Multiple acrosomal vesicles and their differentiation during spermiogenesis in Ascidia zara and Ascidia gemmata (Ascidiacea, tunicata).

A fully differentiated spermatozoon of both Ascidia zara and Ascidia gemmata is approximately 35 microM long. It contains a head and a tail lacking a midpiece. The head (approximately 4 microM long for A. zara and 5 microM long for A. gemmata) contains an elongated nucleus and a single mitochondrion that flanks the nucleus. Multiple acrosomal vesicles (three or four in number) are present at the apex of the sperm head in both species. Each vesicle is approximately 50 x 50 x 60 nm, and contains moderately electron-dense material. During spermiogenesis of A. zara, three or four vesicles appear in a blister of an early stage spermatid. These vesicles transform into multiple acrosomal vesicles without fusing with each other. Spermiogenesis and acrosome differentiation are similar in A. gemmata and A. zara. Three types of acrosome differentiation in ascidians are described.     

ACROSOME DIFFERENTIATION IN THE SPERMATOGENESIS OF CIONA INTESTINALIS*

The process of acrosome formation in the course of spermatogenesis of Ciona intestinalis has been investigated. At the flute-beak-shaped tip of the head of the mature spermatozoon a small acrosomal vesicle(s) is described. The vesicles migrate to a region where the outer and inner nuclear membranes fuse thus giving rise to a “dense plate”. At the same time the chromatin begins to organize into longitudinally oriented strands which become attached to the inner side of the dense plate. The possible relationships between the dense plate, the formation of the acrosome and the orientation of the chromatin is discussed.     

Morphological aspects of fertilization in Phallusia (Ascidia) nigra (Ascidiacea,Tunicata)

The spermatozoa of Phallusia (Ascidia) nigra have an elongated head (approximately 5 m in length) in which a nucleus and a single mitochondrion are located side by side. There is no midpiece. The apex of the head is wedge-shaped. Acrosomal vesicles (approximately 55–65 nm in diameter) and moderately electron-dense material (MEDM) are present between the plasmalemma and the nuclear membranes in the anterior tip of the head. The MEDM occupies a central position and three or four acrosomal vesicles are seen in a line alongside it. The acrosomal vesicles disappear as the sperm makes contact with the surface of the chorion. Gamete fusion most likely occurs between a small process extending from the peripheral margin of the sperm apex and the egg surface, resulting in incorporation of the sperm into the egg from the anterior region of its head.     

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.     

Ultrastructure of Spermatozoa and Spermatids in Bonellia viridis and Hamingia arctica (Echiura) With Some Phylogenetic Considerations

Spermatozoa of the echiurans Bonellia viridis and Hamingia arctica show a similar ultrastructure. They are of a modified type. The head consists of a roughly cylindrical nucleus, which has a cover of electron-dense material. The acrosome is very large and consists of an acrosomal vesicle and a rod-shaped perforatorium or acrosomal rod. In close association with the nucleus, one or two mitochondria are found forming an irregular ring around the posterior tip of the nucleus and the centriolar apparatus. There are two centrioles, the proximal one with the conventional triplet microtubular structure. The tail flagellum is about 50 μm long and has the 9+2 axonemal structure. The oblique attachment of the acrosome to the anterior part of the nucleus gives the spermatozoon a bilateral symmetry. However, in the nuclear morphology, the arrangement of electron-dense material around the nucleus, in the mitochondria, and in the attachment of the tail flagellum, the spermatozoon shows asymmetric organization. The sperm structure in bonelliids is unique but its genesis and the morphology of the mitochondrial midpiece support the theory that the echiurans are related to the annelids. The main results of the study are summarized in Fig. 11.     

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.     

Trypsin-like enzymes during fertilization in the shrimp Rhynchocinetes typus

The spermatozoon of Rhynchocinetes typus is atypical because it is nonmotile and lacks head and tail. The body has a rigid spike. Neither an acrosome-like structure nor changes during gamete interaction which could be interpreted as an acrosome reaction have been observed in this species. Nevertheless, the spermatozoon exerts a lytic effect on the extracellular envelope of the egg, and in this way it penetrates through egg-coats, forming a channel. In this research we found that crude spermatozoa extracts analyzed by gelatin SDS-PAGE developed one band of protease activity that was completely inhibited by SBTI (soybean trypsin inhibitor) and pAB (p-aminobenzamidine). In sperm extracts an enzymatic activity was determined, using BAEE (N-benzoil-L-arginine ethyl ester), but not ATEE, as substrate. This activity was inhibited by SBTI and pAB. We observed that in vitro fertilization was inhibited by spermatozoon incubation with the trypsin inhibitors SBTI, PMSF (phenyl-methanesulphonyl fluoride), and pAB. Additionally, we observed that when whole isolated egg-coats were incubated with sperm extract and then analyzed by SDS-PAGE, one band of the egg-coats disappeared. These results have been interpreted as sperm trypsin-like enzyme participation in R. typus sperm passage through the egg-coats. Mol. Reprod. Dev. 46:581–586, 1997. © 1997 Wiley-Liss, Inc.     

Comparative sperm ultrastructure of<Emphasis Type="Italic"> Neodasys ciritus</Emphasis> and<Emphasis Type="Italic"> Musellifer delamarei</Emphasis>, two species considered to be basal among Chaetonotida (Gastrotricha)

The spermatozoa of two species supposed to be basal to Gastrotricha Chaetonotida, Neodasys ciritus and Musellifer delamarei, were studied in order to supply further elements to the understanding of sperm evolution in Chaetonotida, a group in which a fully parthenogenetic reproduction is dominant. Two considerably different sperm patterns were found: the spermatozoon of N. ciritus has a simple, conical acrosome, a short, condensed nucleus, few conventional mitochondria randomly arranged along the sperm head, and a 9×2+2 flagellum perpendicular to the sperm major axis. The spermatozoon of M. delamarei is a filiform cell with a simple acrosome, a partially condensed nucleus, four mitochondria at the nuclear base, and a flagellum with a 9×2+2 axoneme and large accessory fibers. Some sperm features of M. delamarei are comparable to those of Xenotrichulidae, the only other Chaetonotida producing conventional spermatozoa, whereas the sperm of N. ciritus appears different from all the other patterns known among Gastrotricha, thus knowledge of it does not help in solving the problem of the discussed phylogenetic position of the genus.     

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.     

Interspecific Variation in Structural Organisation of the Spermatozoon in the Asian Bandicoot Rats,Bandicota Species (family Muridae)

The structural organisation of the spermatozoon from two species of bandicoot rats Bandicota bengalensis and Bandicota indica was investigated by light and electron microscopy together with the effect of incubation in Triton-X 100 and sodium dodecyl sulphate. The sperm head of B. bengalensis is invariably falciform, has a uniform electron-dense nucleus capped by an acrosome with a posteriolateral equatorial segment, a subacrosomal cytoskeleton with a large rostral perforatorium, and a sperm tail, attached to the lower concave surface of the sperm head, with typical coarse fibres and fibrous sheath. By contrast, the sperm head shapes of B. indica are generally conical or bulbous, the nucleus contains a few large vacuoles, the acrosome lacks an equatorial segment, no recognisable perforatorium occurs, and the sperm tail, which is attached basally, is very short with only modest development of coarse fibres and fibrous sheath. These results indicate that, within the genus Bandicota, huge interspecific differences in morphology of the spermatozoon have evolved. The spermatozoa of B. bengalensis are similar to those of Rattus and many other murids and thus presumably represent the ancestral condition, whereas those of B. indica (and B. savilei) are unlike spermatozoa from any other eutherian mammal so far described. © 1998 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd. All rights reserved     

Ultrastructure of sperm development in the plant-parasitic nematode Xiphinema theresiae

Spermatogenesis and sperm ultrastructure were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) in the longidorid Xiphinema theresiae. All germ cell stages, except spermatogonia, are present in the testes of young adult males. The nonflagellated, slightly elongated sperm displays little intraspecific variation and, although never polarized into a head and tail region, has a remarkably precise form, with a high degree of internal organization. Incipient fingerlike pseudopodia appear in the young spermatid and increase to such an extent that the adult sperm has a conspicuous “woolly” appearance. Microfilament bundles encircle the perinuclear mitochondria in the spermatid, and seem to be closely associated with the evaginated plasma membrane, especially in the spermatozoon. A large nucleus with nuclear envelope is prominent in the spermatocyte, but the envelope is absent in the young spermatid. Mitochondria are present in all germ cell stages and undergo certain morphological changes (e.g., in size and number, presence or absence of cristae), as well as changes in intracellular movements during spermatogenesis. Membranous organelles are prominent in the spermatocyte, but disappear in the older spermatid. Annulate lamellae and a residual body (i.e., cytophore) are conspicuous in the spermatocyte and spermatid, respectively; the spermatozoon clearly lacks a refringent body (i.e., acrosome).     

Morphological observations on sperm–egg interactions during in vivo fertilization in the dasyurid marsupial Sminthopsis crassicaudata

The aim of the present study was to determine the morphological changes that take place in the male and female gametes during in vivo fertilization in the Australian marsupial, the fat-tailed dunnart, Sminthopsis crassicaudata. Plastic sections were cut of sperm and eggs recovered from the oviducts of recently mated individuals, and light microscopy of thick, and transmission EM of thin, sections was carried out. It was found that, before penetration of the zona, the spermatozoon came to lie along the outer surface with its rostral tip forming a depression in the zona substance. During penetration, zona material was packed tightly around the spermatozoon, and no large hole was formed. A spermatozoon within the perivitelline space had made contact with the oolemma by way of its apical tip. In a spermatozoon partly incorporated into the ooplasm, fusion appeared to have taken place between its plasma membrane and that of the oolemma. Mucoid coat material became deposited outside the zona at this time; its existence and/or the release of cortical granule content probably prevented polyspermy. Once inside the egg cytoplasm, the sperm head sometimes travelled a considerable distance before chromatin decondensation occurred. In addition, it appeared to rotate somewhat on its axis at this time. Finally, some membranous structures were found around two condensed sperm heads in the ooplasm, which may have been part of the pronuclear envelope. Thus this study on in vivo fertilization in the dunnart documents, for the first time, some aspects of fertilization in an Australian marsupial as seen with the transmission electron microscope; it indicates a few differences from those previously found for the American opossum.     

尼罗罗非鱼精子形成中核内囊泡的释放

通过透射电镜观察了尼罗罗非鱼的精子形成过程。尼罗罗非鱼精子细胞在成熟过程中,细胞核中出现由双层生物膜构成的囊泡。囊泡中均匀分布着电子密度低的物质。该囊泡逐渐从细胞核内排到细胞核外。在此过程中细胞核不但排出不参与染色质浓缩的物质,还将多余的核膜排出。进入袖套的囊泡可以留在精子的袖套中,而排到核前方和核侧面的囊泡继续以出芽的方式排出精子细胞。尼罗罗非鱼成熟精子的头部仅有染色质高度浓缩的细胞核。细胞核前     

Sperm morphology,spermatogenesis and spermiogenesis of three species of chitons (Mollusca,Polyplacophora)

Summary Mature sperm of the three species, Onithochiton quercinus, Chiton pelliserpentis and Plaxiphora paeteliana are eupyrene and basically of the primitive type. The sperm are small, with a distinct head, midpiece with a few spherical to oval mitochondria and a long tail with a (2×9)+2 axoneme. They are unusual among primitive sperm in being bilaterally symmetrical, with a long anterior filament containing an extension of the nucleus and lacking an acrosome. Spermatogenesis occurs synchronously throughout the testis in inwardly folded tissue plates. Spermatogonia arise adjacent to the central blood sinus in each tissue plate. Cells in successive stages of spermatogenesis are displaced towards the luminal surface. The cytoplasm of all stages contains ribosomes, rough endoplasmic reticulum, lysosomes and mitochondria. A Golgi complex is present in secondary spermatocytes and spermatids but does not form an acrosome. During spermiogenesis Golgi complexes are confined to the posterior region of developing sperm and are eventually shed in the residual cytoplasm behind the midpiece. Preacrosomal vesicles are not formed. The long anterior filament of the sperm and lack of an acrosome are features associated with the fertilization of eggs surrounded by a chorion which may have pores or a micropyle. The exact method of fertilization in chitons remains to be elucidated.Abbreviations af anterior filament - bh body of the head - bn body of the nucleus - bs blood sinus - c collar - dc distal centriole - esg early spermatogonium - fc fibrous chromatin - gc granular chromatin - if implantation fossa - lsg later spermatogonium - m mitochondrion - mc muscle cell in blood sinus - mm midpiece mitochondrion - mt microtubule - mI primary spermatocyte undergoing first meiotic division - mII secondary spermatocyte undergoing second meiotic division - n nucleus - ncc nuclear condensing chromatin - ne nuclear envelope - pc proximal centriole - rc resorbing cell - s spermatozoon - 1°sc primary spermatocyte - 2°sc secondary spermatocyte - st spermatid - t tail - tc thinning cytoplasm - tf tail flagellum - tpec tissue plate epithelial cell     

Spermatology of Some Pycnogonida (Arthropoda), with Special Reference to a Microtubule-Nuclear Envelope Complex

The sperm cells of Nymphon leptocheles and N. rubrum are of the primitive type, which is a remarkable condition among arthropods. The motile sperm consist of a somewhat elongated head, a kind of midpiece and a long tail. An acrosome is absent. The nucleus is surrounded by longitudinally oriented microtubules running in furrows in the nuclear envelope. These microtubules are not interconnected by links or connected to the nuclear envelope; they persist in the mature sperm. No appreciable chromatin condensation takes place. The midpiece contains some unmodified mitochondria and a centriole. The tail is a simple, free flagellum. The results are in particular discussed in relation to other known microtubule-nuclear envelope complexes in sperm cells. The sperm cells of Pycnogonum littorale are, on the other hand, highly aberrant. They are unmotile, elongated cells containing a very high number (often more than 1000) of longitudinal microtubules arranged in complex patterns. Some folded membranes may represent the nuclear envelope. Other organelles are unidentificable or may be absent.     

Fertilization in a crab: I. Early events in the ovary,and cytological aspects of the acrosome reaction and gamete contacts

Early events in fertilization were studied in Carcinus maenas by in vitro experiments and ultrastructural analysis; some were found to occur in the lumen of ripe ovaries. The acrosome reaction generally conformed to the usual Reptantia Decapoda pattern. However, a prominent membrane system continuous with the nuclear envelope and located close to the base of the acrosome tubule characterized the type of spermatozoon observed in Carcinus maenas. Such complex anatomical connections linking the three parts of the reacted spermatozoon (acrosome tubule, membrane system and nucleus envelope) may be significant in relation to the membrane system's contribution to the acrosome reaction. The outer layer of the everted acrosomal vesicle was found to comprise tubular elements ending in bell-shaped corpuscles, deeply interdigitated with the oolemma microvilli during the establishment of the initial contacts between the reacted spermatozoon and the egg plasma membrane. At the site of contact, the oolemma formed a minute fertilization cone, locally depressed by the acrosome tubule. During these early fertilization events, the nucleus, like the other spermatozoon components, was seen to penetrate the egg coatings first, and later to be located near the oolemma.     

Ultrastructure of Sperm in <Emphasis Type="Italic">Mercenaria stimpsoni</Emphasis> and <Emphasis Type="Italic">Mactra chinensis</Emphasis> (Mollusca: Bivalvia) from the Sea of Japan

The ultrastructure of the sperm of the common bivalve species Mercenaria stimpsoni and Mactra chinensis from Peter the Great Bay is described. The sperm structure is typical for animals with external insemination. The sperm consists of a head, middle part, and flagellum. The sperm head of M. stimpsoni has a curved crescent form and includes the nucleus and acrosome; the head length is 9.8 μm. The acrosome is subdivided to the acrosome granule and the periacrosomal material. There are 4 mitochondria of about 0.8 μm in size in the middle part of the spermatozoon. The mitochondria surround the centriolar apparatus, which consists of proximal and distal centrioles located at a right angle. The axoneme originates from the distal centriole. The sperm of M. chinensis is barrel-shaped, with a head length of 3.2 μm. The acrosome is relatively larger, and its height is 1–1.2 μm. There are also 4 mitochondria 0.6–0.8 μm in the middle part of the spermatozoon. The sperm structure of the described species is typical of the families to which the mollusks belong, with insignificant variations.     

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

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

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.     

Sperm structure of Mecoptera and Siphonaptera (Insecta) and the phylogenetic position of<Emphasis Type="Italic"> Boreus hyemalis</Emphasis>

Sperm ultrastructure has been studied in three species of the taxa Mecoptera and Siphonaptera. The spermatozoon of the scorpion fly Panorpa germanica shows an apical bilayered acrosome, a helicoidal nucleus, a centriolar region and a 9+2 flagellar axoneme helicoidally arranged around a long mitochondrial derivative. A second mitochondrial derivative is very short and present only in the centriolar region. A single accessory body is present and it is clearly formed as a prolongation of the centriole adjunct material. Two lateral lamellae run parallel to the nucleus. The snow fly Boreus hyemalis has a conventional sperm structure and shows a bilayered acrosome, a long nucleus, a centriolar region, two mitochondrial derivatives and two accessory bodies. The axoneme is of the 9+2 type and is flattened at the tail tip. Both P. germanica and B. hyemalis have two longitudinal extra-axonemal rods and have a glycocalyx consisting of longitudinal parallel ridges or filaments. The spermatozoon of the flea Ctenocephalides canis has a long apical bilayered acrosome, a nucleus, a centriolar region, a 9+2 axoneme wound around two unequally sized mitochondrial derivatives, and two triangular accessory bodies. In the posterior tail end the flagellar axoneme disorganises and a few microtubular doublets run helicoidally around the remnant mitochondrial derivative. The glycocalyx consists of fine transverse striations. In all three species, the posterior tail tip is characterised by a dense matrix embedding the disorganised axoneme. From this comparative analysis of the sperm structure it is concluded that Mecoptera, as traditionally defined, is monophyletic and that B. hyemalis is a member of Mecoptera rather than of Siphonaptera.