Sperm ultrastructure of the spider crab Maja brachydactyla (Decapoda: Brachyura)

This study describes the morphology of the sperm cell of Maja brachydactyla, with emphasis on localizing actin and tubulin. The spermatozoon of M. brachydactyla is similar in appearance and organization to other brachyuran spermatozoa. The spermatozoon is a globular cell composed of a central acrosome, which is surrounded by a thin layer of cytoplasm and a cup‐shaped nucleus with four radiating lateral arms. The acrosome is a subspheroidal vesicle composed of three concentric zones surrounded by a capsule. The acrosome is apically covered by an operculum. The perforatorium penetrates the center of the acrosome and has granular material partially composed of actin. The cytoplasm contains one centriole in the subacrosomal region. A cytoplasmic ring encircles the acrosome in the subapical region of the cell and contains the structures‐organelles complex (SO‐complex), which is composed of a membrane system, mitochondria with few cristae, and microtubules. In the nucleus, slightly condensed chromatin extends along the lateral arms, in which no microtubules have been observed. Chromatin fibers aggregate in certain areas and are often associated with the SO‐complex. During the acrosomal reaction, the acrosome could provide support for the penetration of the sperm nucleus, the SO‐complex could serve as an anchor point for chromatin, and the lateral arms could play an important role triggering the acrosomal reaction, while slightly decondensed chromatin may be necessary for the deformation of the nucleus. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

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.     

Ultrastructural Observations on the Spermatozoon,Oocyte and Fertilization Process in Gonapodasmius,a Gonochoristic Trematode (Trematoda: Digenea: Didymozoidae)

Observations were performed in the uterus of a female Gonapodasmius sp., a gonochoristic didymozoid Trematode. The oocyte is a round cell 6 μm in diameter, which shows a ‘nucleolus-like cytoplasmic body’ and cortical granules. The spermatozoon is filiform, mobile and about 50 μm long. There is no acrosome. The anterior tip of the spermatozoon contains two centrioles made up of singlets and cortical microtubules with associated glycocalyx. The centrioles are continued as two axonemes of the classical 9 + ‘1’ pattern of flatworms, accompanied by a mitochondrion and a short row of cortical longitudinal microtubules. It is the posterior part of the sperm cell which contains the nucleus. At the outset of fertilization, the anterior part of the spermatozoon coils around the oocyte and penetrates it by lateral fusion. The posterior region of the spermatozoon, with the nucleus, is the last part to enter the oocyte, after passing through a perforation in the forming eggshell. The whole spermatozoon thus penetrates the female cell.     

Fine Structure of Spermatozoa in Perkinsiana rubra and Pseudopotamilla reniformis (Sabellidae: Polychaeta)

The Perkinsiana acrosome is elongated, pointed and tapering, strengthened anteriorly by cortical rings of longitudinally running units. The Pseudopotamilla acrosome is cap-like and its apical region contains a laminar body with two electron densities, the laminae crossed by occasional lines of dislocation, as in a crystal. These apparently solid regions are closely followed by peripherally situated lucent zones. The zone in Pseudopotamilla contains tubules, which are very like those in Sabella sperm, except that they lack connections with the acrosome base. Both species are probably broadcast spawners and have nuclei, mitochondria, centrioles and flagella of the primitive type. This may, however, be a secondary reversion through neoteny.     

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.     

Ultrastructure of spermiogenesis in <Emphasis Type="Italic">Cristatella mucedo</Emphasis> Cuvier (Bryozoa: Phylactolaemata: Cristatellidae)

In Cristatella mucedo spermiogenesis occurs in a morula consisting of a large number of spermatids connected with a central cytophore. The mature sperm cell is filiform and consists of a head, a midpiece and a tail region, the latter two separated by a deep circular constriction. The comparatively short head contains a drop-shaped, bilaterally symmetrical and pointed nucleus capped by a minute acrosome. The single centriole is placed in a deep posterior invagination of the nucleus followed by the axoneme with the typical 9 + 2 pattern. The elongated midpiece is 0.9–1.1 μm thick and contains several helices of mitochondria surrounding the axoneme. The tail is thicker (1.3 μm) and richer in cytoplasm with many compact accumulations of an electron-dense substance lying peripherally and another less dense material wrapped around the axoneme. The course of the spermiogenesis and the fine structure of the sperm are very similar to that of Plumatella fungosa. Comparison with other species shows that the same sperm type is recognizable in four of the five families of Phylactolaemata and, provided it occurs also in the fifth family, the Stephanellidae, is a synapomorphy of the entire class.     

An ultrastructural analysis of mature sperm from the crayfish Pacifastacus leniusculus,Dana

Sperm from the crayfish, Pacifastacus leniusculus, resemble other reptantian sperm in that they are composed of an acrosome, subacrosomal region, nucleus, membrane lamellar complex, and spikes which radiate from the nuclear compartment. The acrosome (PAS positive vesicle) can be subdivided into three regions: the apical cap, crystalline inner acrosomal material, and outer acrosomal material which is homogeneous except for a peripheral electron dense band. The nucleus contains uncondensed chromatin and bundles of microtubules which project into the spikes. The orientation of the microtubule bundles relative to the nuclear envelope near the base of the subacrosomal region suggests that the nuclear envelope may function in the organization of the spike microtubules.     

Fine structure of the spermatozoon of Marthasterias glacialis (Linnaeus) (Echinodermata; Asteroidea), with special reference to acrosomal morphology

The sperm of Marthasterias glacialis (Linnaeus) was studied by light and electron microscopy. It is a long uniflagellated cell of the “primitive” type. The head has a spherical shape and contains a nucleus with a spheroid acrosome lying in a cup-shaped anterior fossa. The acrosome is formed by an acrosomal vesicle surrounded by the periacrosomal material. The basal specializations of the acrosomal vesicle show a clear differentiation of its constituents resembling the structure of membrane. The midpiece contains a very large annular mitochondrion which encircles two perpendicular centrioles. The distal centriole is in close association with a pericentriolar radial complex. The tail, containing a common microtubular axoneme, is projected to a variable position.     

The C-kit receptor and its possible signaling transduction pathway in mouse spermatozoa

The presence and role of the c-kit protein was investigated in the mature sperm of the mouse. The c-kit monoclonal antibody (mAb) ACK₂ reacted specifically with the acrosomal region and the principal piece of fixed noncapacitated sperm but did not react with the acrosome region in acrosome-reacted sperm. ACK₂ significantly inhibited the acrosome reaction; this inhibition was relieved by the calcium ionophore A23187. The kit ligand stem cell factor (SCF) significantly increased the percentage of sperm undergoing acrosome reaction. This increase was partially inhibited by the calcium channel inhibitor (verapamil), the PI3k inhibitor (wortmannin), and the PLC inhibitor (U-73122). ACK₂ predominantly recognized c-kit proteins of 33, 48, and 150 kDa by Western blotting of mouse sperm extracts. The 48- and 150-kDa protein bands were released into the media and tyrosine autophosphorylated at low basal levels during acrosome reaction. On stimulation with SCF, the level of c-kit phosphorylation increased significantly. These findings suggest that c-kit is present in mature sperm, and its binding to SCF may result in the activation of PLCγ1 and PI3K, leading to receptor autophosphorylation, and ultimately may play a role in capacitation and/or the acrosome reaction. Mol. Reprod. Dev. 49:317–326, 1998. © 1998 Wiley-Liss, Inc.     

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.     

东方扁虾精子的超微结构

利用电镜研究了东方扁虾（Ｔｈｅｎｕｓ ｏｒｉｅｎｔａｌｉｓ）精子的形态和结构。精子由核、膜复合物区和顶体区３部分组成。核内含非浓缩的染色质、微管及细纤维丝,外被核膜;５～６条辐射臂自核部位伸出,臂内充满微管。膜复合物区位于核与顶体之间,由许多膜片层结构及其衍生的囊泡共同组成。顶体区由顶体囊和围顶体物质组成,顶体结构复杂,由顶体帽、内顶体物质和外顶体物质等构成;围顶体物质呈细颗粒状,主要分布于顶体囊     

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.     

Autoradiographic visualization of the mouse egg's sperm receptor bound to sperm

The extracellular coat, or zona pellucida, of mammalian eggs contains species-specific receptors to which sperm bind as a prelude to fertilization. In mice, ZP3, one of only three zona pellucida glycoproteins, serves as sperm receptor. Acrosome-intact, but not acrosome-reacted, mouse sperm recognize and interact with specific O- linked oligosaccharides of ZP3 resulting in sperm-egg binding. Binding, in turn, causes sperm to undergo the acrosome reaction; a membrane fusion event that results in loss of plasma membrane at the anterior region of the head and exposure of inner acrosomal membrane with its associated acrosomal contents. Bound, acrosome-reacted sperm are able to penetrate the zona pellucida and fuse with the egg's plasma membrane (fertilization). In the present report, we examined binding of radioiodinated, purified, egg ZP3 to both acrosome intact and acrosome reacted sperm by whole-mount autoradiography. Silver grains due to bound 125I-ZP3 were found localized to the acrosomal cap region of heads of acrosome-reacted sperm. Under the same conditions, 125I-fetuin bound at only bacKground levels to heads of both acrosome-intact and - reacted sperm, and 125I-ZP2, another zona pellucida glycoprotein, bound preferentially to acrosome-reacted sperm. These results provide visual evidence that ZP3 binds preferentially and specifically to heads of acrosome intact sperm; properties expected of the mouse egg's sperm receptor.     

Acrosome formation in Ceratitis capitata (Diptera, Tephritidae)

The stages of morphogenesis of the acrosome of Ceratitis capitata are well defined. This organelle is formed by the Golgi complex and, as it matures, takes up a position laterally in relation to the anterior region of the sperm nucleus. An interstitial membrane marks the area of contact between nucleus and acrosome in the spermatid, and is found even in mature sperm cells. The acrosome contains hydrolytic enzymes, as detected by acid phosphatase reaction.     

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.     

Enzyme activity in anuran spermatozoa upon induction of the acrosome reaction.

At the time of sperm-egg fusion in Discoglossus pictus, a large amount of electron-dense material of an unknown nature is liberated from the sperm. In the present work we studied this material in D. pictus sperm, using an assay utilising strips of autoradiographic film as a gelatin substrate for proteolytic enzymes. Upon treatment with A23187, D. pictus sperm produced a large halo on the gelatin substrate, indicating the presence of enzymes released by the sperm at the time of the acrosome reaction. In contrast, Xenopus laevis sperm did not produce halos upon treatment with A23187. The use of protease inhibitors such as TLCK, leupeptin, chymostatin, SBTI and EACA strongly suggests that the D. pictus whole acrosome contains trypsin and chymotrypsin activity while an SBTI-sensitive activity is absent in a small portion of the acrosome, possibly the anteriormost region. Furthermore, the material released at the acrosome reaction also contains an EACA-inhibited activity, indicating the presence of plasminogen activator. We conclude that D. pictus sperm release proteolytic enzyme(s) that may act at the egg surface at the time of gamete fusion.     

Fine structure of the spermatozoon of <Emphasis Type="Italic">Diopatra neapolitana</Emphasis> (Polychaeta,Onuphidae)

The identification of Diopatra species lacks of clear diagnostic features of taxonomic importance and the knowledge of their reproductive characters is scant. The spermatozoa of Diopatra neapolitana were ultrastructurally investigated by electron microscopy in order to correlate the mode of reproduction with sperm cells morphology. The mature male gamete has a depressed subspherical nucleus, a cone-like acrosome, and a long flagellum. The acrosome is conical in shape and radially symmetrical, with a base diameter twice the height. Within the acrosome vesicle, the basal region includes a very electron-dense thickened ring composed of paracrystalline substances. The subacrosomal space is filled with a poorly electron-dense material, with straight filaments axially arranged to form a perforatorium. The nucleus contains the complete axial canal, holding the hind perforatorium region. The middle piece consists of five mitochondria with well-distinct membranes and tubulo-vesicular cristae. Two centrioles are located perpendicularly to each other. The proximal one lies in the central fossa and the distal one, slightly eccentric to the sperm axis, anchors to the plasma membrane by nine satellite rays of the pericentriolar complex. The axoneme has a 9+2 arrangement of microtubules. In general, the spermatozoon of D. neapolitana conforms exteriorly to the typical ect-aquasperm; the acrosome complex ultrastructure, however, shows noticeable modifications from the basic form. This finding agrees with the previously observed reproductive pattern (broadcast spawning—free-swimming larvae) of D. neapolitana belonging to Santa Gilla population, and may be helpful to solve the taxonomic problems of the D. neapolitana complex as well.     

蟹类精子超微结构的比较研究

应用光镜和电镜,比较研究了三疣梭子蟹,中华绒螯蟹和长江华溪蟹的成熟精子。揭示３种蟹精子都是不能游动的无鞭毛精子,呈球形,前后略扁,精子前端出现一光滑的小圆面,圆面四周有内陷的沟环。沟环之后,精子表面凹凸不平,并伸出多数辐射臂。３种蟹精子均为高度特化的细胞,外被质膜,内含细胞核,顶体及退化的细胞质。     

The Spermatozoon of Brachionus plicatilis(Rotifera,Monogononta) With Some Notes on Sperm Ultrastructure in Rotifera

The spermatozoon of B. plicatilisis a thread–like cell with an anterior flagellar portion and a posterior cell body. The flagellum has a lateral ‘undulating membrane’, containing a folded longitudinal cisterna and an axoneme. The basal body of the axoneme is at the anterior tip. The axoneme lacks outer dynein arms and extends through the entire flagellar region and most of the cell body. The main portion of the flagellum and of the cell body contains a series of vesicles with tightly packed tubules that may serve as a cytoskeleton. The cell body contains a partly condensed nucleus, several mitochondria and some cytoplasm. Some elongated mitochondria are arranged in the postnuclear region. When the spermatozoon moves, the undulations propagate from the basal body at the flagellar tip. Late spermatids can be recognized by the nucleus and the flagellum being coiled and enclosed within a common cell membrane. As in other rotifers, there are cigar–like cell products (‘rods’) in the testes. The general organization of the cell, including the absence of an evident acrosome, resembles that of the other known monogonont sperm types.     

平疣桑椹石磺精子结构观察

通过电光学显微镜和透射电子显微镜观察了平疣桑椹石磺精子的形态及其超微结构。平疣桑椹石磺成熟精子属于进化型,由头部、中段和末段组成。头部由顶体和精核构成,顶体长约0.7μm,呈细奶嘴状,内含物分布均匀,电子密度稍低于细胞核。顶体基部与精核前端紧密相连,无间隙。精核长约3.8μm,宽约1.0μm,核质高度浓缩,电子密度高,无核泡,纵切似辣椒状,核后端内凹形成核后窝。中段加长,结构复杂,线粒体演化成线粒体鞘,螺旋状包绕轴丝。精子末段由轴丝及包绕轴丝的质膜组成,轴丝为典型的“9＋2”结构。比较了平疣桑椹石磺精子与相关腹足类精子结构的异同,进一步证实了腹足纲贝类精子结构之间的区别主要在于顶体有无及形态,精核的长短与外形、中段线粒体的数目及其排列方式等。