Ultrastructure of the sperm and spermatogenesis and spermiogenesis of Dina lineata (hirudinea,erpobdellidae)

The mature sperm of Dina lineata is of the modified type. The sperm are 48 μm long and 0.3 μm wide. The sperm are filiform and helicoidal cells with a distinct head, a midpiece, and a tail. There are two distinct regions in the head: the acrosome and the posterior acrosome, each with its own characteristic morphology. The midpiece is the mitochondrial region and has a single mitochondrion. Two distinct portions can be observed in the tail: the axonematic region and the terminal piece. In the process of spermatogenesis the early spermatogonia divide to form a poliplast of 512 spermatic cells. In the spermiogenesis the following sequential stages can be distinguished: elongation of the flagellum; reciprocal migration of mitochondria and Golgi complex; condensation of chromatin and formation of the posterior acrosome; spiralization of nuclear and mitochondrial regions; and, finally, formation of the anterior acrosome. The extreme morphological complexity of the Dina spermatozoon is related to the peculiar hypodermal fertilization which characterizes the erpobdellid family. Correlation between sperm morphology and fertilization biology in the Annelida is revised.     

Nuclear and cytoplasmic differentiation in developing sperm of the crayfish,Cambaroides japonicus

Summary In the present electron microscopic study of spermatogenesis in the crayfish, Cambaroides japonicus, it was possible to clarify several aspects of the unusual differentiation which leads to the production of an aflagellate sperm. The centriole is followed from the metaphase of the second spermatocyte division to the time at which, in the nearly mature sperm, it appears to disintegrate. It has no connection with the acrosome but in the late spermatid and maturing sperm it is found randomly oriented among the convoluted membranes of the filamentous endoplasmic reticulum.There appears to be a close association of mitochondria with the developing acrosomal vesicle. Typical mitochondria, however, are not present after the late spermatid stage of development. It is suggested that the complex lamellar bodies associated with the nuclear envelope in the late stages of spermatogenesis may be related to mitochondria for these lamellar bodies resemble the complex mitochondria found in the adjacent nutritive cells.The development of the acrosome has been traced from an aggregate of dense granules which first appear in the interzonal spindle region and are later segregated at one side of the cell after the second spermatocyte division. As differentiation proceeds, tubular elements appear and disappear within the acrosome, while somewhat later, fibrous elements appear in the matrix. In the mature acrosome, the fibrous elements remain only adjacent to the granular periphery of the acrosome and the core again becomes homogeneous.No typical Golgi complex is found in these cells at any time during their differentiation.In the maturing sperm the development of the arms of the nucleus was studied. Preceding the differentiation of the arms a coarse fibrous material develops in the periphery of the nucleus. It is shown that the fibrillar material in the matrix of the arms is in continuity with the fibrillar material in the matrix of the nucleus proper.Supported in part by Grant No. B 2314 of the National Institute of Neurological Diseases and Blindness, U.S. Public Health Service.Predoctoral Research Fellow of the National Institute of Neurological Diseases and Blindness, U.S. Public Health Service.     

COMPARATIVE SPERMATOLOGY OF FOUR SYMPATRIC SPECIES OF SIPHONARIA (PULMONATA: BASOMMATOPHORA)

The fine structure of the modified sperm and spermatogenesisof four sympatric species of Siphonaria is described. The morphologyof the sperm of all species is very similar. The head, whichis about 6 µm long, is composed of a nucleus with fibrouschromatin capped by an acrosome (about 1 µm long) comprisedof an acrosomal pedestal and apical vesicle. The midpiece hasa mitochondrial derivative which surrounds a single glycogenhelix, posterior to which is a glycogen piece. Although differencesbetween each species exist, the value of sperm morphology forpurposes of taxonomy in this genus is questioned. Comparisonwith other basommatophorans however suggests that sperm morphologymay be of value at a higher taxo-nomic level. The morphologicalchanges that occur during spermatogenesis are similar to thosedescribed for other molluscs with modified sperm, except thatduring early spermiogenesis the Golgi body and smooth endoplasmicreticulum become highly developed. This proliferation of theSER and Golgi occurs at the same time as elongation of the spermatid.Throughout spermatogenesis, the germ cells are closely associatedwith a somatic cell which, because of structural similaritieswith the somatic cell of mammalian seminiferous epithelium,has been termed a Sertoli cell. After the spermatids have beenreleased from the Sertoli cells of the testis, maturation continuesin the hermaphrodite duct where the acrosome reaches its finalsize and glycogen accumulates in the glycogen compartment ofthe mid-piece. (Received 25 April 1990; accepted 1 September 1990)     

Two sperm types in the spermatozeugmata of Tubifex tubifex (annelida,oligochaeta)

The spermatozeugmata (sperm bundles lacking a distinct wall) from the spermathecae of Tubifex tubifex are composed of two different zones: an internal axial cylinder containing conventional spermatozoa and an external cortex composed of modified spermatozoa, tightly packed together. The conventional spermatozoa conform to the classical clitellate scheme: very long and thin with a complex acrosome, a filiform nucleus, small mitochondria, and a flagellum with Y links and β glycogen granules as accessory structures. The modified spermatozoa show “empty” acrosomes, degenerating nuclei, and tails which contain γ glycogen granules. The tails are helically wound around the spermatozeugma and are connected to each other by junctional complexes. The tips of the cortical tails are free and move with a metachronal wave. The presence of two sperm types in tubificids is discussed and a protective function for the modified cortical spermatozoa is proposed.     

Ultrastructure of dimorphic sperm and seminal receptacle in the hermaphrodites Barrimysia siphonosomae and Pseudopythina ochetostomae (Bivalvia, Galeommatoidea)

The intertidal Bivalvia Barrimysia siphonosomae (Montacutidae) and Pseudopythina ochetostomae (Kelliidae) live commensally with Siphonosoma cumanense (Sipuncula) and Ochetostoma erythrogrammon (Echiura), respectively. Both bivalves are hermaphrodites although males and females may occur. Paired, pouch-shaped seminal receptacles are located in the suprabranchial chamber near the genital opening of both species. The interior of the receptacles of sexually mature individuals contains numerous non-epithelial cells separated by narrow spaces that serve as a depot for sperm cells. Specimens of both species produce two sperm morphotypes. Euspermatozoa are oblong with elongate conical acrosomes, and a middlepiece consisting of about eight long mitochondria spirally arranged to form a sheath surrounding the basis of the flagellum. The paraspermatozoa are vermiform, about 4 µm broad and longer (up to 240 µm) in B. siphonosomae than in P. ochetostomae (ca 150 µm). The anterior, bullet-shaped, 4.5- or 3.0-µm-long acrosome is located above an elongate, 4- to 6-µm-long subcylindrical nucleus. Adjacent to the nucleus occurs a bundle of approximately 25 (B. siphonosomae) or ca 10 (P. ochetostomae) flagella. The cytoplasm of the sperm body contains spherical lipid droplets, glycogen deposits and numerous membrane-bound spindle- to rod-shaped electron-dense granules. It is presumed that both sperm types aggregate to form spermatozeugmata. The presence of a combination of almost identical and highly specialised euspermatozoa and paraspermatozoa in species of the two genera qualifies these structures as strong synapomorphies. Pseudopythina, as presently defined, is considered paraphyletic.     

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.     

Spermatogenesis and sperm ultrastructure in the polychaete genusOphryotrocha (Dorvilleidae)

The details of spermatogenesis and spermiogenesis are described forOphryotrocha puerilis. The ultrastructure of mature sperm is shown forO. puerilis, O. hartmanni, O. gracilis, O. diadema, O. labronica, andO. notoglandulata. Clusters of sixteen cells each are proliferated by two stem cells in each setigerous segment ofO. puerilis representing the very early stages of both oogenesis and spermatogenesis. In each spermatocyte-I cluster, the cells are interconnected by cytoplasmic bridges. Early, clusters are enveloped by peritoneal sheath cells. These transient gonad walls break down prior to meiosis. The meiotic processes may start in the clusters with the cells still interconnected, or during breakdown of the original cluster, giving rise to smaller subclusters of both spermatocytes I and spermatocytes II with various numbers of cells. Finally, spermatid tetrads are present. As spermiogenesis progresses, the tetrads disintegrate. Golgi vesicles in both spermatocytes and spermatids contain electron-dense material, presumably preacrosomal. The acrosome is formed by such vesicles. In the six species studied here, the acrosomes appear to be of a similar overall structure but are of different shape. Centrioles are usually located beneath the acrosome. The distal centriole forms the basal body of a flagellum-like cytoplasmic process. The microtubules of these flagellar equivalents do not show a normal ciliar arrangement. The flagellar equivalent appears to be non-motile. InO. hartmanni and inO. notoglandulata, a flagellar equivalent is missing. Microtubules originating from the proximal end of the distal centriole stretch to the nuclear envelope. This feature appears to be especially conspicuous inO. puerilis and inO. labronica. InO. labronica and inO. notoglandulata, bundles of microtubules paralleling the cell perimeter appear to stabilise the sperm. Various numbers of mitochondria are either randomly distributed around the nucleus or accumulate on one side, often directly under the acrosome. Parts of the present paper were presented at the 2^nd International Polychaete Conference, Copenhagen 1986 and at the 3^rd International Polychaete Conference, Long Beach, Ca. 1989.     

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.     

COMPARATIVE SPERMATOLOGY OF THREE SPECIES OF DONAX (BIVALVIA) FROM SOUTH AFRICA

The fine structure of the sperm and spermatogenesis in threespecies of Donax (D. madagascariensis, D. sordidus and D. serra)are described. Although the morphology of the sperm of all speciesis very similar, each has unique features. Donax madagascariensisand D. sordidus reportedly hybridize in regions of sympatryand their spermatozoa are morphologically closer to one anotherthan to D. serra. All sperm are of the primitive type with ahead(about 2 µmu; long), mid-piece of four mitochondria andtail. The head comprises a barrel-shaped nucleus which is cappedby a small, complex acrosome. The structure of the acrosomeis typical of heterodont bivalves. During spermatogenesis thepattern of nuclear chromatin condensation is granular. Glycogenfirst appears in the cytoplasm of spermatids, and in the maturesperm is sited in the mid-piece and base of the acrosome. (Received 15 May 1989; accepted 25 June 1989)     

Morphology, structure of dimorphic sperm, and reproduction in the hermaphroditic commensal bivalve Pseudopythina tsurumaru (Galeommatoidea: Kellidae)

In Japan Pseudopythina tsurumaru is an up to 10.8 mm-long commensal of the burrowing sea cucumber Protankyra bidentata, whereas in Hong Kong the same species is smaller and associated with the crab Hexapus anfractus, itself a commensal of P. bidentata. Japanese P. tsurumaru is a hermaphrodite tending towards protogyny maturing to a female when > or = 7 mm, and entering the hermaphroditic condition when > or = 9 mm long. In addition to normal euspermatozoa, the species produces 30-32 microm long and 7 x 8 microm broad spindle-shaped paraspermatozoa provided with a conical acrosome, a nucleus, and a bundle of approximately 15-16 flagella issuing from the head region. Paired pouch-formed seminal receptacles normally occur in bivalves > or = 6 mm. Bulk sperm transfer presumably takes place by way of spermatozeugmata formed by the two types of sperm cells. Exogenous euspermatozoa attach to particular nonepithelial cells that occupy the interior of the receptacles. These cells, together with their associated sperm, are probably released as syncytial sperm-carrying bodies into the suprabranchial chamber, where the ova are fertilized.     

The fine structure of the sperm of a holothurian and an ophiuroid

The fine structure of the mature sperm of the holothurian, Cucumaria miniata, and the ophiuroid, Ophiopholis aculeata, is described with particular reference to their acrosomal and centriolar satellite complexes, and compared to the sperm of other echinoderms. In Cucumaria, the acrosome is in the form of a diffuse acrosomal vesicle. It is unusual in that it apparently lacks an acrosomal membrane. A membrane separating the acrosomal vesicle from the periacrosomal material may not be equivalent to a typical inner acrosomal membrane. In Ophiopholis, the acrosome is dense, with some internal substructure, and is enclosed by a complete acrosomal membrane. In both species, the acrosome is partially surrounded by an amorphous periacrosomal mass. There is a notable absence of a subacrosomal depression and associated structures as found in other echinoderm sperm. The centriolar satellite complex (CSC) is essentially identical in both species. A reconstruction of the CSC is presented. The CSC consists of nine satellites radiating angularly from the distal centriole, each bifurcating at a dense node before inserting on a marginal ring containing circumferential microtubules. The ring is probably a cytoskeletal element. Immediately below the satellites are nine Y-shaped connectives. connecting each of the axonemal alpha doublets to the flagellar membrane.     

Spermatogenesis and sperm ultrastructure in three species of polydora and in streblospio benedicti (Polychaeta: Spionidae)

Summary Spermatogenesis was studied at the ultrastructural level in Polydora ligni, P. websteri, P. socialis and Streblospio benedicti. Spermatogonia, spermatocytes, spermatids and mature sperm are described. In all four species, meiosis occurs in the coelom following release of spermatogonia from the gonad. In Polydora spp., chromatin condensation is lamellar with no microtubules present during nuclear elongation. In S. benedicti, chromatin condensation is fibrous with a manchette of microtubules present around the nucleus. In all four species, the acrosome forms from a Golgi-derived vesicle situated at the base of spermatids. The acrosome in Polydora spp. is conical with a distinctive substructure whereas the S. benedicti acrosome is long and spiral. The implantation fossa is short in all species except P. ligni. All four species have elongated sperm heads. The middlepiece as well as the nucleus is elongated in Polydora spp. whereas S. benedicti has a long nucleus but a short middlepiece. Platelet-shaped electron-dense bodies are present throughout the nuclear region and middlepiece of Polydora spp. and the nuclear region of S. benedicti. These membrane-bounded bodies may be energy storage organelles. The use of ultrastructural data in analysis of sibling species complexes is discussed.Contribution Number 203 from Harbor Branch Foundation, Inc.     

Derived sperm morphology in the interstitial sea cucumber Rhabdomolgus ruber,with observations on oogenesis and spawning behavior

Some life history features of the interstitial sea cucumber Rhabdomolgus ruber are described from intertidal specimens collected from the northern coast of Maine. Histological studies suggest that the population consists of hermaphrodites with gametogenesis being initiated in April and reproduction beginning in May and continuing through the summer months. Sexually mature adults possess a single, blind‐ended gonadal tubule that functions as an ovotestis by producing both eggs and sperm. The ovotestis wall consists of an outer peritoneum composed of flagellated epithelial cells and muscles; an inner germinal epithelium of germ and somatic cells; and a middle connective tissue (hemal) compartment bounded by the basal laminas of the peritoneum and germinal epithelium. During the reproductive season, the gonadal tubule contains all stages of oocyte development. Vitellogenesis appears to involve the biosynthetic activities of the Golgi complex and rough endoplasmic reticulum. A few specimens had transitional ovotestes with mature sperm in the gonad lumen and asynchronously developing oocytes and a small number of spermatocytes within the germinal epithelium. The mature spermatozoon is an ent‐aquasperm with ultrastructural features significantly different from those described from other echinoderm classes including a highly elongated acrosome, a large periacrosomal region between the acrosome and nucleus, numerous unfused mitochondria in the midpiece, and a cytoplasmic sleeve or collar extending posteriorly along the proximal portion of the flagellum. The sperm head reaches 11.5 μm in length (combined midpiece, nucleus, periacrosomal region, acrosome), making it the longest yet reported from the Holothuroidea and among the longest in the Echinodermata. Some elements of this derived morphology could be attributed to fertilization biology, but others may have phylogenetic significance. Spawning behavior was observed in which two individuals appeared to pseudocopulate by intertwining their oral tentacles for several minutes before one of them abruptly secreted an egg mass containing three eggs.     

Antibody to a sperm surface glycoprotein inhibits the egg jelly-induced acrosome reaction of sea urchin sperm

When the surface of sea urchin (Strongylocentrotus purpuratus) sperm is radioiodinated, 75% of the protein-incorporated radioactivity is associated with two glycoproteins of M_r 84,000 (84K) 64,000 (64K) (Lopo and Vacquier 1980). Antibodies were prepared against these two components by separating a Triton X-100 extract of sperm on SDS-polyacrylamide gels, cutting out the band containing the glycoprotein and injecting the homogenized gel into rabbits. Both anti-84K and anti-64K sera agglutinate sperm. Light and EM immunoperoxidase localization show both antigens are distributed over the entire sperm surface. By the immunoperoxidase technique there is some degree of cross-reactivity of both antisera with sperm of other Strongylocentrotus species, but not with those of other genera. Living sperm incubated with anti-84K Fab fragments are completely inhibited from undergoing the egg jelly-induced acrosome reaction and fertilizing eggs. Anti-64K Fab fragments have no effect on the ability of the sperm to undergo the acrosome reaction or fertilize eggs. Sperm incubated in anti-84K or anti-64K Fab fragments undergo the acrosome reaction in response to the Ca²⁺ ionophore A23187, or when the extracellular pH is increased to 9.2 with NH₄OH, indicating that the inhibition of the egg jelly-induced acrosome reaction results from the binding of the anti-84K Fab to an external molecule involved in the initiation or propagation of the acrosome reaction. The 84K glycoprotein is the first sperm surface component identified that might have a role in the induction of the acrosome reaction.     

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     

Testis structure,spermatogenesis and sperm morphology in pipefishes of the genus Syngnathus

Testes, spermatogenesis and sperm morphology have been analysed in four species of the Syngnathus genus. All species show testes of unrestricted lobular type, characterized by a single germinal compartment, with central lumen, and an external tunica albuginea. The spermatogenesis occurs throughout a process of semicystic type, in which germinal spermatocysts open precociously, so germ cells complete maturation in the testis lumen. Amongst them, aflagellate and flagellate multinucleate cells are recognizable. This type of spermatogenesis may be therefore related to the reduced number of simultaneously mature sperm produced by syngnathids. Only one type of mature sperm has been identified in all examined species. It is always a monoflagellate cell, characterized by an elongated head. Elongated head has generally been correlated with the internal fertilization and/or to the production of spermatophore. As this is not the case of syngnathids, a possible function to explain the particularly elongated head of syngnathids is discussed.     

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.     

Mammalian sperm acrosome: formation, contents, and function

Sperm-egg interaction is a carbohydrate-mediated species-specific event which initiates a signal transduction cascade resulting in the exocytosis of sperm acrosomal contents (i.e., the acrosome reaction). This step is believed to be a prerequisite which enables the acrosome-reacted spermatozoa to penetrate the zona pellucida (ZP) and fertilize the egg. Successful fertilization in the mouse and several other species, including man, involves several sequential steps. These are (1) sperm capacitation in the female genital tract; (2) binding of capacitated spermatozoa to the egg's extracellular coat, the ZP; (3) induction of acrosome reaction (i.e., sperm activation); (4) penetration of the ZP; and (5) fusion of spermatozoon with the egg vitelline membrane. This minireview focuses on the most important aspects of the sperm acrosome, from its formation during sperm development in the testis (spermatogenesis) to its modification in the epididymis and function following sperm-egg interaction. Special emphasis has been given to spermatogenesis, a complex process involving multiple molecular events during mitotic cell division, meiosis, and the process of spermiogenesis. The last event is the final phase when a nondividing round spermatid is transformed into the complex structure of the spermatozoon containing a well-developed acrosome. Our intention is also to briefly discuss the functional significance of the contents of the sperm acrosome during fertilization. It is important to mention that only the carbohydrate-recognizing receptor molecules (glycohydrolases, glycosyltransferases, and/or lectin-like molecules) present on the surface of capacitated spermatozoa are capable of binding to their complementary glycan chains on the ZP. The species-specific binding event starts a calcium-dependent signal transduction pathway resulting in sperm activation. The hydrolytic and proteolytic enzymes released at the site of sperm-zona interaction along with the enhanced thrust of the hyperactivated beat pattern of the bound spermatozoon, are important factors in regulating the penetration of the zona-intact egg.     

Ultrastructure and histochemistry of the testicular efferent duct system and spermiogenesis in Opistognathus whitehurstii (Teleostei, Trachinoidei)

 Testis organization and spermatogenesis, with the emphasis on spermiogenesis, in Opistognathus whitehurstii are described by ultrastructural and histochemical methods. The germinal epithelium is extremely reduced and restricted to the periphery of the testis, while most of the organ is occupied by a highly developed system of testicular efferent ducts. A semicystic type of spermatogenesis is observed and in the germinal epithelium spermatogenesis occurs only until the spermatidal stage. Young spermatids are released into the lumen of the testicular lobules and mature to sperm within the efferent duct system. The epithelial cells of these ducts are involved in protein and glycogen secretion and in phagocytosis of degenerating germ cells and residual bodies cast off by developing spermatids. On the basis of these functions, the testicular efferent duct system cells are considered to be homologous to the Sertoli cells. A correlation between a highly developed testicular efferent duct system and semicystic spermatogenesis is examined and a possible functional meaning of this apparently unusual mode of sperm production is proposed. Accepted: 18 March 1997     

Testicular,spermatogenesis and sperm morphology in Martarega bentoi (Heteroptera: Notonectidae)

The testicular, spermatogenesis and sperm morphology of the backswimmer Martarega bentoi was described using light and transmission electron microscopy. In this species, a pair of testes, two deferent ducts, two different pairs of accessory glands, and an ejaculatory duct form the male reproductive system. Each testis consists of two testicular follicles, which are arranged side by side in snail shape. The follicles are filled with cysts at different stages of spermatogenesis, but in the same cyst the germ cells (up to 64) are in the same stage. At the end of spermatogenesis, the sperm cells are very long, with the flagellum measuring approximately 2500 μm in length, the nucleus only 19 μm, and the acrosome, with two distinct regions, 300 μm. The flagellum is composed of an axoneme, with a 9 + 9 + 2 microtubular pattern, and 2 asymmetric mitochondrial derivatives (MDs). These have the anterior ends inserted into two cavities at the nucleus base, exhibit two paracrystalline inclusions, and have bridges linking them to the axoneme. Few spermatozoa per cyst, asymmetry in size and shape of the MDs, as well as their insertion at the nuclear base are characteristics considered derived, and that differentiate the sperm of M. bentoi from those of the Nepomorpha, Belostomatidae and Nepidae.