An overview of cell renewal in the testis throughout the reproductive cycle of a seasonal breeding teleost, the gilthead seabream (Sparus aurata L)

Fish HERC7: Phylogeny, Characterization, and Potential Implications for Antiviral Immunity in European Sea Bass

E3 ubiquitin ligases, key components of the ubiquitin proteasome system, orchestrate protein degradation through ubiquitylation and profoundly impact cellular biology. Small HERC E3 ligases (HERC3-6) have diverse functions in mammals, including roles in spermatogenesis, protein degradation, and immunity. Until now, only mammals' HERC3, HERC5, and HERC6 are known to participate in immune responses, with major involvement in the antiviral response. Interestingly, an exclusive HERC7 has been characterized in fish showing great molecular conservation and antiviral roles. Thus, this study identifies and characterizes the herc7 gene in the European sea bass teleost. The European sea bass herc7 gene and the putative protein show good conservation of the promoter binding sites for interferons and the RCC1 and HECT domains characteristic of HERC proteins, respectively. The phylogenetic analysis shows a unique cluster with the fish-exclusive HERC7 orthologues. During ontogeny, the herc7 gene is expressed from 3 days post-fertilization onwards, being constitutively and widely distributed in adult tissues. In vitro, stimulated leucocytes up-regulate the herc7 gene in response to mitogens and viruses, pointing to a role in the immune response. Furthermore, sea bass herc7 expression is related to the interferon response intensity and viral load in different tissues upon in vivo infection with red-grouper betanodavirus (RGNNV), suggesting the potential involvement of fish HERC7 in ISGylation-based antiviral activity, similarly to mammalian HERC5. This study broadens the understanding of small HERC proteins in fish species and highlights HERC7 as a potential contributor to the immune response in European sea bass, with implications for antiviral defense mechanisms. Future research is needed to unravel the precise actions and functions of HERC7 in teleost fish immunity, providing insights into direct antiviral activity and viral evasion.

Beyond Prostate Cancer: An Androgen Receptor Splice Variant Expression in Multiple Malignancies, Non-Cancer Pathologies, and Development

Multiple studies have demonstrated the importance of androgen receptor (AR) splice variants (SVs) in the progression of prostate cancer to the castration-resistant phenotype and their utility as a diagnostic. However, studies on AR expression in non-prostatic malignancies uncovered that AR-SVs are expressed in glioblastoma, breast, salivary, bladder, kidney, and liver cancers, where they have diverse roles in tumorigenesis. AR-SVs also have roles in non-cancer pathologies. In granulosa cells from women with polycystic ovarian syndrome, unique AR-SVs lead to an increase in androgen production. In patients with nonobstructive azoospermia, testicular Sertoli cells exhibit differential expression of AR-SVs, which is associated with impaired spermatogenesis. Moreover, AR-SVs have been identified in normal cells, including blood mononuclear cells, neuronal lipid rafts, and the placenta. The detection and characterization of AR-SVs in mammalian and non-mammalian species argue that AR-SV expression is evolutionarily conserved and that AR-SV-dependent signaling is a fundamental regulatory feature in multiple cellular contexts. These discoveries argue that alternative splicing of the AR transcript is a commonly used mechanism that leads to an expansion in the repertoire of signaling molecules needed in certain tissues. Various malignancies appropriate this mechanism of alternative AR splicing to acquire a proliferative and survival advantage.

Male germ cell proliferation and apoptosis in sexually immature meagre Argyrosomus regius (Asso, 1801) treated with recombinant follicle stimulating hormone

The meagre Argyrosomus regius (Asso, 1801) is a marine fish species that has an increasing aquaculture production in Europe. Lowering the age at maturity of hatchery-produced juveniles would support meagre aquaculture by reducing time between generations in selective breeding programs and reducing industrial costs for broodstock maintenance. The aim of this work was to assess the effects of a treatment with recombinant follicle stimulating hormone (rFsh), produced in ovarian cells of Chinese hamsters, on male germ cell proliferation and apoptosis in sexually immature meagre. The rFsh-treated fish had higher gonadosomatic index, larger seminiferous tubules, more abundant luminal spermatozoa, a lower density of anti-PCNA positive single A spermatogonia, a higher density of anti-PCNA positive spermatocysts and a lower incidence of germ cell apoptosis than control groups. The present study demonstrated the effectiveness of the produced rFsh in stimulating testis development and spermatogenesis in pre-pubertal meagre. Moreover, the rFsh treatment proved to be highly efficient in removing the apoptotic block of spermatogenesis observed in juvenile meagre, allowing spermatogonial survival and progress towards meiosis. The administration of rFsh did not stimulate spermatogonial self-renewal, a process whose control still needs to be elucidated.

Crosstalk between reproductive and immune systems: the teleostean perspective

The bidirectional interaction between the hypothalamic-pituitary-gonadal (HPG) axis and the immune system plays a crucial role in the adaptation of an organism to its environment, its survival and the continuance of a species. Nonetheless, very little is known about this interaction among teleost, the largest group of extant vertebrates. Fishes being seasonal breeders, their immune system is exposed to seasonally changing levels of HPG hormones. On the contrary, the presence and infiltration of leukocytes, the expression of pattern recognition receptors as well as cytokines in gonads suggest their key role in teleostean gametogenesis as in the case of mammals. Moreover, the modulation of gametogenesis and steroidogenesis by lipopolysaccharide implicates the pathological significance of inflammation on reproduction. Thus, it is important to engage in the understanding of the interaction between these two important physiological systems, not only from a phylogenetic perspective but also due to the importance of fish as an important economic resource. In view of this, the authors have reviewed the crosstalk between the reproductive and immune systems in teleosts and tried to explore the importance of this interaction in their survival and reproductive fitness.

Insulin-like growth factors 1 and 2 are associated with testicular germ cell proliferation and apoptosis during fish reproduction

To support sperm production, fish testes undergo intense tissue remodelling, with endocrine, paracrine and autocrine signals regulating gonad physiology. The aim of this study was to investigate the testicular expression of insulin-like growth factor (Igf) 1 and Igf2 during spermatogenesis, and their relationship with cell proliferation and apoptosis throughout the reproductive cycle. The study was performed in male Hypostomus garmani, a catfish living in headwater rivers of the São Francisco River basin, Brazil. Spermatogenesis was analysed using histology, morphometry, immunohistochemistry and terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL) analysis at different maturity stages. The results showed the proliferation of spermatogonia throughout the reproductive cycle, with a higher rate during the ripe stage. Germ and Sertoli cells expressed Igf1 at all stages of testicular maturity, Igf2 was predominant at the ripe stage and both Igf1 and Igf2 occurred at the spent stage. Caspase-3 and TUNEL analysis revealed a higher rate of apoptosis at the spent stage associated with reduced expression of Igf1 and Igf2. Sertoli cell proliferation was associated with spermatogonia and spermatocyte cysts at different stages of the reproductive cycle. Together, the data support a proliferative role for Igf1 and Igf2 in regulating testicular apoptosis in H. garmani, with cyclical variation in their expression during gonad maturation.

Stress responses of testicular development, inflammatory and apoptotic activities in male zebrafish (Danio rerio) under starvation

Food deprivation is a severe stress across multiple fields and challenged to organismal development and immune system. Here, adult male zebrafish were used to investigate the starvation stress on organismal development, spermatogenesis, testicular inflammation and apoptosis. Results showed that the biological indexes, blood parameters, and RNA/DNA ratio in testis dramatically decreased after 1-3 weeks of starvation. The testicular architecture was impaired and the spermatogenesis was retarded with increased proportions of spermatogonia and spermatocytes, and decreased proportion of spermatozoa in the starved fish. The mRNA expressions of amh and sycp3 were downregulated, the retinoic acid content increased at later stage of starvation through the transcriptional regulation of aldh1a2 and cyp26a1. Besides, the immune response was elevated with upregulated mRNA and protein expressions of TNF-α, IL-6, and IL-1β, which indicated the inflammation of opportunistic risk in testis. The apoptotic activity was stimulated, accompanied by differentially upregulated expressions of baxa, casp9, casp3, casp2, and decreased ratio of Bcl-2/Bax in the attenuate testis. Taken together, our findings revealed that the stress responses of testicular development, inflammatory and apoptotic activities in male zebrafish under starvation and pointed out the susceptibility of fish gonad to food fluctuation.

Functions of interleukin-6 in ovulation of female climbing perch, Anabas testudineus

In mammals, interleukin 6 (IL-6) has an important function during ovulation, however, the functions of IL-6 in fish have not been elucidated. In the present study, there was quantification of de novo synthesis of ovarian IL-6 and tumor necrosis factor-alpha (TNFα) in control and hCG-treated fish and results were compared with those from an in vitro study where there was evaluation of the regulatory functions of gonadotropins and TNFα of IL-6 secretions. Relatively greater concentrations of ovarian IL-6 at the post-GVBD (post-germinal vesicle breakdown) stage indicates IL-6 modulates ovulatory processes. The hCG-induced increase in relative abundance of IL-6 (in vitro) mRNA transcript and secretion from the ovary were attenuated when there was administration of the inhibitor of TNFα secreting enzyme, TAPI-I, which indicates TNFα modulates IL-6 secretion. Treatments with IL-6 induced a marked increase in ovulation rate in vitro when there was induction of activating matrix metalloproteinase (MMP). Furthermore, treatment with IL-6 resulted in production of prostaglandin as indicated by the IL-6 induced increase in the abundance of ptgs2 mRNA transcript in the ovary of Anabas testudineus. Furthermore, results indicate the source of IL-6 in the ovary is the granulosa cells with secretion of IL-6 being induced by the additions of hCG and TNFα in the medium. There was also an IL-6-induced increase in abundance of receptors (IL-6 Rα and gp130) to which it binds indicating IL-6 autoregulates this population of receptors. Results from this study, for the first time, elucidate the reproductive functions of IL-6 in a teleost fish.

Meagre Argyrosomus regius (Asso, 1801) Stem Spermatogonia: Histological Characterization, Immunostaining, In Vitro Proliferation, and Cryopreservation

The meagre, Argyrosomus regius, is a valued fish species of which aquaculture production might be supported by the development of a stem germ cell xenotransplantation technology. Meagre males were sampled at a fish farm in the Ionian Sea (Italy) at the beginning and end of the reproductive season. Small and large Type A undifferentiated spermatogonia were histologically identified in the germinal epithelium. Among the tested stemness markers, anti-oct4 and anti-vasa antibodies labeled cells likely corresponding to the small single Type A spermatogonia; no labeling was obtained with anti-GFRA1 and anti-Nanos2 antibodies. Two types of single A spermatogonia were purified via density gradient centrifugation of enzymatically digested testes. Testes from fish in active spermatogenesis resulted in a more efficient spermatogonial stem cell (SSC) yield. After cell seeding, meagre SSCs showed active proliferation from Day 7 to Day 21 and were cultured up to Day 41. After cryopreservation in dimethyl-sulfoxide-based medium, cell viability was 28.5%. In conclusion, these results indicated that meagre SSCs could be isolated, characterized, cultured in vitro, successfully cryopreserved, and used after thawing. This is a first step towards the development of a xenotransplantation technology that might facilitate the reproduction of this valuable species in captivity.

Endocrine disrupter chemicals affect the humoral antimicrobial activities of gilthead seabream males even upon the cease of the exposure

17α-ethynilestradiol (EE₂) and tamoxifen (Tmx) are pollutants world-wide distributed in aquatic environments. Gilthead seabream, Sparus aurata L., is highlighted as a species model of intensively culture in anthropogenic disturbed environments. The effects of these pollutants on gilthead seabream reproduction and some immune responses have been described but, the humoral innate antimicrobial activities have never received attention. In this work we analysed the latest in the plasma of gilthead seabream males of different ages and reproductive stages treated with 0, 2.5, 5 or 50 μg EE₂ or 100 μg Tmx g^-1 food during different times of exposure and of reverting to commercial diet (recovery). The peroxidase and protease activities decreased as the spermatogenesis of the first reproductive cycle (RC) proceeded in control fish. However, only protease and antiprotease activities showed different level at different stages of the second RC in control fish, but showed scarce disruption in fish treated with EE₂ or Tmx. Peroxidase and bactericide activities are more sensitive to EE₂, than to Tmx. The effects induced by EE₂ varied depending on the activity analyzed, the dose and the time of exposure and the reproductive stage and the age of the specimens.

Variable occurrence of apoptosis in the testes of diploid and sterile allotetraploid Cobitis (Teleostei, Cobitidae) males during the reproductive cycle

Cobitis species exist in both diploid and diploid-polyploid (d-p) populations, but mostly occur in the latter. They are considered an important model organism to study the biology and physiology of natural hybrid and polyploid vertebrates. Indeed, polyploidization causes a huge stress for in terms of cell physiology and alters spermatogenesis in polyploid fish. The most extensively studied mode of germ cell death during spermatogenesis in vertebrates is apoptosis. The aim of this study was to examine caspase-3 immunoexpression in the testes of Cobitis taenia from a diploid population as well as C. taenia and sterile tetraploid Cobitis from d-p populations before, during and after spawning. The obtained results suggest a different performance of apoptosis in the testes of C. taenia from the two studied populations and seems to be conditioned by their role as the only sperm donors in d-p populations. Moreover, apoptosis was an active cell death process in the testes of tetraploid Cobitis.

Testis structure, spermatogonial niche and Sertoli cell efficiency in Neotropical fish

Neotropical icthyofauna represents one of the most diverse and extreme ecosystems in the world. Likewise, reproduction showed enormous diversity with different reproductive systems, modes and behavior. On the other hand, information on Neotropical fish species, in particular on male reproductive physiology is restricted to few species. This mini-review aimed to compile the existing information on spermatogenesis of Neotropical teleosts focusing on testis structure, spermatogonial niche and Sertoli cell efficiency. The first topic covers the histological analysis of the testicular structure, showing a conserved testicular pattern in relation to the phylogenetic position: basal species present anastomosing tubular testis (e.g. Astyanax altiparanae, Conorhynchos conirostris, Pimelodus maculatus, Lophiosilurus alexandri, Rhinelepis aspera, among others), while derived teleosts showed lobular testis (e.g. Cichlasoma dimerus, Cichla kelberi, Odontesthes bonariensis, Synbranchus marmoratus and others). Next to testicular structure, existing data showed that type A undifferentiated spermatogonia (A_und) is differentially distributed among the Neotropical species. A_und can be restricted at the blind-end of the germinal compartment (O. bonariensis), or spread along the germinal epithelium (A. altiparanae), or even distributed along the germinal epithelium but concentrated at the blind-end (C. kelberi and C. intermedia). Moreover, recent studies in A. altiparanae have demonstrated that within the germinal compartment, A_und have a preferential distribution in areas neighboring the interstitial compartment - the spermatogonial niche. The proximity with the interstitium suggests that interstitial cells, such as Leydig cells, are important for A_und maintenance in the testis. Finally, this mini-review highlighted Sertoli cell efficiency, showing that a single Sertoli cell can support a higher number of germ cells (80-140 spermatids) in Neotropical species evaluated at the moment (e.g. A. altiparanae, Hoplias malabaricus, Poecilia reticulata, Serrasalmus spilopleura, C. intermedia). Overall, this review provided basic and functional information on spermatogenesis of Neotropical species. More studies in this field are necessary since Neotropical region is considered one of the hotspot regions to discovery new species providing, therefore, new opportunities to investigate spermatogenesis in fish.

Effects of diisononyl phthalate (DiNP) on the endocannabinoid and reproductive systems of male gilthead sea bream (Sparus aurata) during the spawning season

Diisononyl phthalate (DiNP) is a plasticizer used to improve plastic performance in a large variety of items which has been reported as an endocrine-disrupting chemical (EDC) in several organisms. The endocannabinoid system (ECS) is a cellular signaling system, whose functionality is tightly involved with reproductive function. The aim of the present study was the assessment of the effects of DiNP on the gonadal ECS and on the reproductive function of male gilthead sea bream Sparus aurata, an important marine aquacultured species in Europe, during the reproductive season. Fish were fed for 21 days with two diets contaminated with different nominal concentrations of DiNP (DiNP LOW at 15 µg DiNP kg^-1 bw day^-1 and DiNP HIGH at 1500 µg DiNP kg^-1 bw day^-1), based on the tolerable daily intake (TDI) ruled by the European Food Safety Authority for humans. The transcription of several genes related to the ECS was affected by the DiNP. Specifically, DiNP reduced the levels of endocannabinoids and endocannabinoid-like mediators, concomitant with the increase of fatty acid amide hydrolase (FAAH) activity. At the histological level, DiNP LOW induced the highest occurrence of individuals with regressed testes. Steroidogenesis was affected significantly, since plasma 11-ketotestosterone (11-KT), the main active androgen in fish, was significantly decreased by the DiNP HIGH treatment, while plasma 17β-estradiol (E₂) levels were raised, associated with an increase of the gonadosomatic index (GSI). Additionally, the level of testosterone (T) was significantly increased in the DiNP LOW group, however, the same DiNP concentration reduced the levels of 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P). The production of sperm was in general not affected, since spermiation index, sperm density, survival and the duration of forward motility did not exhibit any changes compared to controls. However, computer-assisted sperm analysis (CASA) showed that DiNP reduced the percentage of motile cells. The results clearly suggest a negative effect of DiNP via the diet on the male endocrine system of gilthead sea bream during the reproductive season.

Role of 5α-dihydrotestosterone in testicular development of gilthead seabream following finasteride administration

In teleosts, spermatogenesis is regulated by pituitary gonadotropins and sex steroids. 5α-dihydrotestosterone (DHT), derived from testosterone (T) through the action of 5α-reductase, has recently been suggested to play a physiologically important role in some fish species. In this study, gilthead seabream, Sparus aurata L., males received an implant of 1μgT/g body mass (bm) or vehicle alone and, 7days later, 1mg finasteride (FIN, an inhibitor of 5α-reductase)/kg bm or vehicle. Serum levels of T, 11-ketotestosterone (11KT), DHT and 17β-estradiol (E₂), and the mRNA levels of the main enzymes involved in their synthesis, were analysed. T promoted a transient increase in the serum levels of T, 11KT and E₂ but a decrease in those of DHT at day 15 following T injection, in accordance with the up-regulation of mRNA levels of the enzymes involved in T transformation to 11KT (coding genes: cyp11b1 and hsd11b) and the down-regulation of mRNA levels of the enzyme responsible for T transformation to DHT (coding gene: srd5a). Interestingly, a similar effect was observed when FIN was injected. However, when fish were injected with T and FIN successively (T+FIN), control levels were not recovered at the end of the experimental period (28days). DHT seems to regulate E₂ serum levels via the down-regulation of mRNA levels of aromatase (coding gene: cyp19a1a), which is needed for the transformation of T into E₂. The testis histology, together with the proliferative rates recorded upon T, FIN or T+FIN treatment, suggests that DHT is involved in the onset of the meiotic phase of spermatogenesis.

BMP15 in catfish testis: Cellular distribution, seasonal variation, and its role in steroidogenesis

Considering the absence of information on testicular growth factors in fishes, present study was aimed to elucidate the existence of BMP15, an important member of TGF-β superfamily, in the testis of a seasonally breeding freshwater catfish, Clarias batrachus and its role in regulation of testicular activities. The study demonstrated the expression of BMP15 in the somatic cells (Sertoli and interstitial cells) in fish testis. The expression varied with changing testicular activity; the expression was very high in the quiescent and early recrudescing testis coinciding with the renewal of spermatogonial cells. Expression then declined gradually with progression of spermatogenesis and steroidogenesis. Expression of BMP15 showed positive correlation with seasonally changing testicular 17β-estradiol but negatively with testicular testosterone and 11-ketotestosterone. In vitro treatment of testis with recombinant human BMP15 enhanced the production of estradiol-17β but concurrently suppressed the production of testosterone and 11-ketotestosterone in testis. Though BMP15 did not alter the expression of StAR protein in the testis, it promoted the expression of 3β-hydroxysteroid dehydrogenase and aromatase in fish testis. Thus the present study for the first time demonstrates that fish testis is capable of producing BMP15 and is expressed by the somatic cells unlike mammals wherein it is produced exclusively by germ cells. Study also suggests that BMP15 may modulate the testicular steroidogenesis by altering the expression of steroidogenic enzymes. BMP15 also appears to play crucial role in renewal of spermatogial cells by augmenting the testicular production of 17β-estradiol.

Flow-cytometric enrichment of Pacific bluefin tuna type A spermatogonia based on light-scattering properties

We previously established surrogate broodstock in which the donor germ cells transplanted into the peritoneal cavities of xenogeneic recipients were capable of developing into functional eggs and sperm in teleost fish. In this transplantation system, only the undifferentiated germ cells such as type A spermatogonia (ASG) or a portion of the ASG population were capable of being incorporated into the genital ridges of the recipients and undergo gametogenesis. Therefore, the use of enriched ASGs can be expected to achieve efficient donor-cell incorporation. Here, we established a method of isolation and enrichment of the ASG of Pacific bluefin tuna using flow cytometry. Whole testicular cell suspensions were fractionated by forward and side scatter properties, following which ASGs were enriched in a fraction in which the forward scatter signal was relatively high and side scatter signal was relatively low. The diameter of sorted cells using the fraction was identical to the size of ASGs observed in histological analysis, and these cells also expressed the vasa gene. In addition, we succeeded in applying this method to several maturation stages of Pacific bluefin tuna. Since this method was based on light-scattering characteristics of ASGs, it can potentially be applied to various teleosts. We expect that this method can contribute to the production of seeds of Pacific bluefin tuna using surrogate broodstock.

Cimetidine disrupts the renewal of testicular cells and the steroidogenesis in a hermaphrodite fish

The importance of histamine in the physiology of the testis in mammals and reptiles has been recently shown. Histamine receptors (Hrs) are well conserved in fish and are functional in several fish species. We report here for the first time that histamine and the mRNA of Hrh1, Hrh2 and Hrh3 are all present in the gonad of the hermaphrodite teleost fish gilthead seabream. Moreover, cimetidine, which acts in vitro as an agonist of Hrh1 and Hrh2 on this species, was intraperitoneally injected in one and two years old gilthead seabream males. After three and five days of cimetidine injection, we found that this compound differently modified the gonadal hrs transcript levels and affects the testicular cell renewal and the gene expression of steroidogenesis-related molecules as well as the serum steroid levels. Our data point to cimetidine as a reproductive disruptor and elucidate a role for histamine in the gonad of this hermaphrodite fish species through Hr signalling.

Seasonality of reproduction in male spotted murrel Channa punctatus: correlation of environmental variables and plasma sex steroids with histological changes in testis

The present study was undertaken to develop a comprehensive understanding of how environmental cues and sex steroids relate with cyclic changes in spermatogenesis in freshwater spotted snakehead Channa punctatus that is nutritious and economically important. The seasonal histological changes in testis and annual profile of gonadosomatic index (GSI) of C. punctatus delineated the testicular cycle into four phases: regressed (December-March), preparatory (April-June), spawning (July and August) and postspawning (September-November). Among environmental variables, correlation and regression analyses exhibited an important relationship between photoperiod and testicular weight while role of rainfall was seen confined to spawning. The seasonal profile of plasma sex steroids when correlated with cyclic changes in spermatogenesis in spotted snakehead, testosterone (T) seems to be involved in controlling the major events of spermatogenesis from renewal of stem cells to spawning of spermatozoa. Another important androgen prevalent in teleosts, 11-ketotestosterone (11-KT), was high during preparatory phase, suggesting that 11-KT in addition to T plays an important role in progression of spermatogenesis and spermiation in C. punctatus. However, 11-KT was not seen to be associated with milt production and release of spermatozoa during spawning. Plasma profile of estradiol-17β (E2) during different reproductive phases revealed the involvement of E2 in repopulation of stem cells during postspawning phase and in maintaining quiescence of testis during regressed phase.

The Bromodomain testis-specific gene (Brdt) characterization and expression in gilthead seabream, Sparus aurata, and European seabass, Dicentrarchus labrax

Multiple genes and transcription factors are involved in regulation and control of the complex process of sex determination and differentiation of fish species. Also more, several hormonal factors and some environmental conditions can also be adequate spawning strategies and stimuli for inducing reproduction of fish species. Brdt gene belongs to the bromodomain-extraterminal domain (BET) family of transcriptional coregulators. In mammals, Brdt gene is almost exclusively expressed in testis. Furthermore, Brdt protein is involved in elongating spermatids, and is required for proper spermatogenesis and male fertility. However, from our understanding of fish species, the role of this gene as key, during gametogenesis, still remains unknown. In this study, two Brdt mRNA transcripts were isolated from two teleostean fish species, gilt-head seabream and European seabass. In both species the shorter form lacked a functional C-terminal domain, which may involve a different function as transcriptional regulator. The pattern of Brdt expression showed that the highest levels occurred in the gonads. Significantly lower levels of expression were detected in brain, pituitary and different organ systems (heart, kidney, gills, among other somatic tissues) from both studied species. In situ hybridization approach evidenced that Brdt mRNA expression was restricted to specific cell-types of the germ line, during both oogenesis and spermatogenesis processes.

Tamoxifen disrupts the reproductive process in gilthead seabream males and modulates the effects promoted by 17α-ethynylestradiol

17α-Ethynylestradiol (EE2), which is used in oral contraceptives and hormone replacement therapy, is a well documented estrogenic endocrine disruptor and an aquatic contaminant. In the present study, adult male specimens of the marine hermaphrodite teleost gilthead (Sparus aurata L.) were fed a diet containing tamoxifen (Tmx), an estrogen receptor ligand used in cancer therapy, alone or combined with EE2, for 25 days and then fed a commercial diet for a further 25 days (recovery period). The effects of short (5days) and long (25 days) treatments on several reproductive and gonad immune parameters and the reversibility of the disruptive effects after the recovery period were examined. Our data showed that Tmx acted as an estrogenic endocrine disruptor as revealed by the increase in the hepatic transcription of the vitellogenin gene in males, the serum levels of 17β-estradiol and the gonad expression levels of the estrogen receptor α and G protein-coupled estrogen receptor genes, and the recruitment of leukocytes into the gonad, a well known estrogenic-dependent process in gilthead seabream males. On the other hand, Tmx also increased sperm concentration and motility as well as the serum levels of androgens and the expression levels of genes that codify for androgenic enzymes, while decreasing the expression levels of the gene that code for gonadal aromatase. When applied simultaneously, Tmx and EE2 could act in synergy or counteract, each other, depending on the parameter measured. The disruptive effect of EE2 and/or Tmx was not reversible after a 25 day recovery period.

Nodavirus Colonizes and Replicates in the Testis of Gilthead Seabream and European Sea Bass Modulating Its Immune and Reproductive Functions

Viruses are threatening pathogens for fish aquaculture. Some of them are transmitted through gonad fluids or gametes as occurs with nervous necrosis virus (NNV). In order to be transmitted through the gonad, the virus should colonize and replicate inside some cell types of this tissue and avoid the subsequent immune response locally. However, whether NNV colonizes the gonad, the cell types that are infected, and how the immune response in the gonad is regulated has never been studied. We have demonstrated for the first time the presence and localization of NNV into the testis after an experimental infection in the European sea bass (Dicentrarchus labrax), and in the gilthead seabream (Sparus aurata), a very susceptible and an asymptomatic host fish species, respectively. Thus, we localized in the testis viral RNA in both species using in situ PCR and viral proteins in gilthead seabream by immunohistochemistry, suggesting that males might also transmit the virus. In addition, we were able to isolate infective particles from the testis of both species demonstrating that NNV colonizes and replicates into the testis of both species. Blood contamination of the tissues sampled was discarded by completely fish bleeding, furthermore the in situ PCR and immunocytochemistry techniques never showed staining in blood vessels or cells. Moreover, we also determined how the immune and reproductive functions are affected comparing the effects in the testis with those found in the brain, the main target tissue of the virus. Interestingly, NNV triggered the immune response in the European sea bass but not in the gilthead seabream testis. Regarding reproductive functions, NNV infection alters 17β-estradiol and 11-ketotestosterone production and the potential sensitivity of brain and testis to these hormones, whereas there is no disruption of testicular functions according to several reproductive parameters. Moreover, we have also studied the NNV infection of the testis in vitro to assess local responses. Our in vitro results show that the changes observed on the expression of immune and reproductive genes in the testis of both species are different to those observed upon in vivo infections in most of the cases.

Characterization of the IFN pathway in the teleost fish gonad against vertically transmitted viral nervous necrosis virus

One of the most powerful innate immune responses against viruses is mediated by type I IFN. In teleost fish, it is known that virus infection triggers the expression of ifn and many IFN-stimulated genes, but the viral RNA sensors and mediators leading to IFN production are scarcely known. Thus, we have searched for the presence of these genes in gilt-head sea bream (Sparus aurata) and European sea bass (Dicentrarchus labrax), and evaluated their expression after infection with viral nervous necrosis virus (VNNV) in the brain, the main viral target tissue, and the gonad, used to transmit the virus vertically. In sea bream, a fish species resistant to the VNNV strain used, we found an upregulation of the genes encoding MDA5 (melanoma differentiation-associated gene 5), TBK1 (TANK-binding kinase 1), IRF3 (IFN regulatory factor 3), IFN, Mx [myxovirus (influenza) resistance protein] and PKR (dsRNA-dependent protein kinase receptor) proteins in the brain, which were unaltered in the gonad and could favour the dissemination by gonad fluids or gametes. Strikingly, in European sea bass, a very susceptible species, we also identified, transcripts coding for LGP2 (Laboratory of Genetics and Physiology 2), MAVS (mitochondrial antiviral signalling), TRAF3 (TNF receptor-associated factor 3), TANK (TRAF family member-associated NFκB activator) and IRF7 (IFN regulatory factor 7), and found that all the genes analysed were upregulated in the gonad, but only mda5, lgp2, irf3, mx and pkr were upregulated in the brain. These findings supported the notion that the European sea bass brain innate immune response is unable to clear the virus and pointed to the importance of gonad immunity to control the dissemination of VNNV to the progeny--an aspect that is worth investigating in aquatic animals.

Characterization of the annual regulation of reproductive and immune parameters on the testis of European sea bass

The European sea bass, Dicentrarchus labrax L., is a seasonal gonochoristic species, the males of which are generally mature during their second year of life. It has been demonstrated that cytokines and immune cells play a key role in the testicular development. This reproductive-immune interaction might be very important in the sea bass since several pathogens are able to colonise the gonad and persist in this tissue, altering further reproductive functions and spreading disease. This study aims to investigate the reproductive cycle of 1-year European sea bass males by analysing cell proliferation and apoptosis and the expression profile of some reproductive and immune-related genes in the testis, as well as the serum sex steroid levels. Our data demonstrate that, in 1-year-old European sea bass males, the testis undergoes the spermatogenesis process and that the reproductive and immune parameters analysed varied during the reproductive cycle. In the testis, the highest proliferative rates were recorded at the spermatogenesis stage, while the highest apoptotic rates were recorded at the spawning stage. We have also analysed, for the first time in European sea bass males, the serum levels of 17β-estradiol (E2) and dihydrotestosterone and the gene expression profile of the enzymes implied in their production, determining that at least E2 might be involved in the regulation of the reproductive cycle. Some immune relevant genes, including cytokines, lymphocyte receptors, and anti-viral and anti-bacterial molecules were detected in the testis of naïve European sea bass specimens, and their expression profile was related to the stages of the reproductive cycle, suggesting an important role for the defence of the reproductive tissues.

Comparative testicular structure and spermatogenesis in bony fishes

In most bony fishes, testes are paired elongated organs that are attached to the dorsal wall of the body by a mesorchium. Histological examination of teleost testes, and also in all vertebrates, shows that the testes are formed of germ cells and somatic cells, comprising the germinal and interstitial compartments. Both compartments are separated by a basement membrane. The germ cells may be spermatogonia, meiotic spermatocytes and haploid spermatids that differentiate into spermatozoa. The process of spermatogenesis includes a sequence of morphological and physiological changes of germ cells that begin with the differentiation of spermatogonia that become meiotic spermatocytes. After the second meiotic division, through a process of spermiogenesis, these differentiate into spermatozoa. Spermatogonia associate with Sertoli cells to form spermatocysts or cysts. The cyst is the unit of spermatogenic function, composed of a cohort of isogenic germ cells surrounded by encompassing Sertoli cells. The teleost testis is organized morphologically into 3 types of testis: 1) tubular testis type, present in lower bony fishes as salmonids, cyprinids and lepisosteids; 2) unrestricted spermatogonial testis type, found in neoteleosts except Atherinomorpha; and 3) restricted spermatogonial testis type, characteristic of all Atherinomorpha. The morphology of the testicular germinal epithelium changes during the annual reproductive cycle, reflecting reproductive seasonality.

Extracellular matrix remodeling of the testes through the male reproductive cycle in Teleostei fish

During the fish reproductive cycle, testes undergo morphological changes related to germinal epithelium and remodeling of extracellular matrix components (ECM). ECM is degraded mainly by action of matrix metalloproteinases (MMPs). Due to the natural renewal of ECM in fish testes, we choose Pimelodus maculatus to study remodeling of ECM throughout reproductive cycle, using picrosirius (to identify type I, II, III collagen) and reticulin (type III collagen), and to immunolocalize MT1-MMP (membrane type 1-matrix metalloproteinase) and MMP-2 in testis cells. Testes were classified in four reproductive phases: regenerating, development, spawning capable and regressing. Picrosirius and reticulin demonstrated a differential distribution of total collagen fibers during the reproductive cycle. Immunohistochemistry showed MT1-MMP only in acidophilic granulocyte cells mainly inside blood vessels, in connective tissue of capsule close to the germinal compartment, and also infiltrated in interstitial connective tissue. MMP-2 was detected in fibroblast and endothelial cells of interstitial and capsule blood vessels, in epithelial cells of capsule, and in acidophilic granulocyte cells at same description for MT1-MMP. The fish testes ECM were remodeled throughout reproductive cycle in according to morphophysiological alterations. During reproductive season (spawning capable), the interstitium increased in total collagen fibers (type I, II, III). After spermiation period (regression and regenerating), the amount of collagen fibers decreased in response to action of MMPs on collagen degradation and other interstitial components (not assessed in this study). MMPs seem to be indispensable components for natural cyclic events of ECM remodeling of fish testes and for guarantee tissue homeostasis throughout reproductive cycle.

Sperm competition and the evolution of spermatogenesis

Spermatogenesis is a long and complex process that, despite the shared overall goal of producing the male gamete, displays striking amounts of interspecific diversity. In this review, we argue that sperm competition has been an important selection pressure acting on multiple aspects of spermatogenesis, causing variation in the number and morphology of sperm produced, and in the molecular and cellular processes by which this happens. We begin by reviewing the basic biology of spermatogenesis in some of the main animal model systems to illustrate this diversity, and then ask to what extent this variation arises from the evolutionary forces acting on spermatogenesis, most notably sperm competition. We explore five specific aspects of spermatogenesis from an evolutionary perspective, namely: (i) interspecific diversity in the number and morphology of sperm produced; (ii) the testicular organizations and stem cell systems used to produce them; (iii) the large number and high evolutionary rate of genes underpinning spermatogenesis; (iv) the repression of transcription during spermiogenesis and its link to the potential for haploid selection; and (v) the phenomenon of selection acting at the level of the germline. Overall we conclude that adopting an evolutionary perspective can shed light on many otherwise opaque features of spermatogenesis, and help to explain the diversity of ways in which males of different species perform this fundamentally important process.

MicroRNA in teleost fish

MicroRNAs (miRNAs) are transcriptional and posttranscriptional regulators involved in nearly all known biological processes in distant eukaryotic clades. Their discovery and functional characterization have broadened our understanding of biological regulatory mechanisms in animals and plants. They show both evolutionary conserved and unique features across Metazoa. Here, we present the current status of the knowledge about the role of miRNA in development, growth, and physiology of teleost fishes, in comparison to other vertebrates. Infraclass Teleostei is the most abundant group among vertebrate lineage. Fish are an important component of aquatic ecosystems and human life, being the prolific source of animal proteins worldwide and a vertebrate model for biomedical research. We review miRNA biogenesis, regulation, modifications, and mechanisms of action. Specific sections are devoted to the role of miRNA in teleost development, organogenesis, tissue differentiation, growth, regeneration, reproduction, endocrine system, and responses to environmental stimuli. Each section discusses gaps in the current knowledge and pinpoints the future directions of research on miRNA in teleosts.

Fish granulocytes express a constitutively active androgen receptor variant

In humans, alternative splicing of androgen receptor (AR) is usually involved in some diseases. However, our knowledge about the presence of AR variants in other species and its importance for immunity is scant. Here, we report the identification of a constitutively active AR variant lacking the ligand-binding domain (LBD), ARΔLBD, in the fish gilthead seabream. ARΔLBD is expressed in the testis and the head-kidney (HK), and its expression varies with the reproductive stage and is correlated with plasma testosterone (T). In addition, ARΔLBD is expressed in acidophilic granulocytes (AGs), which are the functional equivalent of mammalian neutrophils, but not in macrophages, and its expression is modulated by both T and immune stimuli. Notably, AR and ARΔLBD were able to interact, being the activity of AR dominant at all concentrations tested of the ligand. These results reveal a new mechanism for the regulation of neutrophil biology in vertebrates and explain the conflicting results that suggest that androgens are less important than AR in human and mouse neutrophil homeostasis.

The effect of 17α-ethynylestradiol on steroidogenesis and gonadal cytokine gene expression is related to the reproductive stage in marine hermaphrodite fish

Pollutants have been reported to disrupt the endocrine system of marine animals, which may be exposed through contaminated seawater or through the food chain. Although 17α-ethynylestradiol (EE₂), a drug used in hormone therapies, is widely present in the aquatic environment, current knowledge on the sensitivity of marine fish to estrogenic pollutants is limited. We report the effect of the dietary intake of 5 µg EE₂/g food on different processes of testicular physiology, ranging from steroidogenesis to pathogen recognition, at both pre-spermatogenesis (pre-SG) and spermatogenesis (SG) reproductive stages, of gilthead seabream (Sparus aurata L.), a marine hermaphrodite teleost. A differential effect between pre-SG and SG specimens was detected in the sex steroid serum levels and in the expression profile of some steroidogenic-relevant molecules, vitellogenin, double sex- and mab3-related transcription factor 1 and some hormone receptors. Interestingly, EE₂ modified the expression pattern of some immune molecules involved in testicular physiology. These differences probably reflect a developmental adjustment of the sensitivity to EE₂ in the gilthead seabream gonad.

Characterization of four nr5a genes and gene expression profiling for testicular steroidogenesis-related genes and their regulatory factors in response to bisphenol A in rare minnow Gobiocypris rarus

Bisphenol A (BPA) widely used in the manufacture of numerous products is ubiquitous in aquatic environment. To explore the mechanisms of BPA-mediated actions, male rare minnow Gobiocypris rarus were exposed to BPA at concentrations of 5, 15, and 50 μg/L for 14 and 35 days in the present study. Four subtypes of nr5a gene encoding important transcription factors for steroidogenesis were characterized, and tissue distribution analysis demonstrated distinct expression profiling of the four genes in G. rarus. BPA at environmentally relevant concentration (5 μg/L) caused increase of gonadosomatic index (GSI) of male fish. In response to BPA, no obvious changes on the testis development were observed. Modulation of vtg mRNA expression by BPA suggests estrogenic and/or anti-estrogenic effects of BPA were dependent on exposed duration (14 or 35 days). Gene expression profiling for testicular steroidogenesis-related genes, sexual steroid receptors, gonadotropin receptors, and transcription factors indicates differential regulation was dependent on exposure duration and dose of BPA. The correlation analysis at mRNA level demonstrates that the BPA-mediated actions on testicular steroidogenesis might involve sex steroid hormone receptor signaling, gonadotropin/gonadotropin receptor pathway, and transcription factors such as nuclear receptor subfamily 5, group A (Nr5a), fork head box protein L2 (Foxl2).

Analysis of germ cell proliferation, apoptosis, and androgenesis in the Lake Van fish (Chalcalburnus tarichi) during testicular development

In the present study, the testis histology, gonadosomatic index (GSI), germ cell proliferation and apoptosis, and the plasma 11-ketotestosterone (11-KT) and testosterone (T) levels of male Chalcalburnus tarichi were analyzed. According to the histological examinations of the specimens that were caught between February 2009 and January 2010, three testicular stages were determined. Those stages were as follows: (1) recrudescence or prespawning (July-April), (2) spawning (May-June), and (3) postspawning (July). It was observed that the GSI increased gradually, starting from the recrudescence stage, and it reached peak values at the spawning stage, while the lowest values were in the postspawning. Germ cell proliferation in the testis was detected using a proliferating cell nuclear antigen (PCNA), and germ cell apoptosis was detected by transferase dUTP nick end labeling staining. The germ cell PCNA and apoptosis index values were calculated. It was indicated that germ cell proliferation was observed in all of the testicular stages. The highest germ cell PCNA index (PI) levels were detected in July, August, and September, which then dropped in October and stabilized between February and April. The lowest PI values were detected in the spawning stage (May-June). Germ cell apoptosis was observed in all of the months, and the highest apoptotic index values were detected in August, September, October, May, and June. Plasma 11-KT and T levels were at their highest levels in May and June, and it was detected as stabile in the other months. There was a correlation between GSI, PI, and plasma androgen levels. In conclusion, the present data illustrate testicular development stages for C. tarichi and show changes in the level of GSI and sex steroid biosynthesis through spermatogenesis.

Testosterone implants modify the steroid hormone balance and the gonadal physiology of gilthead seabream (Sparus aurata L.) males

Androgens can induce complete spermatogenesis in immature or prepubertal teleost fish; however, many aspects of the role of androgens in adult teleost spermatogenesis remain elusive. We used the in situ forming microparticle (ISM) system containing 1mg of testosterone (T)/kg body weight (T-ISM) in a homogenous population of gilthead seabream at testicular involution stage to study in vivo the effects of T on the sex steroid hormone balance and on the physiology of the gilthead seabream gonad. The levels of T, 11-ketotestosterone (11KT) and 17β-estradiol (E2) in plasma, gonad and liver were determined in T-ISM implanted specimens after 7, 14, 21 and 28 days. The effect of T-ISM was evaluated on (i) de novo synthesis and metabolism of T in the gonad and liver by measuring the gene expression levels of the main steroidogenic proteins involved, (ii) the progress of spermatogenesis, (iii) the presence of different leukocyte cell types in the gonad, and (iv) the mRNA expression of some genes involved in the leukocyte migratory influx into the gonad and of some immune-relevant molecules. T-ISM implants promote an increase of T up to supra-physiological levels which induce a depletion of E2 levels and maintain the 11KT levels at physiological concentrations. The gene expression profile of some steroidogenic enzymes in gonad and liver ruled out the transformation of T into estrogenic compounds following T-ISM implantation. Moreover, androgens may also be involved in the leukocyte migratory influx, which occurred even when cytokine, chemokine and cell adhesion molecule gene expressions were down-regulated. Moreover, T-ISM implants block germ cell proliferation, although increased dmrt1 gene expression may prevent the complete depletion of germ cells in the gonad. Furthermore, T down-regulated the expression of several tlr genes, which may result in the inhibition of the immune response in the gonad through the impaired ability to recognize and respond to pathogens.

Expression of developmental-stage-specific genes in the gilthead sea bream Sparus aurata L

The mechanism of early fish development as well as the control of egg quality is of great importance for the ability of the oocyte to develop after fertilization. Embryonic development is initially regulated by maternally provided mRNAs and later by the zygotic genome. Maternal mRNAs have an important role in initiating processes crucial to patterning the developing fish embryo. Furthermore, it has been shown that maternal RNA plays an important role in egg quality. The identification and characterization of candidate maternal genes in non-model fish species with important aquaculture interest like the gilthead sea bream Sparus aurata L. is of importance for future studies related to egg quality. The broodstock of the gilthead sea bream produces large quantities of eggs with a high and non-controllable quality variation. In the present study, we have studied the gene expression of 16 genes (gapdh 1 and 2, cathepsin D, L, S and Z, erk1, jnk1, p38 alpha and p38 delta, ppar alpha, beta and gamma, tubulin beta, ferritin M, cyclinA2) of different functional categories in seven developmental stages. The 16 genes were chosen based on their putative involvement in egg quality and regulation of early development. In total, 11 showed a characteristic gene expression pattern pinpointing to the possible function as maternal genes and thus may function as molecular biomarker for egg quality.

Assessment of spermatogenesis and plasma sex steroids in a seasonal breeding teleost: a comparative study in an area of influence of a tributary, downstream from a hydroelectric power dam, Brazil

River damming and building of hydroelectric power plants interrupt the reproductive migration routes and change the major physicochemical parameters of water quality, with drastic consequences for populations of migratory fishes. The goal of this study was to evaluate proliferation and cell death during spermatogenesis and serum profiles of sex steroids in Prochilodus argenteus, from the São Francisco River, downstream from the Três Marias Dam. A total of 257 adult males were caught quarterly during a reproductive cycle in two sites: the first 34 km of the river after the dam (site 1) and the second 34-54 km after the dam (site 2), after the confluence with a tributary, the Abaeté River. Seasonal changes in the testicular activity associated with morphometric analyses of germ cells as well as proliferation and testicular apoptosis support a more active spermatogenesis in fish from site 2, where higher levels of sex steroids and gonadosomatic index (GSI) were also found. In site 1, fish presented low serum levels of testosterone, 17β-estradiol and 17α-hydroxyprogesterone and a low GSI during gonadal maturation. Spermatogonial proliferation (PCNA) and apoptosis (TUNEL) were more elevated in fish from site 1, but spermatocytes were mainly labelled in fish from site 2. Overall, these data demonstrate changes in testicular activity and plasma sex steroids in a neotropical teleost fish living downstream from a hydroelectric dam, supplying new data on fish reproduction in regulated rivers. Moreover, morphometric analyses associated with sex steroids profiles provide reliable tools to assess fish spermatogenesis under environmental stress conditions.

17α-Ethynylestradiol alters the immune response of the teleost gilthead seabream (Sparus aurata L.) both in vivo and in vitro

There is increasing public attention concerning the effect of endocrine disruptor chemicals (EDCs) on the immune system. One important group belonging to EDCs are the environmental estrogens. Commonly found in the effluents in wastewater treatment plants, 17α-ethynylestradiol (EE(2)) which is used in contraceptive pills, is an endocrine disruptor with strong estrogenic effects. This study aims to investigate the capacity of EE(2) to modulate in vivo and in vitro the innate immune response of the gilthead seabream (Sparus aurata L.), a teleost species of great commercial value. For this purpose, adult specimens were bath-exposed to EE(2) (0, 5 and 50 ng/L) and then immunized with hemocyanin in the presence of the adjuvant aluminum. The results indicate that, after 15 days of EE(2)-exposure, the disruptor was able to inhibit in a dose-dependent manner the induction of interleukin-1β (IL-1β) gene expression, but did not significantly alter the specific antibody titer. To shed light on the role played by EE(2) into seabream immune response, leukocytes were exposed in vitro to several concentrations of EE(2) (0, 0.5, 5, 50 and 500 ng/ml) for 3, 16 and 48 h and the production of reactive oxygen intermediates, the phagocytic activity and the gene expression profile of these cells were analyzed. EE(2) was seen to inhibit both cellular activities and to alter the immune gene expression profile in primary macrophages. Thus, low concentrations of EE(2) increase the mRNA levels of IL-1 β, IL-6, tumour necrosis factor α and tumour growth factor β in non-activated macrophages. In contrast, EE(2) treatment of activated macrophages resulted in the decreased expression of pro-inflammatory genes and the increased expression of genes encoding anti-inflammatory and tissue remodeling/repair enzymes. Taken together, our results suggest that EE(2) might alter the capacity of fish to appropriately respond to infection although it does not behave as an immunosuppressor.

The social status of the male Nile tilapia (Oreochromis niloticus) influences testis structure and gene expression

Dominant and territorial behaviour are known social phenomena in cichlids and social stress influences reproduction and growth. The gonadotropic hormones trigger spermatogenesis and subordinate males have typically lower levels of gonadotropins than dominant males. In this study, we compared testis morphology and gene expression of dominant and subordinate Nile tilapia males (d- and s-males) in socially stable communities. The d-males had the highest gonadosomatic index but they were not the largest animals in the majority of studied cases. Long-term d-males showed large groups of Leydig cells and hyperplasia of the tunica albuginea due to numerous cytochrome-P450-11β-hydroxylase (Cyp11b) expressing myoid cells. Increased Cyp11b expression in d-males was reflected by elevated 11-ketotestosterone plasma values. However, immunofluorescence microscopy and expression analysis of selected genes revealed that most s-males conserved their capability for spermatogenesis and are, therefore, ready for reproduction when the social environment changes. Moreover, in s-males gene expression analysis by quantitative RT-PCR showed increased transcript levels for germ line-specific genes (vasa,sox2anddmc1) and Sertoli-specific genes (amh,amhrIIanddmrt1) whereas gene expression of key factors for steroid production (sf1andcyp11b) were reduced. The Nile tilapia is a promising model to study social cues and gonadotropic signals on testis development in vertebrates.

Estrogen-responsive genes in macrophages of the bony fish gilthead seabream: a transcriptomic approach

The role of sex steroids in the modulation of fish immune responses has received little attention. Previous studies have demonstrated that 17β-estradiol (E(2)) is able to alter the response of gilthead seabream leukocytes to infectious agents. We have used suppression subtractive hybridization to identify genes upregulated by E(2) (50 ng/ml) in macrophage cultures from gilthead seabream. We isolated 393 up-regulated cDNA fragments that led to the identification of 162 candidate estrogen-responsive genes. Functional analyses revealed the presence of several enriched immune processes and molecular pathways. The E(2) up-regulation of some immune-relevant genes was further confirmed by real time RT-PCR. Bioinformatics analysis revealed the ability of E(2) to orchestrate profound alterations in the macrophage expression profile, especially immune-related processes and pathways. This is the first report on E(2)-dependent modifications of fish macrophage transcriptome and lends weight to a suggested role for estrogen in the immune system, the possible significance of which is discussed.

Identification of a β1 integrin isoform with restricted tissue expression in a teleost fish

The composition and organisation of extracellular matrix (ECM)-related molecules change during development. These components interact with different cell surface receptors to modulate the transduction of signals for cell growth, differentiation, migration, proliferation and apoptosis. Previous findings in the teleost fish gilthead seabream (Sparus aurata L., Teleostei), a marine protandrous hermaphrodite fish, showed that endocrine and immune stimuli are able to modulate the expression of ECM-related molecules, as well as specific correlations between them. In the present study, quantitative reverse transcription–polymerase chain reaction was used to examine the gene expression profile of β1 integrin isoform b (ITGB1b) and its possible role in reproductive physiology, especially in relation to spermatogenesis. Expression profiles were analysed in the context of the reproductive cycle (RC) and in relation with other ECM-related molecules, including matrix metalloproteinase (MMP)-2, MMP-9, MMP-13, tissue-specific inhibitor of metalloproteinase (TIMP)-2a, TIMP-2b, collagen (COL1A1) and ITGB1a. Expression of ITGB1b was found in the testis and brain and, to some extent, in endothelial cells. In contrast, ITGB1a was expressed ubiquitously. In the testis, the ITGB1b expression peaked during spermatogenesis, whereas the expression of the other ECM-related molecules is induced mainly during the post-spawning stage, both stages of marked tissue remodelling during the first and second RC in males. In addition, in fish exposed to the endocrine disruptor 17α-ethynyloestradiol (at 5 and 50 μg g–1 food during 7, 14 and 21 days), ITGB1b expression in the testis was inhibited in a dose- and time-dependent manner and was related to reduced serum levels of testosterone. Together, these results suggest a different functionality for the two ITGB1 isoforms in the gilthead seabream, where ITGB1b is more specifically involved in reproduction. This is the first report of an ITGB1 gene isoform whose expression is restricted to endocrine-related tissues in vertebrates.

17β-Estradiol regulates gilthead seabream professional phagocyte responses through macrophage activation

In mammals, estrogens regulate the immune system, either directly or indirectly via several leukocyte types through autocrine/paracrine mechanisms. In the gilthead seabream (Sparus aurata L.) gonad, an intensive remodeling process accompanied by the massive infiltration of acidophilic granulocytes (AG) is partially triggered by 17β-estradiol (E(2)). Once AG infiltrated the gonad, show impaired activities. In this study we first demonstrate that neither testicular nor head-kidney AG express any of the three estrogen receptor (ER) genes (ERa, ERb1 and ERb2) described in the gilthead seabream, while head-kidney macrophages (Mc) and lymphocytes (Ly) constitutively express ERa gene. Moreover, Mc are important in the immune-modulatory role of E(2), as suggested by its ability to induce ERb2 gene expression and up-regulate the expression of genes coding for ERa, ERb1, pro-inflammatory cytokines, chemokines and tissue remodeling molecules. Furthermore, the soluble factors produced by E(2)-treated Mc decreased in head-kidney phagocytes, their phagocytic ability and capacity, while no effects were observed on their reactive oxygen intermediate (ROI) production or their migratory capabilities. However, the role of Ly in the regulation of AG migration and the modulation of phagocytic and ROI production activities triggered by E(2) can not be ruled out, so that further studies are necessary to clarify these issues.

Viral hemorrhagic septicemia and infectious pancreatic necrosis viruses replicate differently in rainbow trout gonad and induce different chemokine transcription profiles

Viral hemorrhagic septicemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV) are two rainbow trout (Oncorhynchus mykiss) pathogens. While IPNV is known to be vertically transmitted to the next generation through the oocyte, VHSV is known to replicate in the ovary and be transmitted horizontally through the ovarian fluid. In this work, we wanted to study whether these differences had an effect on the immune response triggered in the ovary, with a focus on the chemokine response. We have studied the kinetics of viral gene expression and the sites of replication, confirming that great differences exist between the replication of the two viruses in the gonad. Next, we studied the levels of expression of several CXC and CC chemokines in the ovary and found that while VHSV strongly triggered chemokine transcription, IPNV had almost no effect. This lack of immune response might be an advantage that permits its vertical transmission.

Seasonality in expression and distribution of nitric oxide synthase isoforms in the testis of the catfish, Clarias batrachus: role of nitric oxide in testosterone production

Nitric oxide (NO) is a well-recognized versatile signaling molecule. It is produced by catalytic action of nitric oxide synthase (NOS) on L-arginine in a variety of animal tissues. Existence of different isoforms of NOS has been shown in mammalian testis, but report on their presence in the testis of ectothermic vertebrates is non-existent. This study demonstrates the differential expressions of two isoforms of nitric oxide synthase (neuronal-nNOS and inducible-iNOS) like molecules in different cell types in the testis of seasonally breeding catfish, Clarias batrachus through immunohistochemistry. Positive immunoprecipitation of nNOS and iNOS like molecules were detected in germ cells as well as interstitial cells only in the recrudescing and fully mature fish. The immunoreactions differed in intensity and varied with changing reproductive status. Treatment of adult male fish with NO donor, sodium nitroprusside, and a NOS inhibitor, N-nitro-L-arginine methyl ester (L-NAME) increased and decreased the total nitrate and nitrite concentration in the testis, respectively. Sodium nitroprusside and L-NAME also induced simultaneous decline and rise in the testicular testosterone level, respectively. These findings, thus, suggest that NOS isoforms are expressed variedly in different cell types in the testis of reproductively active fish. This investigation also suggests that NO inhibits testosterone production in the testis.

The rainbow trout (Oncorhynchus mykiss) interferon response in the ovary

Immune responses in the ovary are tightly regulated to provide protection for the developing germ cells, which are very sensitive to inflammatory responses. This characteristic immune response is often used by viral pathogens to evade the immune system, replicate and be transmitted to other specimens through the ovary. Taking into account that in teleost fish, the innate immune system is considered crucial to the outcome of viral infections and the interferon (IFN) system is considered as the first line of defence against viruses, we have studied the IFN response in rainbow trout (Oncorhynchus mykiss) ovary using two viruses with different replicative capacity in this organ, namely viral haemorrhagic septicaemia virus (VHSV) and infectious pancreatic necrosis virus (IPNV). Both VHSV and IPNV are shed from the ovary, but while VHSV actively replicates at this site, IPNV remains silent. In this context, we have determined the levels of expression of IFNs and the IFN-induced Mx genes in the ovary upon in vivo and in vitro infections with VHSV and IPNV, and compared to the effects provoked by the viral mimic poly I:C in vivo. We have demonstrated that while VHSV strongly up-regulates all the IFN genes studied, IPNV in vivo exposure either has no effect or even provokes strong suppression of IFN gene expression. These differences are not observed in vitro, even though IPNV does not replicate actively in this case either. Finally, to better understand the role that the production of type I IFN plays in the ovary, we have studied the effects of two type I recombinant rainbow trout IFNs (rtIFN1 and rtIFN2) to modulate both the expression of immune genes and to establish an antiviral state in the ovary. Interestingly, the ovary was able to respond to both rtIFN1 and 2, despite the fact that the IFN1 gene was not expressed here. Moreover, rtIFN1 and rtIFN2 not only modulated the expression of genes related to the IFN response, but also modulated inflammatory genes and significantly suppressed VHSV replication.