Spermiogenesis and fine structure of the spermatozoon in a headstander, Chilodus punctatus (Teleostei, Characiformes, Anostomidae)

The main characteristic features of spermiogenesis in Chilodus punctatus (Characiformes) are rotation of the nucleus, development of a nuclear fossa, which extends as a narrow invagination deep into the nucleus and the way in which flagellum is formed. The chromatin condensation proceeds during the spermiogenesis from heterogeneous through homogenous and granular to a highly compact one present in the mature spermatozoon. Mature Ch. punctatus spermatozoon shows a spherical nucleus, short midpiece and flagellum with lateral fins. The centrioles are in perpendicular arrangement and are located in the deep nuclear fossa, which extends towards the anterior pole of the nucleus. The midpiece contains a few mitochondria, which are separated from the anterior fragment of flagellum by the cytoplasmic channel. Spermiogenesis and spermatozoon ultrastructure conform to the pattern observed in other ostariophysans, but for the first time the presence of lateral fins along flagellum has been documented in a representative of Characiformes.     

Spermatogenesis in the black porgy,Acanthopagrus schlegeli (teleostei: Perciformes: Sparidae)

The ultrastructure of spermatogenesis and of the spermatozoon of Acanthopagrus schlegeli (Sparidae) are described. The testis is of the unrestricted type. Germ cells are surrounded by cyst cells. Spermiogenesis involves conspicuous modifications such as intracellular movements (diplosome and mitochondria migration, nuclear rotation, and depression) and structural changes (chromatin condensation, shape of mitochondria, and loss of cytoplasm). The mature spermatozoon has a spherical nucleus with a deep, axial nuclear fossa, and an unusual notch, shaped like a bow tie. The short midpiece contains four spherical mitochondria and encircles the basal body of the flagellum. It is concluded that the A. schlegeli spermatozoon is of a primitive type, but that it is characterized by a unique feature which may provide a useful systematic character. © 1993 Wiley-Liss, Inc.     

Nuclear changes during spermiogenesis in two chrysomelid beetles

Ultrastructural and cytochemical studies were carried out on sperm nucleus of the beetles, Coelomera lanio and Diabrotica speciosa. Nuclear development involves changes in the shape and in the degree of chromatin condensation, with specific aggregation patterns of DNA-histone complex occurring during this process. Lamellar and paracrystalline arrangements of the nuclear material were observed in the Diabrotica speciosa spermatid and in the Coelomera lanio spermatozoon, respectively. Ethanolic-phosphotungstic acid technique suggest the presence of basic proteins in the nuclear material of spermatids. This reaction disappears during chromatin condensation. Chromatin condensation patterns may reflect specific intranuclear mechanisms and offers protection to the genome during spermatozoon transport to the oocyte.     

埃及尼罗河鲶的精子发生和精子的超微结构

用扫描和透射电子显微镜研究了尼罗河鲶——盾头歧须鮠(Synodontis schall)的精子发生和精子的超微结构。精巢中含有无数肾形的生精小叶,我们将其称为"精原无限型"。尽管其精子发生的大体过程与同类鱼无异。但是,在细节上仍具其独特之处。这些特点未见在其他硬骨鱼中报道过。其特点主要是:生精过程中不发生细胞核的旋转,中心粒复合体和轴丝起始段直接发生在核的基底面垂直线上,有无数的粗的固定纤维将近端中心粒和远端中心粒的近侧部连接到细胞核上。另外,精子发生过程中还包括染色质浓缩,细胞质和线粒体向细胞核的尾端迁移,在核的后端中轴位置上形成中等大小的核后凹,近端中心粒和远端中心粒的一部分嵌在核后凹之内,短的胞质内陷管将线粒体与鞭毛分隔开。精子头部接近圆形,无顶体或顶体泡,鞭毛的中段及胞质内陷管均较短,整个鞭毛却很长,鞭毛侧面无翼膜,轴丝呈典型的9 2结构。上述结果显示,盾头歧须鮠的精子发生具有类型Ⅰ和类型Ⅱ的共同派生特征,这种特征在常见的其他硬骨鱼中也是常有的。但是,正如文献所报道过的另两种尼罗河鲶——金鯵(Chrysichthys auratus)和电鲶(Malapterurus electricus)中的情况一样,盾头歧须的精子发生与类型Ⅲ的精子发生过程更为相似。     

Spermiogenesis in the Nile tilapia Oreochromis niloticus with notes on a unique pattern of nuclear chromatin condensation

Spermiogenesis in the Nile tilapia, Oreochromis niloticus, was observed ultrastructurally. The process of spermatid differentiation can be divided into six distinct stages based mainly on changes in the nucleus of spermatids. During the latter half of the process, nuclear chromatin condenses progressively to form many dense globules, which ultimately adhere tightly to pack the head of mature spermatozoa. During chromatin condensation the nucleus diminishes in size, and part of the nuclear envelope and nucleoplasm forms a vesicular structure that is finally discarded from the cells together with an associated thin layer of cytoplasm. The spermatozoon comprises a roundish head, a relatively small midpiece, and a relatively short flagellum consisting of the usual 9+2 axoneme. No acrosomal structure is developed during spermiogenesis.     

Ultrastructure of spermiogenesis and the spermatozoon of Macracanthorhynchus hirudinaceus (Pallas, 1781) (Acanthocephala: Archiacanthocephala), a parasite of the wild boar Sus scrofa

The present paper describes the ultrastructure of spermiogenesis and the spermatozoon of Macracanthorhynchus hirudinaceus, an acanthocephalan parasite of the wild boar Sus scrofa. At the beginning of spermatogenesis, spermatocytes exhibit synaptonemal complexes and 2 centrioles. In the spermatid, only 1 centriole remains, generating a flagellum with a 9+2 pattern. Another ultrastructural feature observed during the spermiogenesis of M. hirudinaceus is the condensation of the chromatin, forming a "honeycomb" structure in the old spermatid and a homogeneous, electron-dense structure in the spermatozoon. The mature spermatozoon of M. hirudinaceus presents a reversed anatomy, as has been described previously in other species of the Acanthocephala. The spermatozoon is divided into 2 parts: an axoneme, and a nucleocytoplasmic derivative. The spermatozoon flagellum exhibits a 9+2 or 9+0 pattern. The process of spermiogenesis and the ultrastructural organization of the spermatozoon of M. hirudinaceus are compared with available data regarding other acanthocephalan species.     

Ultrastructure of nuclear condensation and localization of DNA and proteins in spermatozoa of a dasyurid marsupial,Sminthopsis crassicaudata

In the dasyurid marsupial, Sminthopsis crassicaudata, the mature spermatozoon has an inner homogeneous (C1) and a peripheral indented (C2) region. Using DNase-gold conjugates, and biotinylated genomic DNA probes, DNA was found to occur in both C1 and C2 regions. The morphogenesis of the spermatozoon nucleus was investigated using ultrastructural and cytochemical studies. Spermiogenesis was divided into 15 steps. By step 10, condensation of the C1 region was complete, and at the caudal extremity of the spermatid nucleus, the nuclear envelope enclosed an electron-lucent space. This space and the surrounding nuclear envelope became very enlarged at step 11. At this stage, a plate of approximately 70 nm in thickness was present along the caudal segment of the C1 region; this “nuclear mantle” did not bind DNase-gold conjugates but stained for lysine-rich proteins using alcoholic phosphotungstic acid. Chromatin condensation resumed at step 12 with the appearance of spherical chromatin structures peripheral to the C1 chromatin. These structures then partially coalesced and the indentations of the C2 region were observed. The expanded nuclear envelope at the caudal extremity persisted in caput epididymal spermatozoa. Spherical inclusions within it did not bind to DNase-gold conjugates but stained for lysine-rich proteins. As the sperm traveled down the epididymis, these inclusions amassed near the nuclear pores and were then removed from the nucleus. In addition, the nuclear mantle was found to have disappeared by the time the spermatozoa reached the corpus epididymidis. © 1996 Wiley-Liss, Inc.     

Semicystic spermatogenesis and biflagellate spermatozoon ultrastructure in the Nile electric catfish Malapterurus electricus (Teleostei: Siluriformes: Malapteruridae)

Spermatogenesis and spermatozoon ultrastructure in the Nile electric catfish Malapterurus electricus are described using scanning and transmission electron microscopy. Although the testis organization conforms to the ‘unrestricted’ spermatogonial type, the species has a rare type of spermatogenesis not previously described among catfishes, ‘semicystic’, in which the cyst ruptures before the spermatozoon stage. Spermiogenesis also involves some peculiar features such as condensation of the chromatin in the posterior part of the nucleus to form a compact electron‐dense mass with some irregular electron‐lucent lacunae, while the uppermost part of the nucleus is a loose electron‐lucent area, absence of the nuclear rotation and, as a consequence, the centriolar complex and the initial segment of each flagellum arise directly in a position perpendicular to the basal pole of the nucleus, and occurrence of numerous vesicles in the midpiece. In addition, spermiogenesis includes migration of the diplosome and mitochondria to the basal pole of the nucleus, formation of two moderate nuclear fossae, each of which contains the centriolar complex, development of two independent flagella and elimination of the excess cytoplasm. The mature spermatozoon has a more or less round head with no acrosome or acrosomal vesicle, a long midpiece with numerous mitochondria and vesicles and two long tails or flagella having the classical axoneme structure of 9 + 2 microtubular doublet pattern and with no lateral fins and membranous compartment. These findings suggest that the ultrastructural features of spermiogenesis and spermatozoa of M. electricus are synapomorphies of types I and II spermiogenesis and spermiogenesis is closely similar to the type described in the Nile catfish Chrysichthys auratus.     

Spermiogenesis and structure of spermatozoa in the oribatid mite,Hafenrefferia gilvipes (C.L. Koch) (Acari,Oribatida)

The process of spermiogenesis and the structure of spermatozoa in the mite, Hafenrefferia gilvipes (Koch) were studied ultrastructurally. Spermiogenesis was divided into six stages. The spermatids at stage 1 have the usual structure. At stage 2 the structure of the mitochondria and their distribution in the spermatid start to change, leading to the formation of specific mitochondrial derivatives which are subsequently incorporated into the nucleus of the spermatozoon. Parallel to the transformation of mitochondria occurs a reorganization of the nuclear material. The fully formed spermatozoon has a tadpole-like shape, with the cell nucleus located in the distended part of the cell, and containing mitochondrial derivatives in its karyoplasm. Acrosome, flagellum and centrioles are absent. The participation of peripherally distributed microtubules, present in spermatids at stages 4 to 6, in the shaping of the spermatozoon has been suggested.     

白肛海地瓜精子发生及形态的超微结构

通过透射和扫描电镜观察了白肛海地瓜(Acaudina leucoprocta)的精子发生过程及其形态结构,揭示了白肛海地瓜精子发生时期一系列变化,其精子发生分为精原细胞、初级精母细胞、次级精母细胞、精细胞、成熟精子5个时期。精原细胞体积最大。精母细胞染色质开始凝集。精细胞前顶体颗粒形成。白肛海地瓜成熟精子的超微结构为原生型,由头部、中部、尾部组成,头部圆形,最前端为顶体,核染色质凝集成团块状,中部是线粒体和中心粒复合体融合成1个超大结构,尾部长约60μm,尾部鞭毛横切面为典型的"9+2"型结构。     

Ultrastructure of spermiogenesis and synthesis of enigmatic cytoplasmic inclusions in the spirally shaped spermatozoon of the polychaete Spio setosa (Annelida: Spionidae)

The sperm of Spio setosa (Polychaeta, Spionidae) are known to be very unusual in form; here, spermiogenesis and the structure of the spermatozoon in this species are described by transmission electron microscopy. While spermiogenesis is similar to that described for many other polychaetes, two notable exceptions to this process include the synthesis of abundant ring‐shaped and tubular, membrane‐bounded cytoplasmic inclusions in the midpiece, and the differentiation of a spirally shaped sperm head. Spermatids develop as free‐floating tetrads in the male's coelom. A microtubular manchette does not develop during chromatin condensation and nuclear elongation, and the spiral acrosome forms as a single Golgi‐derived vesicle that migrates anteriorly to become housed in a deep anterior nuclear fossa. Early in spermiogenesis, numerous Golgi‐derived, membrane‐bounded cytoplasmic inclusions appear in the cytoplasm; these ultimately occupy the sperm midpiece only. The mature spermatozoon in the male has a 15‐μm‐long head consisting of a nucleus coiled like a spring and a spiral acrosome with differentiated substructure, the posterior two thirds of which sits in an anterior nuclear fossa. The midpiece is wider than the rest of the spermatozoon and contains 9–10 spherical mitochondria surrounding the two centrioles, as well as numerous membrane‐bounded conoid and tubular cytoplasmic inclusions. The axoneme has a 9 + 2 arrangement of microtubules. By contrast, stored sperm in the female's seminal receptacles have lost the midpiece inclusions but contain an abundance of glycogen. The function of the midpiece inclusions remains unresolved, and the significance of their absence in stored sperm within the seminal receptacle and the appearance of midpiece glycogen stores remains unclear and requires additional investigation.     

On sperm ultrastructure,spermiogenesis and the spermatophore of Heterolaophonte minuta (Copepoda,Harpacticoida)

Summary The spermatophore, mature spermatozoon and spermiogenesis of Heterolaophonte minuta have been investigated by light and electron microscopy. The spermatophore contains three different secretions which are responsible for the discharge of the contents of the spermatophore, the formation of the fertilization tube and the storage of the spermatozoa. The spermatozoon represents a type new for the Copepoda. It is a filiform cell about 25 m in length, ellipsoid in transverse section and tapered at the posterior end. The elongated nucleus contains chromatin fibrils and does not possess a nuclear envelope. Posterior to the nucleus, six mitochondria are placed one after the other. The posterior part of the spermatozoon contains parallel pseudomembranes. The gamete is not helically twisted and is without a flagellum and centrioles. The most remarkable feature of the spermatozoon is an osmiophilic cap in front of the nucleus. This cap corresponds to the acrosome of the spermatozoon. Early stages of spermiogenesis take place in the testis, where the spermatids are incorporated into accessory cells. The origin of the chromatin fibrils and the glycocalyx, as well as the breakdown of the nuclear envelope and centrioles, represent the final steps of spermiogenesis which occur in the vas deferens.     

Spermiogenesis and spermatozoon of the tapeworm Ligula intestinalis (Diphyllobothriidea): phylogenetic implications

Using transmission electron microscopy, spermiogenesis and the spermatozoon ultrastructural organization are described in Ligula intestinalis (Linnaeus, 1758) (Diphyllobothriidea), a parasite of the great crested grebe Podiceps cristatus (Linnaeus, 1758). Spermiogenesis starts with the differentiation zone of 2 striated rootlets, 2 centrioles giving rise to 2 flagella, and an intercentriolar body. The latter is composed of 5 electron-dense layers separating 4 electron-lucent layers. In the early stages of spermiogenesis, an electron-dense material is present in the apical region of the differentiation zone. Later, the flagella undergo a rotation and fuse with the cytoplasmic extension in a proximo-distal process. The spermatozoon contains 2 axonemes with a 9 + "1" trepaxonematan pattern, the nucleus, the cortical microtubules, and an electron-dense zone. The spermatozoon anterior extremity in L. intestinalis is characterized by the absence of crested bodies and a ring of electron-dense cortical microtubules. Some characters of spermiogenesis and spermatozoon in L. intestinalis confirm the recent splitting of "Pseudophyllidea" into 2 new orders, i.e., Bothriocephalidea and Diphyllobothriidea. The process of spermiogenesis is similar in both orders for the "type I" of spermiogenesis and the presence of electron-dense material. However, the intercentriolar body is clearly more developed in the Diphyllobothriidea than in the Bothriocephalidea. Moreover, these 2 orders seem to differ in the presence or absence of a ring of electron-dense cortical microtubules in the anterior extremity of the spermatozoon.     

尼罗罗非鱼精子形成中核内囊泡的释放

通过透射电镜观察了尼罗罗非鱼的精子形成过程。尼罗罗非鱼精子细胞在成熟过程中,细胞核中出现由双层生物膜构成的囊泡。囊泡中均匀分布着电子密度低的物质。该囊泡逐渐从细胞核内排到细胞核外。在此过程中细胞核不但排出不参与染色质浓缩的物质,还将多余的核膜排出。进入袖套的囊泡可以留在精子的袖套中,而排到核前方和核侧面的囊泡继续以出芽的方式排出精子细胞。尼罗罗非鱼成熟精子的头部仅有染色质高度浓缩的细胞核。细胞核前     

Spermiogenesis and the spermatozoon ultrastructure of Robphildollfusium fractum (Digenea: Gyliauchenidae), an intestinal parasite of Sarpa salpa (Pisces: Teleostei)

Spermiogenesis in Robphildollfusium fractum begins with the formation of a differentiation zone containing: two centrioles, each bearing striated rootlets, nucleus, several mitochondria and an intercentriolar body constituted by seven electron-dense layers. The two centrioles originate two free flagella growing orthogonally to the median cytoplasmic process. Later, the free flagella rotate and undergo proximodistal fusion with the median cytoplasmic process. Nuclear and mitochondrial migrations occur before this proximodistal fusion. Finally, the young spermatozoon detaches from the residual cytoplasm after the constriction of the ring of arched membranes. The spermatozoon of R. fractum exhibits two axonemes of different length of the 9 + ‘1’ trepaxonematan pattern, nucleus, two mitochondria, two bundles of parallel cortical microtubules, external ornamentation of the plasma membrane, spine-like bodies and granules of glycogen. Additionally, a shorter axoneme, which does not reach the nuclear region, the presence of an electron-dense material in the anterior spermatozoon extremity and the morphologies of both spermatozoon extremities characterize the mature sperm of R. fractum.     

斑节对虾精子发生的超微结构

斑节对虾精子发生划分为精原细胞、初级精母细胞、次级精母细胞、精子细胞和精子五个阶段。精子发生中，从精原细胞到精子，染色质经历了从以异染色质为主变为高度凝聚态，再经解聚为弥散絮状的变化过程。同时，核从具有完整核膜变为核膜不完整。成熟的的精子含有核仁。顶体由高尔基囊泡逐渐演化而成，并向外伸长成为棘突。这是斑节对虾精子发生的主要特征。     

Fine structure of spermatozoa in the gilthead sea bream (Sparus aurata Linnaeus, 1758) (Perciformes, Sparidae)

Scanning and transmission electron microscopy were used to investigate the fine structure of the sperm of the sparid fish Sparus aurata L. The mature spermatozoon of gilthead sea bream belongs, like that of the other sparid fish, to a "type I" as defined by Mattei (1970). It has a spherical head which lacks an acrosome, a short, irregularly-shaped midpiece and a long cylindrical tail. The nucleus reveals a deep invagination (nuclear fossa) in which the centriolar complex is located. The two centrioles are approximately perpendicular to each other and show a conventional "9+0" pattern. The proximal centriole is associated with a cross-striated cylindrical body lying inside a peculiar satellite nuclear notch which appears as a narrow invagination of the nuclear fossa. The distal centriole is attached to the nuclear envelope by means of a lateral plate and radial fibres made of an electron-dense material. The short midpiece houses one mitochondrion. The flagellum is inserted perpendicularly into the base of the nucleus and contains the conventional 9+2 axoneme.     

Cytological steps during spermiogenesis in the house sparrow (Passer domesticus,Linnaeus)

Spermiogenesis of the domestic sparrow was investigated with the light and electron microscopes and a step by step classification is proposed. Three cell populations corresponding to early, mid and late spermatids were easily divided according to their positions in the seminiferous epithelium. In addition to this initial separation, six steps were recognized, based on nuclear morphology and the degree of chromatin condensation, in association to their acrosomal and flagellar development. Early spermiogenesis is the period previous to chromatin condensation. The first step can be recognized by the extending flagellum and the second by the pro-acrosome development in contact with the nucleus. During the third or intermediate step, chromatin condenses and the cell becomes polarized with the pro-acrosomic vesicle and the tail occupying opposite sides of the nucleus. Late spermiogenesis, including steps IV-VI, is marked by complete chromatin condensation. The final cellular modifications lead to the formation of a spiraled spermatozoon. This shape is due to the twisting of the acrosome and nucleus, as well as the helical arrangement of mitochondria around the axoneme along most of the flagellum, making an exceptionally long middle piece.     

Ultrastructure of the spermatozoon of the teleost fish Acanthopagrus schlegeli (Perciformes: Sparidae)

Ultrastructurally the spermatozoon of Acanthopagrus schlegeli (Sparidae) has a spherical, homogeneously electron-dense nucleus with a deep axial nuclear fossa, and an unusual notch, shaped like a bowtie, in the nuclear region. The short midpiece contains four spherical mitochondria and encircles the basal body of the flagellum. It is concluded that the spermatozoon is of a primitive type, although it is characterized by several unique features which may provide useful systematic characters. © 1993 Wiley-Liss, Inc.     

Ultrastructure of the unusual spermatozoon of the Eurasian bullfinch (Pyrrhula pyrrhula)

The Eurasian bullfinch spermatozoon differs from typical passeridan spermatozoa in several major respects. The mature acrosome consists of a concavo‐convex vesicle differing from the typical passeridan acrosome, which is a helical structure, is usually longer than the nucleus and has a prominent helical keel. The nucleus differs from that of other oscines in not showing a twisted cylindrical form, in being shorter, and in tending to be an elongate ellipsoid in shape. The chromatin often appears in an uncondensed form reminiscent of a spermatid and consists of discrete fascicles. A small proportion of the mature sperm population however, is characterized by marked chromatin condensation. The midpiece comprises a small group of mitochondria clustered around the nuclear–axonemal junction in contrast to the single, long mitochondrion wound helically around the axoneme that is found in typical Passerida. The presence of a proximal centriole (in addition to the distal one) is a notable difference from all other oscine passerines. We suggest that the unusual morphology of the Eurasian bullfinch spermatozoon, resembling that of a spermatid, is the result of the progressive suppression of the final stages of spermiogenesis and is associated with the likelihood that sperm competition is infrequent in this species.