The sperm ultrastructure of Caurinus dectes Russell (Mecoptera: Boreidae) and its phylogenetic implications

The sperm structure of the enigmatic mecopteran species Caurinus dectes (Boreidae) is described for the first time. Diagnostic features are the bi-layered acrosome, a cylindric nucleus provided with two longitudinal opposite grooves, and a simple 9 + 2 axoneme which degenerates in the posterior tail end. The results are conform with the monophyly of Mecoptera including Boreidae. A possible autapomorphy of the order is the presence of the two longitudinal opposite grooves along the nucleus, and the presence of two electron-dense fibres beneath the axoneme. Some apparently plesiomorphic features are preserved in the sperm of Caurinus. Features characterizing the distal part of the flagellum, including the presence of an axial cylindrical structure and the distinctive type of axoneme degeneration, are potential synapomorphies of Caurinus and Boreus, i.e. autapomorphic traits of Boreidae.     

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.     

蟋蟀精子形成部分时期尾部超微结构观察

通过对黄脸油葫芦精子尾部形成过程4～10期超微结构的观察,发现该虫精子细胞发育至第6期轴丝微管束9 9 2完整形成;7、8两期精子细胞内一些高尔基体、内质网膜系统结构包绕着轴丝;第9期精子细胞及成熟精子轴丝内副微管、双微管中的A微管、中央单微管内充满小圆柱状纤维;中心粒侧体纤维状,成熟精子的线粒体衍生体内不具纵嵴;细胞质膜外不具发达的糖蛋白套。通过比较发现该虫精子与蝗总科癞蝗科精子类型比较相似,同属于原始类型精子。     

Fine structure of spermatozoa in the common pandora (Pagellus erythrinus Linnaeus, 1758) (Perciformes, Sparidae)

Scanning and transmission electron microscopy were used to investigate the fine structure of the sperm of the Sparid fish Pagellus erythrinus L. The spermatozoon of pandora has a spherical head lacking an acrosome, a cone-shaped midpiece and a long tail. The midpiece houses a single mitochondrion. The centriolar complex lies inside the nuclear fossa and is composed of a proximal and a distal centriole which are arranged at right angles to each other. The flagellum is inserted medio-laterally into the head, contains the conventional 9+2 axoneme and possesses one pair of lateral fins. On the basis of its ultrastructural organization, the pandora sperm can be regarded as an evolved form of the primitive spermatozoon found in Teleosts. According to the morphological classification proposed by Mattei (1970), the sperm of pandora belongs to a "type I" designation, like that of the other Sparid fish.     

The best of all worlds or the best possible world? Developmental constraint in the evolution of β-tubulin and the sperm tail axoneme

Through evolutionary history, some features of the phenotype show little variation. Stabilizing selection could produce this result, but the possibility also exists that a feature is conserved because it is developmentally constrained--only one or a few developmental mechanisms can produce that feature. We present experimental data documenting developmental constraint in the assembly of the motile sperm tail axoneme. The 9+2 microtubule architecture of the eukaryotic axoneme has been deeply conserved. We argue that the quality of motility supported by axonemes with this morphology explains their long conservation, rather than a developmental necessity for the 9+2 architecture. However, our functional tests in Drosophila spermatogenesis reveal considerable constraint in the coevolution of testis-specific beta-tubulin and the sperm tail axoneme. The evolution of testis beta-tubulins used in insect sperm tail axonemes is highly punctuated, indicating some pressure acting on their evolution. We provide a mechanistic explanation for their punctuated evolution by testing structure-function relationships between testis beta-tubulin and the motile axoneme in D. melanogaster. We discovered that a highly conserved sequence feature of beta-tubulins used in motile axonemes is needed to specify central pair formation. Second, our data suggest that cooperativity in the function of internal beta-tubulin amino acids is needed to support the long axonemes characteristic of Drosophila sperm tails. Thus, central pair formation constrains the evolution of the axoneme motif, and intramolecular cooperativity makes the evolution of the internal residues path dependent, which slows their evolution. Our results explain why a highly specialized beta-tubulin is needed to construct the Drosophila sperm tail axoneme. We conclude that these constraints have fixed testis-specific beta-tubulin identity in Drosophila.     

Sperm ultrastructure and spermiogenesis in the relic species Tricholepidion gertschi Wygodzinsky (Insecta, Zygentoma)

The silverfish Tricholepidion gertschi is of interest in that it is the most basal representative of Zygentoma. An ultrastructural study of its spermiogenesis was performed to find out whether there are traits which resemble those of other, more advanced insects. This was found to be the case; spermiogenesis can be considered to be of a common insectan type, leading to the formation of elongated sperm cells with acrosome, nucleus, neck region and a tail with axoneme and two mitochondrial derivatives. Total cell length, 50 microm, is short for an insect. There are some specializations, which probably represent autapomorphies. The acrosome has a posterior canal or cleft that makes a U-turn. The centriole adjunct forms a prominent post-nuclear ring surrounding the centriole and have a posterior extension, and further originates nine intertubular fibers with a longitudinal periodicity and two accessory bodies. The mitochondrial derivatives have five rows of regularly spaced cristae within a crystalline matrix. The axoneme has accessory tubules consisting of 16 protofilaments, formed at the B-tubules of the doublets and placed at some distance from them in the posterior part of the sperm tail.     

Ultrastructure of the spermatozoon ofElenchus japonicus and its bearing on the phylogeny of strepsiptera

The fine structure of the mature spermatozoon of the strepsipteranElenchus japonicus Esaki and Hashimoto (Elenchidae) is described using transmission electron microscopy. The spermatozoon was seen to have an elongated head, a tail containing a 9 + 9 + 2 axoneme, two mitochondrial derivatives and two accessory sheaths. The monolayered acrosome is conical in shape while the nucleus exhibits an internal channel of uncondensed chromatin. The tail is long, and in its final portion, the axoneme, loses its elements progressively. These results are compared with the sperm ultrastructure ofXenos moutoni De Buysson (Stylopidae) and with those of other insect orders, particularly the Coleoptera.     

Ultrastructure of spermiogenesis in a freshwater stingray, Himantura signifer

Ultrastructural changes of spermatids during spermiogenesis in a freshwater stingray, Himantura signifer, are described. Differentiation of spermatids begins with modification of the nuclear envelope adjacent to the Golgi apparatus, before the attachment of the acrosomal vesicle. A fibrous nuclear sheath extends over the nuclear surface from the site of acrosomal adherence. The conical apical acrosome is formed during nuclear elongation. At the same time, chromatin fibers shift from an initially random arrangement, assume a longitudinal orientation, and become helical before final nuclear condensation. An axial midpiece rod is formed at the posterior end of nucleus and connects to the base of the sperm tail. Numerous spherical mitochondria surround the midpiece axis. The tail originating from the posterior end of the midpiece is composed of the usual 9 + 2 axoneme accompanied by two longitudinal columns, which are equal in size and round in cross section. The two longitudinal columns are absent at the end piece. A distinctive feature of freshwater stingray sperm is its spiral configuration.     

Characteristics of the sperm tail of the velvet worm, Euperipatoides leuckarti (Onychophora)

The onychophoran sperm tail contains several kinds of microtubulcs; probably more than that of any other animal group. There are thus a peripheral manchette consisting of many tightly spaced microtubules, a ring of nine 'peripheral singlets' and a central axoneme of the classical 9 + 2 type (nine doublets and two central singlets). The protofilament organization of these various microtubules was examined and compared to the structure and mode of formation of the peripheral singlets with that of its analogues in other animal groups. The onychophoran peripheral singlets were found to differ in two respects from those in insects: they are formed from the manchette rather than from the axonemal doublets and their transient connection to the axoneme is to the A-subtubules of the doublet rather than to the B-subtubules. The manchette microtubules as well as the peripheral singlets consist of 13 protoh'laments. The manchette may serve a mechanical function (to strengthen the unusually thick sperm tail) hut the role of the peripheral singlets remains unknown.     

Zipper lines in the flagellar plasma membrane of the squid (Loligo) spermatozoon

Spermatozoa of the common squid, Loligo vulgaris, have been examined in a combined thin-sectioning and freeze-fracture study. Zipper-lines were seen in freeze-fracture replicas as rows of particles located on the proximal end of the axoneme. In thin section granules were visible on both sides of the tail membrane surrounding the axoneme at the proximal level, but another structure that could be identified as a zipper-line was also seen in thin section; this structure links accessory fibres to the tail membrane of the sperm. The role(s) of zipper-lines is discussed.     

Ultrastructure of the biflagellate spermatozoon of tomopteris helgolandica greef, 1879 (annelida,polychaeta)

The spermatozoon of the polychaete Tomopteris helgolandica is of an aberrant type with two flagella, each measuring about 40μm. The nucleus is roughly conical and weakly bent. At the anterior end it is rounded and covered only by the nuclear and plasma membranes. Membraneous, electron-dense structures are applied laterally to the nucleus. These structures may have a helical arrangement. The middle piece contains about ten mitochondria, two centrioles, and two centriolar satellite complexes. The centriolar regions are connected with the posterior part of the nucleus. The axonemes of the two tail flagella lack the usual central complex with central tubules, radial spokes, or related structures. No arms seem to be present on the A tubules of the doublets. In the middle piece the tail flagella are surrounded by invaginations of the plasma membrane forming flagellar canals. The sperm has a bilateral symmetry whereas the primitive sperm has a radial symmetry. The occurrence of two tail flagella in this spermatozoon has no phylogenetical connection with biflagellate spermatozoa in other animal groups. A series of mutations has resulted in the development of two flagella emerging from the two centrioles, the lack of a central complex in the axoneme, and the lack of a typical acrosome. In the Polychaeta, sperm structure is generally more related to function that to phylogenetics. During swimming the spermatozoon of Tomopteris rotates around its longitudinal axis.     

The giant sperm of a minute beetle

The mature sperm of Ptinella aptera is a helically coiled, flagellate gamete ca. 1.4 mm long—twice the length of the beetle itself. The rod-like acrosome, comprising the anterior part of the sperm, is 0.4 μm thick but is expanded as a flange around the nucleus and the base of the tail, increasing the diameter of the sperm to 2 μm. The bulk of the tail consists of a pair of bodies with a characteristic ultrastructure of longitudinal tubules beneath a lamellar cortical layer. These bodies are probably homologous with the mitochondrial derivatives of other insect sperm. The axoneme is helically coiled and is flanked by a single accessory body. One of the ‘structured bodies’ is connected to the acrosome and the other to the accessory body. The sperm move actively in the female reproductive tract. The functional significance of this behaviour and of the evolution of the large gamete itself is discussed in relation to existing hypotheses.     

Structure and function of the undulating membrane in spermatozoan propulsion in the toad Bufo marinus

Accessory fibers in most sperm surround the axoneme so that their function in propulsion is difficult to assess. In the sperm of the toad Bufo marinus, an accessory fiber is displaced from the axoneme, being connected to it by the thin undulating membrane in such a way that the movement of axoneme and accessory fiber can be viewed independently. The axoneme is highly convoluted in whole mounts, and the axial fiber is straight. Cinemicrographic analysis shows that it is the longer, flexuous fiber, the presumed axoneme, that move actively. The accessory fiber follows it passively with a lower amplitude of movement. The accessory fiber does not move independent of the axoneme, even after demembranation and reactivation of the sperm. On the basis of anatomical relations in the neck region, it appears that the accessory fibers of amphibians are analogous to the dense fibers of mammalian sperm. SDS polyacrylamide gel electrophoresis of demembranated toad sperm tails reveals two principal proteins in addition to the tubulins, the former probably arising from the accessory fibers and the matrix of the undulating membrane. The function of displacing an accessory fiber into an undulating membrane may be to provide stiffness for the tail without incurring an energy deficit large enough to require a long middle piece. A long middle piece is not present in toad sperm, in contrast to those sperm that have accessory fibers around the axoneme. However, the toad sperm suffers a reduction in speed of about one- third, compared with the speed expected for a sperm without an undulating membrane.     

The proximal region of the beta-tubulin C-terminal tail is sufficient for axoneme assembly

We have used Drosophila testis-specific beta2-tubulin to determine sequence requirements for different microtubules. The beta2-tubulin C-terminal tail has unique sperm-specific functions [Dev Biol 158:267-286 (2003)] and is also important for forming stable heterodimers with alpha-tubulin, a general function common to all microtubules [Mol Biol Cell 12(7):2185-2194 (2001)]. beta-tubulins utilized in motile 9 + 2 axonemes contain a C-terminal sequence "axoneme motif" [Science 275 (1997) 70-73]. C-terminal truncated beta2-tubulin cannot form the sperm tail axoneme. Here we show that a partially truncated beta2-tubulin (beta2Delta7) containing only the proximal portion of the C-terminal tail, including the axoneme motif, can support production of functional motile sperm. We conclude that these proximal eight amino acids specify the binding site for protein(s) essential to support assembly of the motile axoneme. Males that express beta2Delta7, although they are fertile, produce fewer sperm than wild type males. Beta2Delta7 causes a slightly increased error rate in spermatogenesis attributable to loss of stabilizing properties intrinsic to the full-length C-terminal tail. Therefore, beta2Delta7 males would be at a selective disadvantage and it is likely that the full-length C-terminus would be essential in the wild and in evolution.     

奶牛精子尾部主段外周致密纤维的电子显微镜观察

奶牛精子尾部主段的中央结构为轴丝。在轴丝的外方有外周致密纤维。外周致密纤维由中段延伸而来。进入主段后,9条外周致密纤维逐一终止。最早终止的是第8条纤维。随后的终止顺序是第3、7、4、2、6、5、9、1条。因此,9条外周致密纤维中,最长的是第1条纤维,最短的是第8条纤维。9条纤维按长短顺序排列依次是第1、9、5、6、2、4、7、3、8条。根据外周致密纤维数量的多寡,可以将主段分为10个区域。从近中段端至近末段端,这10个区域依次是9条、8条、7条、6条、5条、4条、3条、2条、1条、0条纤维区域。外周致密纤维的外方有一纤维鞘。纤维鞘的背侧纵柱和腹侧纵柱分别向内伸出一个嵴。在主段的0条纤维区域,纤维鞘直接位于轴丝之外。在纤维鞘的外方还有精子的细胞质膜。     

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.     

Dynamics of spermiogenesis in Drosophila melanogaster: III. Relation between axoneme and mitochondrial derivatives

In cross sections of developing spermatid tails of D. melanogaster, the angular positions of the mitochondrial derivatives relative to the axoneme are precisely defined at each stage of development. Nearly mature sperm in the coiling stage, however, exhibit a variable angular relation between the axonome and the rest of the tail. A similar variation is also found among cross sections of mature sperm tails. These observations, together with other morphological evidence, are interpreted as indicating limited rotational freedom between the axoneme and the rest of the tail in mature sperm. Such a freedom seems to be related to the swimming pattern of sperm and the fertilization process. It is suspected that specific shapes and natures of mitochondrial derivatives in sperm tails of insects are related to a particular swimming pattern of sperm, which must be highly precise in order to meet the requirements of species-specific modes of fertilization.     

文昌鱼精子的超显微结构

文昌鱼(Branchiostoma belcheri tsingtaoensis)的成熟精子由一个锥形的顶体,头部,颈(被核包裹)和尾部组成。尾可分为中段,主段和末段。微管对复合体为9+2。 文昌鱼精子的超显微结构与前人报道的线粒体由4—6个组成的不同。它由一个大的线粒体围绕尾主轴中段,而且精子属于对称性类型,可以见到核内管,中心粒和致密纤维,终环结构与隐窝位于尾中段与主段之间。本文并对文昌鱼在系统发生中的重要位置和意义作了讨论。     

Sperm structure and spermiogenesis in Coletinia sp. (Nicoletiidae, Zygentoma, Insecta) with a comparative analysis of sperm structure in Zygentoma

The spermatozoon of Coletinia sp. has a bilayered acrosome, a short nucleus (4 microm) and a relatively short sperm tail with two mitochondrial derivatives. The chromatin is uniformly dense except for several electron-lucid channels or strands which permeate the nucleus and which originate in the spermatid as invaginations of the nuclear envelope. The invaginations occur mostly or exclusively along two meridians of the spermatid that are also characterized by the presence of a longitudinal rod of medium electron density. The two rods (designated as 'mid-spermatid rods') evidently are instrumental in the formation of the electron-lucid channels. The significance of this elaborate system of intranuclear channels is not understood. The sperm tail has a 9 + 9 + 2 axoneme with each of the nine microtubular doublets accompanied by an accessory microtubule; scant intertubular material can also be distinguished. Hence, the tail axoneme resembles that of many pterygote insects. Each of the two mitochondrial derivatives contains a crystalline inclusion that has periodically spaced layers going in different directions on either side of the midline. Two synapomorphic traits appear to be shared by Ateluridae and Nicoletiidae, namely the invaginations of the nuclear membrane along two meridians of the nucleus and the shape of the crystalline inclusions of the mitochondrial derivatives. Four species from the family Lepismatidae were also examined as to their sperm ultrastructure. Three of them, Allacrotelsa kraepelini, Ctenolepisma longicaudata and Ctenolepisma sp., were found to be very similar to the two previously examined lepismatids, Thermobia domestica and Lepisma saccharina. On the other hand, spermatozoa of Tricholepisma aurea were aggregated in small groups rather than pairwise joined as seen in the other lepismatids. Sperm characters are also used to reconstruct a phylogenetic hypothesis which suggests a close relationship between Ateluridae and Nicoletiidae.     

Fine structure of spermatozoa in the gilthead sea bream (Sparus aurata Linnaeus, 1758) (Perciformes, Sparidae)

Scanning and transmission electron microscopy were used to investigate the fine structure of the sperm of the sparid fish Sparus aurata L. The mature spermatozoon of gilthead sea bream belongs, like that of the other sparid fish, to a "type I" as defined by Mattei (1970). It has a spherical head which lacks an acrosome, a short, irregularly-shaped midpiece and a long cylindrical tail. The nucleus reveals a deep invagination (nuclear fossa) in which the centriolar complex is located. The two centrioles are approximately perpendicular to each other and show a conventional "9+0" pattern. The proximal centriole is associated with a cross-striated cylindrical body lying inside a peculiar satellite nuclear notch which appears as a narrow invagination of the nuclear fossa. The distal centriole is attached to the nuclear envelope by means of a lateral plate and radial fibres made of an electron-dense material. The short midpiece houses one mitochondrion. The flagellum is inserted perpendicularly into the base of the nucleus and contains the conventional 9+2 axoneme.