Spermatogenesis in Animals as Revealed by Electron Microscopy : VI. Researches on the Spermatozoon-Dimorphism in a Pond Snail, Cipangopaludina malleata

This paper reports an electron microscope study of typical and atypical spermatogenesis in the pond snail, Cipangopaludina malteata. In the typical spermatid the nucleus undergoes profound changes as development proceeds, affecting both its form and internal fine structure. A large number of roughly parallel, dense filaments, arranged along the long axis of the nucleus, fuse with each other to form in the end the homogeneous helical body characteristic of the head of the adult spermatozoa. The nebenkern is apparently mitochondrial in nature and, in its early development, is similar to that of insects except that it appears as a double structure from the beginning. As differentiation proceeds, the mitochondria lose their membranes, and the residual, now denuded cristae, reorganize to give a parallel radial arrangement. In the last stages of development, the nebenkern derivations become applied to the sheath of the middle piece in a compact helical fashion. In the development of the atypical spermatozoa, the nucleus fails to differentiate and simply shrinks in volume until only a remnant, devoid of DNA, is left. The cytoplasm shows numerous vesicles containing small Feulgen-positive bodies, 80 to 130 mµ in diameter. These vesicles plus contents increase in number as spermatogenesis proceeds. The "head" structure of the atypical spermatozoa consists of a bundle (7 to 17) of tail flagella, each with a centriole at its anterior end. The end-piece of the atypical form appears brush-like and is made up of the free ends of the several flagella.     

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.     

Differentiation of binuclear spermatozoa in mice

In an electron microscopy study of abnormal spermatogenesis in mice, we have found that two discrete haploid nuclei may be located in a single spermatid cytoplasm after the second meiotic division. The spermatid continues to differentiate and forms a binucleate spermatozoon with both nuclei separately packaged within the sperm head. The Golgi apparatus of the double spermatid forms a single proacrosome that attaches to both nuclei. Apparently, one acrosomal structure differentiates to cover and compartmentalize the two haploid nuclei within the sperm head. Chromatin condensation appears normal. The head morphology and number of flagella vary in mature spermatozoa produced by this process. This work demonstrates one pathway by which polyploid spermatids continue to differentiate to spermatozoa after failure of cytoplasmic division or possibly cellular fusion.     

Ultrastructure of the spermatozoa of five species of South African bivalves (Mollusca), and an examination of early spermatogenesis

Transmission electron microscopy of the spermatozoa of five species from three families of bivalves has shown that each species has a sperm with unique morphology. However, the morphology of the acrosomes of each species is typical of the subclass of bivalve to which they belong. An examination of spermatogenesis in the five species, along with a re-examination of material from six other species of bivalves, has revealed that pre-spermiogenic cells possess flagella. In addition, acrosome formation begins in the spermatocytes with the formation of proacrosomal vesicles in the Golgi body. During spermiogenesis the proacrosomal vesicles coalesce at the presumptive posterior of the spermatid, with a larger vesicle produced by the Golgi body. The single acrosomal vesicle eventually migrates to the anterior of the spermatid where it assumes its mature form. © 1994 Wiley-Liss, Inc.     

Ultrastructure of the biflagellate spermatozoon of tomopteris helgolandica greef, 1879 (annelida,polychaeta)

The spermatozoon of the polychaete Tomopteris helgolandica is of an aberrant type with two flagella, each measuring about 40μm. The nucleus is roughly conical and weakly bent. At the anterior end it is rounded and covered only by the nuclear and plasma membranes. Membraneous, electron-dense structures are applied laterally to the nucleus. These structures may have a helical arrangement. The middle piece contains about ten mitochondria, two centrioles, and two centriolar satellite complexes. The centriolar regions are connected with the posterior part of the nucleus. The axonemes of the two tail flagella lack the usual central complex with central tubules, radial spokes, or related structures. No arms seem to be present on the A tubules of the doublets. In the middle piece the tail flagella are surrounded by invaginations of the plasma membrane forming flagellar canals. The sperm has a bilateral symmetry whereas the primitive sperm has a radial symmetry. The occurrence of two tail flagella in this spermatozoon has no phylogenetical connection with biflagellate spermatozoa in other animal groups. A series of mutations has resulted in the development of two flagella emerging from the two centrioles, the lack of a central complex in the axoneme, and the lack of a typical acrosome. In the Polychaeta, sperm structure is generally more related to function that to phylogenetics. During swimming the spermatozoon of Tomopteris rotates around its longitudinal axis.     

Spermatozoa and spermatogenesis in the northern quahaug <Emphasis Type="Italic">Mercenaria mercenaria</Emphasis> (Mollusca,Bivalvia)

We studied the ultrastructure of spermatogenesis and spermatozoa in the northern quahaug, the clam Mercenaria mercenaria. Spermatogenetic cells gradually elongate. Mitochondria gradually fuse and increase in size and electron density. During spermatid differentiation, proacrosomal vesicles migrate towards the presumptive anterior pole of the nucleus and eventually form the acrosome. The spermatozoon of M. mercenaria is of a primitive type. It is composed of head, mid-piece, and tail. The acrosome shows a subacrosomal space with a short conical contour. The slightly curved nucleus of the spermatozoon contains fine-grained dense chromatin. The middle piece consists of a centriolar complex which is surrounded by four mitochondria. The flagellum has a standard “9 + 2” microtubular structure. The ultrastructure of spermatozoa and spermatogenesis of M. mercenaria shares a number of features with other species of the family Veneridae. M. mercenaria may be a suitable model species for further investigations into the mechanisms of spermatogenesis in the Bivalvia.     

Ultrastructural studies on the reproductive system of gyrocotylidea and amphilinidea (Cestoda): Spermatogenesis, spermatozoa, testes and vas deferens of Gyrocotyle

The ultrastructure of the vas deferens, testes, spermatogenesis and spermatozoa of Gyrocotyle urna and G. parvispinosa is described. The vas deferens is ciliated and syncytial. Within the testes primary spermatocytes arise from the primary spermatogonia by incomplete mitotic divisions; the primary spermatocytes undergo two meiotic divisions leading to spermatids. In early spermatids microtubules are formed at the cell periphery. Later the spermatozoal cytoplasm (the ‘middle-piece’) grows out and the two spermatozoal flagella with their typical 9 + ‘1’ axonemes are formed. During ciliogenesis the flagella are at an angle of about 60° to the axis of the middle-piece. The flagella are inserted into basal bodies terminating in striated rootlets. Subsequently, the nucleus and isolated mitochondria migrate into the central axis. The angle between the flagella and the axis decreases; the flagella are incorporated to form the spermatozoon. In mature spermatozoa no basal body or rootlet elements were found. The phylogeny of parasitic Platyhelminthes is discussed with respect to the evolution of spermatozoa. The reduction of the acrosinoid granules which are found in spermatozoa of free-living Platyhelminthes and the incorporation of the spermatozoal flagella into the sperm body constitute autapomorphies of the Neodermata (the parasitic Platyhelminthes). Included in the Cestoda because of several common derived characters, Amphilinidea and Gyrocotylidea are the only cestodes with spermatozoa containing mitochondria. Their absence in Cestoidea—all taxa with a six-hooked larva and other characteristics—is an autapomorphy of this group.     

Spermatozoa and sperm aggregates in the vestimentiferan Lamellibrachia luymesi compared with those of Riftia pachyptila (Polychaeta: Siboglinidae: Vestimentifera)

The spermatozoa and the sperm bundles of the vestimentiferans Riftia pachyptila and Lamellibrachia luymesi (Annelida: Siboglinidae) were studied using several microscopical techniques (transmission and scanning electron microscopy, and confocal microscopy) and compared with some other annelid sperm. The spermatozoa and sperm bundles of both species show a similar structure, but they differ in the dimensions of the components of individual cells and in the number of spermatozoa forming each sperm bundle. The spermatozoa of R. pachyptila and L. luymesi are filiform cells composed, in sequence, by an acrosome in the form of a thread-like helical vesicle, an elongated coiled nucleus surrounded by two helical mitochondria, and a long flagellum. In the spermatozoa of both species, the apical portion of the nucleus is completely devoid of chromatin and is delimited by a thickened nuclear envelope with a fibrillar appearance. Both species have sperm bundles that resemble buds, having a calyx-like portion formed by the helical heads, and a stalk-like portion formed by the tightly packed flagella. A parsimony analysis based on spermatozoal characters showed monophyly of the Siboglinidae and the Vestimentifera. We propose a new set of autapomorphies characterizing vestimentiferan spermatozoa. Our analysis suggests that spermatozoal characters are useful to the understanding of the phylogeny of the group.     

Spermatogenesis inDrosophila hydei: A genetic survey

Summary We constructed balancer-chromosomes for the large autosomes ofDrosophila hydei and screened more than 16000 chromosomes for male sterile mutations in order to dissect spermatogenesis genetically. 365 mutants on the X chromosome and the autosomes 2, 3, and 4 were recovered and analysed cytologically in squash preparations under phase-contrast optics. The majority of the mutations allows a rather advanced differentiation of the spermatozoa. At the light-microscopical level, it is possible to classify these mutations with respect to individualization, coiling or motility of the mutant spermatozoa. In contrast, a small number of mutants exhibits conspicuous, pleiotropic phenotypes. Gonial divisions, the shaping of the spermatocyte nucleus and male meiotic divisions are controlled by X chromosomal or autosomal genes which can mutate to male sterile alleles. A number of nonallelic 3^rd chromosome male sterile mutations interfere with the unfolding of the Y chromosomal lampbrush loops. Other autosomal male sterile mutations modify the morphology of these lampbrush loops. Another group of mutations inhibits the formation of the nebenkern while the development of the spermatid nucleus and the flagellum can proceed. Such male sterile mutations can decouple the development of nucleus, protein body, nebenkern, and flagellum of the spermatid. Thus, we can describe spermatogenesis inDrosophila as the coordinate execution of the individual developmental programs of the different components of the spermatozoon.     

Spermatogenesis of the spider crab Maja brachydactyla (Decapoda: Brachyura)

This study describes spermatogenesis in a majid crab (Maja brachydactyla) using electron microscopy and reports the origin of the different organelles present in the spermatozoa. Spermatogenesis in M. brachydactyla follows the general pattern observed in other brachyuran species but with several peculiarities. Annulate lamellae have been reported in brachyuran spermatogenesis during the diplotene stage of first spermatocytes, the early and mid‐spermatids. Unlike previous observations, a Golgi complex has been found in mid‐spermatids and is involved in the development of the acrosome. The Golgi complex produces two types of vesicles: light vesicles and electron‐dense vesicles. The light vesicles merge into the cytoplasm, giving rise to the proacrosomal vesicle. The electron‐dense vesicles are implicated in the formation of an electron‐dense granule, which later merges with the proacrosomal vesicle. In the late spermatid, the endoplasmic reticulum and the Golgi complex degenerate and form the structures–organelles complex found in the spermatozoa. At the end of spermatogenesis, the materials in the proacrosomal vesicle aggregate in a two‐step process, forming the characteristic concentric three‐layered structure of the spermatozoon acrosome. The newly formed spermatozoa from testis show the typical brachyuran morphology. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Electron microscope study of spermatogenesis in two cestodes acanthobothrium filicolle benedenii Loennberg, 1889 and Onchobothrium uncinatum (Rud., 1819) (Tetraphyllidea, Onchobothriidae) (author's transl)]

The spermatogenesis, spermatozoon differentiation and fine structure of Acanthobothrium filicolle benedenii Loennberg, 1889 and Onchobothrium uncinatum (Rud., 1819) were studied by means of light and electron microscopy. Spermatogenesis in both species is of the rosette type. During sperm differentiation, the five following stages have been distinguished: (1) formation of arching membranes and differentiation zone; (2) nuclear elongation; (3) formation of two flagella with a median cytoplasmic process; (4) flagellar rotation; (5) fusion of two flagella with the median cytoplasmic process induced by the migration of nucleus into the latter. The mature spermatozoa of both species are threadlike structures about 250 mum long. They consist of two axonemes of the platyhelminth type (9+1 pattern), elongated nucleus and cortical microtubules embedded in a cytoplasmic matrix containing numerus beta-glycogen particles. The body which appears on cross-sections as crest, lateral with respect to the axoneme, is present in both species. Such a body is reported for the first time in Cestode spermatozoa. There is no mitochondrion in the two Onchobothriidae sperms studied.     

THE INFLUENCE OF X-RAYS ON ORGANELLE INDUCTION AND DIFFERENTIATION IN GRASSHOPPER SPERMATOGENESIS

The effect of x-irradiation on grasshopper spermatogenesis was studied with the aid of light and electron microscopy. The insects were irradiated at the second instar prior to the presence of maturation stages and observed at the last instar and imago stages. Dosages of 100 to 600 roentgens were found to retard the differentiation of the nucleus and mitochondrial nebenkern in spermatids. Evidence is presented that irradiation causes a curtailment and disorganization in the differentiation of the nebenkern from mitochondria. The above doses also induced the formation of supernumerary centrioles, flagellar filaments and acrosomes; nuclear disorganization as well as pycnosis and fragmentation also occur. The nucleus appears to be drawn toward each radiation-induced supernumerary acrosome, with consequent multipolarity of the nucleus. Induction of a set of flagellar filaments is seen only where the centriolar structure is in contact with the nucleus. Details are given of an organelle, heretofore not described, that is composed of anastomosed and interwoven cytoplasmic strands.     

Spermatogenesis in Animals as Revealed by Electron Microscopy : VIII. Relation between the Nutritive Cells and the Developing Spermatids in a Pond Snail, Cipangopaludina malleata Reeve

This paper deals with spermatogenesis in Cipangopaludina malleata Reeve, with special regard to the relation between the nutritive cells and the developing spermatids. The nutritive cell gives rise to numerous, slender or broad, elongate pseudopodia which extend from its surface toward the seminiferous lumen. They are characteristically provided with rows of circular, oval, and elongate profiles identical in form and position with the profiles of the endoplasmic reticulum. As the elongate pseudopodia increase in number, they become more slender and more closely packed until they coalesce into a continuous sheet circumferentially disposed around the nucleus and the full length of the middle piece of the typical spermatid. Thus the mantle of the typical spermatozoon of the pond snail is formed by a thin fold of the cytoplasm of the nutritive cells. This wrapping appears to contain 16 to 18 elements of the smooth surfaced endoplasmic reticulum, which run parallel and helically (50 to 100 mµ apart). It is suggested that these constitute a conductor system for nutritional supply from the nutritive cells to the developing typical spermatids. The mantle is assumed to be a transient structure which disappears when the sperms are detached. The atypical spermatids develop while lodged in deep indentations of the surface of the nutritive cells.     

Differentiation of the Opercular Integument in Rana pipiens

The opercular skin develops in its own specific fashion differing from other areas of the integument previously studied. It remains typically larval until it is sloughed off.
The opercular integument first deviates from the common skin development pathway at stage XV [1] when the rough endoplasmic reticulum. proliferates to form a large part of the cytoplasm and is accompanied by numerous large mitochondria. The Golgi apparatus becomes very large and many vesicles are found in the cytoplasm.
The mitochondria become large and swollen with atypical structure. The cytoplasm becomes highly vesiculated. Degeneration begins at the dermal edge of the basement lamella and proceeds toward the epidermis, being marked by the disorientation of collagen fibrils.
Epidermal cells become progressively more necrotic having cytoplasm consisting mainly of residual bodies and vesicles: the nucleus is the last cellular structure to undergo autolysis.
The dermal cells are the first to be lost (stages XVIII–XIX). The opercular integument is shed as a sheet of cells at stage XX when the forelimbs emerge. The necrotic zone of the opercular integument appears to stop at the junction of the body skin and the skin of the forelimb.     

Ultrastructure and motility pattern of the spermatozoa of Aleochara curtula (Coleoptera, Staphylinidae)

Ultrastructure and motility pattern of spermatozoa of the rove beetle Aleochara curtula were examined using electron and light microscopic methods. The spermatozoon is about 100 microm long and filiform. The head piece comprises a 5 microm long triple layered acrosome and 10 microm long nucleus. The flagellum consists of a 9+9+2 axoneme, two accessory bodies and two mitochondrial derivatives about equal in size but of different shape in their cross sections. In both derivatives there are paracrystalline inclusions. The flagellum is attached to the head by a 2 microm long centriole adjunct which is characterized by its electron dense material that forms a three layered folded lamellar structure. When liberated in buffer solution the sperm flagella assume a coiled hook-like form with the excentric stiff head protruding in front. The spermatozoa are driven through the medium by a small helicoidal wave of high frequency superimposed to the bent flagella. The maximum speed measured was 15.2 microm/s. The sperm architecture of A. curtula is similar to that of other Aleochara species but differs in total length and dimensions of the mitochondrial derivatives. For that reason Aleochara sperm can certainly prove useful to study the effect of the mitochondrial derivatives on sperm motility.     

Variability in the size of the nucleus in spermatozoa from Houbara bustards, Chlamydotis undulata undulata

Semen collected from 3-year-old male Houbara bustards contained large proportions (6-40%) of spermatozoa with large nuclei. In these spermatozoa, the length of the nucleus was up to twice the mean length of the nucleus in normal spermatozoa. The lengths of the acrosome, midpiece and flagella were all normally distributed, but the length of the nucleus formed a bimodal distribution. The proportion of spermatozoa with large nuclei varied among males, but not among different semen samples collected from the same male throughout the breeding season. The proportion of motile spermatozoa with large nuclei was half that of normal spermatozoa, but their velocity was significantly greater. After insemination into females, spermatozoa with large nuclei were observed in the outer perivitelline layer of eggs laid, indicating that they were stored and transported within the oviduct and reached the egg at about the time of fertilization. Furthermore, there was no difference in the ability to produce viable progeny in females that were mated with males producing greater proportions of spermatozoa with large nuclei compared with those producing 'normal' spermatozoa. Thus, the abnormal spermatozoa did not appear to impede fertility. There were no signs of triploidy in the males that produced spermatozoa with large nuclei, or in their progeny, as demonstrated by the size of erythrocytes. Therefore, it appears that the spermatozoa with large nuclei were the result of aberrant spermatogenesis.     

Ultrastructure of Spermatogenesis in the Testis of Paragonimus heterotremus

Lung fluke, Paragonimus heterotremus, is a flatworm causing pulmonary paragonimiasis in cats, dogs, and humans in Southeast Asia. We examined the ultrastructure of the testis of adult P. heterotremus with special attention to spermatogenesis and spermiogenesis using scanning and transmission electron microscopy. The full sequence of spermatogenesis and spermiogenesis, from the capsular basal lamina to the luminal surface, was demonstrated. The sequence comprises spermatogonia, spermatocytes with obvious nuclear synaptonemal complexes, spermatids, and eventual spermatozoa. Moreover, full steps of spermatid differentiation were shown which consisted of 1) early stage, 2) differentiation stage representing the flagella, intercentriolar body, basal body, striated rootlets, and electron dense nucleus of thread-like lamellar configuration, and 3) growing spermatid flagella. Detailed ultrastructure of 2 different types of spermatozoa was also shown in this study.