Identification of an androgen receptor in the zonal testis of the salamander (Necturus maculosus)

Functional characterization and expression analysis of the androgen receptor in zebrafish (Danio rerio) testis

The biological activity of androgens, important for male sexual differentiation and development, is mediated by the androgen receptor (AR) that binds to specific DNA recognition sites regulating the transcription of androgen target genes. We investigated androgen production by adult zebrafish testis tissue, and identified 11β-hydroxyandrostenedione, 11-ketoandrostenedione (OA), and 11-ketotestosterone (11-KT) as main products, and hence potential ligands, for the zebrafish Ar. These androgens were then included in the pharmacological characterization of the zebrafish Ar. The zebrafish Ar responded well in terms of binding and transactivation to synthetic androgens as well as to testosterone and 11-KT, and reasonably well to OA and androstenedione. In situ hybridization analysis of zebrafish testis revealed that ar mRNA expression was detected in the subpopulation of Sertoli cells contacting early spermatogonia.

Androgen receptor in the oviduct of the turtle, Trachemys scripta

Circulating androgens reach high concentrations in females of some reptiles and amphibians. We are testing the hypothesis that androgens can act directly in female reptilian reproductive tissues, via the androgen receptor. In this study, we sought to determine if androgen receptors are present in the oviduct of the turtle, Trachemys scripta, using radioligand-binding assays and immunological assays. An androgen-binding site was detected in turtle oviductal cytosol and oviductal nuclear extract by radioligand binding assay, using (3)H-dihydrotestosterone (DHT) as the ligand. This site was saturable (B(max)=11 pmol/g tissue), had a high affinity (10(-10) M), and showed specificity typical of androgen receptors (DHT>testosterone, progesterone>>estradiol, cortisol). Western blotting using an anti-androgen receptor antibody revealed a band of immunoreactivity in oviductal cytosol at approximately 115 kDa, and a more prominent band at 50 kDa, possibly indicating a truncated form of the androgen receptor. Immunohistochemistry revealed crossreactivity of the androgen receptor antibody against oviductal glandular cells but not against oviductal luminal epithelial or muscularis cells. The presence of androgen receptor in the turtle oviduct suggests that androgens have a role in female reproduction and that their action can be mediated directly by androgen receptor.

Alteration of the hypothalamic-pituitary-gonadal axis in estrogen- and androgen-treated adult male leopard frog, Rana pipiens

BACKGROUND

Gonadal steroids, in particular 5 alpha-dihydrotestosterone (DHT) and 17 beta-estradiol (E2), have been shown to feed back on the hypothalamic-pituitary-gonadal (HPG) axis of the ranid frog. However, questions still remain on how DHT and E2 impact two of the less-studied components of the ranid HPG axis, the hypothalamus and the gonad, and if the feedback effects are consistently negative. Thus, the goal of the study was to examine the effects of DHT and E2 upon the HPG axis of the gonadally-intact, sexually mature male leopard frogs, Rana pipiens.

METHODS

R. pipiens were implanted with silastic capsules containing either cholesterol (Ch, a control), DHT, or E2 for 10 or 30 days. At each time point, steroid-induced changes in hypothalamic GnRH and pituitary LH concentrations, circulating luteinizing hormone (LH), and testicular histology were examined.

RESULTS

Frogs implanted with DHT or E2 for 10 days did not show significant alterations in the HPG axis. In contrast, frogs implanted with hormones for 30 days had significantly lower circulating LH (for both DHT and E2), decreased pituitary LH concentration (for E2 only), and disrupted spermatogenesis (for both DHT and E2). The disruption of spermatogenesis was qualitatively similar between DHT and E2, although the effects of E2 were consistently more potent. In both DHT and E2-treated animals, a marked loss of all pre-meiotic germ cells was observed, although the loss of secondary spermatogonia appeared to be the primary cause of disrupted spermatogenesis. Unexpectedly, the presence of post-meiotic germ cells was either unaffected or enhanced by DHT or E2 treatment.

CONCLUSIONS

Overall, these results showed that both DHT and E2 inhibited circulating LH and disrupted spermatogenesis progressively in a time-dependent manner, with the longer duration of treatment producing the more pronounced effects. Further, the feedback effects exerted by both steroid hormones upon the HPG axis were largely negative, although the possibility exists for a stimulatory effect upon the post-meiotic germ cells.

Glycoconjugates of the urodele amphibian testis shown by lectin cytochemical methods

Lectin histochemistry is a useful method that allows the in situ identification of the terminal sugar moieties of the carbohydrates that form the glycoconjugates. Moreover, when it is combined with chemical or enzymatic deglycosylation pretreatments, lectin histochemistry can be employed to determine if carbohydrates are linked to the protein core by means of an N- or O-glycosidic linkage or, indeed, to partially sequence the sugar chains. One of the most interesting model organs for the study of spermatogenesis is the amphibian urodele testis. However, this organ has not been very widely investigated with lectin histochemical research. In the last few years, we have carried out a research project to identify and locate glycoconjugates in the testis of the urodele Pleurodeles waltl, the Spanish newt, as a first approach to identify possible carbohydrates with key roles in spermatogenesis. Our findings reveal some glycan chains located in a fusome-like structure in early (diploid) germ cells, oligosaccharides with terminal GalNAc in the acrosome, the occurrence of glycan modifications in the acrosomal contents during spermiogenesis, and changes in glycan composition of follicle and interstitial cells during the spermatogenetic cycle. Furthermore, the similar labeling pattern of follicle and duct cells supports the hypothesis for a common origin of both cell types.

Targeted expression of androgen receptors in tooth-forming tissues of a neotropical salamander (Bolitoglossa schizodactyla) enables region-specific formation of dimorphic types of teeth in the male

Bicuspid teeth are a morphological characteristic in adult metamorphosed urodeles. However, during the mating season the males of many species of plethodontid salamanders (Urodela, Plethodontidae) from northern America bear large monocuspid teeth on their jaws. Since androgen levels are elevated during the mating season, it is likely that the formation of monocuspid teeth is controlled by androgens. However, many plethodontid salamanders from southern Central America live in habitats which lack significant seasonal changes and therefore are no seasonal breeders. These males constantly bear monocuspid teeth, however their presence is restricted to the premaxillary bone, which forms the most frontal element of the upper jaw. Teeth of all other dentigerous bones are bicuspid. This study is based on an immunohistochemical localisation of androgen receptors and reveals a differential expression of androgen receptors in the three separate dental laminae of the upper jaw of Bolitoglossa schizodactyla (Urodela, Plethodontidae) from western Panama. Our findings suggest that the restriction of androgen receptor expression to the premaxillary dental lamina of the male and its absence in all other tooth-forming tissues leads to the differences in tooth morphogenesis. In conclusion, a differential and cell-specific expression of androgen receptors in urodeles-similar to the situation in mammalian species-allows a selective response of differentiating tissues to the hormonal status of the animal.

Evolutionary aspects of cellular communication in the vertebrate hypothalamo-hypophysio-gonadal axis

This review emphasizes the comparative approach for developing insight into knowledge related to cellular communications occurring in the hypothalamus-pituitary-gonadal axis. Indeed, research on adaptive phenomena leads to evolutionary tracks. Thus, going through recent results, we suggest that pheromonal communication precedes local communication which, in turn, precedes communication via the blood stream. Furthermore, the use of different routes of communication by a certain mediator leads to a conceptual change related to what hormones are. Nevertheless, endocrine communication should leave out of consideration the source (glandular or not) of mediator. Finally, we point out that the use of lower vertebrate animal models is fundamental to understanding general physiological mechanisms. In fact, different anatomical organization permits access to tissues not readily approachable in mammals.

Glycan composition of follicle (Sertoli) cells of the amphibian Pleurodeles waltl. A lectin histochemical study

The glycan composition of the N- and O-linked oligosaccharides of the follicle (Sertoli) cells of the urodele amphibian Pleurodeles waltl testis were identified by lectin histochemistry, performed alone or in combination with enzymatic and chemical deglycosylation methods. The follicle cells were shown to contain: (1) Fuc, Galbeta(1,4)GlcNAc, GalNAc and Neu5Acalpha(2,3)Galbeta(1,4)GlcNAc in both N- and O-linked oligosaccharides; (2) Man in N-linked glycans; and (3) Galbeta(1,3)GalNAc in O-linked sugar chains. The follicle cells at the pre- and postmeiotic stages showed some differences in the UEA-1-positive Fuc characterisation, suggesting differences in the glycan composition. In addition, the sequence Neu5Acalpha(2,6)Gal/GalNAc was shown in the follicle cells only after spermiation, in the sperm-empty lobules of the developing glandular tissue. These results suggest that the follicle cells modify their glycoprotein content, probably for the performance of new roles, as the spermatogenetic cells develop. Thus the follicle cells surrounding male germ cells at different spermatogenetic stages would contain different glycoproteins involved in specific roles during male germ cell proliferation and maturation.

Characterization of two nuclear androgen receptors in Atlantic croaker: comparison of their biochemical properties and binding specificities

Two distinct androgen receptors (ARs) with different characteristics were identified in the brain and ovary of Atlantic croaker, Micropogonias undulatus. A nuclear AR, AR1, was identified in the brain that had high affinity binding sites for testosterone (T; Kd, 1.1 +/- 0.15 nM; binding capacity, 1.4 +/- 0.14 pmol/g tissue; n = 16). A second nuclear AR, AR2, was found in the ovary that had high affinity binding sites for 5alpha-dihydrotestosterone (DHT; Kd, 0.62 +/- 0.1 nM; binding capacity, 0.38 +/- 0.06 pmol/g tissue; n = 14). AR2 has physiochemical properties similar to those of other vertebrate ARs. AR2 has high affinity binding for a broad spectrum of natural and synthetic androgens, including 17alpha-methyl-5alpha-dihydrotestosterone, which has a relative binding affinity of DHT = 100% > T > mibolerone > 11-ketotestosterone = 16%, a rapid association (t1/2, 44 min) and a slow dissociation (t1/2, 45 h) rate, as well as specific binding to purified DNA. The cytosolic AR2 interacts with heat shock proteins in a manner similar to other steroid receptors, as sodium molybdate stabilizes the receptor, and it has a 7.4-7.8S sedimentation coefficient in a 5-20% sucrose gradient. In contrast, AR1 is highly specific for only a few androgens, with T = 100% relative binding affinity >> DHT >> 11-ketotestosterone > mibolerone > 17alpha-methyl-5alpha-dihydrotestosterone = 0, has rapid association (t1/2, 15 min) and dissociation (t1/2, 2.6 +/- 0.7 h) rates, and has specific binding to purified DNA upon heat activation. The cytosolic binding component sediments at 5.6-5.7S in a 5-20% sucrose gradient and is not affected by sodium molybdate, which suggests that AR1 does not interact with heat shock proteins in the usual manner. This is the first report of the presence of two different nuclear ARs displaying markedly different steroid binding specificities within a single vertebrate species.