扩张莫尼茨绦虫(圆叶目:裸头科)精细胞分化、精子形成及精子形态

摘要

本项研究应用光学显微镜、扫描和透射电子显微镜,观察了扩张莫尼茨绦虫的精细胞分化、精子形成全过程及精子的精细结构.扩张莫尼茨绦虫的精细胞分化过程为:1)初级精原细胞主要发生于幼节的睾丸滤泡中;2)次级精原细胞发生不完全分裂形成16个细胞一簇的初级精母细胞群,以共同的中央细胞质相连;3)初级精母细胞的特征为细胞核中出现联会复合体结构;4)紧接着的第二次成熟分裂,产生64个由中央细胞质相连的细胞核较小的精细胞.精子形成始于精细胞中分化区的形成, 成熟精子缺乏线粒体,具有质膜和冠状体、1～4个领域排布的质膜下皮层微管,细胞质中存在电子致密的颗粒状物质,具一个不规则形态的细胞核,具有"9+1"类型的轴丝构造,缺乏轴丝周围鞘.从精子的纵切面上可将精子区分为5个区段(Ⅰ～Ⅴ区).在精子形成过程中,中心粒基部出现螺旋形小根结构在寄生虫中为首次报导;成熟精子具有游离鞭毛,在绦虫中为首次发现.%The processes of spermatogenesis and spermiogenesis,and the fine str ucture of the spermatozoon in the cyclophyllidean cestode Moniezia expansa, were examined using a combination of light, scanning and transmission electron microscopy. Primary spermatogonia were found mainly in the testes of young proglottid s. Primary spermatogonia divided into two secondary spermatogonia and thereafter incomplete divisions gave rise to 16 primary spermatocytes in the form of a rosette, with all cells sharing a common cytoplasm. Synaptonemal complexes appear ed in the nucleus of the primary spermatocyte and mark the meiotic prophase, the first mature division leading to 32 secondary spermatocytes. Successive second mature divisions gave rise to a rosette of 64 spermatids. Spermiogenesis began with the formation of a differentiation zone in the form of a conical-shaped projection of cytoplasm delimited by a ring of arched membrane. Within this area , there were two centrioles and associated spiral rootlets. During spermiogenes is, only one of the centrioles developed an axoneme that grew directly into the cytoplasmic extension; the other centriole was aborted. The nucleus elongated and moved into the cytoplasmic extension. After transformation, the spermatozoa left the cytophore and mature. Any remaining rosettes of spermatids de-differe n tiated to form an electron-dense residual body. The mature spermatozoon of M oniezia was filiform, tapered at both ends and lacked mitochondria. In cross sectio ns, the spermatozoon had: (1) a plasma membrane and crested-like body; (2) 1-4 f ields of microtubules beneath the plasma membrane. The number of cortical micro tubules varied in different regions; (3) electron-dense granular material in the cytoplasm; (4) an irregular-shaped nucleus; (5) an axoneme of "9+1" pattern lacking a peri-axonemal sheath. Based on longitudinal sections of the spermatozo on, five regions could be distinguished. Its anterior extremity exhibited an ap ical cone of electron-dense material, and two crested-like bodies. The cor tical m icrotubles varied in length and follow a 25-45 degree helicoidal path along t heir lengths. They were arranged in 1-4 fields in different regions. The ax oneme did not reach the very end of the anterior extremity; near the posterior extremity it formed a free flagellum. The nucleus was arranged in an elongated, compact and irregular cord that spirals around the axoneme. Numerous small elect ron-dense granules occupied the cytoplasm in regions Ⅲ to Ⅴ. To the best of our knowledge, this is the first report of a free flagellum in the spermatozoon of a cestode.