Spermatogenesis In Fish Research Articles

Testis structure, spermatogenesis, spermatocytogenesis, and sperm structure in cardinal fish (Apogonidae, Perciformes)

The testes in all 16 of the studied cardinal fish species are shown to be bilobed, with spermatogonia dispersed throughout the gametogenic epithelium of the seminiferous tubules. Each testicular lobe is covered luminally by an epithelium consisting of primary germ cells and Sertoli cells. At maturation the seminiferous tubules reach around 0.6-2.3 mm in length. They number from 60 in the smallest species to over 300 in the largest one, increasing both in dimension and number with increase in length of the male, and are species-specific. The highest number of spermatogonia is found at the apical ends of the tubules. During maturation extensions of Sertoli cells surround single or small groups of B-spermatogonia, forming the spermatocysts, the final dimensions of which reflect the final number of contained spermatozoids. Back-calculations of serial sections reveal that within the spermatocysts the spermatogonia undergo eight generations of mitotic divisions before the first and second meiotic divisions and formation of spermatids. The largest mature spermatocysts in large species attain around 180 microm in diameter, a volume of 25 mm(3), and contain around 8,200 spermatids. The total volume of sperm in the mature spermatocysts leaves enough space for the discarded cytoplasm and developing flagella. The bursting cysts liberate the ripe sperm and maturing spermatids, into the tubule lumen and spermduct, with the spermatids often still connected by cytoplasm bridges. The sperm, with one or two flagella, features round or oval heads and a cytoplasmic collar bearing a few mitochondria. The percentage of biflagellate or monoflagellate sperm differs in proportion in males of different lengths and in different species. Differences in spermatogenesis of small and larger species of cardinal fish are discussed.

Differential expression of vasa RNA and protein during spermatogenesis and oogenesis in the gibel carp (Carassius auratus gibelio), a bisexually and gynogenetically reproducing vertebrate

The RNA helicase Vasa is a germ cell marker in animals, and its homolog in vertebrates to date has been limited to bisexual reproduction. We cloned and characterized CagVasa, a Vasa homolog from the gibel carp, a fish that reproduces bisexually or gynogenetically. CagVasa possesses 14 RGG repeats and eight conserved motifs of Vasa proteins. In bisexually reproducing gibel carp, vasa is maternally supplied and its zygotic expression is restricted to gonads. By in situ hybridization on testicular sections, vasa is low in spermatogonia, high in primary spermatocytes, reduced in secondary spermatocytes, but disappears in spermatids and sperm. In contrast, vasa persists throughout oogenesis, displaying low-high-low levels from oogonia over vitellogenic oocytes to maturing oocytes. A rabbit anti-Vasa antibody (alphaVasa) was raised against the N-terminal CagVasa for fluorescent immunohistochemistry. On testicular sections, Vasa is the highest in spermatogonia, reduced in spermatocytes, low in spermatids, and absent in sperm. In the ovary, Vasa is the highest in oogonia but persists throughout oogenesis. Subcellular localization of vasa and its protein changes dynamically during oogenesis. The alphaVasa stains putative primordial germ cells in gibel carp fry. It detects gonadal germ cells also in several other teleosts. Therefore, Cagvasa encodes a Vasa ortholog that is differentially expressed in the testis and ovary. Interestingly, the alphaVasa in combination with a nuclear dye can differentiate critical stages of spermatogenesis and oogenesis in fish. The cross-reactivity and the ability to stain stage-specific germ cells make this antibody a useful tool to identify fish germ cell development and differentiation.

SEX STEROIDS AND SPERMATOGENESIS IN THE AFRICAN CATFISH (CLARIAS GARIEPINUS)

Little is known about the physiological regulations of spermatogenesis of the African catfish (Clarias gariepinus), a species used as an experimental model for two decades. After a brief introduction to the cystic type of spermatogenesis in fish, the role of androgens and estrogens will be discussed, leading to a conclusion that androgens are required for spermatogenesis while their mode of action is poorly understood. In the cystic mode of spermatogenesis in fish, the Sertoli cells are formed cystic, in the somniferous lobules enclosing a single germ cell clone, providing suitable experimental models to address questions of relevance for vertebrate spermatogenesis in general.

Endocrine changes during onset of puberty in male spring Chinook salmon, Oncorhynchus tshawytscha.

In male salmonids, the age of maturation varies from 1 to 6 years and is influenced by growth during critical periods of the life cycle. The endocrine mechanisms controlling spermatogenesis and how growth affects this process are poorly understood. Recent research has indicated that gonadotropins, 11-ketotestosterone, and insulin-like growth factor I play roles in spermatogenesis in fish. To expand our understanding of the roles of these endocrine factors in onset of puberty, male spring chinook salmon (Oncorhynchus tshawytscha) were sampled at monthly intervals 14 mo prior to spermiation. This sampling regime encompassed two hypothesized critical periods when growth influences the initiation and completion of puberty for this species. Approximately 80% of the males matured during the experimental period, at age 2 in September 1999. An initial decline in the ratio of primary A to transitional spermatogonia was observed from July to December 1998, and during this period plasma levels of 11-ketotestosterone and pituitary levels of FSH increased. From January 1999 onward, males with low plasma 11-ketotestosterone levels (<1 ng/ml) had low pituitary and plasma FSH levels and no advanced development of germ cells. Conversely, from January through September 1999, males with high plasma 11-ketotestosterone levels (>1 ng/ml) had testes with progressively more advanced germ cell stages along with elevated pituitary and plasma FSH. Plasma levels of insulin-like growth factor I increased during maturation. These data provide the first physiological evidence for activation of the pituitary-testis axis during the fall critical period when maturation is initiated for the following year.

Spermatogenesis in teleost: insights from the Nile tilapia (Oreochromis niloticus) model

The morphometric study of spermatogenic cysts in sexually mature tilapias, during the evolution of spermatogenesis, showed a dramatic increase in both number of germ cells and cyst volume. However, the opposite trend was observed for germ cell size. Nevertheless, the number of Sertoli cells increased gradually up to leptotene/zygotene cysts, stabilizing thereafter. Based on the number of spermatids supported by each Sertoli cell and compared to mammals, Sertoli cell efficiency in tilapias is remarkably high. Sertoli cell proliferation was frequently observed, mainly in spermatogonial cysts, and probably is the major factor related to the testis growth and the increase in sperm production that normally occurs in adult tilapias. The combined duration of spermatocytes (5 days) and spermiogenic (5–6 days) phases of spermatogenesis in fish kept at 25 ◦ C was 10–11 days. Mainly due to acceleration in meiosis, these two phases lasted a total of 6 days in tilapias kept at 30 ◦ C, in the opposite way, at 20 ◦ C spermatogenesis was arrested at pachytene spermatocytes. To our knowledge, this is the most comprehensive investigation performed up to date on testis morphometry and function in adult tilapias.

Molecular control mechanisms of fish spermatogenesis

Fish spermatogenesis, from spermatogonial stem-cell renewal to sperm maturation, is controlled by the sex steroid hormones. Mitotic divisions of spermatogonia can be categorized by spermatogonial stem cell renewal and spermatogonial proliferation. Spermatogonial renewal is regulated by estradiol-17β (E2; the natural estrogen in vertebrates), and spermatogonial proliferation toward meiosis is promoted by 11-ketotestosterone (11-KT), the main androgen in teleost. The action of E2 and 11-KT is mediated by other factors produced by Sertoli cells; E2 is mediated by spermatogonial stem-cell renewal factor and 11-KT is mediated by spermatogenesis preventing substance and activin B. Although 11-KT also induce meiosis and spermiogenesis, the control mechanisms of these processe are not clear. After spermiogenesis, immature spermatozoa undergo sperm maturation. Sperm maturation is regulated by 17α,20β-dihydroxy-4-pregnen-3-one (DHP), which is progestin in teleost. The DHP acts directly on spermatozoa to active the carbonic anhydrase existed in the spermatozoa. This enzymatic activation causes an increase in the seminal plasma pH, enabling spermatozoa to motile.

Gonadosomatic index and testis morphology of common carp (Cyprinus carpio) in rivers contaminated with estrogenic chemicals.

To study the effect of estrogenic chemicals on fish, the gonadosomatic index (GSI = [testis weight/body weight] x 100) and testis histology of mature common carp (Cyprinus carpio) from 2 contaminated sites (Ishizu and Wada rivers, Osaka) and a control site were examined between June 1998 and March 2001. The concentration of nonylphenol, bisphenol A and 17beta-estradiol in the Ishizu river was 3-4 times higher than in the Wada river. In the pre-breeding and breeding seasons, there were no significant differences in body weight among carp from the 3 sites, the body weight of Ishizu river carp being significantly lower (p<0.05) than that of Wada river fish only in the post-breeding season. The GSI and testis weight in fish from the Ishizu river were significantly lower (p<0.05) than in control fish during all phases of gonadal cycle and lower than in Wada river fish in the pre-breeding and post-breeding season. No histological abnormalities were found in the testes of the males examined. Histological observation of the testes revealed a delay in the onset of spermatogenesis in fish from the Ishizu river compared with those from the other sites. These results clearly imply that the estrogenic chemicals in the Ishizu river adversely affect the testis development of the fish.

Serum vitellogenin levels and reproductive impairment of male Japanese Medaka (Oryzias latipes) exposed to 4-tert-octylphenol.

The induction of synthesis of the "female" yolk precursor protein vitellogenin (VTG) in male fish by estrogenic chemicals in the environment has been demonstrated in many recent reports. However, little is known about the organismal and biological significance of this phenomenon. To examine the relationship between VTG production in male fish and reproductive impairment, adult male medaka were exposed to 4-tert-octylphenol (OP), a known environmental estrogen, in concentrations ranging from 20 to 230 ppb for 21 days, under flow-through conditions. Following exposure, male fish were mated, in the absence of OP, with unexposed females. Breeding groups composed of exposed males and control females produced about 50% fewer eggs than control groups. VTG levels in serum of male fish increased with increasing OP exposure concentration and decreased after OP exposure was discontinued. Nevertheless, significant correlations (p<0.01) were observed between VTG levels in exposed male fish and 1) OP exposure concentrations, 2) percent of fertilized eggs, and 3) survival of embryos. OP-induced VTG synthesis and reproductive impairment appear to be closely linked phenomena. Histological examination indicated spermatogenesis in OP-exposed fish was inhibited, and some exposed fish had oocytes in their testes. Finally, OP caused a significant increase in the number of abnormally developing embryos, suggesting that OP may be genotoxic as well as estrogenic.

Serum Vitellogenin Levels and Reproductive Impairment of Male Japanese Medaka (Oryzias latipes) Exposed to 4-tert-Octylphenol

The induction of synthesis of the "female" yolk precursor protein vitellogenin (VTG) in male fish by estrogenic chemicals in the environment has been demonstrated in many recent reports. However, little is known about the organismal and biological significance of this phenomenon. To examine the relationship between VTG production in male fish and reproductive impairment, adult male medaka were exposed to 4-tert-octylphenol (OP), a known environmental estrogen, in concentrations ranging from 20 to 230 ppb for 21 days, under flow-through conditions. Following exposure, male fish were mated, in the absence of OP, with unexposed females. Breeding groups composed of exposed males and control females produced about 50% fewer eggs than control groups. VTG levels in serum of male fish increased with increasing OP exposure concentration and decreased after OP exposure was discontinued. Nevertheless, significant correlations (p&lt;0.01) were observed between VTG levels in exposed male fish and 1) OP exposure concentrations, 2) percent of fertilized eggs, and 3) survival of embryos. OP-induced VTG synthesis and reproductive impairment appear to be closely linked phenomena. Histological examination indicated spermatogenesis in OP-exposed fish was inhibited, and some exposed fish had oocytes in their testes. Finally, OP caused a significant increase in the number of abnormally developing embryos, suggesting that OP may be genotoxic as well as estrogenic.

魚類精子形成の分子制御機構

魚類精子形成の分子制御機構

Peculiarities in the organization of testis of Ophidian sp. (Pisces Teleostei). Evidence for two types of spermatogenesis in teleost fish

The walls of lobules in the testis of Ophidion sp. are composed of Scrtoli cells and young germinal cells (spermatogonia and spermatocytes). Spermatocytes are linked by cytoplasmic bridges. The associations of Sertoli cells and spermatocytes constitute true cysts. Meiosis takes place in the cysts. When meiosis is complete, cysts open. Spermatids are released into the lumen of the lobules and the cyloplasmic bridges break down. Spermiogenesis occurs in the lumen. Spermatids at various levels of spermiogenesis are then mixed with ripe spermatozoa. In teleosts we thus recognize two types of spermatogenesis: a cystic type where spermatogenesis is completed within cysts, and leads to synchronous development of germ‐cells; and a semi‐cystic type, where spermatogenesis occurs partly outside cysts. This may produce asynchronous spermatogenesis.

Peculiarities in the organization of testis of Ophidion sp. (Pisces Teleostei). Evidence for two types of spermatogenesis in teleost fish

Peculiarities in the organization of testis of Ophidion sp. (Pisces Teleostei). Evidence for two types of spermatogenesis in teleost fish

In vivo and in vitro evidence for the role of hormones in fish spermatogenesis

AbstractIn an attempt to discern general mechanisms by which specific hormones control certain aspects of fish spermatogenesis, we focus on a single fish species (Fundulus heteroclitus), and, by analogy, generalize to other fishes. At least three androgenic steroids (testosterone, 11‐ketotestosterone, 11β‐hydroxytestosterone) are present in the serum of Fundulus heteroclitus, but only testosterone appears to be associated with spermatogenesis in vitro as well as in vivo. 11‐Ketotestosterone appears to be associated with spermiation in vivo, but has not yet been tested for its ability to cause spermiation in vitro. The preponderant androgen present in the serum, 11β‐hydroxytestosterone, does not appear to be directly associated with spermatogenic process either in vitro or in vivo.In F. heteroclitus, in vivo studies indicate that at least two different gonadotropins are produced, on that primarily causes steroid production and a second that causes testicular growth. Indirect evidence suggests that production of these gonadotropins is seasonal in terms of both their amounts and their relative proportions.

Effects of Coal Leachates on Fish Spermatogenesis

Coal leachates were examined for toxic effects on fish spermatogenesis. Nonbreeding mummichogs, Fundulus heteroclitus, were induced to enter breeding condition in the laboratory by exposure to 20 °C and a photoperiod of 16L: 8D for 6 wk. During this 6-wk period, mummichogs were dosed in static exposure tanks with water extracts of coal (leachates). Chi-square analysis and Z test of proportions revealed a significant reduction in sperm production by fish exposed to some, but not all, coal leachates. This reduction was as much as 40-fold and occurred in a dose-dependent manner. Ordinarily, nonbreeding mummichogs collected immediately after the breeding season will not enter breeding condition in response to 16L: 8D and 20 °C. Exposure of these photo-insensitive mummichogs to coal leachates under long photoperiod conditions for 8 wk resulted in a significant increase in sperm production. Analysis of weekly sperm production by mummichogs from six field populations, either adjacent to or 2 miles upstream from coal-fired power plants, did not reveal significant differences during the breeding season. However, this sperm production was less than 1/10 that of a mummichog field population sampled concomitantly at the Chesapeake Bay Institute. The reduced sperm levels could not be related to reproductive toxin(s) contained in coal leachate.

Ultrastructure of primary spermatocyte in fish (Tilapia: Oreochromis niloticus): The synaptonemal complex

The Primary Spermatocytes represent a stage in spermatogenesis when the first meiotic cell division occurs. They are derived from Spermatogonium or Stem cell through mitotic division. At the zygotene phase of meiotic prophase the Synaptonemal complex appears in these cells in the space between the paired homologous chromosomes. Spermatogenesis and sperm structure in fish have been studied at the electron microscope level in a few species? However, no work has yet been reported on ultrastructure of tilapia, O. niloticus, spermatozoa and spermatogenetic process. In this short communication we are reporting the Ultrastructure of Primary Spermatocytes in tilapia, O. niloticus, and the fine structure of synaptonemal complexes seen in the spermatocyte nuclei.

Endocrine Control of Spermatogenesis in Teleost Fish

Very different testicular structures and spermatogenetic patterns have been found in fish of the teleost group. Two types of structures may be identified: (i) a tubular type with no lumen (in cyprinodonts); the cysts migrate from the blind end to the vas efferens during the process of spermatogenesis; (ii) a lobular type having a central lumen receiving the spermatozoa released from cysts which remain stationary along the lobule during spermatogenesis. Different spermatogenetic patterns are distinguished in salmonids and cyprinids. In the latter (carp, Cyprinus carpio, and goldfish, Carassius auratus), some germ cell types (e.g. type B spermatogonia and spermatozoa) are present throughout the year, allowing nearly continuous production of good-quality sperm. Studies of their endocrine patterns suggest that the GTH involved is controlled by external (mainly temperature but also photoperiod) and gonadal factors. The GTH stimulates androgen production and eventually controls spermatogenesis and spermiation. In salmonids, the two major events of the testicular cycle, spermatogenesis and spermiation, are temporally separated by a stage of spermatozoal "maturation" during which the spermatozoa undergo physiological changes. Sperm quality declines during the period of spermiation. The initiation of a new spermatogenetic cycle seems possible only when the spermatozoa have been eliminated from the testis, either by the normal process of spermiation or by intratesticular resorption. This also illustrates the spatial independence of spermatogenesis and spermiation. The endocrine pattern of spermatogenesis in salmonids is similar to that in carp but seems different as regards spermiation. This spermiation process includes two steps, initiation and amplification, which require different GTH levels and steroid balance. Among the steroids, 11-ketotestosterone is the major androgen found in the plasma, but its superiority over other androgens in regard to spermiation remains to be demonstrated. Environmental factors (photoperiodic changes and temperature) may act directly on the central nervous system to control gonadotropin secretion. Temperature may also directly influence the gonad, somatic or germ cells, and steroid metabolism which acts either locally on the gonad or more centrally. The regulation of spermatogenesis in fish appears to be more subtle than previously believed. Major unknowns are whether there is a second GTH and, if so, its site of action; which steroids are directly involved in the control of spermatogenesis in the lobules, and which are the target cells; and which factors regulate testicular size and which pituitary GTH secretion. Finally, the poor yield of spermiation is intriguing and requires further study, considering its practical implication in fish-farming.Key words: spermatogenesis, teleosts, salmonids, cyprinids

Cellular Organization of the Testis and Spermatogenesis in Fishes

Synopsis. Tubular structure of the teleost testis can be divided into two basic types distinguished from each other by the distribution of spermatogonia. In most teleosts, spermatogonia occur along the length of the tubules, but in atheriniform fishes they are confined to the terrriinus of the tubule. Variations in these testis-types are discussed particularly in light of modifications leading to the production of spermatozeugmata or spermatophores. Teleost boundary are located immediately outside of the tubule basement mem? brane. Previous reports homologizing lobule boundary cells with Leydig or Sertoli are in error. Leydig have been described for species of teleosts wherein they have previously been thought to be absent and are a typical component of the interstitium. Sperm morphology reflects mode of reproduction. Nuclear elongation, coupled with possible elongation of the sperm midpiece, is characteristic of most species wherein fer? tilization is internal. Teleost sperm lack an acrosome.

Fractionation of somatic and sperm chromatin during spermatogenesis in fish

A new approach is suggested for studying changes in the interactions of protein with DNA in the cells. Measurements of the buoyant density of chromatin were performed in somatic cells and in cells undergoing meiosis in fish. During the process of spermatogenesis some of the somatic histones on the DNA are replaced by a new class of proteins; consequently, the mature sperm contains a unique type of protein having a low mol. wt and a high proportion of arginine. The chromatin obtained from mature sperm is composed of a single component with a density of 1.48–1.49 g/cm 3 as measured by CsCl equilibrium sedimentation. On the other hand, somatic cells contain chromatin with lower densities. Chromatin obtained from erythrocytes contains a single component with a density of 1.41–1.42 g/cm 3 while liver chromatin shows two components; a main component with a density of 1.45–1.46 and a more heterogeneous component with a lighter density (1.32–1.35). There is a correlation between the buoyant density of the chromatin, the type of its basic proteins and the level of biosynthetic activity in the cells.

Chronology of spermatogenesis and spermiogenesis in poeciliid fishes

AbstractAnalysis by autoradiography after a single pulse label with 3H‐thymidine was used to mark the chronology of cell progression through spermatogenesis and spermatid differentiation in the ovoviviparous teleost fish, Poecilia sphenops, the aquarists' “black molly.” A minimum of 21 days was required from initiation of meiotic prophase to the development of mature, aggregated sperm. An additional two weeks elapsed during transport of sperm through testicular ducts, so that shed spermatophores with labeled sperm were found only after 35 or more days following isotope injection. Time estimates for various stages of spermiogenesis were independently confirmed by assessment of the duration of elapsed time using frequency of occurrence of particular stages within the total population of testicular crypts as an index of relative elapsed time.

Biosynthesis of protamine during spermatogenesis in salmonoid fish

Biosynthesis of protamine during spermatogenesis in salmonoid fish