Fine structure of spermatozoa of Chondrostoma nasus and Rutilus meidingerii (Teleostei, Cyprinidae), as revealed by scanning and transmission electron microscopy

Fürböck, S., Patzner, R.A. and Lahnsteiner, F. 2008. Fine structure of spermatozoa of Chondrostoma nasus and Rutilus meidingerii (Teleostei, Cyprinidae), as revealed by scanning and transmission electron microscopy. — Acta Zoologica (Stockholm) 91 : 88–95
The fine structure of spermatozoa of sneep or nase, Chondrostoma nasus , and lake chub, Rutilus meidingerii , was investigated by means of scanning and transmission electron microscopy. The uniflagellate spermatozoa of C. nasus lacked an acrosome. The flagellum contained the conventional nine peripheral doublets and one central pair of microtubules (9 + 2 pattern) and lacked lateral fins. The uniflagellate spermatozoa of R. meidingerii were made up of a head, also without an acrosome. For both species the sperm tail was covered by a plasma membrane. The midpiece of C. nasus contained five or six mitochondria on average, vesicles and glycogen granules, whereas the midpiece of R. meidingerii had seven mitochondria of a spherical or ovoid shape. The centriolar complex was located caudolaterally with respect to the nucleus. In C. nasus , the centrioles were orientated at an angle of 125° to each other, whereas the centrioles of R. meidingerii were at an angle of 110°. The fine structure of C. nasus and R. meidingerii spermatozoa showed species-specific differences in the position of the proximal centriole relative to the distal centriole, the position and number of mitochondria, size of the head and the length of the flagellum. (Correction added on 11 June 2009, after first online publication: The word 'axoneme' was deleted from the sentence 'The flagellum contained the conventional nine peripheral doublets and one central pair of microtubules (9 + 2 pattern) axoneme and lacked lateral fins.')     

Spermatozoa ultrastructure in Sciaenidae and Polynemidae (Teleostei:Perciformes) with some consideration on Percoidei spermatozoa ultrastructure

Spermatozoa ultrastructure was studied in five marines (Paralonchurus brasiliensis, Larimus breviceps, Cynoscion striatus, Micropogonias furnieri, Menticirrhus americanus, Umbrina coroides, Stellifer rastrifer), and one freshwater (Plagioscion squamosissimus) species of Sciaenidae and one species of Polynemidae (Polydactylus virginicus). The investigation revealed that, in all species, spermatozoa display a round head, a nucleus containing highly condensed, filamentous chromatin clusters, no acrosome, a short midpiece with a short cytoplasmic channel, and a flagellum showing the classic axoneme structure (9+2) and short irregular lateral fins. In Sciaenidae, the spermatozoa are type II, the flagellar axis is parallel to the nucleus, the lateral nuclear fossa is double arched, the centriolar complex is outside the nuclear fossa, the proximal centriole is anterior and perpendicular to the distal centriole, and no more than ten spherical (marine species) or elongate (freshwater species) mitochondria are observed. Polynemidae spermatozoa are of the intermediate type with the flagellar axis eccentric to the hemi-arc-shaped nucleus, and exhibit no nuclear fossa, the centriolar complex close to the upper nuclear end, the proximal centriole lateral and oblique to the distal centriole, and one large ring-shaped mitocondrion. The data available show that no characteristic is exclusively found in the spermatozoa of members of the Sciaenidae family when compared to other Percoidei with type II spermatozoa. However, three characteristics were exclusively found in Polynemidae: (1) the hemi-arched nucleus; the positioning of the centrioles; and (2) the ring-shaped mitocondrion. The interrelationships between Sciaenidae and Polynemidae as well as between these two families and other Percoidei are herein discussed.     

Sperm ultrastructure in the marine bivalve families Carditidae and Crassatellidae and its bearing on unification of the Crassatelloidea with the Carditoidea

An investigation of sperm ultrastructure in representatives of the marine bivalve families Carditidae (Carditoidea) and Crassatellidae (Crassatelloidea) reveals features o f taxonomic significance. Spermatozoa of Cardita muricata (Carditidae) and Eucrassatella cumingii, E. kingicola, Talabrica aurora (Crassatellidae) differ from the classic aquasperm type in having an elongate acrosomal vesicle and elongate nucleus. In addition, the midpiece region in these species is composed of a distinctive, and here considered t o be apomorphic. arrangement of 8 (rarely 7 or 9), tightly abutted mitochondria grouped around ii dense rod which is continuous with the distal centriole (basal body). A recognizable (i.e. triplet-substructure) proximal centriole is therefore absent in mature spermatozoa of crassatellids and carditids. This situation contrasts with the presence of an unmodified proximal centriole in the spermatozoa o f all other investigated bivalves. Observations on crassatellid and carditid spermatids indicate that the dense r o d is derived through metamorphosis of the proximal centriole. The shared and highly characteristic midpiece features of spermatozoa of the Crassatellidae and Carditidae clearly indicate ii close relationship between these families and support the unification of the Crassatelloidea and Carditoidea into a single superfamily Carditoidea Fleming. 1820 (date priority over Crassatelloidea Férussac. 1822).     

Spermatozoa morphology and ultrastructure in Nile perch,Lates niloticus (Linnaeus, 1758)

Lates niloticus is a valuable commercial fish species with good potential for aquaculture. However, there is limited information on the type and structure of the Nile perch spermatozoon, which could potentially aid in culture of this species. Here, we describe the spermatozoon ultrastructure in L. niloticus using transmission and scanning electron microscopy. The spermatozoon had a round head-shape, medio-laterally flat, no acrosome, a short midpiece located laterally to the nucleus, uniflagella with one wing. The head of the spermatozoon contained the nucleus, centriolar system, proximal part of the flagellum, and cytoplasmic channel. Centrioles were arranged at an angle of 90° to each other, forming a T-shape, parallel to the nucleus. The midpiece was cylindrical, loaded with cytoplasm, five to seven spherical mitochondria; and the flagellum’s plasma membrane extended to form one lateral wing. The spermatozoa were classified as type II spermatozoa. L. niloticus spermatozoon differed from that of its Australian congener L. calcarifer, especially in the centriole arrangement and nuclear shape, length of the midpiece and the number of mitochondria and lateral wings.     

Morphology and fine structure of Barbus barbus (Teleostei: Cyprinidae) spermatozoa

Morphology and fine structure of Barbus barbus L 1758 spermatozoa were studied using scanning (SEM) and transmission (TEM) electron microscopy. The results confirm that spermatozoa exhibit morphological features typical to all teleost fishes. They are differentiated into a head, a midpiece and a flagellum with the typical '9 + 2' pairs of microtubules. Both dynein arms are present in the flagellum. The spermatozoa have spherical nuclei, 4–6 mitochondria located in the postnuclear cytoplasmic region and centriolar complex (proximal and distal centrioles). Total length, head width, length of midpiece and length of flagellum were measured to be 56.35 ± 7.42, 1.80 ± 0.06, 0.48 ± 0.14 and 54.30 ± 6.97 μm, respectively. Highly significant linear correlation was observed between posterior and anterior width of midpiece (P < 0.01). Principal component analysis (PCA) was used to explore which parameters can explain the individual variation of sperm morphology. About 44% of the total accumulated variance was absorbed by the analysis of the two first components, distinguishing different groups of parameters related to head and midpiece. The lengths of flagellum and head are more isolated; indicating that the individual variation of sperm morphology depends on these two parameters. Comparing the results of this study with information on cyprinids spermatozoa reveals that the number of mitochondria and the length of the flagellum are good characters to characterize spermatozoa of the Cyprinidae in a phylogenetic arrangement.     

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.     

Four lines of spermatid development and dimorphic spermatozoa in the sea urchin Anthocidaris crassispina (Echinodermata, Echinoida)

 The process of sperm development in the sea urchin Anthocidaris crassispina was studied by light and electron microscopy. Similar to other echinoids studied, a single flagellum, striated rootlet and nuage-like materials were present in spermatogonia of A. crassispina. Spermatocytes near the diplotene stage showed intracellular localization of the axoneme which appeared to be a retracted flagellum prior to cell division. Fibrous filaments were associated with a proximal centriole in spermatocytes and spermatids and might be involved in movement of the proximal centriole. An acrosomal vesicle was developed and a residual body was formed in spermatids. The special development patterns in A. crassispina attributed to the presence of two patterns of tail development and two patterns of mitochondrial development during spermiogenesis. These four lines of spermiogenesis resulted in the formation of four morphological types of sperm cell, i.e. sperms with: (1) a symmetrical midpiece and posterior tail, (2) an asymmetrical midpiece and posterior tail, (3) a symmetrical midpiece and bent tail and (4) an asymmetrical midpiece and bent tail. Sperm cells with bent tails (type 3+4) were probably still at the late spermatid stage because results of scanning electron microscopy demonstrated gradual detachment and eventual straightening of the bent tail, and their percentage occurrence in the sperm population decreased significantly (P<0.05) towards the spawning season of A. crassispina. Spermatozoa with a symmetrical midpiece were dominant (averaging 70% occurrence in the sperm population) over those with an asymmetrical midpiece. The dimorphic spermatozoa in A. crassispina (types 1, 2) are both considered to be euspermatozoa as their morphology is typical for Echinoida. Accepted: 4 May 1998     

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.     

Spermatozoon structure and motility in the anuran Lepidobatrachus laevis

Synthetic human gonadotropin releasing hormone (GnRH) injections were used for induction of spermatozoon release followed by cloacal lavage or mechanical stimulation of sperm release in Lepidobatrachus laevis . Light microscopic observations of Lepidobatrachus laevis spermatozoa indicated an acrosomal segment with a length of 4.1 μm delineated by an indentation, a nuclear region of 12.6 μm in length and a midpiece of 0.87 μm in length. The tail was 54.9 μm long by 1.35 μm wide with two lateral axial fibers and a central undulating membrane. At the electron microscopic level, the unusual tail had two complete axonemes that emanated from the distal centriole. The tail also contained two axial fibers 77 nm in diameter medial to the axonemes and was connected by an undulating membrane. An unusual accessory cell adherent to the head of the spermatozoon was noted in freshly obtained suspensions of spermatozoa. Spermatozoa with the accessory cell were motile and a subsequent loss of motility was correlated with the shedding of the accessory cell.     

Ultrastructure of the spermatozoon of Apus apus (Linnaeus 1758), the common swift (Aves; Apodiformes; Apodidae), with phylogenetic implications

The spermatozoon of Apus apus is typical of non‐passerines in many respects. Features shared with palaeognaths and the Galloanserae are the conical acrosome, shorter than the nucleus; the presence of a proximal as well as distal centriole; the elongate midpiece with mitochondria grouped around an elongate distal centriole; and the presence of a fibrous or amorphous sheath around the principal piece of the axoneme. The perforatorium and endonuclear canal are lost in A. apus as in some other non‐passerines. All non‐passerines differ from palaeognaths in that the latter have a transversely ribbed fibrous sheath whereas in non‐passerines it is amorphous, as in Apus, or absent. The absence of an annulus is an apomorphic but homoplastic feature of swift, psittaciform, gruiform and passerine spermatozoa. The long distal centriole, penetrating the entire midpiece, is a remarkably plesiomorphic feature of the swift spermatozoa, known elsewhere only in palaeognaths. The long centriole of Apus, if not a reversal, would be inconsistent with the former placement of the Apodiformes above the Psittaciformes from DNA–DNA hybridization. In contrast to passerines, in A. apus the microtubules in the spermatid are restricted to a transient single row encircling the cell. The form of the spermatozoon fully justifies the exclusion of swifts from the passerine family Hirundinidae.     

Ultrastructural study of spermiogenesis and the testicular and spermathecal spermatozoon of the Gonochoristic Tardigrade Xerobiotus pseudohufelandi (Eutardigrada,Macrobiotidae)

This paper investigates by scanning and transmission electron microscopy spermiogenesis and spermatozoon morphology of the gonochoristic eutardigrade Xerobiotus pseudohufelandi (Macrobiotidae). During spermiogenesis clusters of spermatids are connected by cytoplasmic bridges that persist up to an advanced stage of maturation. Spermiogenesis is characterized by distinctive modifications of the nucleus and by the differentiation of an acrosome, tail and substantial midpiece. Testicular spermatozoa are folded with the hinge located between the head and midpiece, thus resembling a nut-cracker. The head includes a rod-shaped, bilayered acrosome and an elongated, helicoidal nucleus with condensed chromatin. The large kidney-shaped midpiece has hemispherical swellings/ovoid elements surrounding the centriole and an incomplete mitochondrial sleeve. The flagellum contains a ‘9+2’ axoneme and terminates in a tuft of microtubules. Spermathecal spermatozoa always have linear profiles. The acrosome and nucleus have the same morphological pattern as in testicular spermatozoa, whereas the midpiece is thin and lacks the hemispherical swellings, and the tail is reduced to a short stub. Functional considerations are presented, based upon this different morphology. Moreover, phyletic comparisons are made on the basis of sperm morphology, both for the family Macrobiotidae and the class Eutardigrada. J. Morphol. 234:11–24, 1997. © 1997 Wiley-Liss, Inc.     

Structure and formation of the unusual sperm of Patelloida latistrigata (Mollusca : Patellogastropoda): implications for fertilization biology

The structure of the spermatozoa and spermatogenesis of the lottiid limpet Patelloida latistrigata is described by transmission electron microscopy. Although the lengths of the spermatozoa (about 60 μm) and their head region (about 12 μm) are similar to those of other patellogastropods, the structure of the sperm head and midpiece are very different. The head consists of an unusually large acrosome (about 11-μm long) with a broad posterior invagination that houses the relatively small nucleus. The midpiece mitochondria, which are rather elongate with large folded tubular cristae, are housed in a cytoplasmic sheath posterior to the nucleus. The proximal centriole is unusually elongate (about 2-μm long). The axoneme that emerges from the distal centriole is surrounded anteriorly by the cytoplasmic sheath in which the cytoplasmic side of the plasma membrane has electron-dense material. The flagellum is enlarged at its terminal end. Spermatogenesis is similar to that described for other patellogastropods. Patelloida latistrigata, therefore, has spermatozoa that seem to meet the morphological criteria of ent-aquasperm, which raises the question of whether fertilization is truly external in this limpet. However, it is also possible that the modifications to the sperm are linked to unknown specializations of the egg or egg envelope.     

The ultrastructure of the spermatozoa of Boa constrictor occidentalis, with considerations on its mating system and sperm competition theories

Sperm ultrastructure has been described for several families of Squamata in which it has been considered a valuable character source for phylogenetic studies. However, sperm competition and mating systems have been demonstrated to influence variations in the sperm morphology and dynamics. The mating system of Boa constrictor occidentalis is likely to have a high degree of sperm competition. We investigated, for the first time, the ultrastructure of the spermatozoa of B. c. occidentalis and, thus, of the family Boidae. Active mating groups were captured from the field, and the spermatozoa of the males was collected by ejaculation and processed to obtain transmission electron micrographs and fluorescence micrographs. The spermatozoa are filiform and their morphology fits the general model described for snakes, and several synapomorphies belonging to the squamates can be identified in these cells. Nevertheless, the head is 25% longer and the midpiece presents a lower frequency of mitochondrial transformations than that of other snakes. We propose that this last trait, along with the extraordinary elongation of the midpiece and the system of multilaminar membranes covering this section (both synapomorphies of the snake spermatozoa), are adaptive responses to processes of sperm competition and sperm storage.     

Spindle formation and cleavage in Xenopus eggs injected with centriole-containing fractions from sperm

The eggs of Xenopus laevis are capable of initiating spindle formation and cleavage in response to microinjection of partially purified components of sea urchin sperm. High activity was assayed from a sperm head fraction obtained after removal of the plasma and nuclear membranes, acrosome, midpiece mitochondrion, and tail. Chromatin, the basal plate, and the distal centriole comprised the components of the head fraction. Disruption of the chromatin did not impair activity and purified chromatin lacked activity, suggesting the centriole and basal plate as the active materials. Low doses of active material induced apparently normal cleavage at 90 min after injection, with 16% of the eggs reaching the late blastula stage. High doses of active material induced precocious multiple cleavage, with some eggs cleaving into 3–10 segments within 20 min after injection. These eggs contained numerous spindles and asters in the animal hemisphere, as judged by light microscopy of stained sections. Microinjection of eggs is presented as a semi-quantitative bioassay for agents initiating spindle formation and cleavage.     

The fate of the normal-anucleated spermatozoa in inseminated females of the silkworm Bombyx mori

Both typical (haploid) and atypical (anucleated) spermatozoa reach the receptaculum seminis of inseminated females of Bombyx mori intermingled. However, only typical spermatozoa both leave the receptaculum and fertilize the eggs. Atypical spermatozoa, which are in fact anucleated flagellar apparatuses, probably function in transporting typical fertilizing spermatozoa to the receptaculum seminis. In the male ejaculatory duct both kinds of spermatozoa are wrapped with extra-cellular sleeves that presumably protect them on their way to the receptaculum. Typical spermatozoa “hatch” from the sleeves before leaving the receptaculum to fertilize the eggs. The presence of a centriole in the extra-testicular spermatozoa of this species supports the generalization that insect spermatozoa do have a centriole at the base of the flagellum.     

山羊精子发生不同阶段的显微与超微结构观察

应用光镜和透射电镜技术研究山羊精子发生不同阶段各级生精细胞显微、超微结构及山羊精子分化成熟过程。结果表明：山羊精子发生经历了精原细胞、初级精母细胞、次级精母细胞、精子细胞及变态精子阶段发育成成熟的精子。精原细胞期核呈椭圆形,染色质凝集成团分布于核质中,线粒体开始出现;精母细胞期有高尔基体分布;精子细胞经过核质浓缩、线粒体迁移等过程发育成成熟精子,成熟的山羊精子头部细长,核质高度浓缩,中段膨大,线粒体丰富。线粒体、中心粒对精子变态发生起重要作用,同时观察到头部与中段脱落的畸形精子。     

蓝尾石龙子精子的超微结构

蓝尾石龙子(Eumeces elegans)附睾以2．5％戊二醛和1％锇酸双重固定,按常规制作超薄切片,用H-600透射电镜研究观察精子的超微结构。精子由头部和尾组成,头部由顶体复合体和核组成,尾由颈段、中段、主段和末段组成。头部的顶体囊前部扁平,分为皮质和髓质,顶体下锥由类结晶状的顶体下物质组成,穿孔器顶端尖,、穿孔器基板塞子状,细胞核延长,核内小管缺,核伸展部前端具一电子透明区,核肩圆,核陷窝锥形。颈段具片层结构,近端中心粒和远端中心粒的长轴呈直角,9束外周致密纤维与远端中心粒相应的9束三联微管相联,向后与轴丝相应的9束双联微管相联,中央纤维与2个中央单微管相联。中段短,含有线状嵴的柱状线粒体,由连续的规则小卵状或小梯形致密体组成线粒体间的环状结构,纤维鞘伸入中段,终环紧贴于细胞膜的内表面。线粒体与环状结构的模式为：rs1／mi1,rs2／mi2,rs3／mi3,rs4／mi4,横切面上每圈线粒体数目为10个。主段前面部分具薄的细胞质颗粒区。纤维3和8至主段前端消失。轴丝复合体呈“9 2”型。蓝尾石龙子精子超微结构与已描述的石龙子科种类比较发现,与蜓蜥群和胎生群的石龙子相似;但没有发现石龙子科精子的独征。     

Spermatozoa of the Anomalodesmata (Bivalvia, Mollusca) with special reference to relationships within the group

Sperm ultrastructure in the marine bivalve order Anomalodesmata is considered in the light of new information for Australian Myochama anomioides and Cuspidaria latesulcata . In M. anomioides , the acrosomal complex lies posterior to the nucleus, in contact with the asymmetrical midpiece mitochondria – an unusual configuration reported from most of the studied Anomalodesmata. Spermatozoa of M. anomioides resemble those of Myadora brevis (both in family Myochamidae). Myochamid spermatozoa are considerably less modified than those of the Lyonsiidae or Laternulidae, and may prove a basal type within the non-septibranch anomalodesmatans. In contrast, C. latesulcata differs from other examined anomalodesmatans in having an anterior acrosomal complex and radial midpiece mitochondria (classic aquasperm features). Sperm data for the Anomalodesmata are limited but congruent with the most recent phylogenetic analyses that recognize distinct 'thraciid' and 'lyonsiid' clades. Results for C. latesulcata suggest septibranch origins before the development of a posteriorly positioned acrosomal complex and mitochondrial asymmetry.     

Sperm entry into zona-free oocytes in the hamster oviduct: Implications for the mechanisms of acrosome reaction induction

The possible importance of the zona pellucida for induction of the acrosome reaction (AR) and establishment of sperm/egg associations in the fallopian tube was investigated by instilling zona-free eggs into the oviductal ampulla of hamsters that had been inseminated with epididymal spermatozoa 6–7 hours previously. The eggs were recovered only 60–90 minutes later because of increasing difficulty with time of collecting zona-free eggs from the oviduct. In the zona-free group, 41 (4%) of 1,101 transferred eggs were recovered, of which 20% contained spermatozoa with decondensing nuclei (mean 4.4/egg). A similar (22%) fertilization rate (mean 3.2 spermatozoa/egg) was found among intact (control) eggs recovered after instillation into the contralateral oviduct. Mammalian spermatozoa are not incorporated even into zona-free eggs before AR occurs. These results thus demonstrate that an AR in functional hamster spermatozoa in vivo and establishment of sperm/egg associations in vivo require no interaction with the zona pellucida nor with other products of ovulation.     

Differential distribution of tubulin epitopes in human spermatozoa

Two monoclonal antibodies (16 D3 and 24 E3) were used to map tubulin domains in human spermatozoa by indirect immunofluorescence. Their specificity to tubulin in these cells was established by Western blotting. Whereas 16 D3 uniformly stained the principal piece of the flagellum, the staining provided by 24 E3 decreased along the tail to become very weak 30 micron further away from the midpiece. This latter antibody also reacted with the proximal centriole as well as the midpiece, but not all spermatozoa stained identically at this level indicating heterogeneity within the population of sperm cells from a given donor. 16 D3 reacted weakly with the head, and the staining was interrupted after a bright spot in the neck. The study of a pathological case (the short tail spermatozoon) with an abnormal arrangement of dense fibers was consistent with a correlation between the distribution of the epitope defined by 24 E3 and that of peri-axenomal structures. The existence of tubulin domains interacting with these structures is postulated.