Developmental expression and estrogen responses of endocrine genes in juvenile yellow perch (Perca flavescens)

Diethylstilbestrol arrested spermatogenesis and somatic growth in the juveniles of yellow catfish (Pelteobagrus fulvidraco), a fish with sexual dimorphic growth

In fish, spermatogenesis and somatic growth are mainly regulated by hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-somatic (HPS) axes, respectively. Xenoestrogens have been reported to impair spermatogenesis in some fishes, and arrest somatic growth in some others, whereas, whether xenoestrogens are capable of disrupting spermatogenesis and somatic growth simultaneously in fish that exhibits sexual dimorphic growth is little known, and the underlying mechanisms remain poorly understood. In this study, male juveniles of yellow catfish (Pelteobagrus fulvidraco), which exhibits a sexual dimorphic growth that favors males, were exposed to diethylstilbestrol (DES) for 28 days. After exposure, DES significantly disrupted the spermatogenesis (decreased gonadal-somatic index (GSI) and germ cell number) and arrested the somatic growth (declined body weight) of the catfish juveniles. Gene expression and plasma steroid analyses demonstrated the suppressed mRNA levels of genes in HPG axis (gnrh-II, fshβ, and lhβ in the brain and dmrt1, sf1, fshr, cyp17a1, cyp19a1a, and cyp11b2 in the testis) and decreased 17β-estrodial (E2) and 11-ketotestosterone (11-KT) levels in plasma. Further analysis revealed the arrested germ cell proliferation (cyclin d1), meiosis (dmc1, sycp3), and enhanced apoptosis (decreased bcl-2 and elevated bax/bcl-2 ratio) in the testis. Besides, DES also suppressed the mRNA levels of genes in HPS axis (ghrh, gh, and prl in the brain and ghr, igf1, igf2a, and igf2b in the liver). The suppressed HPG and HPS axes were thus supposed to disturb spermatogenesis and arrest somatic growth in yellow catfish. The present study greatly extended our understanding on the mechanisms underlying the toxicity of DES on spermatogenesis and somatic growth of fish.

Sex hormones and the development of sexual size dimorphism: 5α-dihydrotestosterone inhibits growth in a female-larger lizard (Sceloporus undulatus)

Sexual differences in adult body size [sexual size dimorphism (SSD)] and color (sexual dichromatism) are widespread, and both male- and female-biased dimorphisms are observed even among closely related species. A growing body of evidence indicates testosterone can regulate growth, thus the development of SSD, and sexual dichromatism. However, the mechanism(s) underlying these effects are conjectural, including possible conversions of testosterone to estradiol (E₂) or 5α-dihydrotestosterone (DHT). In the present study, we hypothesized that the effects of testosterone are physiological responses mediated by androgen receptors, and we tested two specific predictions: (1) that DHT would mimic the effects of testosterone by inhibiting growth and enhancing coloration, and (2) that removal of endogenous testosterone via surgical castration would stimulate growth. We also hypothesized that females share downstream regulatory networks with males and predicted that females and males would respond similarly to DHT. We conducted experiments on eastern fence lizards (Sceloporus undulatus), a female-larger species with striking sexual dichromatism. We implanted Silastic^® tubules containing 150 µg DHT into intact females and intact and castrated males. We measured linear growth rates and quantified color for ventral and dorsal surfaces. We found that DHT decreased growth rate and enhanced male-typical coloration in both males and females. We also found that, given adequate time, castration alone is sufficient to stimulate growth rate in males. The results presented here suggest that: (1) the effects of testosterone on growth and coloration are mediated by androgen receptors without requiring aromatization of testosterone into E₂, and (2) females possess the androgen-receptor-mediated regulatory networks required for initiating male-typical inhibition of growth and enhanced coloration in response to androgens.

17β-Estradiol induces changes in cytokine levels in head kidney and blood of juvenile sea bass (Dicentrarchus labrax, L., 1758)

The cytokine network is involved in the immune system communication. As estrogens influence the cytokine expression in mammals, this study investigated the impact of exogenous estrogenic pollutants on selected cytokines in Dicentrarchus labrax. The gene expression of Interleukin 6, Tumour Necrosis Factor α, Transforming Growth Factor β1 and Interleukin 1β was assessed and accomplished with protein measurements in the blood for the last two. Impacts through 17β-estradiol mainly occurred at the beginning of organ regionalisation, thus falling together with a developmentally induced increase of Interleukin 1β and Tumour Necrosis Factor α gene expression in 102 dph fish. 17β-estradiol depressed this modification after 35 days of exposure and the cytokine gene expression tended to be generally down-regulated independently of the 17β-estradiol concentrations after 56 days of exposure. This impact was confirmed at the protein level, showing that 17β-estradiol affects the fine control of the cytokine network in sea bass.

Characterization and evaluation of sex-specific expression of suppressors of cytokine signaling (SOCS)-1 and -3 in juvenile yellow perch (Perca flavescens) treated with lipopolysaccharide

The suppressor of cytokine signaling (SOCS) proteins are a family of intracellular proteins that are centrally involved with vertebrate growth, development and immunity via their effects as negative feed-back regulators of cytokine (and hormone) signaling. The genes for SOCS-1 & -3 were cloned, sequences analyzed and expression patterns examined in the commercially-important teleost, yellow perch (Perca flavescens). The deduced (mature) proteins for yellow perch (yp)SOCS-1 and (yp)SOCS-3 consist of 211 and 205 amino acids, respectively. Functional domains such as the Src homology-2 (SH2) and SOCS-box were present in ypSOCS-1 and ypSOCS-3 and these domains were well conserved between teleost species. Sequence analysis showed that ypSOCS-1 & -3 share highest homology (among similar teleost sequences), to the stickleback (Gasterosteus aculatus) SOCS-1 & -3 protein homologs. To investigate sex-specific expression of the ypSOCS-1 and ypSOCS-3 mRNAs, juvenile male and female yellow perch were immunologically challenged with a single injection (10 μg/g bw) of lipopolysaccharide (LPS) and tissues (gill, head kidney, kidney, liver and spleen) were sampled over a 48-h time-course. Quantitative real-time PCR analysis showed that ypSOCS-1 & -3 were expressed in all tissues examined and at all sampling time-points. LPS injection significantly induced ypSOCS-1 & -3 mRNA levels in gill, head kidney, liver, kidney and spleen, with maximal induction occurring at 6 h post-injection in each tissue. By 48-h post-injection, expression levels for ypSOCS-1 & -3 mRNAs approached, or reached, control levels in all tissues examined. While there were statistical interactions among variables (treatment, time and sex) for ypSOCS-1, we only found a main effect of sex on SOCS-3 mRNA expression in head kidney with higher copy numbers occurring in males than in females treated with LPS. Sexually-dimorphic expression of SOCS-1 or -3 mRNA has not been examined, or described, in a teleost. Our findings suggest the involvement of the SOCS genes in the yellow perch immune response and that differences among the sexes are evident and should be explored further.