Fine structure of the ladybird spermatozoa (Insecta,Coleoptera, Coccinellidae)

The sperm structure of several ladybird species belonging to different subfamilies of Coccinellidae was studied. Three main sperm types were clearly recognized, and were characterized by differences in acrosomal length, the presence of a dense coat around the acrosome, the length of the basal body, the amount of the centriole adjunct material, and the diameter of the mitochondrial derivatives. However, the whole group shares a pattern of the posterior sperm region uncommon for insects, in which the axoneme and other flagellar components are running parallel with the nucleus. As a general conclusion, this study has revealed an inconsistency between the sperm structure and the systematics of the group, indicating that the generic concepts within the group do not reflect a natural classification, a statement also shared by molecular studies.     

Fine structure of the spermatozoon of the viviparous teleost, Cymatogaster aggregata

The approximately 50 μm long sperm of Cymatoguster aggregata is composed of an elongate head (4 μm), an elongate mitochondria1 midpiece (3.5 μm) and a tail flagellum (roughly 40 μm). The sperm lacks an acrosome. Contained within depressions on one surface of the compressed head are a proximal centriole and a distal centriole separated by an electron dense, intercentriolar body. The anterior portion of the tail flagellum originates at the basal body (distal centriole) and is contained within an extracellular, flagellar tunnel within the mitochondria1 midpiece. The morphological similarity of C. uggregutu sperm to sperm of other internally fertilizing fishes supports the hypothesis that spermatozoan morphology is related to the mode of fertilization and that an elongate head and midpiece are specializations for internal fertilization.     

Spermatogenesis and sperm structure of Acerella muscorum, (Ionescu, 1930) (Hexapoda, Protura)

The general organization of the male genital system, the spermatogenesis and the sperm structure of the proturan Acerella muscorum have been described. At the apex of testis apical huge cells are present; their cytoplasm contains a conventional centriole, a large amount of dense material and several less electron-dense masses surrounded by mitochondria. Spermatocytes have normal centrioles and are interconnected by cytoplasmic bridges. Such bridges seem to be absent between spermatid cells and justify the lack of synchronization of cell maturation. Spermatids are almost globular cells with a spheroidal nucleus and a large mass of dense material corresponding to the centriole adjunct. Within this mass a centriole is preserved. Mitochondria of normal structure are located between the nucleus and the plasma membrane. The spermatids are surrounded by a thick membrane. No flagellar structure is formed. Sperm have a compact spheroidal nucleus, a large cap of centriole adjunct material within which a centriole is still visible. A layer of mitochondria is located over the nucleus. The cytoplasm is reduced in comparison to spermatids; many dense bodies are interspersed with sperm in the testicular lumen. The sperm are small, immotile cells of about 2.5-3 μm in diameter.     

Sperm ultrastructure and spermiogenesis in two Exogone species (Polychaeta, Syllidae, Exogoninae)

Abstract. The spermatozoa of Exogone naidina and E. dispar are characterized by a prominent bell-shaped acrosome, a spheroidal nucleus, and a conventional flagellum. During spermiogenesis, the acrosomal vesicle undergoes conspicuous modifications leading to its final bell shape with a posterior opening. The subacrosomal material initially shows radiating filaments but in mature sperms it appears as a meshwork of electron-opaque material. The acrosomal axis is oblique with respect to the main longitudinal sperm axis. The chromatin is arranged in electron-opaque strands in the early spermatids, then becomes amorphous, and is finally organized in filaments in mature sperms. Centrioles are orthogonally arranged beneath the nucleus and fibers radiate from the distal centriole to contact the plasma membrane and the single mitochondrion. The latter is located eccentrically on the side of the nucleus opposite the acrosome. A disk-shaped structure is evident beneath the distal centriole. The flagellar axoneme has a 9+2 microtubule pattern. A conspicuous glycocalyx surrounds the flagellar plasma membrane, and an electron-lucent space is present between these two structures at the distal tip of the flagellum. We compare the sperm morphology of these two species of Exogone with that described in other members of the subfamily Exogoninae. The fine structure of these two species supports the occurrence of an ent-aquasperm type within Exogoninae, in accordance with the brood strategy present within this subfamily. The mode of reproduction is of taxonomic importance for defining subfamilies within Syllidae, and is likely also of phylogenetic significance. Because epitoky is probably plesiomorphic, the ent-aquasperm type found in Exogoninae can be considered a derived feature within Syllidae.     

The ultrastructure of amberjack (Seriola dumerilii) sperm

Scanning and transmission electron microscopy were used to investigate the fine structure of sperm of the Mediterranean amberjack Seriola dumerilii. Each spermatozoon has an ovoid head which lacks an acrosome, a short, irregularly-shaped midpiece and a long flagellar tail. The midpiece houses eight spherical mitochondria, which are separated from the axoneme by the cytoplasmic canal. The centrioles are arranged approximately at right angles to each other. The proximal centriole lies inside, and the distal centriole outside, the nuclear fossa. The flagellum is inserted eccentrically into the head and is tangential to the nucleus, so that the spermatozoon is asymmetrical. It contains the conventional 9 + 2 axoneme, shows intratubular differentiations in the A microtubules of doublets 1, 2, 5 and 6, and possesses one pair of lateral fins. On the basis of its ultrastructural organization, the amberjack sperm resembles type II sperm as defined previously, except for the presence of the proximal centriole inside the nuclear fossa. This could result from a partial rotation of the nucleus during spermiogenesis.     

The Spermatozoa of the Holothuroidea (Echinodermata): an Ultrastructural Review with Data on two Australian Species and Phylogenetic Discussion

Holothuroidea, like the Crinoidea, Asteroidea and Ophiuroidea have aquatic sperm with a subspherical nucleus in which is embedded a subspherical acrosome and its surrounding periacrosomal material. A ring-shaped mitochondrion behind the nucleus surrounds two centrioles from the distal of which a 9 + 2 axoneme arises. The term "echinosperm" is proposed for this sperm type. Holothuroid echinosperm are characterized by anterior constriction of the periacrosomal fossa; a rounded posterior limit to the acrosome; absence of a distinct subacrosomal depression; outgrowth of a flagellar rootlet from the proximal centriole, of which vestigial homologues are known only in one crinoid and one echinoid. Modified sperm, though not greatly divergent from the echinosperm, are known in two holothuroids and one crinoid. The sperm of echinoids, which are not referable to the echinosperm, are considered plesiomorphic in failure of the acrosome to become embedded in the nucleus (a feature retained from an ancestry shared with enteropneusts), but apomorphic in the conical form of the nucleus and development of spine-like structures around the anterior rim of the nucleus. Spermatozoa1 data suggest that the holothuroid-crinozoan-asterozoan assemblage is the sister group of the Echinoidea. Inclusion of holothuroids in the Echinozoa is not supported.     

褶纹冠蚌精子发生的研究

光镜和透射电镜研究结果表明：褶纹冠蚌精子发生是非同步的,精子发生经历了一系列重要的形态和结构变化,主要包括：核逐步延长、染色质浓缩、线粒体逐渐发达与融合、胞质消除以及鞭毛的形成。精原细胞胞质中含有许多致密的轴纤丝,它们后来形成鞭毛轴丝。精母细胞质中含有线粒体、中心粒、内质网和电子透明的囊泡。精细胞分化为４个时期。成熟精子属原始类型,由头部、中段和尾部三部分组成。多核结构和细胞间桥自始至终存在于精子     

Flagellar gyration and midpiece rotation during extension of the acrosomal process of Thyone sperm: how and why this occurs

The midpiece of Thyone sperm contains a large mitochondrion and a centriolar pair. Associated with one of the pair, i.e., the basal body of the flagellum, are satellite structures which apparently anchor the flagellar axoneme to the mitochondrion and to the plasma membrane covering the midpiece. Immediately before and as the acrosomal process elongates, the flagellum and the midpiece begin to rotate at 1-2 rotations per second even though the head of the sperm, by being firmly attached on its lateral surfaces to the coverslip, does not rotate at all. This rotation is not observed in the absence of flagellar beating whose frequency is much greater than that of its gyration. To understand how the midpiece rotates relative to the sperm head, it is first necessary to realize that in Thyone the flagellar axoneme projects at an acute angle to the principal axis of the sperm and is bent towards one side of this axis. Thus movement of the flagellum induces the sperm to tumble or yaw in solution. If the head is stuck, the midpiece will rotate because all that connects the sperm head to the midpiece is the plasma membrane, a liquid-like layer. A finger-like projection extends from the proximal centriole into an indentation in the basal end of the nucleus. In contrast to the asymmetry of the flagellum, this indentation is situated exactly on the principal axis of the sperm and, along with the finger-like projection, acts as a biological bearing to maintain the orderly rotation of the midpiece. The biological purpose of flagellar gyration during fertilization is discussed.     

Evidence of a procentriole during spermiogenesis in the coccinellid insect Adalia decempunctata (L): An ultrastructural study

We studied spermatogenesis and spermiogenesis in Adalia decempunctata (L), a beetle of the Coccinellidae family. The spermatocyte exhibits two centrioles which elongate to form a pair of primary cilia. A novel structure, appearing in cross sections as a dense droplet, is observed near the long centriole during spermiogenesis, and is soon accompanied by a procentriole (PCL). PCL structure consists of singlet microtubules, a central tubule and an incomplete cartwheel. The PCL persists until the end of spermiogenesis, when it vanishes together with the dense droplet. The sperm has an exceptionally long basal body and the nucleus is disposed parallel to the flagellar components, a peculiar trait shared by other species of the coccinellid group. The presence of a procentriole suggested by the use of antibodies is discussed.     

An aurora kinase is essential for flagellar disassembly in Chlamydomonas

Cilia and flagella play key roles in development and sensory transduction, and several human disorders, including polycystic kidney disease, are associated with the failure to assemble cilia. Here, we show that the aurora protein kinase CALK in the biflagellated alga Chlamydomonas has a central role in two pathways for eliminating flagella. Cells rendered deficient in CALK were defective in regulated flagellar excision and regulated flagellar disassembly. Exposure of cells to altered ionic conditions, the absence of a centriole/basal body for nucleating flagellar assembly, cessation of delivery of flagellar components to their tip assembly site, and formation of zygotes all led to activation of the regulated disassembly pathway as indicated by phosphorylation of CALK and the absence of flagella. We propose that cells have a sensory pathway that detects conditions that are inappropriate for possession of a flagellum, and that CALK is a key effector of flagellar disassembly in that pathway.     

三角帆蚌精子的发生

报道了光镜和透射电镜下三角帆蚌精子的发生过程及其一系列重要的形态变化。包括核延长,染色质浓缩,线粒体逐渐融合并后移;胞质减少及鞭毛形成,精原细胞是精巢中体积最大的细胞,细胞膜界限不明显,内质网发达,精母细胞开始出现中心粒,精细胞分化可分为3个阶段。成熟精子属原生型,由头部、中段和尾部三部分组成。     

Cytodifferentiation during spermiogenesis in Lumbricus terrestris

The structural changes during spermiogenesis were studied on developing spermatids in seminal vesicles and receptacles of Lumbricus terrestris fixed in glutaraldehyde-osmium tetroxide and embedded in Epon-Araldite. The centriole plays a prominent role in the morphogenesis and organization of the microtubules of the manchette and flagellum. Microtubules arising from the centriole extend anteriorly to encase the developing middle piece, the nucleus, and the acrosome. The manchette not only provides a supporting framework for the cell during elongation, but also may provide the motive force for the elimination of both nucleoplasm and cytoplasm. The manchette participates in segregation and elimination of the nuclear vesicle that contains the nonchromatin nucleoplasm. Compartmentalization and conservation may also be a function of the manchette since those elements which remain within the framework of microtubules are retained, while all the cytoplasm outside the manchette is discarded. At maturation, the endoplasmic reticulum plays a key role in dismantling the manchette and reducing the cytoplasm external to it. During the early stages of middle-piece formation, six ovoid mitochondria aggregate at the posterior pole of the spermatid nucleus. Concurrent with manchette formation, the mitochondria are compressed laterally into elongate wedge-shaped components, and their outer limiting membranes fuse to form an hexagonal framework that surrounds the dense intramitochondrial matrices. Dense glycogen granules are arranged linearly between the peripheral flagellar tubules and the outer membrane of the mature sperm tail.     

Peptide-induced hyperactivation-like vigorous flagellar movement in starfish sperm

Asterosap, a sperm-activating peptide (SAP) from the starfish egg jelly coat, is diffusible and controls a cGMP-signalling pathway in starfish sperm in the same manner as resact, a potent chemoattracting SAP in sea urchins. This fact suggests that asterosap may serve as a chemoattractant like resact at concentrations with appropriate gradients. Since asterosap is one of three egg jelly components, which in concert induce the acrosome reaction, it is still worthwhile to evaluate how asterosap modulates sperm motility prior to this reaction. We analysed the flagellar movement of sperm of the starfish Aphelasterias japonica in artificial seawater (ASW) containing the asterosap isoform P15 at 1 micromol l(-1). We found that sperm swim straighter with more symmetrical flagellar movement in P15 than in ASW, but without any significant difference in the flagellar beat frequency and the swimming velocity. The flagellar movement is, however, dramatically different between sperm firmly attached to the solid surface by the head in P15 and those attached in ASW: in P15 the flagellum bends to a greater extent, with higher curvature and with higher shear angle up to a right angle to the flagellar wave axis, and beats at an increased frequency. The vigorous flagellar movement of sperm, which can be activated when sperm are placed in high-load circumstances just as entering into a jelly layer, may increase propulsive forces and hydrodynamic resistances, allowing sperm to undergo the acrosome reaction as effectively as possible.     

Studies on the polymorphic spermatozoa of a marine snail. 2. Genesis of the eupyrene sperm

Spermiogenesis of the eupyrene sperm in the snail, Fusitriton oregonensis, was studied with light and electron microscopes. Endoplasmic reticulum, which encircles the nucleus in each spermatid, appears to connect with the Golgi body and to interconnect between adjacent spermatids via cytoplasmic bridges. It is suggested that as the Golgi body migrates around the nucleus the endoplasmic reticulum may circulate with it. The alignment of the proacrosome with the nucleus is effected by a 180° rotation of the Golgi body, after which it separates and migrates posteriorly with the residual cytoplasm. Each sperm possesses a well-developed intracellular digestive system as indicated by multivesicular bodies, residual bodies, and myeloid figures. Autophagy begins in the residual cytoplasm before it is released from the middle piece. Microtubules are found outside the nucleus and mitochondria during the final stages of spermiogenesis, when elongation is almost complete. These microtubules appear to be involved in the final shaping and twisting process, in which torsion is locked in the nucleus and the mitochondria spiral around the axoneme. The annulus attaches the distal centriole to the plasma membrane in the early spermatid and as flagellar production begins they move towards the implantation fossa at the base of the nucleus. There are two centrioles in the early spermatid, the distal centriole and procentriole. The small procentriole fuses with the distal centriole in the intranuclear canal to form the centriolar cap of the basal body. This cap is pushed through the end of the nuclear tube and is separated from the subacrosomal space by only the nuclear membranes.     

INDUCTION OF ASTER FORMATION AND CLEAVAGE IN EGGS OF THE SEA URCHIN HEMICENTROTUS PULCHERRIMUS BY INJECTION OF SPERM COMPONENTS*

Studies were made on which components of sperm were able to induce aster formation and cleavage of eggs of the sea urchin Hemicentrotus pulcherrimus. The sperm components were separated by homogenization and centrifugation into the following 3 fractions: the head-midpiece, midpiece and tail. The head-midpiece fraction was then divided into 2 sub-fractions, the centriole sub-fraction and the centriole-free sub-fractions. Each fraction was injected into unfertilized eggs and after 15–30 min the eggs were inseminated. The ability of a fraction or a sub-fraction to induce aster formation and cleavage was deduced from the frequency of multipolar cleavage. The head-midpiece fraction and the centriole sub-fraction were effective in inducing aster formation and cleavage, but the other fractions were not. It was concluded that isolated centrioles from sea urchin sperm act as division centers in the egg.     

Proteomic analysis of isolated chlamydomonas centrioles reveals orthologs of ciliary-disease genes

BACKGROUND: The centriole is one of the most enigmatic organelles in the cell. Centrioles are cylindrical, microtubule-based barrels found in the core of the centrosome. Centrioles also act as basal bodies during interphase to nucleate the assembly of cilia and flagella. There are currently only a handful of known centriole proteins. RESULTS: We used mass-spectrometry-based MudPIT (multidimensional protein identification technology) to identify the protein composition of basal bodies (centrioles) isolated from the green alga Chlamydomonas reinhardtii. This analysis detected the majority of known centriole proteins, including centrin, epsilon tubulin, and the cartwheel protein BLD10p. By combining proteomic data with information about gene expression and comparative genomics, we identified 45 cross-validated centriole candidate proteins in two classes. Members of the first class of proteins (BUG1-BUG27) are encoded by genes whose expression correlates with flagellar assembly and which therefore may play a role in ciliogenesis-related functions of basal bodies. Members of the second class (POC1-POC18) are implicated by comparative-genomics and -proteomics studies to be conserved components of the centriole. We confirmed centriolar localization for the human homologs of four candidate proteins. Three of the cross-validated centriole candidate proteins are encoded by orthologs of genes (OFD1, NPHP-4, and PACRG) implicated in mammalian ciliary function and disease, suggesting that oral-facial-digital syndrome and nephronophthisis may involve a dysfunction of centrioles and/or basal bodies. CONCLUSIONS: By analyzing isolated Chlamydomonas basal bodies, we have been able to obtain the first reported proteomic analysis of the centriole.     

New insights into the assembly of the periaxonemal structures in mammalian spermatozoa

Disruption of Ube2b in the mouse has revealed that the regular and symmetric organization of the fibrous sheath of the sperm flagella is dependent on expression of the ubiquitin-conjugating enzyme UBE2B. These data could cast light on how a component of the ubiquitin-proteasome pathway participates in the assembly of flagellar periaxonemal structures. Data in the literature support the notion of involvement of ubiquitin-proteasome pathways in the assembly of cytoskeletal components in somatic cells. This review attempts to integrate recent knowledge regarding flagellar components that could be related to proteasome components and, therefore, could be targets of UBE2B in the spermatid. An attempt is made to characterize the human flagellar anomalies of infertile patients, which are the closest to those of Ube2b-deficient mice. These new insights regarding the assembly of mammalian sperm flagella provide a basis for studying the ontogenesis of flagellar accessory structures and suggest leads for medical and genetic investigations.     

Complex spermatozoon of the live-bearing half-beak,Hemirhamphodon pogonognathus (Bleeker): Ultrastructural description (Euteleostei,Atherinomorpha, Beloniformes)

The spermatozoon of Hemirhamphodon pogonognalhus shows modifications that are frequent though not obligate in internally fertilizing sperm, notably elongation of the nucleus and extension of the mitochondria of the midpiece as an elongate sheath around the proximal region of the axoneme. These similarities to poecilid and jenynsid sperm are considered homoplasic. As in the mature sperm of all but one investigated teleost, an acrosome is absent. The elongate, blade-shaped, electron-dense nucleus has a mean length of 3.2 μm; its basal implantation fossa, less than one-tenth of the length of the nucleus, houses the anterior half of the distal and only centriole (of triplet construction with satellite rays), a centriolar plug, and a mass connecting the centriole to the wall of the fossa. A unilateral putative centriole adjunct is present. The anterior region of the axoneme is surrounded by a mitochondrial sleeve, and internal to this, separated by a cisterna, by a submitochondrial sleeve. The mitochondrial sleeve unites posteriorly with the submitochondrial sleeve. Between the submitochondrial sleeve and the axoneme is a space, the cytoplasmic canal, that is open to the exterior posteriorly. The discrete, cristate mitochondria, in their sleeve, are unique in investigated atherinomorph sperm in being bilateral, grouped on only two opposing sides of the axoneme, with an arc-shaped ‘intermitochondrial link’ between. The 9 + 2 flagellum is unique for the Animalia in having 23 radial subplasmalemmal rods, repeated longitudinally (periodicity 0.025 pm) in a quasicrystalline array. Internal fertilization is deduced to have arisen in the Exocoetoidei independently of that in the Cyprinidcntiformes.     

OBSERVATIONS ON THE CENTRIOLES OF THE SEA URCHIN SPERMATOZOON

The spermatozoon of Lytechinus variegatus has two parallel centrioles. The basal body of the flagellum consists of the proximal centriole (a short cylinder of nine tubule-triplets) and its distal extension of nine tubule-doublets. The distal centriole lies near the distal end of the basal body, between the nucleus and the mitochondrion. The observations suggest that both the proximal and the distal centrioles are polarized structures, their tubule-triplets pitched in the same direction and their distal ends associated with the flagellar axoneme and with the mitochondrion, respectively. The distal centriole in different spermatozoa occupies different positions around the basal body-flagellum complex.     

Structural and immunocytochemical characterization of the Ginkgo biloba L. sperm motility apparatus

Summary. Ginkgo biloba and the cycads are the only extant seed plants with motile sperm cells. However, there has been no immunocytochemical characterization of these gametes to determine if they share characteristics with the flagellated sperm found in bryophytes and pteridophytes or might give clues as to the relationships to nonflagellated sperm in all other seed plants. To determine characteristics of proteins associated with the motility apparatus in these motile sperm, we probed thin sections of developing spermatogenous cells of Ginkgo biloba with antibodies to acetylated and tyrosinated tubulin and monoclonal antibodies that recognize mammalian centrosomes and centrin. The blepharoplast that occurs as a precursor to the motility apparatus consists of an amorphous core, pitted with cavities containing microtubules and a surface studded with probasal bodies. The probasal bodies and microtubules within the blepharoplast cavities are labeled with antibodies specific to acetylated tubulin. Positive but weak reactions of the blepharoplast core occur with the centrosomereactive antibodies MPM-2 and C-9. Reactions to centrin antibodies are negative at this developmental stage. From this pre-motility apparatus structure, an assemblage of about 1000 flagella and associated structures arises as the precursor to the motility apparatus for the sperm. The flagellar apparatus consists of a three-layered multilayered structure that subtends a layer of spline microtubules, a zone of amorphous material similar to that in the blepharoplast, and the flagellar band. Centrin antibodies react strongly with the multilayered structure, the transition zone of the flagella, and fibrillar material near the flagellar base at the surface of the amorphous material. Both the spline microtubules and all of the tubules in the flagella react strongly with the antibodies to acetylated tubulin. These localizations are consistent with the localizations of these components in pteridophyte and bryophyte spermatogenous cells, although the blepharoplast material surrounding and connecting flagellar bases does not occur in the seedless (nonseed) land plants. These data indicate that despite the large size of ginkgo gametes and the taxonomic separation between pteridophytes and Ginkgo biloba, similar proteins in gametes of both groups perform similar functions and are therefore homologous among these plants. Moreover, the presence of acetylated tubulin in bands of microtubules may be a characteristic shared with more derived non-flagellated sperm of other conifers and angiosperms. Correspondence and reprints: Southern Weed Science Research Unit, USDA Agricultural Research Service, P.O. Box 350, Stoneville, MS 38776, U.S.A.