Ovarian germinal epithelium and folliculogenesis in the common snook, Centropomus undecimalis (Teleostei: centropomidae)

Cloning and expression of the translocator protein (18 kDa), voltage-dependent anion channel, and diazepam binding inhibitor in the gonad of largemouth bass (Micropterus salmoides) across the reproductive cycle

Cholesterol transport across the mitochondrial membrane is rate-limiting for steroidogenesis in vertebrates. Previous studies in fish have characterized expression of the steroidogenic acute regulatory protein, however the function and regulation of other genes and proteins involved in piscine cholesterol transport have not been evaluated. In the current study, mRNA sequences of the 18 kDa translocator protein (tspo; formerly peripheral benzodiazepine receptor), voltage-dependent anion channel (vdac), and diazepam binding inhibitor (dbi; also acyl-CoA binding protein) were cloned from largemouth bass. Gonadal expression was examined across reproductive stages to determine if expression is correlated with changes in steroid levels and with indicators of reproductive maturation. In testis, transcript abundance of tspo and dbi increased with reproductive maturation (6- and 23-fold maximal increase, respectively) and expression of tspo and dbi was positively correlated with reproductive stage, gonadosomatic index (GSI), and circulating levels of testosterone. Testis vdac expression was positively correlated with reproductive stage and GSI. In females, gonadal tspo and vdac expression was negatively correlated with GSI and levels of plasma testosterone and 17β-estradiol. Ovarian dbi expression was not correlated with indicators of reproductive maturation. These studies represent the first investigation of the steroidogenic role of tspo, vdac, and dbi in fish. Findings suggest that cholesterol transport in largemouth bass testis, but not in ovary, may be transcriptionally-regulated, however further investigation will be necessary to fully elucidate the role of these genes in largemouth bass steroidogenesis.

Mechanisms of oocyte development in European sea bass (Dicentrarchus labrax L.): investigations via application of unilateral ovariectomy

Unilateral ovariectomy (ULO) was performed in European sea bass (Dicentrarchus labrax L.) during late pre-vitellogenesis/early vitellogenesis. Plasma steroid levels and the expression of a suite of potential oogenesis-relevant genes in the ovary, brain, and pituitary were evaluated with the aim of understanding their involvement in the compensatory oocyte development occurring within the remaining ovarian lobe. After 69 days of surgery the remaining ovarian lobe in ULO fish was gravimetrically equivalent to an intact-paired ovary of sham operated, control fish. This compensatory ovarian growth was based on an increased number of early perinucleolar oocytes and mid-late stage vitellogenic follicles without an apparent recruitment of primary oocytes into the secondary growth phase. Plasma steroid levels were similar in ULO and control females at all time points analyzed, suggesting an increased steroid production of the remaining ovarian lobe in hemi-castrated females. Results of the gene expression survey conducted indicate that the signaling pathways mediated by Fsh and Gnrh1 constitute the central axes orchestrating the observed ovarian compensatory growth. In addition, steroid receptors, Star protein, Igfs, and members of the transforming growth factor beta superfamily including anti-Mullerian hormone and bone morphogenetic protein 4 were identified as potentially relevant players within this process, although their specific actions and interactions remain to be established. Our results demonstrate that ULO provides an excellent in vivo model for elucidating the interconnected endocrine and molecular mechanisms controlling oocyte development in European sea bass.

Estradiol-17beta treatment induces intersexual gonadal development in the pufferfish, Takifugu rubripes

Estrogens are responsible for most characteristics of the female sex of a species, such as metabolic, behavioral, and morphological changes during reproduction. Artificial estradiol-17beta (E2) treatment Induces sex reversal in some fish. The Japanese pufferfish (Takifugu rubripes) has the most compact genome among vertebrates and great pottial for comparative genome analysis. In this paper, we describe the Influence of E2 treatment during gonadal development in the pufferfish. After hatching, fry were treated with no (control) or a 0.1, 1, 10, or 100 microg/g diet from 21 to 80 days after hatching (dah). Doublesex-mab3-related transcription factor (DMRT1) is Involved in testicular development. VASA is responsible for germ cell development, and CYP19A plays a role in E2 biosynthesis during ovarian development across animal phyla as well as in gonadal morphology after E2 treatment. DMRT1, VASA, and CYP19A were Investigated in the gonads of E2-treated pufferfish. Fish fed with the highest dose (E2 100 microg/g diet) developed Intersexual gonads in the testis; the majority of germ cells were oocytes, but some spermatocytes were detected. RT-PCR results showed the expression of VASA and CYP19A in all intersexual gonads and DMRT1 in some. Furthermore, abnormalities in the epithelium-tunica layer were detected, and gonadal somatic cells (e.g., granulosa cells, theca cells, or germinal epithelium) proliferated extensively in the intersexual gonad. These results suggest that E2 treatment Induces ovarian development in the bipotential gonads of genetic males by modification of gonadal somatic cells and E2 production, mediated by CYP19A.

A new vision of the origin and the oocyte development in the Ostariophysi applied to Gymnotus sylvius (Teleostei: Gymnotiformes)

Based on new knowledge coming from marine perciform species, the origin of oocytes and their development in the Ostariophysi, Gymnotus sylvius is described. In both Gymnotus sylvius and marine perciform fish, oogonia are found in the germinal epithelium that forms the surface of the ovarian lamellae. At the commencement of folliculogenesis, proliferation of oogonia and their entrance into meiosis gives rise to germ cell nests that extend into the stroma from the germinal epithelium. Both cell nests and the germinal epithelium are supported by the same basement membrane that separates them from the stroma. At the time of meiotic arrest, oocytes in a cell nest become separated one from the other as processes of prefollicle cells, these being derived from epithelial cells in the germinal epithelium, gradually encompass and individualize them while also synthesizing a basement membrane around themselves during folliculogenesis. The oocyte enters primary growth while still within the cell nest. At the completion of folliculogenesis, the oocyte and follicle cells, composing the follicle, are encompassed by a basement membrane. The follicle remains connected to the germinal epithelium as the both share a portion of common basement membrane. Cells originating from the stroma encompass the ovarian follicle, except where there is a shared basement membrane, to form the theca. The follicle, basement membrane and theca form the follicular complex. Oocyte development occurs inside the follicular complex. Development is divided into the stages primary and secondary growth, oocyte maturation and ovulation. Cortical alveoli appear in the ooplasm just prior to the beginning of secondary growth, the vitellogenic stage that begins with yolk deposition and proceeds until the oocyte is full-grown and the ooplasm is filled with yolk globules. Maturation is characterized by the germinal vesicle or nuclear migration, germinal vesicle breakdown or nuclear envelop fragmentation and the resumption of meiosis. At the ovulation the egg is released from the follicular complex into the ovarian lumen. When compared to marine Perciformes that lay pelagic eggs, oocyte development in Gymnotus sylvius has fewer steps within the stages of development, the two most remarkable being the absence of oil droplet formation during primary and secondary growth, (and the consequent absence of the oil droplets fusion during maturation), and the hydrolysis of yolf preceding ovulation.

Pharmacological characterization, localization and quantification of expression of gonadotropin receptors in Atlantic salmon (Salmo salar L.) ovaries

The gonadotropins Fsh and Lh interact with their receptors (Fshr and Lhr, respectively) in a highly specific manner in mammals with little overlap in biological activities. In fish, the biological activities seem less clearly separated considering, for example, the steroidogenic potency of both Fsh and Lh. Important determinants of the biological activity are the specificity of hormone-receptor interaction and the cellular site of receptor expression. Here, we report the pharmacological characterization of Atlantic salmon Fshr and Lhr, identify receptor-expressing cells in the ovary, and validate receptor mRNA quantification systems. For the pharmacological studies, we used highly purified coho salmon gonadotropins and found that the Fshr preferentially responded to Fsh, but was also activated by approximately 6-fold higher levels of Lh. The Lhr was specific for Lh and did not respond to Fsh. Photoperiod manipulation was used to generate ovarian tissue samples with largely differing stages of maturation. Specific real-time, quantitative (rtq) PCR assays revealed up to 40-fold (fshr) and up to 350-fold (lhr) changes in ovarian expression levels, which correlated well with the differences in ovarian weight, histology, and circulating oestrogen levels recorded in January and June, respectively. Vitellogenic ovaries were used to localise receptor-expressing cells by in situ hybridization. Granulosa cells of small and large vitellogenic follicles were positive for both receptors. Also theca cells of small and large vitellogenic follicles expressed fshr mRNA, while only in large vitellogenic follicles theca cells were (weakly) positive for lhr mRNA. While only ovulatory Lh levels seem high enough to cross-activate the Fshr, expression by both receptors by granulosa and theca cells suggests that homologous ligand receptor interaction will prevail.

Morphological and histochemical characteristics of the epithelium of ovarian lamellae of Genypterus blacodes (Schneider, 1801)

The physiological significance of the glycoproteins (GPs) secreted by the epithelium of ovarian lamellae is discussed in reference to the reproductive biology of G. blacodes. Histochemical procedures for localising and characterising GPs were used to determine the cytoplasmic components of cells of the epithelium that covers the ovarian lamellae of pink cuskeel, Genypterus blacodes (Schneider, 1801) (Pisces, Ophidiidae), during spawning. This species is one of the most valuable demersal fish resources in the Argentine Sea, mainly due its large size and flesh quality. GPs with oxidizable vicinal diol groups, sialic acid with or without O-acyl substituents, O-acyl sugars, neutral sugars and GPs with carboxyl and sulphate groups were detected. Light microscope examination showed morphological changes in the epithelium of ovarian lamellae during the spawning season, associated with a secretory activity of mucus. Optical density studies revealed the presence of polyploid cells encompassing those morphological changes. Results of the present study suggest that the epithelium of ovarian lamellae of G. blacodes performs a secretory role, which is intensified during ovarian maturity, suggesting that G. blacodes could release masses of eggs enveloped in mucus.

Gonad morphogenesis in vertebrates: divergent means to a convergent end

A critical element of successful sexual reproduction is the generation of sexually dimorphic adult reproductive organs, the testis and ovary, which produce functional gametes. Examination of different vertebrate species shows that the adult gonad is remarkably similar in its morphology across different phylogenetic classes. Surprisingly, however, the cellular and molecular programs employed to create similar organs are not evolutionarily conserved. We highlight the mechanisms used by different vertebrate model systems to generate the somatic architecture necessary to support gametogenesis. In addition, we examine the different vertebrate patterns of germ cell migration from their site of origin to colonize the gonad and highlight their roles in sex-specific morphogenesis. We also discuss the plasticity of the adult gonad and consider how different genetic and environmental conditions can induce transitions between testis and ovary morphology.

Gonad plasticity and gametogenesis in the endangered Spanish toothcarp Aphanius iberus (Teleostei: Cyprinodontidae)

The Spanish toothcarp Aphanius iberus is an endangered species which inhabits small rivers, creeks, salt marshes and marine salt pans in the Mediterranean coast of Spain. No differences in weights were observed among females or males taken from different environments. Analyses of the morphology of the gonads and the gametogenesis were performed in fish taken from different environments by comparing gamete development in females and in males and gonadal cell proliferation in the testis. A high degree of plasticity was observed in the gonad morphology of A. iberus. Females possess two ovaries which show non-restricted oogenesis with all germ cell stages within the same ovigerous lamellae, while males possess gonads without any clear division with the typical restricted pattern observed in cyprinodontid fish. Some females and males showed asymetrically developed gonads. Proliferation of germ cells in testis is located only in the periphery of the gonads corresponding with primary and secondary spermatogonia. Salinity did not influence gonad plasticity or the appearance of mature germ cells in either females or males. This is the first study to provide a microscopic description of oogenesis and spermatogenesis in A. iberus at extreme different environmental conditions.

Germ cells are essential for sexual dimorphism in the medaka gonad

To further elucidate the roles of germ cells in the sex differentiation of gonads, we have used the medaka, a teleost fish, to generate mutants that lack germ cells from the onset of gonadogenesis by the morpholino-mediated knockdown of cxcr4. The resulting germ-cell-deficient medaka show female-to-male sex reversal of their secondary sex characteristics, accompanied by increased levels of androgen and reduced levels of estrogen. A failure to maintain granulosa cells or estrogen-producing cells also occurs at early stages of sex differentiation in the cxcr4 morphants, before the initiation of gonadal morphogenesis. In contrast, androgen-producing cells are unaffected in germ-cell-deficient medaka of either sex. In addition, a single tube-like gonad that expresses male-specific genes is formed in these mutants irrespective of the genetic sex. Significantly, each of these mutant phenotypes occurs in a somatic cell-autonomous manner, suggesting that gonadal somatic cells are predisposed toward male development in the absence of germ cells. This highlights the importance of germ cells in the sexual dimorphism of the gonads.

Morphological aspects of gonadal morphogenesis in Bufo bufo (Amphibia Anura): Bidder's organ differentiation

We have described the architecture of Bidder's organ, defined its compartmented structure, and affirmed the presence of basal laminae. We did not find morphological differences between sexes in Bidder's organ. All specimens initially developed gonads with a peripheral fertile layer surrounding a thin primary cavity. The first oogenetic wave was observed early, showing all phases of meiosis, including leptotene, zygotene, and pachytene, which had been previously thought to be lacking. The peculiar presence of an asynchronous germ cell nest was discussed. Diplotene oocytes issued from the peripheral layer and migrated inside the primary cavity. They were surrounded by a single layer of follicular cells, which originated from the peripheral layer somatic cells and were delimited by a basal lamina. There were few medulla or central layer cells. At the end of metamorphosis, while the oocytes of the first oogenetic wave came into close contact with blood vessels, a second oogenetic wave took place just as the first, except for the presence of synchronous germ cell nests. The central layer was not visible and we did not observe the formation of an ovarian pocket. Stocks of stem germ cells remained in the peripheral layer during both the first and second oogenetic waves. The asymmetric model, in which there is a tendency toward a primary female differentiation, was confirmed. The female differentiation becomes stable in the Bidder's organ because of the absence of further interaction between germ and medullary somatic cells, which would have led toward a male differentiation.

Assembly of ovarian follicles in the caecilians Ichthyophis tricolor and Gegeneophis ramaswamii: light and transmission electron microscopic study

Though much is known about various aspects of reproductive biology of amphibia, there is little information on the cellular and mechanistic basis of assembly of ovarian follicles in this group. This is especially true of the caecilians. Therefore, taking advantage of the abundant distribution of caecilians in the Western Ghats of India, two species of caecilians, Ichthyophis tricolor and Gegeneophis ramaswamii, were subjected to light and transmission electron microscopic analysis to trace the sequential changes during the assembly of ovarian follicles. The paired ovaries of these caecilians are elongated sac-like structures each including numerous vitellogenic follicles. The follicles are connected by a connective tissue stroma. This stroma contains nests of oogonia, primary oocytes and pregranulosa cells as spatially separated nests. During assembly of follicles the oocytes increase in size and enter the meiotic prophase when the number of nucleoli in the nucleus increases. The mitochondrial cloud or Balbiani vitelline body, initially localized at one pole of the nucleus, disperses through out the cytoplasm subsequently. Synaptonemal complexes are prominent in the pachytene stage oocytes. The pregranulosa cells migrate through the connective tissue fibrils of the stroma and arrive at the vicinity of the meiotic prophase oocytes. On contacting the oocyte, the pregranulosa cells become cuboidal in shape, wrap the diplotene stage oocyte as a discontinuous layer and increase the content of cytoplasmic organelles and inclusions. The oocytes increase in size and are arrested in diplotene when the granulosa cells become flat and form a continuous layer. Soon a perivitelline space appears between the oolemma and granulosa cells, completing the process of assembly of follicles. Thus, the events in the establishment of follicles in the caecilian ovary are described.

nanos1 is required to maintain oocyte production in adult zebrafish

Development of the germline requires the specification and survival of primordial germ cells (PGCs) in the embryo as well as the maintenance of gamete production during the reproductive life of the adult. These processes appear to be fundamental to all Metazoans, and some components of the genetic pathway regulating germ cell development and function are evolutionarily conserved. In both vertebrates and invertebrates, nanos-related genes, which encode RNA-binding zinc finger proteins, have been shown to play essential and conserved roles during germ cell formation. In Drosophila, maternally supplied nanos is required for survival of PGCs in the embryo, while in adults, nanos is required for the continued production of oocytes by maintaining germline stem cells self-renewal. In mice and zebrafish, nanos orthologs are required for PGC survival during embryogenesis, but a role in adults has not been explored. We show here that nanos1 in zebrafish is expressed in early stage oocytes in the adult female germline. We have identified a mutation in nanos1 using a reverse genetics method and show that young female nanos mutants contain oocytes, but fail to maintain oocyte production. This progressive loss of fertility in homozygous females is not a phenotype that has been described previously in the zebrafish and underlines the value of a reverse genetics approach in this model system.

Reproductive apparatus and gametogenesis of Lophiosilurus alexandri Steindachner (Pisces, Teleostei, Siluriformes)

The gonad morphology and gametogenesis of Lophiosilurus alexandri Steindachner, 1877 from Santo Antônio river (Minas Gerais, Brazil) were studied through anatomical and histological techniques. Examination of the testis revealed that they were paired, fringed organs with two distinct regions: cranial spermatogenic and caudal spermatogenic and secretory. The cranial region represents ca. 60% of the mature/maturing testis, containing 41 to 73 fringes, while the caudal portion represents ca. 40% and contains 44 to 68 fringes. At the cranial portion the length of the fringes was 3.70 ± 1.70 mm and in the caudal portion was 0.20 ± 0.10 mm. The spermatogenesis was cystic, synchronic, and occurred throughout the whole extension of the seminiferous tubules. The ovaries were saculiforms, paired organs, which present ovigerous lamellae containing cells of the oogenic lineage. The oocytes were classified into four developmental stages according to their cytological characteristics and the characteristics of the cell layers that surround them.

Germinal epithelium, folliculogenesis, and postovulatory follicles in ovaries of rainbow trout,Oncorhynchus mykiss(Walbaum, 1792) (Teleostei, protacanthopterygii, salmoniformes)

The rainbow trout, Oncorhynchus mykiss (Walbaum, 1792), is a salmoniform fish that spawns once per year. Ripe females that had ovulated naturally, and those induced to ovulate using salmon gonadotropin-releasing hormone, were studied to determine whether follicles were forming at the time of spawning and to describe the process of folliculogenesis. After ovulation, the ovaries of postspawned rainbow trout were examined histologically, using the periodic acid-Schiff procedure, to stain basement membranes that subtend the germinal epithelium and to interpret and define the activity of the germinal epithelium. After spawning, the ovary contained a few ripe oocytes that did not ovulate, numerous primary growth oocytes including oocytes with cortical alveoli, and postovulatory follicles. The germinal epithelium was active in postspawned rainbow trout, as determined by the presence of numerous cell nests, composed of oogonia, mitotic oogonia, early diplotene oocytes, and prefollicle cells. Cell nests were separated from the stroma by a basement membrane continuous with that subtending the germinal epithelium. Furthermore, follicles containing primary growth oocytes were connected to the germinal epithelium; the basement membrane surrounding the follicle joined that of the germinal epithelium. After ovulation, the basement membrane of the postovulatory follicle was continuous with that of the germinal epithelium. We observed consistent separation of the follicle, composed of an oocyte and surrounding follicle cells, from the ovarian stroma by a basement membrane. The follicle is derived from the germinal epithelium. As with the germinal epithelium, follicle cells derived from it never contact those of the connective tissue stroma. As with epithelia, they are always separated from connective tissue by a basement membrane.

Ovarian follicle growth in the catfish Iheringichthys labrosus (Siluriformes: Pimelodidae)

The morphofunctional organisation of the female reproductive system, the oocyte growth and the follicular envelope ultrastructure were studied by the first time in the catfish Iheringichthys labrosus from Upper Paraná River basin, Southeastern Brazil, in order to contribute to the knowledge of the reproductive behaviour strategies of this species. As in other Neotropical freshwater siluriforms, the ovaries are of the cystovarian type, the oocytes develop in an asynchronous pattern and mature oocytes are released in clusters in the ovarian lumen, being transported through the oviduct to the urogenital papilla. During the primary growth, nuclear material is transported to the ooplasm, forming the yolk nucleus, where proliferate membranous organelles. The onset of the zona radiata formation occurs during the late perionucleolar stage with the deposition of the outer layer. At the vitellogenic stage, this envelope reaches 6.35+/-0.84microm of thickness, being constituted by three distinct layers crossed by pore-canals containing oocyte and follicular cells processes. Cytochemical analyses evidence neutral glycoproteins in cortical alveoli, yolk globules and zona radiata. Follicular cells with squamous shape during the primary growth acquire synthetic activity at the secondary growth, reaching 37.82+/-4.72mum in height at the mature vitellogenic follicles. These cells accumulate sulphated polysaccharides in large electron-lucent vesicles during the vitellogenic stage which are possibly secreted to form a mucous coat at the egg surface. These evidences suggest that I. labrosus may have adhesive eggs as also detected in other Neotropical freshwater Siluriformes.

Identification of the stages of ovarian maturation of the Argentine hake Merluccius hubbsi Marini, 1933 (Teleostei: Merlucciidae): advantages and disadvantages of the use of the macroscopic and microscopic scales

The Argentine hake Merluccius hubbsi is a demersal-pelagic species on which few studies have been undertaken, despite its importance for the fisheries of the South-Southeastern Brazilian region, . The species is the most important commercial fishery resource in Uruguay and Argentina, where several studies have permitted the proper monitoring of the species. The ovarian maturation of the Argentine hake is analysed in this study. A scale of maturation is presented in the light of the oocyte development and the use of macro and microscopic scales of ovarian maturation are compared. It was detected that the oocyte types and derived structures present in the ovaries are similar to those already described both for the species and for teleosts in general; group synchronous development and multiple spawning are typical. The identification of ovarian maturation based only on external morphological characteristics of the gonads presents many errors, mainly in the characterization of the stages of maturation, which makes imperative the parallel analysis of the oocyte development, undertaken through histological ovarian cross-sections.

Cytochemical characterization of the endomembranous system during the oocyte primary growth in Serrasalmus spilopleura (Teleostei, Characiformes, Characidae)

The morphophysiological changes that occur during oocyte primary growth in Serrasalmus spilopleura were studied using ultrastructural cytochemical techniques. In the previtellogenic oocytes endoplasmic reticulum components, Golgi complex cisternae and vesicles, lysosomes, multivesicular bodies and some electron-dense vesicles react to acid phosphatase (AcPase) detection. The endoplasmic reticulum components, Golgi complex cisternae and vesicles also react to osmium tetroxide and potassium iodide impregnation (KI). These structures, except for the Golgi complex cisternae, are strongly contrasted by osmium tetroxide and zinc iodide impregnation (ZIO). Some electron-dense vesicles are ZIO-stained, while microvesicles in the multivesicular bodies and other large isolated cytoplasmic vesicles are contrasted by KI. At primary oocyte growth, the activity of the endomembranous system and the proliferation of membranous organelles are intense. The biosynthetic pathway of the lysosomal proteins such as acid phosphatase, involves the endoplasmic reticulum, Golgi complex, vesicles with inactive hydrolytic enzymes and, finally, the lysosomes. The oocyte endomembranous system have reduction capacity and are involved in the metabolism of rich in SH groups.

Gonadal structure and gametogenesis of Loricaria lentiginosa Isbrücker (Pisces, Teleostei, Siluriformes)

The gonadal structure and gametogenesis of Loricaria lentiginosa Isbrücker, 1979 were studied through anatomical and histological techniques. Forty two males and ten females in maturation/mature stage were captured in the reservoir of Porto Colombia, Paraná river basin, Minas Gerais, using gill nets, from November 2001 to October 2002 (tri-monthly captures). Examination of the testes revealed that they were paired, elongated and not fringed organs. Histologically, the testes presented three distinct regions: cranial espermatogenic; transistion espermatogenic and secretory; and caudal exclusively secretory. Standard histochemical techniques detected neutral glycoproteins from the secretion of the tubules of the caudal region. Espermatogenesis occurred in cysts throughout the whole extension of the wall of the seminiferous tubules, which anastomosis themselves and liberated the spermatozoa into the lumen of the espermatic ducts. The ovaries were paired, saculiformes and, histologically, they presented ovigerous lamellae that contained the cells of ovogenic ancestry. The oocytes were classified into four stages, based on their cytological characteristics and the cell layers that surrounded them. Post-ovulatory follicles and vitelogenic oocytes in the follicular atresia process also were observed.

Follicular diameter range based on morphological features in Synbranchus marmoratus (Bloch, 1795) (Teleostei, Synbranchiformes, Synbranchidae) from the South-central region of Brazil

The morphological characteristics of Synbranchus marmoratus female germ cells in various development stages were described in details; then measurements of ovarian follicle diameters were taken from primary and secondary growth as during these development stages the oocyte size varied considerably along the fish growth. The results were correlated to total fish length, using the individuals division in six size classes. It was possible to group oocytes by stages according to histological characteristics but not according to morphometric diameter, as there was a wide variation in diameter in each stage and overlap between different maturation stages. These data make available new information on the reproductive biology of Synbranchidae.

A Comprehensive Survey of the Genes Involved in Maturation and Development of the Rainbow Trout Ovary1

Development and maturation of the ovary requires precisely coordinated expression of specific gene classes to produce viable oocytes. We undertook identification of some of the genes involved in these processes by creating ovary-specific cDNA libraries by suppression subtractive hybridization and by microarray-based analyses. We present 5778 tissue- and sex-specific genes from subtracted ovary and testis libraries, many of which remain unidentified. A microarray containing 3557 salmonid cDNAs was used to compare the transcriptomes of precocious ovary at three different stages during the second year of life with a reference (normal ovary) transcriptome. On average, approximately 240 genes were developmentally regulated during the study period from June to October. Classes of genes maintaining relatively steady-state levels of expression, such as those controlling tissue remodeling, immunoregulation, cell-cycle progression, apoptosis, and growth also were identified. Concurrent expression of various cell division and ubiquitin-mediated proteolysis regulators revealed the utility of microarray analysis to monitor important maturation events. We also report unequivocal evidence for expression of the transcripts that encode the common glycoprotein alpha, LH beta, FSH beta, thyroid-stimulating hormone beta, and retinol-binding protein in both the ovary and testis of trout.

Gonadal development and sex differentiation in the cichlid fishCichlasoma dimerus (Teleostei, perciformes): A light- and electron-microscopic study

Although the overall pattern and timing of gonadal sex differentiation have been established in a considerable number of teleosts, the ultrastructure of early stages of gonadal development is not well documented. In this study, gonads from larval and juvenile stages of laboratory-reared Cichlasoma dimerus were examined at the light-microscopic and ultrastructural levels. This freshwater species adapts easily to captivity and spawns with high frequency during 8 months of the year, providing an appropriate model for developmental studies. Larvae and juveniles were kept at a water temperature of 26.5 +/- 1 degrees C and a 12:12 hour photoperiod. Gonadal development was documented from 14-100 days postfertilization, covering the period of histologically discernible sex differentiation. Gonadal tissue was processed according to standard techniques for light and electron microscopy. C. dimerus, a perciform teleost, is classified as a differentiated gonochorist, in which an indifferent gonad develops directly into a testis or ovary. On day 14, the gonadal primordium consists of a few germ cells surrounded by enveloping somatic cells. Ovarian differentiation precedes testicular differentiation, as usual in teleost fishes. The earliest signs of differentiation, detected from day 42 onward, include the onset of meiotic activity in newly formed oocytes, which is soon accompanied by increased oogonial mitotic proliferation and the somatic reorganization of the presumptive ovary. The ovarian cavity is completely formed by day 65. Numerous follicles containing perinucleolar oocytes are observed by day 100. In contrast, signs of morphological differentiation in the presumptive testis are not observed until day 72. By day 100, the unrestricted lobular organization of the testis is evident. The latest stage of spermatogenesis observed by this time of testicular development is spermatocyte II.

Ultrastructure of oogenesis in the bluefin tuna,Thunnus thynnus

Ovarian ultrastructure of the Atlantic bluefin tuna (Thunnus thynnus) was investigated during the reproductive season with the aim of improving our understanding of the reproductive biology in this species. The bluefin, like the other tunas, has an asynchronous mode of ovarian development; therefore, all developmental stages of the oocyte can be found in mature ovaries. The process of oocyte development can be divided into five distinct stages (formation of oocytes from oogonia, primary growth, lipid stage, vitellogenesis, and maturation). Although histological and ultrastructural features of most these stages are similar among all studied teleosts, the transitional period between primary growth and vitellogenesis exhibits interspecific morphological differences that depend on the egg physiology. Although the most remarkable feature of this stage in many teleosts is the occurrence of cortical alveoli, in the bluefin tuna, as is common in marine fishes, the predominant cytoplasmic inclusions are lipid droplets. Nests of early meiotic oocytes derive from the germinal epithelium that borders the ovarian lumen. Each oocyte in the nest becomes surrounded by extensions of prefollicle cells derived from somatic epithelial cells and these form the follicle that is located in the stromal tissue. The primary growth stage is characterized by intense RNA synthesis and the differentiation of the vitelline envelope. Secondary growth commences with the accumulation of lipid droplets in the oocyte cytoplasm (lipid stage), which is then followed by massive uptake and processing of proteins into yolk platelets (vitellogenic stage). During the maturation stage the lipid inclusions coalesce into a single oil droplet, and hydrolysis of the yolk platelets leads to the formation of a homogeneous mass of fluid yolk in mature eggs.

Involvement of the gonadal germinal epithelium during sex reversal and seasonal testicular cycling in the protogynous swamp eel, Synbranchus marmoratus Bloch 1795 (Teleostei, Synbranchidae)

The swamp eel, Synbranchus marmoratus, is a protogynous, diandric species. During sex reversal, the ovarian germinal epithelium, which forms follicles containing an oocyte and encompassing follicle cells during the female portion of the life cycle, produces numerous invaginations, or acini, into the ovarian stroma. Within the acini, the gonia that formerly produced oocytes become spermatogonia, enter meiosis, and produce sperm. The acini are bounded by the basement membrane of the germinal epithelium. Epithelial cells of the female germinal epithelium, which formerly became follicle (granulosa) cells, now become Sertoli cells in the developing testis. Subsequently, lobules and testicular ducts form. The swamp eel testis has a lobular germinal compartment in both primary and secondary males, although the germinal compartment in testes of secondary males resides within the former ovarian lamellae. The germinal compartment, supported by a basement membrane, is composed of Sertoli and germ cells that give rise to sperm. Histological and immunohistochemical techniques were used to describe the five reproductive classes that were observed to occur during the annual reproductive cycle: regressed, early maturation, mid-maturation, late maturation, and regression. These classes are differentiated by the presence of continuous or discontinuous germinal epithelia and by the types of germ cells present. Synbranchus marmoratus has a permanent germinal epithelium. Differences between the germinal compartment of the testes of primary and secondary males were not observed.

Ultrastructure of the testis in Synbranchus marmoratus (Teleostei, Synbranchidae): the germinal compartment

Synbranchus marmoratus, is a protogynic diandric species in which two types of males, primary and secondary, are found. In both types, the germinal compartment in the testes is of the unrestricted lobular type, but in secondary (sex reversed females) males the lobules develop within the former ovarian lamellae. In the present study, the germinal compartment was examined in both types of males using light microscopy as well as scanning and transmission electron microscopy. Germinal compartment is limited by a basement membrane and contains Sertoli and germ cells. During maturation, processes of Sertoli cells form the borders of spermatocysts containing isogenic germ cells. Characteristically, type A and type B spermatogonia have a single nucleolus and grouped mitochondria associated with dense bodies or nuage. Type B spermatogonia, spermatocytes and spermatids are joined by cytoplasmatic bridges and are confined within spermatocysts. Secondary spermatocytes are difficult to find, indicating that this stage is of short duration. Biflagellated spermatozoa have a rounded head, no acrosome, and possess a midpiece consisting of two basal bodies, each of which produces a flagellum with a typical 9+2 microtubular composition. No associations occur between sperm and Sertoli cells. There were no differences between spermatogenesis in primary and secondary males in this protogynic, diandric fish.

Ovarian follicle ultrastructure in the teleost Synbranchus marmoratus (Bloch, 1795), with special reference to the vitelline envelope development

Synbranchus marmoratus is a protogynous diandric teleost fish widely distributed throughout South America. The aim of this work was to study the ultrastructure of the vitelline envelope and the relationship among oocyte and their follicular cells during oogenesis. During perinucleolar stage, the oocyte and the follicular cells form microvillar processes that project into the perivitelline space. The oocyte secretes a dense and amorphous material, which appears as the first evidence of the vitelline envelope (VE) development. The VE passes from a double to a multilayered structure during oocyte growth. In mature oocytes, the VE reach a mean thickness of 11 microm, having up to 30 layers. Oocyte microvilli are thinner than the follicular ones and were seen in contact with the follicular plasmalema, however we could not find any contact between the follicular microvilli and the oolemma. Before ovulation, microvillar processes retract and the pore canals seem to collapse. An outer electron dense layer occludes the superficial pore and forms a continuous layer. No jelly or adhesive coatings were seen at least in ovulated eggs sampled from ovarian lumen. Follicular cell and oocyte cytological characteristics do not differ from those described in other teleosts species.

Organization of the male gonad in a protogynous fish, Thalassoma bifasciatum (Teleostei: Labridae)

Although the testis in teleosts has been investigated for many years, little attention has been paid to the structure of the outer layers that enclose the testis and to their possible contributions to its organization. The present study in a protogynous male labrid, Thalassoma bifasciatum (bluehead wrasse), describes the arrangement and cytology of these tissues (for convenience, referred to collectively as the outer wall, OW) which include: the outer peritoneal layer and subjacent collagen fibers, myoid cells and diverse other cells and tissues, e.g., fibrocytes, presumptive mesenchyme, macrophages, granulocytes, nerves, and blood vessels. Beneath the OW are two compartments; one is the gamete-laden spermatocysts, the other the interstitium, which is composed of cells and tissues that lie between the spermatocysts. Both OW and interstitium contain similar kinds of tissues and cells. Moreover, the layers of the OW immediately subjacent to the peritoneum are continuous with that in the interstitium. It is suggested that the continuity between these two areas provides opportunities for the exchange of cells that could aid in the maintenance and reorganization of the testis and with the myoid and neural tissue to establish an extensive, coordinated motile system that aids movement of sperm from spermatocysts to the ducts. A recent report on the reexamination of the germinal epithelium concept and its identification in the common snook, Centropomus undecimalis, stimulated us to examine the feasibility of applying this concept to gonad organization and gamete development in T. bifasciatum. In addition, the ultrastructure of the Sertoli cell and formation of spermatocysts are described. Spermatocysts increase in size during the development of gametes. Observations and discussion are presented suggesting how Sertoli cells may accommodate this growth and how new populations of these cells may arise in the mature adult. Finally, ultrastructural characteristics for each stage of spermatogenesis are presented and, using (3H)thymidine and autoradiography, data on the chronology of spermatogonia-sperm cycle are included.

Continuous gametogenesis in the neotropical freshwater teleost, Bryconops affinis (Pisces:Characidae)

The gametogenesis of Bryconops affinis was studied by light, transmission and scanning electron microscopy. The spermatogenesis is semi-cystic and spermatids are released into the lumen of seminiferous tubules, where spermiogenesis is completed. Spermatozoa have an ovoid head, a rudimentary middle piece with a small number of mitochondria and long flagellum (primitive spermatozoa). The Sertoli and Leydig cells show secretory activity during spermatogenesis. By the end of this phenomenon, the Sertoli cells phagocytize the residual spermatozoa, while the Leydig cells show involuted characteristics. With regard to the oogenesis process, the oocyte development was divided into four stages based on the cytological characteristics of the oocyte and its surrounding layers. Ultrastructural analysis revealed that the zona pellucida is formed during the previtellogenic stage. Specializations associated to the outer layer of the zona pellucida may be related to the egg's adherence to the substrata.