Spermiogenesis and sperm structure in the crabUca tangeri (Crustacea,Brachyura), with special reference to the acrosome differentiation

Summary Early spermatids of the crabUca tangeri consists of the nucleus of granular chromatin and the cytoplasm, which contains a proacrosomal vesicle in close association with membrane lamellae. In the mid spermatids an invagination of the acrosomal vesicle membrane gives rise to the formation of the perforatorium, a spindle-shaped tubule which encloses tubular membranous structures. The pair of centrioles located at the base of the acrosome is not directly involved in perforatorial differentiation. The acrosomal vesicle shows a heterogeneous content composed of the operculum, the thickened ring, and three layers of different materials concentrically arranged around the perforatorium. During the late spermatid stage the nuclear profile differentiates numerous slender arms and the chromatin arranges into fibers. Membranous tubules from the cytoplasm become incorporated into the tubular structures of the perforatorium. The mature spermatozoon has the typical structure of the branchyuran sperm, with a complex acrosome, cupped by the nucleus, and a thin cytoplasmic band intervening between the former main elements. The centrioles are degenerate. The nuclear arms are unusually numerous (more than 20) and lack microtubules or microtubular derivatives.     

东方扁虾精子的超微结构

利用电镜研究了东方扁虾（Ｔｈｅｎｕｓ ｏｒｉｅｎｔａｌｉｓ）精子的形态和结构。精子由核、膜复合物区和顶体区３部分组成。核内含非浓缩的染色质、微管及细纤维丝,外被核膜;５～６条辐射臂自核部位伸出,臂内充满微管。膜复合物区位于核与顶体之间,由许多膜片层结构及其衍生的囊泡共同组成。顶体区由顶体囊和围顶体物质组成,顶体结构复杂,由顶体帽、内顶体物质和外顶体物质等构成;围顶体物质呈细颗粒状,主要分布于顶体囊     

An ultrastructural analysis of mature sperm from the crayfish Pacifastacus leniusculus,Dana

Sperm from the crayfish, Pacifastacus leniusculus, resemble other reptantian sperm in that they are composed of an acrosome, subacrosomal region, nucleus, membrane lamellar complex, and spikes which radiate from the nuclear compartment. The acrosome (PAS positive vesicle) can be subdivided into three regions: the apical cap, crystalline inner acrosomal material, and outer acrosomal material which is homogeneous except for a peripheral electron dense band. The nucleus contains uncondensed chromatin and bundles of microtubules which project into the spikes. The orientation of the microtubule bundles relative to the nuclear envelope near the base of the subacrosomal region suggests that the nuclear envelope may function in the organization of the spike microtubules.     

SPERMIOGENESIS IN CANCER CRABS

Spermiogenesis in Cancer crabs was studied by light and electron microscopy. The sperm are aflagellate, and when mature consist primarily of a spherical acrosome surrounded by the nucleus with its short radiating arms. The acrosome forms by a coalescence of periodic acid-Schiff-positive (PAS-positive) vesicles. During spermiogenesis one edge of the acrosomal vesicle invaginates to form a PAS-negative central core. The inner region of the acrosome bounding the core contains basic proteins which are not complexed to nucleic acid. The formation of an elaborate lattice-like complex of fused membranes, principally from membranes of the endoplasmic reticulum, is described. These membranes are later taken into the nucleus and subsequently degenerate. In late spermatids, when most of the cytoplasm is sloughed, the nuclear envelope and the cell membrane apparently fuse to become the limiting boundary over most of the sperm cell. In the mature sperm the chromatin of the nucleus and arms, which is Feulgen-positive, contains no detectable protein. The chromatin filaments appear clumped, branched, and anastomosed; morphologically, they resemble the DNA of bacterial nuclei. Mitochondria are absent or degenerate in mature sperm of Cancer crabs, but the centrioles persist in the nucleoplasm at the base of the acrosome.     

Ultrastructure of the spermatogenesis of the cockle Anadara granosa L. (Bivalvia: Arcidae)

In this paper spermatogenesis and sperm ultrastructure of the cockle Anadara granosa are studied using transmission electron microscopy. The spermatocyte presents electron-dense vesicles and the arising axoneme that begins to form the flagellum. During spermatid differentiation, proacrosomal vesicles appear to migrate towards the presumptive anterior pole of the nucleus; eventually these vesicles become acrosome. The spermatozoon of Anadara granosa is of the primitive type. The acrosome, situated at the apex of the nucleus, is cap-shaped and deeply invaginated at the inner side. The spherical nucleus of the spermatozoon contains dense granular chromatin and shows invagination at the posterior poles. The centriole shows the classic nine triplets of microtubules. The middle piece consists of the centriolar complex surrounded by five giant mitochondria. It is shown that the ultrastructure of spermatozoa and spermiogenesis of Anadara granosa reveals a number of features that are common among bivalves. Received: 29 September 1998 / Received in revised form: 20 May 1999 / Accepted: 14 June 1999     

Structure, cytoskeleton, and development of the acrosome of Platycleis albopunctata (Orthoptera: Tettigoniidae).

The acrosome of Platycleis albopunctata (Orthoptera: Tettigoniidae) is relatively large and complex, consisting of an apical vesicle and two large wing-like extensions that give the spermatozoon the shape of an arrow. The wings have actin microfilaments and microtubules and are covered with a noticeable extracellular material. Actin filaments are present in the acrosome when it first appears in spermatid stages. The acrosome and the acrosomal attachment to the nucleus are more resistant than other structures to the reducing agents DTT and SDS. At the end of spermiogenesis, groups of spermatozoa juxtapose their sperm heads and become joined to form a spermatodesm encircled by an amorphous material. Treatment with the ionophore A23187 rapidly disrupted acrosomes of the free gametes, but acrosomes from spermatozoa contained in the spermatodesm were not disassembled. Packaging of sperm in a spermatodesm appears to protect the acrosome.     

暗褐蝈螽与优雅蝈螽精子超微结构的比较研究(直翅目,螽斯科)

研究了暗褐蝈螽Gampsocleis sedakovii(Fischer von Waldheim)和优雅蝈螽G.gratiosa Brunner von Wattenwyl精子的超微结构。这两种蝈螽精子头部的顶体复合体由顶体外层、顶体本体和顶体组成,顶体复合体位于细胞核前端,并包裹部分细胞核;颈部具5纵层细胞器;尾部鞭毛轴丝为典型的9+9+2型,线粒体衍生体部分晶状化。暗褐蝈螽精子较短,顶体复合体夹角较大,精子鞭毛横切面直径稍大;优雅蝈螽精子稍长,顶体复合体夹角较小,精子鞭毛横切面直径较小,两种精子超微结构差异不显著,其生殖隔离机制有待进一步研究。     

MICROTUBULES IN RELATION TO THE MOTILITY OF A SPERM SYNCYTIUM IN AN ARMORED SCALE INSECT

Male scale insects of the species Parlatoria oleae Colvée (Homoptera: Coccoidea) produce motile sperm bundles. The bundle is a syncytium consisting of 10 to 20 closely packed, filamentous spermatozoa, which share a common cytoplasm and are enclosed in a common membrane. The individual spermatozoon is not surrounded by a plasma membrane, but is delimited by a scroll-like sheath composed of 45 to 50 microtubules. The microtubules run parallel to the long axis of the spermatozoon and are arranged in a spiral pattern as seen in transection. The outside diameter measures approximately 140 to 220 A and the inside diameter, 70 to 100 A. The spermatozoon is about 300 µ long and tapers gradually from a diameter of approximately 0.3 µ anteriorly to 0.1 µ posteriorly. The anterior half (150 µ) has a threadlike core of chromatin about 0.07 µ in diameter. A homogeneous cytoplasm surrounds the nuclear core and fills the posterior half of the spermatozoon. Neither osmium tetroxide nor glutaraldehyde fixation revealed the presence of a nuclear envelope, acrosomal membranes, mitochondria, flagellum, or centrioles. In spite of the apparent lack of orthodox cell organelles, the spermatozoon is actively motile upon release from the bundle. It exhibits capactiy for motility throughout its entire length. Since the sheath of microtubules is the only structure which extends the full length of the spermatozoon, it probably plays a significant role in spermatozoan motility.     

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.     

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.     

Ultrastructural study of spermiogenesis in a rare desert amphisbaenian Diplometopon zarudnyi

Spermiogenesis, in particular the head differentiation of Diplometopon zarudnyi, was studied at the ultrastructural level by Transmission Electron Microscope (TEM). The process includes acrosomal vesicle development, nuclear elongation, chromatin condensation and exclusion of excess cytoplasm. In stage I, the proacrosomal vesicle occurs next to a shallow fossa of the nucleus, and a dense acrosomal granule forms beneath it. This step commences with an acrosome vesicle forming from Golgi transport vesicles; simultaneously, the nucleus begins to move eccentrically. In stage II, the round proacrosomal vesicle is flattened by projection of the nuclear fossa, and the dense acrosomal granule diffuses into the vesicle as the fibrous layer forms the subacrosomal cone. Circular manchettes surrounded by mitochondria develop around the nucleus, and the chromatin coagulates into small granules. The movement of the nucleus causes rearrangement of the cytoplasm. The nucleus has uniform diffuse chromatin with small indices of heterochromatin. The subacrosome space develops early, enlarges during elongation, and accumulates a thick layer of dark staining granules. In stage III, the front of the elongating nucleus protrudes out of the spermatid and is covered by the flat acrosome; coarse granules replace the small ones within the nucleus. One endonuclear canal is present where the perforatorium resides. In stage IV, the chromatin concentrates to dense homogeneous phase. The circular manchette is reorganized longitudinally. The Sertoli process covers the acrosome and the residues of the cytoplasmic lobes are removed. In stage V, the sperm head matures.     

东方扁虾精子发生的超微结构

应用电镜技术研究了东方扁虾（Thenus orientalis)精子发生的全过程,精原细胞呈椭圆形,其染色质分布较均匀,线粒体集中于细胞一端形成“线粒体区”。初级精母细胞较大,染色质凝聚成块,次级精母细胞核质间常出现大的囊泡,胞质内囊泡丰富而线粒体数量却明显减少,早期精细胞核发生极化、解聚,部分胞质被抛弃。中期精细胞外观呈金字塔形,分为三区;正在形成的顶体位于塔顶,核位于塔基部,居间的细胞质基质内富含膜复合物,后期精细胞顶体进一步分化。形成顶体帽和内、外顶体物质等三个结构组份。成熟精子核呈盘状或碗状,具有5-6条内部充满微管的辐射臂。     

蟹类精子超微结构的比较研究

应用光镜和电镜,比较研究了三疣梭子蟹,中华绒螯蟹和长江华溪蟹的成熟精子。揭示３种蟹精子都是不能游动的无鞭毛精子,呈球形,前后略扁,精子前端出现一光滑的小圆面,圆面四周有内陷的沟环。沟环之后,精子表面凹凸不平,并伸出多数辐射臂。３种蟹精子均为高度特化的细胞,外被质膜,内含细胞核,顶体及退化的细胞质。     

Spermiogenesis in Coenobita clypeatus,I. Sperm structure

The sperm of the tropical land hermit crab, C. clypeatus, has an elongate acrosome anterior to a lamellar region of cytoplasm. Mitochondria near the lamellar region are associated with microtubules. These microtubules project into the 3 cytoplasmic arms. The nucleus occupies the posterior-most position in the sperm. The chromatin is not condensed and numerous projections of nuclear materials are seen. It is not known how the various organelles of the sperm function during fertilization.     

Comparative study of sperm ultrastructure of Donax hanleyanus and Donax gemmula (Bivalvia: Donacidae)

The ultrastructure of bivalve spermatozoa can be species‐specific and often provides important taxonomic traits for systematic reviews and phylogenetic reconstructions. Young individuals of the Donacidae species Donax hanleyanus are often identified as samples of Donax gemmula. Hence, the spermatozoa ultrastructure of both species was described in the present work, aiming to identify characters that could be useful for further taxonomic and phylogenetic analyses. D. hanleyanus and D. gemmula spermatozoa were different especially in relation to acrosomal characteristics and chromatin condensation. The spermatozoon produced by D. hanleyanus had a nucleus (exhibiting granular chromatin with a rope‐like appearance) capped by a long and conical acrosomal vesicle, which extended itself outward beyond the anterior nuclear fossa. Otherwise, the nucleus of the sperm cell of D. gemmula showed well‐compacted chromatin, and its acrosome, which was partially inserted into the anterior nuclear fossa, had a bubble‐like tip. In conclusion, the conspicuous ultra‐structural differences found between the spermatozoan morphologies were helpful for the discrimination of the species. In conclusion, our results suggest that analyses of sperm ultrastructure of the bivalves in the family Donacidae can be valuable to investigate their taxonomic relatedness. The present results also contribute to assess the monophyletic status of the family.     

Spermiogenesis in the Pycnogonid Pycnogonum littorale (Ström)

Abstract Spermatids in different stages of development are connected by intercellular bridges. Later the disappearance of these is correlated with sloughing off the residual cytoplasm. At the onset of spermiogenesis, chromatin is agglomerated at the periphery of the nucleus. Later this disperses and no chromatin condensation takes place. There is a steady reduction in the nucleus size. This is correlated with increase in the number of small vesicles and microtubules in the cytoplasm. Eventually the nucleus becomes very small, and is surrounded by a complex system of microtubules. Following spermiogenesis process the mitochondria lose their cristae and contain adielectronic material. The mature sperm is spindle-shaped, tapering at both ends. In both ends there are only microtubules present terminating freely in the cytoplasm. In its middle there are a number of rod-shaped mitochondria containing an electron dense material. The microtubules in the middle part of the sperm are arranged in a hexagonal pattern and in others in rows interspersed with single ones. The structure of Pycnogonum littorale sperm is highly modified, which may explain the special mode of fertilisation.     

Ultrastructure of spermiogenesis in the American alligator,Alligator mississippiensis (Reptilia,Crocodylia, Alligatoridae)

Testicular samples were collected to describe the ultrastructure of spermiogenisis in Alligator mississipiensis (American Alligator). Spermiogenesis commences with an acrosome vesicle forming from Golgi transport vesicles. An acrosome granule forms during vesicle contact with the nucleus, and remains posterior until mid to late elongation when it diffuses uniformly throughout the acrosomal lumen. The nucleus has uniform diffuse chromatin with small indices of heterochromatin, and the condensation of DNA is granular. The subacrosome space develops early, enlarges during elongation, and accumulates a thick layer of dark staining granules. Once the acrosome has completed its development, the nucleus of the early elongating spermatid becomes associated with the cell membrane flattening the acrosome vesicle on the apical surface of the nucleus, which aids in the migration of the acrosomal shoulders laterally. One endonuclear canal is present where the perforatorium resides. A prominent longitudinal manchette is associated with the nuclei of late elongating spermatids, and less numerous circular microtubules are observed close to the acrosome complex. The microtubule doublets of the midpiece axoneme are surrounded by a layer of dense staining granular material. The mitochondria of the midpiece abut the proximal centriole resulting in a very short neck region, and possess tubular cristae internally and concentric layers of cristae superficially. A fibrous sheath surrounds only the axoneme of the principal piece. Characters not previously described during spermiogenesis in any other amniote are observed and include (1) an endoplasmic reticulum cap during early acrosome development, (2) a concentric ring of endoplasmic reticulum around the nucleus of early to middle elongating spermatids, (3) a band of endoplasmic reticulum around the acrosome complex of late developing elongate spermatids, and (4) midpiece mitochondria that have both tubular and concentric layers of cristae. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Ultrastructure of the Geogarypus nigrimanus Spermatozoon (Arachnida,Pseudoscorpionida)

The ultrastructure of the spermatozoon of Geogarypus nigrimanus (Arachnida, Pseudoscorpionida) is described. The spermatozoon is composed of a small elliptic nucleus, a short flagellum and a very long and complex acrosome. In the male genital ducts, as in other studied species of pseudoscorpions, the sperm components are rolled up to form a globular structure enclosed in a cyst wall. The Geogarypus spermatozoon with a reduced flagellum and a giant acrosome seems to be evolutionary more advanced than spermatozoa from other pseudoscorpions.     

The Spermatozoon of Siboglinum (Pogonophora)

The spermatozoon and some spermatid stages of Siboglinum (Pogonophora) have been examined by light and electron microscopy. In the spermatozoon a helical acrosome, a helical nucleus and a “body” with axonema follow each other in normal sequence. Head and tail are joined by a very short neck region containing two modified centrioles. The posterior portion of the nucleus is surrounded by a mitochondrial sheath consisting of three tightly wound mitochondrial helices. In the main portion of the tail the 9+2 unit is sorrounded by a granular sheath of dense material. In the neck region a centriole adjunct develops into a dense substance containing about nine rods. At an early stage, when the centriolar apparatus and flagellum become associated with the nucleus, three large mitochondria with fairly regular cristae are seen at the base of the nucleus. A well developed Golgi apparatus is present in early stages. Rows of microtubules are observed encircling the spermatid nucleus. Compared with the primitive type of spermatozoon the pogonophore sperm shows elongated and specialized nucleus, acrosome and mitochondria. It is concluded that the ancestral form must have had a fairly primitive spermatozoon and that evolution has proceeded towards a modified sperm with complicated spiral structure in connection with the evolution of a modified biology of fertilization, viz. specialized spermatophores. It is not known how the spermatophore discharges the spermatozoa nor how the spermatozoa find their way to the eggs. Two kinds of sperms are produced in the gonads of Siboglinum. The atypical sperm is smaller than the typical one.