中国圆田螺典型精子及其发生的超微结构研究

AN ULTRASTRUCTURAL STUDY OF THE TYPICAL SPERMATOGEN ESIS AND MATURE SPERMATOZOON OFCIPANGOPALUDINA CHINENSISGRAY

运用光镜和电镜以及细胞化学方法 ,对中国圆田螺Cipangopaludinachinensis典型精子及其发生的超微结构进行了研究。根据染色质和细胞形态的变化 ,可将其典型精子发生分为五个时期 :精原细胞、初级精母细胞、次级精母细胞、精细胞和成熟精子。精子发生过程中 ,线粒体逐渐增大 ,并随着轴的增生而不断发展为螺旋化线粒体系 ;染色质逐渐凝聚 ,经过颗粒化和纤维化而终呈均质 ;随着染色质的变化 ,细胞核先变小再拉长并螺旋化。精细胞期细胞核基部发生内陷 ,伴随有中心粒的移入 ,并向后方形成“9+ 2”式的轴。成熟典型精子单鞭毛 ,全长约 40 μm ,包括头、中、尾三段 :头段螺旋状 ,主要由细胞核构成 ,旋束单股 ;中段螺旋状 ,主要由线粒体和轴丝构成 ,旋束四股 ;尾段非螺旋状 。

Cipangopaludina chinensis Gray,a kind of familiar e conomic freshwater snail,was seldom studied in its breeding biology.In the prese nt study,the ultrastructure of the typical spermatogenesis and mature spermatozo on was studied with light microscopy,electron microscopy and cytochemical method to provide scientific data for the future artificial breeding ofCipangopalud ina chinensisGray. It was found that,according to the changes of the structure of chromatin and the morphology of cell,the typical spermatogenesis could be divided into five stage s. They are spermatogonium, primary spermatocyte,secondary spermatocyte,spermati d and mature spermatozoon. At the stage of spermatogonium,the shape of cell and nucleus was not regular. Nucleolus existed in nucleus and cytoplasm had only lit tle granular mitochondria and few endoplasmic reticulum vesicles.Primary spermat ocyte and its nucleus approximately took on elliptical shapes.Nucleus had two la yers of membrane and the clearance between them was narrow. Endoplasmic reticulu m vesicles became more,and mitochondrion became more and larger and began to gath er at the posterior of cell and nucleus had synatonemal complex.When secondary s permatocyte,cell and nucleus presented elliptical shapes,nucleus still had two l a yers of membrane and the clearance was wide,part of mitochondrion began to amalg amate, and endoplasmic reticulum vesicles became larger.Spermatid was the most c omplex changing stage in the whole process of spermatogenesis,which could be fur ther divided into six stages. At the early stage of spermatid cell and nucleus p resented spherical shape and then gradually changed greatly.In spermatid,chromat in first condensed partly from exterior to interior and from top to basis, then condensed wholly into granules,into fibers and finally into homogeneous appearan ce;following the changes of chromatin nucleus decreased in size,the basal nucleu s membrane thickened and invaginated, followed with centriole transporting into t he fosse of invagination,and then nucleus gradually elongated and finally spire d. Mitochondrion,symmetrically gathering at the rear of nucleus, amalgamated int o four blocks, elongated with the production of axoneme and spired too with the spire of nucleus.In the late stage of spermatid, some cytoplasm transported to t he posterior of mitochondrion and formed the chamber of glycogen granule and the n formed the sh eath of glycogen granules.Meanwhile the relict of cytoplasm removed out of cell and the spermatid was still covered with a layer of membrane relict. After membr ane relict disappeared,spermatid changed in to mature spermatozoon. Mature sperm atozoon was about 40μm in length,including a spiral head, a spiral middle piece and a nonspiral tail.The head,mainly composed of nucleus,had only one spiral bu ndle with seven spires.The middle piece,mainly constituted of mitochondria and a xoneme,had four spiral bundles of mitochondria.The tail was mainly composed of g lycogen granules and axoneme with the “9+2” pattern.Between middle piece and t ail,there existed a interface with an annular. At the bottom of tail,g lycogen granules gradually decreased from two layers to one layer,and disappeare d finally. The spermatozoon of most gastropod had acrosome,but it couldn't be observed in t h e whole spermatogenesis ofCipangopaludina chinensisGray.According to the v iewpoint of Franzen,that the functional need of fertilization determined the exi sting or not or the shape of acrosome,the spermatozoon ofCipangopaludina chinensis Gray perhaps had no acrosome.With spiral head and spiral middle pie ce,perhaps they could directly enter into eggs without the complex acrosome reac tion. In the stage of spermatid,no obvious microtubule occurred around nucleus,a nd the changes of nucleus were closely connected with the condensation of chroma tin. When chromatin condensed into granules nucleus decreased in size,and when c hromatin condensed in fibers nucleus elongated.So the mechanism that determined the final shape of nucleus of the spermatozoon ofCipangopal