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.     

Studies on the fine structure of spermatids and spermatozoa of the crab, Pinnixia sp

Early spermatids of the carb, Pinnixia sp., are characterized by a large nuclear/cytoplasmic ratio. During early spermiogenesis an organelle, composed of pentalaminar membranes derived from the endoplasmic reticulum and nuclear membranes, is formed. Portions of this organelle become incorporated within a cylinder-shaped invagination of the acrosome. Portions of the nuclear membrane disappear beneath the acrosome resulting in intermingling of nucleoplasm, centrioles and mitochondria. The nuclear membrane elsewhere is found as a pentalaminar membrane underlying the plasma membrane. Centrioles are found in mature spermatozoa at the base of the cylinder-shaped acrosomal invagination, and mitochondria are found intermingled with nuclear remanants surrounding the acrosome. This datum is compared to previously described events in spermiogenesis of other decapod crustacea and arthropods exhibiting similar modes of spermiogenesis. It is concluded that the differences and/or similarities exhibited by centrioles and mitochondria in these forms could be significant in terms of subsequent zygote differentiation.     

Immotile,aflagellate spermatozoa in Ptiliidae coleopterans

The first aflagellate and immotile Coleopteran spermatozoon is described in a group of species belonging to the family Ptiliidae. The mature spermatozoon is devoid of flagellum, centrioles and mitochondria, includes a three-layered acrosomal complex (extraacrosomal layer, acrosome and perforatorium) and a long nucleus made up of two regions of different densities. A compact submembranary capsule and a thick glycocalyx are also present. Motility organelles are absent during the whole spermiogenesis, which is not regressive. The new structures peculiar for this type of sperma are designed for protection. No other sperm models with these characteristics have been described so far.     

Ultrastuctural and cytochemical study of spermatogenesis in Scrobicularia plana (Mollusca,Bivalvia)

The ultrastructure of the mature spermatozoa and spermatogenesis of the bivalve Scrobicularia plana are described. Support cells extend from the basal lamina to the lumen of the testis and are laterally connected to the germinal epithelium. Germ cells present intercellular bridges and flagella since the spermatogonial stage. While spermatogonia and spermatocytes appear connected to support cells by desmosome-like junctions, elongated spermatids are held at the acrosomal region by support cell finger-like processes. During spermiogenesis, the acrosomal vesicle differentiates from a golgian saccule and then migrates to the nuclear apex. A microtubular manchette arising from centrioles surrounds the acrosomal vesicle, the nucleus, and the mitochondria at the time these three organelles start their elongation, disappearing after that. The mature spermatozoon of S. plana lacks a distinct midpiece because the mitochondria extend from the region of the pericentriolar complex along the nucleus anteriorly for approximately 1.4 μm. The features of this bivalve type of modified spermatozoon are compared with those of other animal groups having similar modifications.     

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.     

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.     

The role of sertoli cells in spermatid maturation in the testis of the crayfish, Procambarus paeninsulanus

With the onset of spermiogenesis, many changes become apparent in the crayfish spermatid during its transition to mature sperm. The nucleus passes through a series of stages, excess cytoplasm is removed, the acrosome develops, and nuclear arms form and become wrapped around the sperm prior to its enclosure in a capsule. Changes are also apparent in the Sertoli cells surrounding the germ cells in the crayfish testis. The amount of cytoplasm of individual Sertoli cells appears to increase in quantity and changes in the intracellular organelles become apparent. As spermiogenesis commences, the cytoplasm along one side of Sertoli cells adjacent to the spermatids is devoid of obvious organelles. Numerous finger/like projections of Sertoli cytoplasm penetrate into the spermatid and appear to isolate portions of the sperm cytoplasm. During later stages of spermiogenesis, several vesicles in the Sertoli cells which appear to contain droplets of this isolated sperm cytoplasm. appear to undergo lytic changes, As the amount of cytoplasm of the spermatid is reduced, contact is maintained between the spermatid and Sertoli cell in the area of the acrosome. The nuclear arms of the sperm extend into the Sertoli cell during their formation and later become wrapped around the acrosomal area of the sperm. At this time, very little space exists between the Sertoli cell and its many sperm. Large vesicles of electron dense material appear to be released by the Sertoli cells into the space between the sperm and Sertoli cell. This material completely surrounds the sperm and forms the sperm capsule. Spermiation involves the gradual dissolution of the points of contact between the sperm capsule and the Sertoli cell.     

Spermiogenesis in the horseshoe crab,Limulus polyphemus

Groups of spermatids of Limulus polyphemus undergo differentiation in thin-walled cysts within the seminiferous tubules. The nucleus compacts to a spherical shape, but retains a much less condensed nuclear appendage, whose unique pores are each surrounded by a microtubule. The appendage, unmodified mitochondria, glycogen, and coated vesicles, all present in the mature spermatozoon, suggest an unusual degree of metabolic self-sufficiency of the cell. The acrosome is associated with a 50 μ-long acrosomal filament that penetrates the nucleus during spermiogenesis and coils up in the cytoplasm, enveloped by two outer nuclear membranes. The filament, which eventually comes to lie in the circumnuclear cisterna, retains a covering of one membrane during its discharge at the time of the acrosome reaction. The posterior region of the head forms a thin-walled collar with peculiar internal supports around the base of the flagellum. Serverance of intercellular bridges between spermatids, cytoplasm elimination, and rupture of the cyst precede liberation of the immature spermatozoa into the lumen of the seminiferous tubules. Notwithstanding its peculiarities, the Limulus spermatozoon, with its simple shape closely resembling that of annelids and molluscs, represents the most primitive arthropod spermatozoon congruent with the evolutionary stability of the xiphosurans.     

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.     

Dynamics of satellite binding protein CENP-B and telomere binding protein TRF2/MTBP in the nuclei of mouse spermatogenic line

The location of centromeric protein CENP-B and telomeric protein TRF2/MTBP in the mouse spermatogenic line has been studied using indirect immunofluorescent and immunoelectron microscopy. CENP-B localized to the heterochromatic parts of the nuclei at meiotic stages. A clearly distinct chromocenter forms in the nucleus at stages 3-4 of spermatid maturation; CENP-B localizes in it and in the area adjacent to the future acrosome. CENP-B localization in the subacrosomal area and in the chromocenters' periphery demonstrates that centromeres are organized in two groups in mouse spermatozoa, unlike human centromeres. TRF2/MTBP concentrates around the forming chromocenter at spermiogenesis early stages. The TRF2/MTBP main signal migrates into the area of acrosomal membrane at the course of spermatozoon maturation. TRF2/MTBP never localizes inside the synaptonemal complex but can be found in the areas where the synaptonemal complex attaches to the nuclear envelope. At the pachytene and diplotene stages when chromosomes separate from the nuclear envelope, some amount of the protein remains bound to the nuclear membrane while the other part reveals itself in chromosomes. TRF2/MTBP accumulates in the future acrosome from the very beginning of its formation. In the mature spermatozoon TRF2/MTBP decorates the acrosomal membrane as well as spreads in condensed chromatin.     

SPERMIOGENESIS IN THE PULMONATE SNAIL, EUHADRA HICKONIS 1. ACROSOME FORMATION

Electron microscopical observations of the course of acrosomal differentiation in Euhadra hickonis show that the vesicular component of the mature acrosome is produced by early Golgi activity, whereas an equivalent amount of material that forms a basal component is added later to the outside of the vesicle. It is also suggested that similar material which concurrently accumulates against part of the outer surface of the nuclear envelope is finally incorporated into the basal part of the acrosome.
In the early spermatid, which has a highly polymorphic nucleus, material derived from the well-developed Golgi complex accumulates within a network of tubules in its central maturing zone to form a single acrosomal vesicle ca. 150 nm in diameter. The next stage is characterized by the strikingly spherical shape of the nucleus, as well as by the addition of electron-dense material to the outside of the nuclear envelope over the future anterior surface, and to its inside in the posterior region where the centriolar fossa will form.
At mid-spermiogenesis the Golgi complex moves posteriorly away from the acrosomal vesicle, which remains in the anterior cytoplasm. A growing mass of densely filamentous material forms a hollowed hemisphere around one side of the vesicle. This complex approaches the coated anterior part of the nuclear envelope, turning if necessary so that the filamentous material is in the lead, and the latter merges with the electron-dense material at the center of the coated area. As the late spermatid nucleus elongates, this material passes through a series of changes in arrangement and electron density, finally forming a homogeneously particulate element of medium density that surrounds the proximal half of the acrosomal vesicle and caps the slender tip of the nucleus in the mature spermatozoon.     

A light and electron microscopical study of spermatogenesis in Hydra cauliculata

Morphological changes in the interstitial cells were studied during their differentiation into spermatozoa. Development of the spermatogonium involves an increase in nuclear and nucleolar size, and the formation of a dense mass of cytoplasmic ribosomes. The mature spermatozoon has a relatively simple structure. The head consists of a bullet shaped, homogeneous nucleus, which lacks an acrosome but bears distal membrane specializations. The middle piece is composed of four large spherical mitochondria at the base of nucleus. A single flagellum projects from one of the two centrioles lodged between the mitochondria. The flagellum appears early during development in the primary spermatocyte. During spermiogenesis microtubules associated with the basal body flagellum complex appear to define the axis of chromatin condensation.     

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.     

Spermiogenesis in Polyplacophora,with special reference to acrosome formation (Mollusca)

Summary The present study examines spermiogenesis, and in particular the formation of the acrosome, in ten species of chitons belonging to four families. This study emphasizes the formation of the acrosome but brings to light several other structures that have received little or no mention in previous studies. The process of spermiogenesis is essentially similar in each species, although Chaetopleura exhibits some significant differences. In early spermiogenesis the Golgi body secretes numerous small pro-acrosomal vesicles that gradually migrate into the apical cytoplasm. The chromatin condenses from granules into fibres which become twisted within the nucleus. A small bundle of chromatin fibres projects from the main nuclear mass into the anterior filament; this coincides with the appearance of a developing manchette of microtubules around the nucleus that originates from the two centrioles. Radiating from the distal centriole is the centriolar satellite complex, which is attached to the plasma membrane by the annulus. The distal centriole produces the flagellum posteriorly and it exits eccentrically through a ring of folded membrane that houses the annulus. Extending from the annulus on one side of the flagellum, in all but one species, is a dense fibrous body that has not been previously reported. The proximal centriole lies perpendicular to the end of the distal centriole and is attached to it by fibro-granular material. Pro-acrosomal vesicles migrate anteriorly through the cytoplasm and move into the anterior filament to one side of the expanding nucleus. Eventually these vesicles migrate all the way to the tip of the sperm, where they fuse to form one of two granules in the acrosome. In mature sperm the nucleus is bullet-shaped with a long anterior filament and contains dense chromatin with occasional lacunae. The mitochondria vary in both number and position in the mature sperm of different species. Both centrioles are housed eccentrically in a posterior indentation of the nucleus, where the membranes are modified. The elongate flagellum tapers to a long filamentous end-piece that roughly corresponds to the anterior filament and may be important in sperm locomotion for hydrodynamic reasons. An acrosome is present in all ten species and stained positively for acid phosphatase in three species that were tested.     

Localization of boar sperm proacrosin during spermatogenesis and during sperm maturation in the epididymis.

The localization of proacrosin was determined by using colloidal gold labeling and electron microscopy of boar germ cells during spermiogenesis to post-ejaculation. Proacrosin was first localized in round spermatids during the Golgi phase of spermiogenesis; it was associated with the electron-dense granule, or acrosomal granule that was conspicuous within the acrosome. It remained within the acrosomal granule during the cap and acrosome phases of spermiogenesis. At these stages, there was no apparent association of the proacrosin molecule with the acrosomal membranes. During the maturation phase of spermiogenesis, proacrosin was seen to become dispersed into all regions of the acrosome except the equatorial segment. When sperm from different segments of the epididymis and ejaculated sperm were examined, localization was observed throughout the acrosome except for the equatorial segment. Here proacrosin appeared to be localized on both the inner and outer acrosomal membranes as well as with the acrosomal matrix, although further studies are required to verify the membrane localization. No labeling was seen on the plasma membrane. These data suggest that the synthesis and movement of proacrosin to sites in the acrosome are controlled by an as yet unknown process. The absence of proacrosin on the plasma membrane of mature ejaculated sperm makes it unlikely that this enzyme plays a role in sperm-zona adhesion prior to capacitation.     

中国鲎精子发生的研究:Ⅱ.精子形成

应用电技术研究中国鲎精子形成过程和特点,早期精子细胞核圆,染色质呈网状分布,胞质中有许多线粒体和高尔基液泡,精子形成期间,出现合胞体现象,核分裂而胞质不分裂,细胞通过胞质桥相联系,随后出现隔板,逐渐将细胞核分开。细胞随访核向后移动而呈现极化现象。核的顶部出现一个高尔基－线粒体区,顶体由高在液泡演变而。精子形成期间,核中央位置形成贯穿整个的中央通道,并在核中形成植入窝,中心粒位于其中,成熟精子胞质极     

Ultrastructural studies of spermatozoa in three bivalve species with notes on evolution of elongated sperm nucleus in primitive spermatozoa

Sperm ultrastructure and spermiogenesis of the three bivalve species Musculus discors, Nucula sulcata, and Dreissena polymorpha have been studied. During spermatid differentiation in Musculus discors and Nucula sulcata the nucleus attains an elongated rod-like shape. The spermatozoon from Nucula sulcata was found to have a cup-shaped acrosome and five mitochondria surrounding two centrioles in the middle piece. The spermatozoa from Musculus discors has a long complex acrosome. From the distal centriole striated processes extend and attach to the plasma membrane. The spermatozoon of the fresh water species Dreissena polymorpha agrees in all main features with those of other invertebrate groups with external fertilization. It is thus of the primitive type with barrel-shaped nucleus and four to five mitochondria1 spheres in the middle piece. The acrosome is a prominant, complex structure at the apex of the mature spermatozoon. A comparison of sperm ultrastructure among bivalves indicates that there is a certain correlation between the evolution of the elongated sperm nucleus and large, yolk-rich eggs. In species with an elongated sperm nucleus the increased egg size has often led to a lecithotrophic or direct development. The elongated nucleus is a slight modification of the primitive type. There is a great variation in acrosome structure among bivalve spermatozoa, reflecting diverging functional demands at fertilization of the eggs.     

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.     

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.