Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, Bankowa 9, 40-007 Katowice, Poland.
Department of Life Sciences (Zoology), Manipur University, Canchipur 795003, Manipur, India.
Zoology (Jena). 2023 Oct;160:126109. doi: 10.1016/j.zool.2023.126109. Epub 2023 Aug 10.
Ovaries in earthworms belonging to the family Megascolecidae are paired structures attached to the septum in the anterior part of the XIII segment. They are fan to rosette shaped with numerous rows of growing oocytes, known as egg strings, radiating from the ovary center towards the segmental cavity. The histological and ultrastructural ovary organization in megascolecids and the course of oogenesis remain unknown. The paper presents the results of light and electron microscopy analyses of ovaries in six megascolecid species, three from the genus Amynthas and three from Metaphire. Both parthenogenetic and sexually reproducing species were included in the study. The organization and ultrastructure of ovaries in all studied species are broadly similar. Considering the histological organization of ovaries, they could be divided into two zones. Zone I (proximal, close to the connection with the septum) is tightly packed with germline and somatic cells. Germ cells are interconnected via intercellular bridges and thin strands of the central cytoplasm (known as cytophore) and form syncytial cysts. Cysts unite oogonia, early meiotic cells (till diplotene), and clustering cells develop synchronously. During diplotene, interconnected cells lose developmental synchrony; most probably, one cell per cyst grows faster than others, detaches from the cysts, and becomes an oocyte. The remaining cells grow slightly and are still interconnected via the thin and reticular cytophore; these cells are considered nurse cells. Zone II has a form of egg strings where growing oocytes are isolated one from another by thin somatic cells and form short cords. We present the ultrastructural details of germline and somatic cells. We propose the term "Amynthas" type of ovaries for this ovary organization. We suppose that such ovaries are characteristic of other megascolecids and related families.
蚯蚓的卵巢是成对的结构，附着在第十三节段前部的隔膜上。它们呈扇形或玫瑰花形，有许多排生长中的卵母细胞，称为卵索，从卵巢中心向节段腔辐射。关于大型蚯蚓和生殖细胞发生过程中的卵巢组织的组织学和超微结构仍然未知。本文介绍了对 6 种大型蚯蚓物种（3 种来自 Amynthas 属和 3 种来自 Metaphire 属）卵巢的光镜和电镜分析结果。研究包括了孤雌生殖和有性生殖的物种。所有研究物种的卵巢组织和超微结构都非常相似。考虑到卵巢的组织学组织，它们可以分为两个区。一区（靠近与隔膜连接的近端）紧密排列着生殖细胞和体细胞。生殖细胞通过细胞间桥和中央细胞质的细丝（称为胞质体）相互连接，并形成合胞体小囊。小囊将卵原细胞、早期减数分裂细胞（直到二价体）和聚集细胞同步联合起来。在二价体时期，相互连接的细胞失去了发育同步性；很可能，每个小囊中的一个细胞比其他细胞生长得更快，从小囊中分离出来并成为卵母细胞。其余的细胞稍微生长，仍然通过细的和网状的胞质体相互连接；这些细胞被认为是滋养细胞。二区呈卵索的形式，生长中的卵母细胞彼此被薄的体细胞隔开，并形成短的索。我们展示了生殖细胞和体细胞的超微结构细节。我们提出了这种卵巢组织的“Amynthas”型卵巢的术语。我们假设这种卵巢是其他大型蚯蚓和相关科的特征。
