看，该属与其他线蚓科动物有明显区别，其角质层较厚，身体前部的第I - IV节融合成一个“头部”，刚毛束仅由一根粗壮的刚毛组成，环形肌肉组织减少。本研究的目的是描述后刚毛细蚓的卵巢组织和卵子发生过程，并将其与寡毛纲环节动物，特别是线蚓科动物中其他已知的卵巢组织和卵子发生系统进行比较。一般来说，后刚毛细蚓的卵子发生可分为两个阶段：（i）卵子发生的早期阶段，发生在成对的卵巢内——每个卵巢类似于一串葡萄，其中每个“叶”是一个由扁平体细胞包裹的生殖系囊肿；（ii）真正的卵子发生阶段，发生在体腔内，每个正在生长的卵母细胞都伴有其自身的一组滋养细胞。生殖细胞通过细胞质通道（细胞间桥、环管）相互连接，形成合胞体囊肿。与其他寡毛纲环节动物一样，囊肿中心含有一个共同的细胞质（胞质团），每个细胞仅通过一个环管与之相连。最初，在卵巢内，所有相互连接的细胞同步发育，形态相似。当囊肿从卵巢脱离时，其中一个相互连接的细胞开始积累营养物质、生长并成为一个卵母细胞，而其余细胞（滋养细胞）则不再继续减数分裂，而是似乎为卵母细胞提供大分子和细胞器。连续切片分析表明，囊肿总是由16个细胞组成——一个卵母细胞和15个滋养细胞。比较分析表明，后刚毛细蚓卵子发生的几乎所有特征都与线蚓科的其他代表物种（主要是白色线蚓）相似，这表明该过程在这个科中具有进化保守性。
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