Sperm axoneme of two rows of doublets reversely oriented in the gall-midge Lestremia (Diptera, Cecidomyiidae)

The spermatozoon of Lestremia lacks an acrosome and has a giant centriole that gives origin to a giant axoneme with about 150 doublets. The axonemal doublets, disposed in two opposite rows oriented antiparallel, have A doublets with two dynein arms and a B tubule filled with dense proteinaceous material. Mitochondria fuse in two derivatives and show cristae and a longitudinal crystallized axis. The probable origin of the giant axoneme is hypothesized and the more prolonged motility of Lestremia sperm in comparison with that of other gall midges is related to the presence of a more precise axonemal organization. The spermatological results agree with the systematic position of Lestremiinae at the base of the evolutionary trend of the family Cecidomyiidae.     

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.     

Flagellate spermatozoa of Protura (Insecta,Apterygota) are motile

A new model of sperm axoneme with 16 + 0 doublets is described. The spermatozoon of Acerentulus confinis (Apterygota : Protura) has a short conical acrosome, a long helicoidal nucleus, well-developed centriolar adjunct material, and a long flagellum. Using fixation with a glutaraldehyde-tannic acid mixture, without osmium post-fixation, doublet protofilaments, inner dynein arms, radial spokes, nexin bridges, and Y-links of the sperm axoneme of A. confinis and Acerentomon italicum were clearly observed. Optical observation shows that the proturan flagellate spermatozoa are motile cells. The process involving the transformation of the spermatozoa from a coiled to an elongated swimming form was studied by scanning electron microscope. The findings confirmed that flagellar motility is due to the presence of a single dynein arm on doublets in spite of the unusual axonemal pattern.     

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     

The spermatozoon of arthropoda. XXV. A new model of tail having up to 170 doublets: Monarthropalpus buxi

The spermatozoon of M. buxi which belongs to the Cecidomyiidae family have been studied. The spermatozoa have an aberrant flagellum somewhat similar to that of Sciaridae formed by about 170 doublets ranged in rows to form a compact bundle. Accessory tubules and all the other axonemal structures are missing. The sperm is characterized by the lack of acrosome, and by the presence of normal mitochondria apically gathered before the nucleus.     

Living without mitochondria: spermatozoa and spermatogenesis in two species of Urodasys (Gastrotricha, Macrodasyida) from dysoxic sediments

Abstract. The spermatozoa of two species of Macrodasyida (Gastrotricha), Urodasys anorektoxys and U. acanthostylis , show an ultrastructural organization diverging from one another and from other gastrotrichs: their main peculiarity is in the absence of mitochondria. In U. anorektoxys , the acrosome is a long, twisted column inserted into the nucleus, which is basally cylindrical, and the flagellum shows rows of peculiar, large globules parallel to the axonemal doublets. In U. acanthostylis , the acrosome is completely cork-screwed and surrounds the nucleus, and the tail shows columnar accessory fibers. At present, the absence of mitochondria in the mature sperm, and the peculiar fingerprint aspect of condensed chromatin are the only traits shared by the two species. The features of the spermatozoa of these two species of Urodasys widen the range of different models of gastrotrich spermatozoa, and place the genus in a peculiar position, from the spermatological point of view, within the Macrodasyida. The loss of mitochondria in mature spermatozoa is possibly related to either the dysoxic habitat of the two species or a peculiar fertilization mechanism.     

Sperm ultrastructure of<Emphasis Type="Italic"> Mantophasma zephyra</Emphasis> (Insecta,Mantophasmatodea)

The ultrastructure of Mantophasma zephyra spermatozoa is described. Sperm cells have a trilayered acrosome with conspicuous extra-acrosomal material which expands along the nucleus. The nucleus is crossed anteriorly by a canal and its posterior end is embedded in the centriole adjunct material. A centriole with microtubular triplets is present. The flagellum has a 9+9+2 axonemal pattern, two partially crystallised mitochondrial derivatives, two membranous sacs and three connecting bands. The accessory microtubules are filled with dense material and have 16 protofilaments in their tubular wall. The intertubular material is not very expanded. In the seminal vesicles spermatozoa are stuck together to form spermatodesms, and their heads are also joined by adherens junctions. A cladistic analysis based on sperm features indicates a close relationship of Mantophasmatodea with Mantodea.     

Spermiogenesis in the Flatworm, Notoplana Japonica with Special Attention to the Organization of an Acrosome and Flagella

Ultrastructural changes during spermiogenesis in the flatworm, Notoplana japonica were studied with special attention to organizing process of an acrosome and flagella. During spermiogenesis, the G olgi complex develops conspicuously but it fails to organize the structure of an acrosomal vesicle. Consequently, no acrosome is formed at the apex of the sperm. As a substitute for an acrosomal structure, the slender process at the tip of the mature sperm is prominently occupied with glycogen granules.
The axoneme of the flagellum is formed from the basal body in the protrusion which is juxtaposed to the nucleus of the early spermatid. Two flagella associated with an electron-dense structure (EDS) extend superficially from the spermatid body in opposite directions. Progressively, they take an acute angle to each other and finally run alongside the sperm body. The axoneme consits of nine peripheral doublets with arms, a central cylinder containing an electron dense core, a less dense intermediate zone and fine spokes between the cylinder and doublets.     

Immunoelectron microscopic localization of calmodulin and phospholipase A2 in spermatozoa. I

Using the Lowicryl K4M embedding technique, together with indirect immunoferritin or immunogold labeling on ultra-thin sections, tubulin, calmodulin and phospholipase A2 were distinctly localized in ejaculated bull spermatozoa. Calmodulin was concentrated on the plasma membrane, nucleus, post-acrosomal substance, and, in lesser amounts, between coarse fibers and axonemal microtubules of the flagellum. Phospholipase A2 was distributed evenly along the plasma membrane, nucleus, acrosome, post-acrosomal substance, and in the flagellum, on mitochondria, fibrous sheath, coarse fibers, between coarse fibers and axonemal microtubules. Antibodies to tubulin labeled only axonemal microtubules, including the central pair of microtubules. Patterns of tubulin labeling were identical when ferritin granule- or gold particle-conjugated antibodies were tested. In agreement with our previous biochemical studies demonstrating calmodulin binding to phospholipase A2, concomitant with enhancement of phospholipase A2 activity (Arch Biochem Biophys 241:413, 1985), the overlapping distribution of calmodulin and phospholipase A2 in several parts of the sperm suggests that these proteins may play a concerted role in male gamete function in preparation for or during fertilization. The distinct distribution of tubulin along flagellum microtubules indicates their special function in sperm mobility.     

Expression of cathepsin H in differentiating rat spermatids: immunoelectron microscopic study

The expression of cathepsin H (CH) in differentiating rat spermatids was studied by an immunoelectron microscopic technique. Cathepsin H was detected in the acrosome throughout differentiation steps but cathepsins B, D, and L and lysosomal membrane protein (LGP107) were not. Early in the formation of the acrosome, CH signals were observed in Golgi vesicles but not in acrosomal vesicles. At steps 3–4, CH signals were associated with a fibrous material attached to the inner surface of the vesicle membrane on the Golgi side. At steps 5–6, this fibrous material accumulated to form an electron-dense sheet to which CH signals were confined. The rest of the acrosome was negative for the enzyme. At steps 11–12, the CH-positive fibrous sheet expanded from the apical to the ventral side of the sperm head. After step 16, the surface of outer dense fibers in the flagellar axoneme and reticulated bodies were stained for CH. In epididymal sperm, CH signals were detected in the acrosome as well as on the surface of the outer dense fibers running from the middle to the principal piece. By immunofluorescence staining, CH was found to be localized to the acrosome, middle piece, and principal piece.     

The spermatogenesis and sperm structure of Acerentomon microrhinus (Protura, Hexapoda) with considerations on the phylogenetic position of the taxon

The spermatogenesis of the proturan Acerentomon microrhinus Berlese, (Redia 6:1–182, 1909) is described for the first time with the aim of comparing the ultrastructure of the flagellated sperm of members of this taxon with that of the supposedly related group, Collembola. The apical region of testes consists of a series of large cells with giant polymorphic nuclei and several centrosomes with 14 microtubule doublets, whose origin is likely a template of a conventional 9-doublet centriole. Beneath this region, there are spermatogonial cells, whose centrosome has two centrioles, both with 14 microtubule doublets; the daughter centriole of the pair has an axial cylinder. Slender parietal cells in the testes have centrioles with nine doublet microtubules. Spermatocytes produce short primary cilia with 14 microtubule doublets. Spermatids have a single basal body with 14 microtubule doublets. Anteriorly, a conical dense material is present, surrounded by a microtubular basket, which can be seen by using an α-anti-tubulin antibody. Behind this region, the basal body expresses a long axoneme of 14 microtubule doublets with only inner arms. An acrosome is lacking. The nucleus is twisted around the apical conical dense structure and the axoneme; this coiling seems to be due to the rotation of the axoneme on its longitudinal axis. The posterior part of the axoneme forms three turns within the spermatid cytoplasm. Few unchanged mitochondria are scattered in the cytoplasm. Sperm consist of encysted, globular cells that descend along the deferent duct lumen. Some of them are engulfed by the epithelial cells, which thus have a spermiophagic activity. Sperm placed in a proper medium extend their flagellar axonemes and start beating. Protura sperm structure is quite different from that of Collembola sperm; and on the basis of sperm characters, a close relationship between the two taxa is not supported.     

Pathology of the cytoskeleton of the human sperm flagellum: axonemal and peri-axonemal anomalies

A quantitative ultrastructural study was performed on 56 ejaculates showing anomalies of the sperm axonemal complex. The anomalies comprised either the absence of one, or more often several, axonemal structures, or defective elongation of the doublets. Several characteristics relating to the extent and superimposition of the various anomalies could be described and enabled the definition of 6 groups of anomalies. In decreasing order of frequency these were: absence of the doublets and peripheral junctions, absence of the central complex, of the outer dynein arms, of the central junctions, of both dynein arms, and absence of the inner dynein arms and peripheral junctions. Some anomalies caused total immobility, whereas others caused abnormal movement patterns. Abnormalities of the peri-axonemal structures were found in each group. The various light microscopic characteristics of each of the 6 groups represented 6 seminal profiles which should permit their detection during a routine semen analysis. Several specific associations of axonemal and/or peri-axonemal anomalies would suggest some morphogenetic links between them. Relationships between the absence of doublets or the absence of the central complex and disturbances of microtubular polymerization are discussed. Finally, the study has provided new data on the composition of the axoneme.     

Ultrastructure of the spermatozoon of the American Alligator,Alligator mississippiensis (Reptilia: Alligatoridae)

This study details the ultrastructure of the spermatozoa of the American Alligator, Alligator mississippiensis. American Alligator spermatozoa are filiform and slightly curved. The acrosome is tapered at its anterior end and surrounded by the acrosome vesicle and an underlying subacrosomal cone, which rests just cephalic to the nuclear rostrum. One endonuclear canal extends from the subacrosomal cone through the rostral nucleus and deep into the nuclear body. The neck region separates the nucleus and midpiece and houses the proximal centriole and pericentriolar material. The distal centriole extends through the midpiece and has 9 × 3 sets of peripheral microtubules with a central doublet pair within the axoneme that is surrounded by a dense sheath. The midpiece is composed of seven to nine rings of mitochondria, which have combinations of concentrically and septate cristae. The principal piece has a dense fibrous sheath that surrounds an axoneme with a 9 + 2 microtubule arrangement. The sheath becomes significantly reduced in size caudally within the principal piece and is completely missing from the endpiece. Dense peripheral fibers, especially those associated with microtubule doublets 3 and 8, penetrate into the anterior portion of the principal piece axoneme. The data reported here hypothesize that sperm morphology is highly conserved in Crocodylia; however, specific morphological differences can exist between species. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Spermatozoa and relationships in Palaeognath birds

In this paper the authors describe the ultrastructure of the mature spermatozoon and the spermatid in Struthio camelus and Dromaius novaehollandiae. The first species is characterized by a rod-like perforatorium within an endonuclear canal in the anterior third of the nucleus, while the second is characterized by an extremely reduced completely extranuclear perforatorium. Other differences are in the sperm dimensions, the number of mitochondria and the length of the axonemal accessory fibers. Considering both the present data and previous findings, Palaeognath birds appear to be a peculiar and monophyletic group, characterized by: 1), a conical acrosome surrounding the nucleus; 2), a fibrous sheath around most of the axoneme; and 3), an elongated distal centriole occupying the entire midpiece. Within this group, Tinamiformes seem to be more primitive than Struthioniformes. In the latter order Dromaius is distinctly different from the reduced Struthio and Rhea which are closely related to one another by the presence of a rod-like endonuclear perforatorium.     

Characterization and subcellular localization of Tektin 3 in rat spermatozoa

Mammalian sperm flagella have filament‐forming Tektin proteins (Tektin 1–5) reported to be involved in the stability and structural complexity of flagella. Male mice null for Tektin3 produce spermatozoa with reduced forward progression and increased flagellar structural bending defects. The subcellular localization of Tektin3 (TEKT3) in spermatozoa, however, has not been clarified at the ultrastructural level. To elucidate the molecular localization of TEKT3 in flagella of rat spermatozoa, we performed extraction studies followed by immunoblot analysis, immunofluorescence microscopy, and immunogold electron microscopy. Extraction of sperm flagella from the cauda epididymis resulted in complete removal of axonemal tubulins, while TEKT3 was resistant to extraction with the same S‐EDTA (1% SDS, 75 mM NaCl, 24 mM EDTA, pH 7.6) solution, suggesting that TEKT3 might be present in the peri‐axonemal component and not directly associated with axonemal tubulins. Resistance to S‐EDTA extraction might be due to disulfide bond formation during epididymal maturation since concentrations of DTT greater than 5 mM drastically promoted release of TEKT3 from flagella. Immunofluorescence microscopy and pre‐embedding immunoelectron microscopy revealed that TEKT3 was predominantly associated with the surface of mitochondria and outer dense fibers in the middle piece. In addition, TEKT3 was found to be present at the equatorial segment region of the acrosome membrane in sperm heads. TEKT3 might not only work as a flagellar constituent required for flagellar stability and sperm motility but also may be involved in acrosome‐related events, such as the acrosome reaction or sperm–egg fusion. Mol. Reprod. Dev. 78:611–620, 2011. © 2011 Wiley‐Liss, Inc.     

Membrane differentiations in spermatozoa of the squid,Loligo pealeii

Regional differences in the structure of the plasma membrane and acrosome membrane of squid spermatozoa were studied by freeze-fracture and thin section electron microscopy. In regions of close apposition the plasma membrane and acrosome membrane are adjoined to one another by regularly spaced linkages. These linkage sites, overlie a set of fibers located at the inner face of the acrosomal membrane. The acrosomal fibers terminate in a layer of granular material located at the base of the acrosome. Detergent treatment of sperm releases the fibers and granular material as an interconnected complex. Freeze-fracture replicas reveal a random arrangement of intramembranous particles in the plasma membrane over the sperm head and linear aggregates of intramembranous particles in the acrosomal membrane. Several regional differences in the structure of the flagellar plasma membrane are present. The thickness of the glycocalyx is progressively reduced distally along the flagellum. Freeze-fracture replicas show evenly spaced linear arrays of intramembranous particles which extend parallel t o the flagellar long axis. Examination of spermatozoa extracted to disrupt flagellar geometry suggest that the dense fiber-doublet microtubule complexes are attached to the plasma membrane. The possible functional role of these membrane differentiations and their relationship t o membrane structures in mammalian spermatozoa are discussed.     

The multi‐scale architecture of mammalian sperm flagella and implications for ciliary motility

Motile cilia are molecular machines used by a myriad of eukaryotic cells to swim through fluid environments. However, available molecular structures represent only a handful of cell types, limiting our understanding of how cilia are modified to support motility in diverse media. Here, we use cryo‐focused ion beam milling‐enabled cryo‐electron tomography to image sperm flagella from three mammalian species. We resolve in‐cell structures of centrioles, axonemal doublets, central pair apparatus, and endpiece singlets, revealing novel protofilament‐bridging microtubule inner proteins throughout the flagellum. We present native structures of the flagellar base, which is crucial for shaping the flagellar beat. We show that outer dense fibers are directly coupled to microtubule doublets in the principal piece but not in the midpiece. Thus, mammalian sperm flagella are ornamented across scales, from protofilament‐bracing structures reinforcing microtubules at the nano‐scale to accessory structures that impose micron‐scale asymmetries on the entire assembly. Our structures provide vital foundations for linking molecular structure to ciliary motility and evolution.     

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.     

Adenylate kinases 1 and 2 are part of the accessory structures in the mouse sperm flagellum

Proper sperm function depends on adequate ATP levels. In the mammalian flagellum, ATP is generated in the midpiece by oxidative respiration and in the principal piece by glycolysis. In locations where ATP is rapidly utilized or produced, adenylate kinases (AKs) maintain a constant adenylate energy charge by interconverting stoichiometric amounts of ATP and AMP with two ADP molecules. We previously identified adenylate kinase 1 and 2 (AK1 and AK2) by mass spectrometry as part of a mouse SDS-insoluble flagellar preparation containing the accessory structures (fibrous sheath, outer dense fibers, and mitochondrial sheath). A germ cell-specific cDNA encoding AK1 was characterized and found to contain a truncated 3' UTR and a different 5' UTR compared to the somatic Ak1 mRNA; however, it encoded an identical protein. Ak1 mRNA was upregulated during late spermiogenesis, a time when the flagellum is being assembled. AK1 was first seen in condensing spermatids and was associated with the outer microtubular doublets and outer dense fibers of sperm. This localization would allow the interconversion of ATP and ADP between the fibrous sheath where ATP is produced by glycolysis and the axonemal dynein ATPases where ATP is consumed. Ak2 mRNA was expressed at relatively low levels throughout spermatogenesis, and the protein was localized to the mitochondrial sheath in the sperm midpiece. AK1 and AK2 in the flagellar accessory structures provide a mechanism to buffer the adenylate energy charge for sperm motility.