Studies on the acrosome. X. Differentiation of the starfish acrosome

The course of acrosomal differentiation observed during spermiogenesis in two starfishes shows that the central components of the mature acrosome are produced by Golgi activity. In the early spermatid, small Golgi-derived vesicles enter the hydrated acrosomal mass and appear to contribute their membrane constituents to the acrosomal-membrane precursor elements. A single lamella of smooth endoplasmic reticulum and fine-fibrillar material associated with it surround the membraneprecursor complex. In a drastic reorganization by which the spermatid acquires antero-posterior symmetry, the acrosome becomes embedded in the anterior part of the nucleus directly beneath the plasma membrane. All the other organelles congregate in the posterior cytoplasm; a thin layer of cytoplasm persists around the sides of the nucleus. During late spermiogenesis two additional acrosomal components become increasingly conspicuous. One is the layer of fine-fibrillar material associated with the smooth endoplasmic reticular vesicles surrounding the Golgi-derived elements. This material is finally pushed towards the center of the sperm head by a late accretion of fibrous product which appears to be synthesized throughout spermiogenesis by the ribosomes, and accumulates around the anterior part of the acrosome as the cytoplasmic matrix diminishes.     

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.     

ELECTRON MICROSCOPE STUDIES ON SPERM DIFFERENTIATION IN MARINE ANNELID WORMS. II. SPERM FORMATION IN ARENICOLA BRASILIENSIS

The course of spermiogenesis in arenicola brasiliensis was observed with the electron microscope. The spermatogonia floating in the body cavity seem to proliferate and differentiate to mature spermatozoa in the coelomic fluid. More than a hundred spermatids are connected to one large central mass of cytoplasm and spermiogenesis proceeds synchronously in one cluster, which changes into a sperm-disc during maturation. The pre-acrosomal vesicle originates from the Golgi-body and gradually changes into the acrosomal vesicle of peculiar structure like a cup upside down. In the process of differentiation of the acrosome, a part of the material in the acrosomal vesicle is transferred into the space between the vesicle and the nucleus. The posterior one-third of the cylindrical nucleus is surrounded by four middle-piece mitochondria. The flagellar axoneme originates from one of the centrioles, which is located near a posterior pit in the nucleus.     

SPERMIOGENESIS IN BARNACLES WITH SPECIAL REFERENCE TO ORGANIZATION OF THE ACCESSORY BODY*

Ultrastructural changes during spermiogenesis in the barnacles, Balanus amphitrite albicostatus, Balanus tintinnabulum rosa, Balanus trigonus and Tetraclita squamosa japonica, and organization of the sperm with special reference to the accessory body were studied. The Golgi complex organizes both the acrosome and the accessory body at different stages during spermiogenesis; the former is formed at the mid-spermatid stage and the latter is formed at the late spermatid stage. The arrangement of the components in the mature filiform sperm is quite unique, with the acrosome, the basal body just behind the acrosome, the axial filament parallel to a long nucleus, and a slender long mitochondrion behind the nucleus. The sperm in the anterior and posterior half of the ejaculatory duct differ from each other in form in that the sperm in the anterior duct are not equipped with the accessory body and the sperm in the posterior duct are. The accessory body can be artificially broken down by some treatments (1 M urea, alkaline sea water: pH 9.0-9.7, low ionic concentration of sea water). The loss of the accessory body from the sperm is assumed to be related to the ferti-lizability of the sperm.     

Ultrastructure of sperm development and mature sperm morphology in three species of commensal bivalves (Mollusca: Galeommatoidea)

Ultrastructural features of the ovotestes, spermatogenesis, and the mature sperm are described for three galeommatid bivalves, Divariscintilla yoyo, Divariscintilla troglodytes, and Scintilla sp., from stomatopod burrows in eastern Florida. All three species yielded similar results except with respect to mature sperm dimensions. The ovotestis contains three types of somatic cells within the testicular portion: flattened myoepithelial cells defining the outer acinal wall; underlying pleomorphic follicle cells containing abundant glycogen deposits; and scattered, amoeboid cells containing lysosomal-like inclusions which are closely associated with developing sperm. Early spermatogenesis is typical of that reported from other bivalves. In contrast, the late stages of spermiogenesis involve the migration and gradual rotation of the acrosomal vesicle, resulting in a mature acrosome tilted about 70° from the long axis of the cell. The mature sperm possesses an elongated, slightly curved nucleus; a subterminal, concave acrosome with a nipple-like central projection; five spherical mitochondria and two centnoles in the middlepiece; and a long flagellum. The rotational asymmetry and the presence of perimitochondrial glycogen deposits in these sperm are unusual in the Bivalvia and may be associated with fertilization specializations and larval brooding common among galeommatoideans.     

Localization of sperm antigen SP-10 during the six stages of the cycle of the seminiferous epithelium in man

The distribution of the sperm protein SP-10 was investigated in plastic-embedded samples of human testes by light and electron microscopy. An immunogold and silver enhancement technique, in conjunction with a monoclonal antibody (MHS-10) raised against SP-10, was used to localize the protein. SP-10 was detected in spermatids at each of the six stages of the cycle of the seminiferous epithelium. Light microscopy showed immunoreactive material at the circumference of developing acrosomes in the early steps of spermiogenesis. As differentiation proceeded and cell shape changed from round to elongated, immunoreactive material appeared in an arc, which gradually became a V shape bordering the spermatid nucleus. The area of the immunoreactive material and its shape corresponded to that of the developing acrosome. At the electron microscopic level, gold particles indicative of the presence of SP-10 were detected on electron-dense material found within the developing acrosomal vesicle in early steps of spermiogenesis. As the electron density of the acrosome increased, a high concentration of gold particles was seen in the vesicle matrix. The gold particles gradually became associated with the inner and outer acrosomal membranes of the most mature spermatids.     

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.     

A comparative study on the fine structure of developing spermatozoa in the isopod,Oniscus asellus,and the amphipod,Orchestoidea sp.

Summary Developing spermatids and mature spermatozoa from the isopod, Oniscus asellus and the amphipod, Orchestoidea sp. have been examined with the light microscope and the electron microscope and have been found to have similar morphologies. As spermiogenesis proceeds the nucleus migrates to one pole of the spermatid at which point an acrosome, contiguous rod, and cross-striated tail develop. The acrosomal vesicle elongates to a cone-shaped, mature acrosome lying at the apex of a cross-striated tail and nucleus which are situated at approximate forty-five degrees to each other. The cross-striated tail originates as an evagination of the spermatid plasma membrane near the acrosomal vesicle. The tail eventually grows to lengths of four to five hundred microns. The mature, tail-like appendage is cross-striated at major 750 to 800 Å, and minor 125 to 150 Å, periodicities. When observed in vitro, mature sperm of both species appear non-motile.Possible homologies of this unusual spermatozoon with other types of spermatozoa are made and it is concluded that: 1) isopod and amphipod spermatozoa should be classified as non-flagellate; 2) the cross-striated tail, previously thought to be a flagellum, is a non-motile structure associated in development and possible function with the acrosome; and 3) the rodlike structure contiguous with the acrosome is similar to perforatoria described in some vertebrate sperm.Supported by U.S.P.H.S. Grant No. NB-06285 and Training Grant No. 5-Tl-GM-202. — The author wishes to express his grateful appreciation for the technical assistance given by Miss Ann Barnett during the course of this investigation.     

Spermiogenesis and spermatozoa ultrastructure of Aonides oxycephala (Annelida: Spionidae) from the Sea of Japan

Adults of Aonides oxycephala, common inhabitants of shallow boreal waters in the Atlantic and Pacific Oceans, release gametes into the water where fertilization and lecithotrophic larval development occur. During spermiogenesis, the acrosomal vesicle migrates from the posterior to the anterior end of the spermatid and the number of mitochondria reduces from six in early spermatids to four in mature spermatozoa. Each spermatozoon has an ovoid head with the acrosome 1.4?±?0.1?µm long and 1.6?±?0.1?µm wide and the nucleus 1.7?±?0.1?µm long and 2.3?±?0.1?µm in diameter, four spherical mitochondria, two centrioles oriented perpendicular to each other, putative glycogen in the shape of dense granules in the midpiece, and a flagellum with 9?×?2?+?2 organization of microtubules. The acrosome is a complex heterogeneous structure with five ordered layers of different electron densities, lying in a shallow depression on the anterior end of the nucleus. The nucleus is barrel-shaped (truncated ovoid) with the centriolar fossa housing the distal and proximal centrioles. Spermiogenesis and ultrastructure of spermatozoa of A. oxycephala are similar to those of another free spawning spionid, Marenzelleria viridis. Aonides and Marenzelleria have not, however, been considered as closely related taxa; thus, similarity in the morphology of their sperm might result from convergence or parallelism.     

Spermiogenesis in the Flatworm, Notoplana Japonica with Special Attention to the Organization of an Acrosome and Flagella

Ultrastructural changes during spermiogenesis in the flatworm, Notoplana japonica were studied with special attention to organizing process of an acrosome and flagella. During spermiogenesis, the G olgi complex develops conspicuously but it fails to organize the structure of an acrosomal vesicle. Consequently, no acrosome is formed at the apex of the sperm. As a substitute for an acrosomal structure, the slender process at the tip of the mature sperm is prominently occupied with glycogen granules.
The axoneme of the flagellum is formed from the basal body in the protrusion which is juxtaposed to the nucleus of the early spermatid. Two flagella associated with an electron-dense structure (EDS) extend superficially from the spermatid body in opposite directions. Progressively, they take an acute angle to each other and finally run alongside the sperm body. The axoneme consits of nine peripheral doublets with arms, a central cylinder containing an electron dense core, a less dense intermediate zone and fine spokes between the cylinder and doublets.     

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 of Philippia (Psilaxis) oxytropis,with special reference to the taxonomic position of the architectonicidae (Gastropoda)

Summary Spermiogenesis of the architectonicid Philippia (Psilaxis) oxytropis was studied using transmission electron microscopy. Both spermatids and mature sperm of Philippia show features comparable to sperm/spermatids of euthyneuran gastropods (opisthobranchs, pulmonates) and not mesogastropods (with which the Architectonicidae are commonly grouped). These features include: (1) Accumulation of dense material on the outer membrane of anterior of the early spermatid nucleus — this material probably incorporated into the acrosome; (2) Structure of the unattached and attached spermatid acrosome (apical vesicle, acrosomal pedestal) accompanied by curved (transient) support structures; (3) Formation of the midpiece by individual mitochondrial wrapping around the axonemal complex, and the subsequent fusion and metamorphosis of the mitochondria to form the midpiece; (4) Presence of periodically banded coarse fibres surrounding the axonemal doublets and intra-axonemal rows of granules. A glycogen piece occurs posterior to the midpiece but is a feature observed in both euspermatozoa of mesogastropods (and neogastropods) and in sperm of some euthyneurans.Despite the lack of paracrystalline material or glycogen helices within the midpiece (both usually associated with sperm of euthyneurans), the features of spermiogenesis and sperm listed indicate that the Architectonicidae may be more appropriately referable to the Euthyneura than the Prosobranchia.Abbreviations a acrosome - ap anterior region of acrosomal pedestal - as support structures of spermatid acrosome - av apical vesicle of acrosome (acrosomal vesicle of un-attached acrosome) - ax axoneme - b basal region of acrosomal pedestal - c centriole - cf coarse fibres - cr cristal derivative of midpiece - db intra-axonemal dense granules - drs dense ring structure - gg glycogen granules - gp glycogen piece - G Golgi complex - m mitochondrion - mt microtubules - n nucleus - pm plasma membrane - sGv small Golgi vesicles     

Ultrastructural Studies on Gametogenesis of the Prawn Palaemon serratus (Pennant). II. Spermiogenesis

Spermiogenesis in Palaemon serratus is described. The mature sperm has an atypical form and is highly modified. In early stages of spermiogenesis mitochondria, golgi complexes, stacks of annulate lamellae and endoplasmic reticulum are present but disappear later in development. Two modified mitochondria are present in the mature sperm. This latter consists of a cup-shaped nucleus, a cross-striated “spike”, has a centriole and lacks an acrosome. The nucleus contains membrane-bounded vesicles which arise by pinocytosis. The “spike” may be a flexible posterior organ which suggests a mode of fertilization requiring limited mobility.     

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.     

Fine structure of spermatozoa and spermatogenesis ofSchizomus palaciosi,Reddell and Cokendolpher, 1986 (Arachnida: Uropygi,Schizomida)

Summary Spermatogenesis ofSchizomus palaciosi occurs in cysts in paired tubular testes located ventrally in the opisthosoma. Only few germ cells comprise one cyst. In early spermiogenesis an acrosomal complex composed of a spherical vacuole and a short acrosomal filament is established opposite of which a 9×2+3 flagellum emerges from a flagellar tunnel. The latter, however, is only a short-lasting structure. A manchette of microtubules surrounds nucleus and part of the acrosomal vacuole. The alterations in the arrangement of the microtubules during spermiogenesis are described. The spermatid finally is an elongate cell with a slender acrosomal vacuole on top of the helical nucleus. A deep implantation fossa filled with dense material is encountered. The acrosomal vacuole is accompanied by an intricate paracrosomal lattice structure not known at present of otherArachnida. This structure disappears during final spermiogenesis. The acrosomal filament (perforatorium) reveals filamentous subunits arranged in a regular pattern. Large ovoid mitochondria do not establish a distinct middle piece. Finally the elongate spermatid is coiled to form the mature spherical spermatozoon.The results are discussed under functional and taxonomical aspects.     

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.     

Ultrastructure of spermiogenesis in a freshwater stingray, Himantura signifer

Ultrastructural changes of spermatids during spermiogenesis in a freshwater stingray, Himantura signifer, are described. Differentiation of spermatids begins with modification of the nuclear envelope adjacent to the Golgi apparatus, before the attachment of the acrosomal vesicle. A fibrous nuclear sheath extends over the nuclear surface from the site of acrosomal adherence. The conical apical acrosome is formed during nuclear elongation. At the same time, chromatin fibers shift from an initially random arrangement, assume a longitudinal orientation, and become helical before final nuclear condensation. An axial midpiece rod is formed at the posterior end of nucleus and connects to the base of the sperm tail. Numerous spherical mitochondria surround the midpiece axis. The tail originating from the posterior end of the midpiece is composed of the usual 9 + 2 axoneme accompanied by two longitudinal columns, which are equal in size and round in cross section. The two longitudinal columns are absent at the end piece. A distinctive feature of freshwater stingray sperm is its spiral configuration.     

Cytodifferentiation of the crayfish spermatozoon: acrosome formation,transformation of mitochondria and development of microtubules

Summary During spermiogenesis in the crayfish, the acrosome, mitochondrial derivatives and the centrioles are retained within the admixed nucleoplasm and cytoplasm (spermioplasm). Fused nuclear and plasma membranes form the tegument that invests the spermioplasm. A well-defined system of small tubules that originate during spermiogenesis from densities surrounding the centrioles also defines the axes of the nuclear processes in the mature spermatozoon. These tubules are larger in diameter than the microtubules in adjacent interstitial cells and their development coincides with the formation and extension of the nuclear processes. The small tubules seem related to the changes in the cell accompanying nucleoplasmic streaming and to the growth and stabilization of form of the elongate, assymmetric nuclear processes.The mitochondria of spermatocytes are transformed into membranous lamellae that lie in the spermioplasm of the mature spermatozoon, and may by oxidative phosphorylation or some alternative pathway provide energy for metabolic activity and motility.The apical cap of the mature acrosome of the crayfish spermatozoon is enveloped by a sheath of PAS-positive material. The acrosomal process is attached to a dense crescent-shaped acrosome embedded in the spermioplasm. A fine granular substance at the base of the acrosome gives rise to beaded filaments that radiate into the central acrosomal concavity.This study was supported by Grants CA-04046, GM-08380 and GM-00582 from the United States Public Health Service.     

Assembly of the fluorescent acrosomal matrix and its fate in fertilization in the water strider,Aquarius remigis

Animal sperm show remarkable diversity in both morphology and molecular composition. Here we provide the first report of intense intrinsic fluorescence in an animal sperm. The sperm from a semi‐aquatic insect, the water strider, Aquarius remigis, contains an intrinsically fluorescent molecule with properties consistent with those of flavin adenine dinucleotide (FAD), which appears first in the acrosomal vesicle of round spermatids and persists in the acrosome throughout spermiogenesis. Fluorescence recovery after photobleaching reveals that the fluorescent molecule exhibits unrestricted mobility in the acrosomal vesicle of round spermatids but is completely immobile in the acrosome of mature sperm. Fluorescence polarization microscopy shows a net alignment of the fluorescent molecules in the acrosome of the mature sperm but not in the acrosomal vesicle of round spermatids. These results suggest that acrosomal molecules are rearranged in the elongating acrosome and FAD is incorporated into the acrosomal matrix during its formation. Further, we followed the fate of the acrosomal matrix in fertilization utilizing the intrinsic fluorescence. The fluorescent acrosomal matrix was observed inside the fertilized egg and remained structurally intact even after gastrulation started. This observation suggests that FAD is not released from the acrosomal matrix during the fertilization process or early development and supports an idea that FAD is involved in the formation of the acrosomal matrix. The intrinsic fluorescence of the A. remigis acrosome will be a useful marker for following spermatogenesis and fertilization. J. Cell. Physiol. 226: 999–1006, 2011. © 2010 Wiley‐Liss, Inc.