半滑舌鳎精子发生和精子形成的超微结构

Ultrastructure of spermatogenesis and spermiogenesis in the half-smooth tongue sole Cynoglossus semilaevis

用电子显微镜对半滑舌鳎(Cynoglossus semilaevis)精子发生的过程及精子的超微结构进行了观察。半滑舌鳎精巢属于小叶型,精小叶由各期生精细胞和支持细胞构成。半滑舌鳎的精子发生经历了初级精原细胞、次级精原细胞、初级精母细胞、次级精母细胞和精子细胞,再经过精子形成过程发育成为精子。初级精母细胞成熟分裂的前期Ⅰ,同源染色体经历了联会复合体形成和解聚的变化。在精子形成的过程中,精细胞大致经历了核质浓缩、线粒体迁移及鞭毛的发生等过程。核质浓缩时,精细胞核内位于植入窝周围的染色质首先由细颗粒状浓缩成粗大颗粒状,然后细胞核其他部位的染色质也逐渐浓缩成粗大颗粒状。这些已浓缩成粗大颗粒状的染色质再进一步浓缩为电子密度高的均匀状物质。随着核质的浓缩,核外膜与核内膜之间的间隙增大形成核膜间隙,核内一些没有参与染色质浓缩的物质通过出芽形成囊泡,先排入核膜间隙,然后再外排到细胞质中。核浓缩过程中细胞核的体积和表面积都大大缩小;鞭毛的形成与细胞核的浓缩是同步进行的,当一对中心粒移近细胞核时,核膜凹陷形成植入窝,其周围染色质浓缩的同时,远端中心粒(基体)逐渐向后产生轴丝。成熟精子无顶体,头细长,主要为核占据,核凹窝发达,线粒体4-5个环绕在鞭毛基部形成袖套,尾细长,具侧鳍,尾部轴丝为"9+2"结构。

The ultrastructure of spermatogenesis and spermiogenesis in the half-smooth tongue sole Cynoglossus semilaevis was studied by transmission electron microscopy. The testes are of the lobular type. Five stages, of spermatagenesis were identified; primary spermatagonia, secondary spermatagonia, primary spermatocytes, secondary spermatocytes and spermatids. During zygotene, prophase Ⅰ , paired homologous chromosomes began to form synaptonemal complexes. The synaptonemal complexes were fully formed at pachytene and dissolved afterward. The synaptonemal complex served as a means of ensuring genetic recombination between two homologous chromosomes. Spermatids differentiated into sperms via the process of spermiagenesis, which included three stages： nuclear condensation, migration of mitochondria and axoneme growth. During condensation of the nucleus, chromatin, surrounding the implantation fossa condensed to form rough particles. The remaining chromatin, located in the other parts of the nucleus, began to concentrate later. Subsequently, , these rough particles condensed into even material, of high electron density. At the same time, the gap between the two layers of nuclear membranes enlarged gradually and aperinuclear space was formed. Uncondensed material was discharged into the perinuclear space by budding and then into the cytoplasm. During nuclear condensation, the volume and surface area of the nucleus decreased markedly. Condensation of nucleus was accompanied by axoneme growth, During the earlier stages of spermiogenesis, a pair of centrioles drew near the nucleus membrane; this caused the nuclear membrane to sag and form the implantation fossa. Chromatin surrounding the implantation fossa became condensed. Meanwhile, the distal centriole gradually started to form the axoneme. Each spermatozoan consists of a head without an acrosome, a midpiece and a long tail which contains the lateral fins and a conventional ＂9 ＋ 2＂ axoneme pattern