An androgen receptor mRNA isoform associated with hormone-induced cell proliferation

RNA Extraction from Cartilage: Issues, Methods, Tips

The increase in degenerative diseases involving articular cartilage has pushed research to focus on their pathogenesis and treatment, exploiting increasingly complex techniques. Gene expression analyses from tissue are representative of the in vivo situation, but the protocols to be applied to obtain a reliable analysis are not completely cleared through customs. Thus, RNA extraction from fresh samples and specifically from musculoskeletal tissue such as cartilage is still a challenging issue. The aim of the review is to provide an overview of the techniques described in the literature for RNA extraction, highlighting limits and possibilities. The research retrieved 65 papers suitable for the purposes. The results highlighted the great difficulty in comparing the different studies, both for the sources of tissue used and for the techniques employed, as well as the details about protocols. Few papers compared different RNA extraction methods or homogenization techniques; the case study reported by authors about RNA extraction from sheep cartilage has not found an analog in the literature, confirming the existence of a relevant blank on studies about RNA extraction from cartilage tissue. However, the state of the art depicted can be used as a starting point to improve and expand studies on this topic.

Peripheral androgen receptors sustain the acrobatics and fine motor skill of elaborate male courtship

Androgenic hormones regulate many aspects of animal social behavior, including the elaborate display routines on which many species rely for advertisement and competition. One way that this might occur is through peripheral effects of androgens, particularly on skeletal muscles that control complex movements and postures of the body and its limbs. However, the specific contribution of peripheral androgen-muscle interactions to the performance of elaborate behavioral displays in the natural world has never been examined. We study this issue in one of the only natural physiological models of animal acrobatics: the golden-collared manakin (Manacus vitellinus). In this tropical bird, males compete with each other and court females by producing firecracker-like wing- snaps and by rapidly dancing among saplings over the forest floor. To test how activation of peripheral androgen receptors (AR) influences this display, we treat reproductively active adult male birds with the peripherally selective antiandrogen bicalutamide (BICAL) and observe the effects of this manipulation on male display performance. We not only validate the peripheral specificity of BICAL in this species, but we also show that BICAL treatment reduces the frequency with which adult male birds perform their acrobatic display maneuvers and disrupts the overall structure and fine-scale patterning of these birds' main complex wing-snap sonation. In addition, this manipulation has no effect on the behavioral metrics associated with male motivation to display. Together, our findings help differentiate the various effects of peripheral and central AR on the performance of a complex sociosexual behavioral phenotype by indicating that peripheral AR can optimize the motor skills necessary for the production of an elaborate animal display.

Developing laryngeal muscle of Xenopus laevis as a model system: androgen-driven myogenesis controls fiber type transformation

The developmental programs that contribute to myogenic stem cell proliferation and muscle fiber differentiation control fiber numbers and twitch type. In this study, we describe the use of an experimental model system-androgen-regulated laryngeal muscle of juvenile clawed frogs, Xenopus laevis-to examine the contribution of proliferation by specific populations of myogenic stem cells to expression of the larynx-specific myosin heavy chain isoform, LM. Androgen treatment of juveniles (Stage PM0) resulted in upregulation of an early (Myf-5) and a late (myogenin) myogenic regulatory factor; the time course of LM upregulation tracked that of myogenin. Myogenic stem cells stimulated to proliferate by androgen include a population that expresses Pax-7, a marker for the satellite cell myogenic stem cell population. Since androgen can switch muscle fiber types from fast to slow even in denervated larynges, we developed an ex vivo culture system to explore the relation between proliferation and LM expression. Cultured whole larynges maintain sensitivity to androgen, increasing in size and LM expression. Blockade of cell proliferation with cis-platin prevents the switch from slow to fast twitch muscle fibers as assayed by ATPase activity. Blockade of cell proliferation in vivo also resulted in inhibition of LM expression. Thus, both in vivo and ex vivo, inhibition of myogenic stem cell proliferation blocks androgen-induced LM expression and fiber type switching in juveniles.

Androgens modulate song effort and aggression in Neotropical singing mice

Androgens are an important class of steroid hormones involved in modulating the expression and evolution of male secondary sex characters. Vocalizations used in the context of aggression and mate attraction are among the most elaborate and diverse androgen-dependent animal displays as reflected in a rich tradition of studies on bird song and anuran calls. Male Alston's singing mice (Scotinomys teguina) commonly emit trilled songs that appear to function in male-male aggression. In this study, we experimentally manipulated androgens in singing mice to assess their role in modulating aggression and song effort. Testosterone- and DHT-treated animals retained aggressive and song attributes similarly. However, castrated mice administered empty implants showed more subordinate behavior and sang fewer songs that were shorter, lower in power, higher in frequency, and less stereotyped. The extensive effects of androgens on a suite of phenotypes highlight their role in linking gonadal status with decisions about investment in reproductive behaviors.

The role of androgen receptors in regulating territorial aggression in male song sparrows

This paper examines the role that androgen receptors (ARs) play in modulating aggressive behavior in male song sparrows, Melospiza melodia morphna. Song sparrows are seasonally breeding, territorial birds that maintain year-round territories with male-female pair bonds formed during the spring breeding season. Plasma testosterone levels peak as territories are established and mates acquired. In late summer, testosterone levels fall and remain basal during the non-breeding season. We examined the role of ARs in regulating territorial aggression in captive song sparrows under short- and long-day conditions as well as just prior to, and at the start of the breading season in freely living birds using the nonsteroidal antiandrogen flutamide to block AR function. Birds were implanted with either empty or drug filled silastic implants for 18 to 42 days and then challenged with a novel male decoy to assess the individual birds level of male-male aggression. Freely living birds remained on their home territory and underwent a simulated territorial intrusion, whereas laboratory-held birds were assessed using a laboratory simulated territorial intrusion and remained in their home cage. Experimental treatment of male song sparrows decreased aggressive behavior during the pre-breeding life history substage (March-April) in freely living birds as well as in laboratory-held birds under long-day (16L:8D) conditions. During the early breeding substage (April-May) there was no measurable effect of flutamide treatment on aggressive behavior, nor was there a difference in behavior in the (8L:16D) laboratory birds. This demonstrates that ARs are an important component of the neuroendocrine control of aggressive behavior. Given that flutamide only affected aggression during the pre-breeding substage and in LD birds, the results suggest that AR dependent control of aggressive behavior changes as song sparrow life history states change.

Phylogenetic conservation of the androgen receptor AR45 variant form in placental mammals

A cDNA coding for a tissue-specific AR45 variant form of the androgen receptor (AR) has recently been identified in humans, with highest expression levels found in heart. The deduced protein comprises the DNA-binding domain, hinge region and ligand-binding domain of the AR, but not the N-terminal domain which is replaced by a unique, short, seven amino-acid-long stretch. This sequence is encoded by the mutually exclusive exon 1B, located between exons 1 and 2 of the human AR gene. As transcript variants of the steroid receptor family have been shown to have important implications for hormone function, we set out to analyse the genomes of different organisms for potential AR45 expression. We found exon 1B to be conserved in the syntenic chromosomal region of non-human primates such as the chimpanzee Pan troglodytes, the orang-utan Pongo pygmaeus, the macaque Macaca mulatta and the marmoset Callithrix jacchus, and of the elephant Loxondonta africana, the pig Sus scrofa and the dog Canis familiaris. Quantification of AR45 transcript levels in heart, skeletal muscle and lung of Macaca fascicularis showed the heart to be the main organ of expression. A complete AR45 cDNA was furthermore isolated from the heart of this species. Comparative analysis of the identified AR45 exon 1B regions and of the deduced amino acids revealed a high conservation among species. The four N-terminal residues were identical in all eight species, whereas a few changes were seen in the other three residues in the marmoset, elephant and pig. In contrast, we observed more divergence in the mouse Mus musculus and rat Rattus norvegicus syntenic regions. Here a stop codon was found downstream of the potential start codon in the putatively deduced protein sequence and it can be inferred that no protein corresponding to AR45 exists in these two species. The existence of AR45 in different placental mammals with the exception of mouse and rat suggests a disappearance in rodents late in evolution, before the separation of the mouse and rat lineages, about 16 million years ago. In view of the potential function of AR45 as a regulator of AR function, and considering the multiple roles of androgens in normal physiology and in several diseases, these findings have important implications with regard to subtle differences in the action of the male sexual hormone in various organisms.

Effects of an androgenic growth promoter 17beta-trenbolone on masculinization of Mosquitofish (Gambusia affinis affinis)

Endocrine disrupting chemicals can affect normal hormone dependent processes through numerous mechanisms, including ligand mimicky. 17beta-Trenbolone (TB), a pharmaceutical, androgenic, anabolic steroid, is a potent agonist of androgen receptors, and has been extensively used as a growth promoter for beef cattle in the US. The effects of TB on adult and newborn mosquitofish (Gambusia affinis affinis) were examined. Two forms of mosquitofish androgen receptor (AR), ARalpha and ARbeta, were cloned. The mRNA expression levels of ARalpha and ARbeta were transiently increased in the anal fin of adult females at day 3 following exposure to TB (1-10 microg/L) or methyltestosterone (MT) (0.1-10 microg/L), a pharmaceutical androgen used as a positive control. Gonopodium differentiation from the adult female anal fin was induced after 28 days of exposure to TB (1-10 microg/L) or MT (0.1-10 microg/L). Gonopodium differentiation also was induced in all mosquitofish fry exposed for 28 days to 0.3, 1 or 10 microg/L TB. Furthermore, spermatozoa were observed histologically in the testes of male fry exposed for 28 days to 1 or 10 microg/L TB; spermatozoa are normally observed only in the testes of mature males. Surprisingly, all female fry exposed for 28 days to 1 or 10 microg/L TB displayed the formation of an ovotestis, as spermatozoa were found in the ovary. Thus, TB, like MT, induced masculinization of the anal fin accompanied by a transient up-regulation of ARalpha and ARbeta in adult females. TB also induced differentiation of the anal fin into a gonopodium in fry of both sexes, stimulated precocious spermatogenesis in the testes of males and the formation of ovotestes in females.

Sea bass (Dicentrarchus labrax) androgen receptor: cDNA cloning, tissue-specific expression, and mRNA levels during early development and sex differentiation

Androgens play key roles in vertebrate sex differentiation, gonadal maturation and reproductive behaviour and their actions are generally mediated through specific nuclear receptors. The present study describes the isolation, sequencing and characterization of the cDNA encoding the androgen receptor (AR) in the European sea bass. AR was cloned from a sea bass testis cDNA library and encoded a predicted protein of 767 residues, with a calculated molecular weight of 86.4 kDa and a theoretical pI of 6.34. Several domains present in all cloned ARs were identified. The domains corresponded to an amino-terminal hypervariable transcriptional activation domain (TAD), a central highly conserved DNA-binding domain (DBD), and a carboxy-terminal ligand-binding domain (LBD). Percentages of homology-similarity among these functional domains in teleost fish ranged between 9 and 75% for the TAD, 73 and 98% for the DBD, and 78 and 96% for the LBD when compared to those of the sea bass. Tissue-specific expression showed that AR was preferentially expressed in testis, ovaries, and brain. Some other tissues such as the head kidney, liver and spleen also showed AR expression although at very low levels. A semiquantitative PCR was developed to study the expression of AR mRNA during the period of development encompassed between 50 and 300 DPH in sea bass gonads. An experimental design, involving repeated size gradings, based on the fact that sea bass females are larger than males already at sex differentiation, was set to obtain a group consisting of the largest fish (female-dominant) and a group consisting of the smallest fish (male-dominant). The results showed very low mRNA expression levels of AR in the gonads during early development. Differences in AR expression between groups were first encountered at 150 DPH and became especially marked at 250 DPH with much higher levels in the male-dominant group. These sex-related differences in expression profiles between males and females by the time of sex differentiation, suggest an important role for AR controlling this process in the sea bass.

Steroid receptors in the adult zebra finch syrinx: a sex difference in androgen receptor mRNA, minimal expression of estrogen receptor alpha and aromatase

The zebra finch syrinx (sound production organ) is a sexually dimorphic component of the song system. Only male zebra finches sing, and in parallel, the overall mass and size of fibers in the two largest syrinx muscles are greater in males than females. Despite these obvious sexual dimorphisms, little is known about the role of steroid hormones in the maintenance of the structure and/or function of the syrinx. In this report, we used in situ hybridization to assess the expression of androgen receptor (AR), estrogen receptor alpha (ERalpha), and aromatase (AROM) mRNAs in the syrinx of adult male and female zebra finches. Increased AR mRNA expression was noted in males compared to females in two regions, over the ventralis muscle and in a band of connective tissue neighboring cartilage (perichondria). In contrast, we did not detect specific ERalpha or AROM mRNA expression within the syrinx. However, substantial ERalpha mRNA was present in oviduct, and aromatase mRNA was expressed at high levels in ovary. In parallel, an assay for AROM detected activity in ovary, but not in syrinx tissue from males or females. Taken together, these data suggest that the adult syrinx is sensitive to androgens; that sex differences in function and morphology of the syrinx may in part be due to increased expression of AR in males compared to females. In contrast, estrogen receptor alpha and AROM appear to have limited roles.

Androgen receptor isoforms AR-A and AR-B display functional differences in cultured human bone cells and genital skin fibroblasts

Two isoforms of the androgen receptor (AR-A and AR-B), differing by a lack of the first 187 amino acids in the NH2-terminal transactivation domain of AR-A, are expressed in connective tissue and bone. Transient transfections of normal human osteoblastic cells (HOB) and of genital skin fibroblasts defective in AR (GSF-540) were utilized to compare the functional properties of AR isoforms in mesenchymal tissues. Overexpression of AR-B or AR-A did not significantly affect type I collagen secretion. However, overexpression of AR-B (but not AR-A) restored androgen-dependent DNA synthesis in AR-defective fibroblasts and increased DHT-mediated DNA synthesis three-fold in osteoblastic cells. Overexpression of AR-A did not affect DHT action but reduced DHT-dependent DNA synthesis when transfected together with AR-B. The need for an NH2-terminal sequence of the AR for complete receptor function was demonstrated using electrophoretic mobility shift assay. A peptide coding for the amino terminus of the complete AR was able to decrease the binding affinity of AR-B and increase the binding affinity of AR-A to the androgen response element. Our results suggest that AR-A lacks the ability to stimulate cell proliferation possibly due to reduced binding of AR co-activating proteins to the truncated N-terminal transactivation domain rather than due to impaired stability of the AR-A isoform.

Cloning and characterization of androgen receptor from bullfrog, Rana catesbeiana

We have cloned and characterized a full-length cDNA of androgen receptor (AR) from the testis of bullfrog, Rana catesbeiana. The cDNA contains an open reading frame of 2328 nucleotides encoding a protein of 776 amino acid residues. The bullfrog AR shows high homology with ARs from other species in its amino acid sequence. Its overall homology with those of African clawed frog, Japanese eel and human is 70, 53, and 63%, respectively. As expected, the N-terminal domain shows much less homology (30-59%) than both DNA-binding domain (85-92%) and ligand binding domain (80-89%). Northern blot analysis detected the bullfrog AR message as a single transcript of around 9 kb only in the testis. However, RT-PCR analysis revealed that AR mRNA is also expressed in other tissues although the levels are very low compared to that in the testis. Western blot analysis of whole tissue extracts showed the presence of AR protein in fore brain, heart, and testis. The AR gene is present as a single copy in bullfrog based on Southern blot analysis of genomic DNA. Altogether, the results suggest that the bullfrog AR is evolutionary conserved and may have functions similar to those shown in other species.

Distribution of androgen receptor mRNA expression and immunoreactivity in the brain of the green anole lizard

Male courtship and copulation are androgen dependent in the green anole lizard, and female receptivity can be facilitated by testosterone. However, only a few, and relatively large, regions in the brain have been implicated in the control of these behaviours. In situ hybridization and immunohistochemistry were therefore used to determine in detail where androgens are likely to act in the brains of breeding males and females. A 697-bp fragment of the anole androgen receptor (AR) was cloned from total RNA isolated from the kidney, which contains the highly androgen-sensitive renal sex segment. The cloned fragment spanned part of the C, the entire D, and part of the E domains, and shared a high degree of similarity with the AR of various species. 35S-labelled antisense and sense probes were generated from the 697-bp fragment for use in in situ hybridization, and the AR antibody PG-21 was used for immunohistochemistry. Both sexes consistently had AR mRNA expression and immunoreactivity in areas associated with vertebrate reproductive behaviours and in motor areas of the brainstem. Interestingly, the PG-21 antibody produced labelling in both the nucleus and cytoplasm, including neuronal processes. The distribution of mRNA and immunoreactivity were comparable in males and females, and the amount of labelling was generally similar, although slightly greater in females. The expression pattern of AR in this species supports the idea that distribution is highly conserved among vertebrates, but that it probably does not dictate behavioural differences between the sexes in anoles.

Two subtypes of androgen and progestogen receptors in fish testes

Two subtypes (alpha and beta) of androgen (AR) and progestogen receptors (PR) are present in the testis of Japanese eel (Anguilla japonica). Amino acid homology of the open reading frames between alpha and beta in AR or PR is approximately 40%, but the DNA- and ligand-binding domains show high homology between subtypes. Judging from these structures, alpha and beta are not isoforms derived from translational initiation at two in-phase ATG codons, alternative splicing, or tetraploidy. In transient transfection assays using a reporter construct containing a steroid-responsive promoter, each subtype showed its corresponding hormone-dependent transactivation. The ligand affinity for transactivation between AR and PR subtypes was similar for physiological ligands. Tissue distribution of both subtype mRNAs was different. Protein interaction between subtypes was demonstrated in vitro by GST pull-down assays. These results clearly indicate that two functional subtypes of AR and PR exist in eel. These findings will advance our understanding of the mechanisms underlying sex steroid signaling.

Analysis of glucocorticoid and androgen receptor gene fusions delineates domains required for transcriptional specificity

Androgen receptor (AR) and glucocorticoid receptor (GR) influence distinct physiologic responses in steroid-responsive cells despite their shared ability to selectively bind in vitro to the same canonical DNA sequence (TGTTCT). While the DNA-binding domains (DBDs) of these receptors are highly conserved, the amino N-terminal domain (NTD) and hormone-binding domain (HBD) are evolutionarily divergent. To determine the relative contribution of these functional domains to steroid-specific effects in vivo, we constructed a panel of AR/GR gene fusions by interchanging the NTD, DBD, and HBD regions of each receptor and measured transcriptional regulatory activities in transfected kidney and prostate cell lines. We found that GR was approximately 10-fold more active than AR when tested with the mouse mammary tumor virus promoter, and that this difference in activity was primarily owing to sequence divergence in the NTDs. We also tested transcriptional activation of the androgen-dependent rat probasin promoter, and in this case, AR was at least twofold more active than GR. Analysis of the chimeric receptors revealed that this difference mapped to the DBD region of the two receptors. Transcriptional repression functions of the wild-type and chimeric receptors were measured using an activator protein 1 (AP-1) transrepression assay and identified the GR HBD as a more potent transrepressor of AP-1 transcriptional activation than the AR HBD. Taken together, our analyses reveal that evolutionary sequence divergence between AR and GR functional domains results in unique promoter-specific activities within biologic systems in which both AR and GR are normally expressed.

Vertebrate Secondary Sexual Characteristics-Physiological Mechanisms and Evolutionary Patterns

As most commonly presented, the organization-activation theory of sexual differentiation emphasizes the importance of the relative age of the organism for understanding steroid hormone effects. However, considering the actual physiological mechanisms of tissue enlargement (hyperplasia/hypertrophy) provides an additional perspective for interpreting patterns of evolutionary change in sexual dimorphism. Using that focus, it is possible to suggest mechanistic explanations for patterns of allometry and the size of some secondary sexual characteristics produced by "runaway" selection. It can also lead to the formulation of testable hypotheses regarding the type of sexually dimorphic characters that might evolve through "good genes" models; the relationship between intrasexual competition, polygyny, and the development and size of male weapons; and the control and type of secondary sexual characteristics that will be present in males with associated and disassociated reproductive patterns.

The role of 5alpha-reductase activity in sexual behaviors of the green anole lizard

Both testosterone (T) and its metabolite, 5alpha-dihydrotestosterone (DHT), can facilitate male sexual behavior in the lizard Anolis carolinensis. The present study addresses the role of DHT synthesis in regulating male sexual behavior by inhibiting 5alpha-reductase, the enzyme that converts T into DHT. In two separate experiments (one replacement and one maintenance paradigm), breeding adult males were castrated and implanted with capsules of T, DHT, or a control capsule (blank, BL). The animals were then injected with the 5alpha-reductase inhibitor, FCE, or with steroid suspending vehicle (SSV) as a control. Both experiments produced similar results. Overall, T was most effective in eliciting courtship and copulatory behaviors above control levels. In both experiments, treatment with FCE attenuated the T-induced effects on courtship behavior, whereas the inhibition of 5alpha-reductase activity resulted in modest and inconsistent effects on the latency to intromission and the proportion of copulating males. DHT treatment did not significantly increase courtship or copulatory behaviors above control levels. These results suggest that (a) 5alpha-reductase activity is necessary but that DHT alone is not sufficient for stimulating courtship in male A. carolinensis; and (b) courtship behavior is more sensitive than copulatory behavior to the activity of the androgen metabolizing enzyme.

Androgen binding profiles of two distinct nuclear androgen receptors in Atlantic croaker (Micropogonias undulatus)

In the present study, the binding affinities of 28 androgens for two nuclear androgen receptors (AR), termed AR1 and AR2, in Atlantic croaker (Micropogonias undulatus) brain and ovarian tissues, respectively, were determined using competitive binding assays. The 5alpha-reduction of steroids, in general, increased the metabolite's binding affinity for AR2 while decreasing it for AR1. In addition, few androgens bound to AR1 with high affinity and modifications to the basic 3-ketone,4-ene,17beta-hydroxy structure of testosterone usually reduced its binding affinity for AR1. However, androgens with ketone groups at the 3- and 17-position bound with high affinity to AR1 provided that the androgen had either a 5alpha-reduced A-ring or a third ketone group at the 11-position. This suggests that there may be several high affinity conformations that AR1 can occupy depending upon whether an androgen possesses a ketone or a hydroxyl group at the 17-position. The binding of androgens to AR2 showed a more predictable pattern, 5alpha-reduced steroids bound better than 4-ene steroids and any changes to the basic 3-keto,17-hydroxy motif of 5alpha-dihydrotestosterone lowered the binding affinity of a steroid. However, these structural changes often caused only minor decreases in binding affinity, such that AR2 has a broader affinity for androgens and a greater affinity than AR1 for structurally diverse androgens. Widely different androgen binding affinities of AR1 and AR2 suggest that these two nuclear androgen receptors may mediate the physiological actions of different androgens in teleosts.

Identification of two nuclear androgen receptors in kelp bass (Paralabrax clathratus) and their binding affinities for xenobiotics: comparison with Atlantic croaker (Micropogonias undulatus) androgen receptors

Two distinct nuclear androgen receptors (ARs) were identified in brain and ovarian tissues of kelp bass, Paralabrax clathratus, termed kbAR1 and kbAR2, which correspond to the two nuclear ARs we have previously characterized in Atlantic croaker, Micropogonias undulatus, termed acAR1 and acAR2. Scatchard analysis of nuclear fractions of whole brain tissue demonstrated that kbAR1 had a single class of high-affinity binding sites for testosterone (T; K(d) of 1. 8 nM and B(max) of 1.0 pmol/g tissue), whereas cytosolic fractions of kbAR2 ovarian tissue had a single class of high-affinity binding sites for dihydrotestosterone (DHT; K(d) of 0.1 nM and B(max) of 0.5 pmol/g tissue). Competition studies showed that both kbAR1 and kbAR2 were specific for androgens. However, kbAR1 bound only T with high affinity, whereas kbAR2 bound DHT, mibolerone, 17alpha-methyl-testosterone, T, and 11-ketotestosterone with high affinity. In addition, we examined the binding affinities of dichlorodiphenyltrichloroethane and its derivatives, several hydroxylated polychlorinated biphenyl (PCB) congeners, PCB mixtures, and the fungicide vinclozolin and its two metabolites M1 and M2 for the two ARs in Atlantic croaker ovarian, testicular, and brain tissues and in kelp bass ovarian and brain tissues. Only 4, 4'-PCB-3-OH and 2',5'-PCB-3-OH demonstrated greater than 50% displacement of [(3)H]testosterone from either acAR1 or kbAR1. In contrast, with the exception of vinclozolin, all of the xenobiotics examined demonstrated binding to acAR2 in testicular and ovarian tissues. The binding affinities were highest in the testicular tissue with M2, 2,2'5'-PCB-4-OH, and o,p'-DDD all binding with EC(50)s less than 10 microM. The binding affinities of xenobiotics to kbAR2 in ovarian tissue were similar to their binding affinities for ovarian acAR2. The finding that AR1 and AR2 possess different binding affinities for natural androgens and synthetic steroids, as well as for xenobiotics, suggests that the activities of androgens and of certain xenobiotics will depend upon the type of AR present within the target tissue.

Sequence and expression of a cDNA encoding the red seabream androgen receptor

The cDNA of the androgen receptor (AR) has been isolated from the ovary of red seabream, Pagrus major, and sequenced. The amino acid sequence of red seabream AR (rsAR) shows about 45% identity with those of Xenopus, rat, mouse, and human ARS. It is shown that rsAR has the ability to trans-activate the responsive gene depending on the presence of androgen.

Seasonal changes in androgen receptor immunoreactivity in the song nucleus HVc of a wild bird

In seasonally breeding songbirds, song behavior and neural morphology change seasonally. Song control nuclei are larger during the breeding season, as determined by multiple cytological labels. Seasonal changes in song nuclei are regulated by testosterone (T), and several song nuclei contain intracellular androgen receptors (AR). Changes in AR levels may interact with changes in plasma T levels to regulate song nuclei morphology. We measured seasonal changes in AR-immunoreactive cells in the telencephalic song nucleus HVc using the affinity-purified PG21 antibody to rat AR. We caught wild adult male Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) during spring breeding in Alaska and during autumn migration in Washington State. To enhance PG21 labeling, animals were treated with T for 90 minutes (as in Smith et al. [1996] J. Histochem. Cytochem. 44:1075-1080). AR+ cells were found in HVc and other song nuclei, hippocampus, nucleus taeniae (homologue to mammalian amygdala), and the hypothalamus. HVc volume was larger in spring (S) than autumn (A), in both the PG21- and Nissl-stained sections (S:A = 1.9 and 1.7, respectively). In spring, but not autumn, PG21 and Nissl measurements were slightly different (PG21:Nissl = 1.07), perhaps because PG21 labeled the most caudal extent of HVc more clearly. In HVc, AR+ cell density and number were greater in spring. The percentage of AR+ cells was also increased in spring. Qualitatively, the staining intensity of individual cells was higher in spring. In time course studies, the T injection enhanced PG21 staining within 15 minutes, suggesting that it increases labeling via AR translocation to and concentration in the cell nucleus.

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.

Sequence and expression of a cDNA encoding the red sea bream androgen receptor

The cDNA of the androgen receptor (AR) has been isolated from the ovary of red sea bream, Pagrus major, and sequenced. The amino acid sequence of red sea bream AR (rsAR) shows about 45% identity with that of Xenopus, rat, mouse, and human AR. It is shown that rsAR has the ability to trans-activate the responsive gene depending on the presence of androgen.

Androgen receptors and sexual dimorphisms in the larynx of the bullfrog

As in most anuran amphibians, both male and female bullfrogs (Rana catesbeiana) vocalize. Sex differences in vocalizations in the bullfrog may be due to sex differences in the larynx. We examined the laryngeal muscle to determine whether it possessed androgen receptors and whether there were morphological sexual dimorphisms in the larynx. Using a polyclonal antibody and immunocytochemistry, we found androgen receptors in the laryngeal dilator muscle of both sexes. Males possessed approximately 13% more receptor-positive muscle nuclei than females. We also stained the dilator muscle for the presence of succinate dehydrogenase. Density of staining for the enzyme was significantly greater in male muscle than in female muscle, indicating greater oxidative capacity of muscle in males. This procedure also showed both a significantly greater cross-sectional area for the dilator muscle in males and a greater area for individual fibers. Male muscle consisted almost entirely of fast-twitch oxidative/glycolytic fibers. Female muscle contained a mixture of fast-twitch glycolytic fibers and two subclasses of fast-twitch oxidative/glycolytic fibers. Finally, both the length and width of the entire laryngeal complex and the length and width of the dilator were significantly greater in males than in females. In summary, laryngeal muscle of bullfrogs possessed androgen receptors and is thus likely to be androgen sensitive. Androgens, during development or at adulthood, may be responsible for the anatomic and enzymatic sexual dimorphisms in the larynx.

Molecular mechanism of androgen action

Androgens affect the growth and development of a wide variety of cell types in both males and females and produce their effects by binding to androgen receptors, which modulate the transcription of specific genes. Testosterone is the major active androgen circulating in blood, but in many tissues it is metabolized by 5alpha-reductase to 5alpha-dihydrotestosterone, which binds to and activates the androgen receptor. Androgen receptors are members of the nuclear receptor family of transcription factors, and these nuclear receptors control transcription by recruitment of a variety of co-activators and co-repressors. Mutations in the androgen receptor and 5alpha-reductase can affect male sexual development. 5alpha-Reductase is also critical for parturition and fetal survival in mice. Inhibitors of 5alpha-reductase are being used increasingly to treat some androgen-dependent disorders. Because androgens also suppress the growth of certain cancer cells, they might also have a role in treating prostate cancer.

Sexual differentiation of the vertebrate brain: principles and mechanisms

A wide variety of sexual dimorphisms, structural differences between the sexes, have been described in the brains of many vertebrate species, including humans. In animal models of neural sexual dimorphism, gonadal steroid hormones, specifically androgens, play a crucial role in engendering these differences by masculinizing the nervous system of males. Usually, the androgen must act early in life, often during the fetal period to masculinize the nervous system and behavior. However, there are a few examples of androgen, in adulthood, masculinizing both the structure of the nervous system and behavior. In the modal pattern, androgens are required both during development and adulthood to fully masculinize brain structure and behavior. In rodent models of neural sexual dimorphism, it is often the aromatized metabolites of androgen, i.e., estrogens, which interact with estrogen receptors to masculinize the brain, but there is little evidence that aromatized metabolites of androgen play this role in primates, including humans. There are other animal models where androgens themselves masculinize the nervous system through interaction with androgen receptors. In the course of masculinizing the nervous system, steroids can affect a wide variety of cellular mechanisms, including neurogenesis, cell death, cell migration, synapse formation, synapse elimination, and cell differentiation. In animal models, there are no known examples where only a single neural center displays sexual dimorphism. Rather, each case of sexual dimorphism seems to be part of a distributed network of sexually dimorphic neuronal populations which normally interact with each other. Finally, there is ample evidence of sexual dimorphism in the human brain, as sex differences in behavior would require, but there has not yet been any definitive proof that steroids acting early in development directly masculinize the human brain.

Generating sexually differentiated songs

The past year has witnessed increased confusion as to the role of gonadal hormones in the development of neuroeffectors for sexually differentiated vocalizations in several species. Are sex differences in levels of circulating gonadal hormones robust enough to account for the full spectrum of male/female differences? Understanding how vocal behaviors are generated has improved, permitting greater insights into how differences in cell number and type contribute to male- and female-specific songs in frogs and birds.

The role of androgens in female vertebrates

The role of androgens in vertebrate females has been overlooked until recently. We examine the functional significance of androgens in females by reviewing studies that document relatively high levels of circulating plasma androgens, androgen receptors, or androgen-metabolizing enzymes in females. Among the mechanisms of androgenic action identified are enhanced neuron survival, stimulation of muscle satellite cell proliferation, alteration of ion current kinetics, and release of somatostatin. These mechanisms are not sex specific and thus we hypothesize that androgens play a significant role in normal female development. We encourage study in this nontraditional research area.

A four-amino-acid insertion in the ligand-binding domain inactivates hRXRbeta and renders dominant negative activity

Retinoid X receptors (RXRs) are members of the steroid and thyroid hormone receptor superfamily of hormone-dependent transcription factors that mediate the pleiotropic effect of retinoids. Here, we report the initial characterization of an isoform of hRXR beta, termed hRXR beta3, which was previously identified as an H-2RIIBP isoform (Epplen and Epplen, 1992). The hRXR beta3 isoform cotains an in-frame insertion of four amino acids (SLSR) in the ligand binding domain at codon 419. The isoform is generated by alternate use of a 3' splice acceptor site and was detectable by reverse transcription polymerase chain reaction (RT-PCR) in all human tumor cell lines and mouse tissues examined. Chimeric receptors, in which the ligand-binding domain of hRXR alpha was substituted by the corresponding domain from hRXR beta3, were used to investigate the consequences of the SLSR insertion on the transactivation and DNA-binding functions of the chimeric receptor. Co-transfection assays revealed that a chimera RXR alpha/beta3 receptor failed to transactivate the RXR-specific CRBPII promoter, whereas the identical chimera lacking the SLSR insertion was active. The RXR alpha/beta3 receptor exhibited dominant negative activity against active retinoid X and retinoic acid receptors on retinoid-responsive promoters. Moreover, the RXR alpha/beta3 protein failed to interact physically with the retinoic acid receptor (RAR) to form heterodimers as detected by physical association assays, and failed to bind DNA containing an RAR-responsive element. Therefore, this suggests that the SLSR insertion in the ligand-binding domain of the RXR alpha/beta3 receptor is responsible for the altered behavior of the chimera. Our findings raise the possibility that RXR alpha/beta3, and perhaps hRXR beta3 isoform, function by titrating a limiting adaptor molecule that is involved in mediating retinoid function.

Trophic effects of androgen: receptor expression and the survival of laryngeal motor neurons after axotomy

To determine whether changes in androgen receptor (AR) expression are associated with trophic actions of androgens, we have examined the laryngeal motor nucleus (N. IX-X) of Xenopus laevis 1 and 5 months after section of the laryngeal nerve. In situ hybridization was used to recognize cells expressing mRNA for the Xenopus AR and bromodeoxyuridine to assess cell proliferation. In addition, the total number of cells was determined in untreated and dihydrotestosterone (DHT)-treated animals after 5 months of axotomy. After 1 month of axotomy, the number of AR mRNA-expressing cells in N. IX-X is 1.8-fold higher than in the intact side. Androgen upregulates expression of AR mRNA in N. IX-X on both the intact and the axotomized sides, suggesting that the increase is independent of contact with muscle. Neither the axotomy- nor the androgen-induced increase in number of cells expressing AR mRNA is attributable to cell proliferation. Five months after axotomy, both the total number of cells and the number of AR mRNA-expressing cells are severely decreased in the axotomized N. IX-X. DHT treatment mitigates the cell loss in N. IX-X induced by prolonged axotomy; the effect includes maintenance of AR mRNA-expressing cells. Gonadally intact males have more cells in the axotomized N. IX-X than castrated animals, suggesting that androgen acts at physiological levels as a trophic hormone. Axotomy-induced upregulation of AR expression may facilitate the trophic actions of androgens.

Trophic effects of androgen: receptor expression and the survival of laryngeal motor neurons after axotomy

To determine whether changes in androgen receptor (AR) expression are associated with trophic actions of androgens, we have examined the laryngeal motor nucleus (N. IX-X) of Xenopus laevis 1 and 5 months after section of the laryngeal nerve. In situ hybridization was used to recognize cells expressing mRNA for the Xenopus AR and bromodeoxyuridine to assess cell proliferation. In addition, the total number of cells was determined in untreated and dihydrotestosterone (DHT)-treated animals after 5 months of axotomy. After 1 month of axotomy, the number of AR mRNA-expressing cells in N. IX-X is 1.8-fold higher than in the intact side. Androgen upregulates expression of AR mRNA in N. IX-X on both the intact and the axotomized sides, suggesting that the increase is independent of contact with muscle. Neither the axotomy- nor the androgen-induced increase in number of cells expressing AR mRNA is attributable to cell proliferation. Five months after axotomy, both the total number of cells and the number of AR mRNA-expressing cells are severely decreased in the axotomized N. IX-X. DHT treatment mitigates the cell loss in N. IX-X induced by prolonged axotomy; the effect includes maintenance of AR mRNA-expressing cells. Gonadally intact males have more cells in the axotomized N. IX-X than castrated animals, suggesting that androgen acts at physiological levels as a trophic hormone. Axotomy-induced upregulation of AR expression may facilitate the trophic actions of androgens.

Androgen receptor mRNA expression in Xenopus laevis CNS: sexual dimorphism and regulation in laryngeal motor nucleus

Using Northern analysis, in situ hybridization, and nuclease protection assays, the expression and regulation of androgen receptor messenger RNA (AR mRNA) was examined in the CNS of juvenile Xenopus laevis. Only one of the AR mRNA isoforms expressed in X. laevis is transcribed in the CNS as shown by Northern blot analysis. Nuclease protection assays demonstrate that the expression of AR mRNA is higher in the brain stem than in the telencephalon and diencephalon. Although expression of AR mRNA is widespread throughout the CNS, cells of cranial nerve nucleus IX-X (N.IX-X) and spinal cord display the highest in situ hybridization signals in their cytoplasm. Double labeling using horseradish peroxidase and digoxigenin labeled AR probes reveals that laryngeal and anterior spinal cord motor neurons express AR mRNA. More cells express AR mRNA in N.IX-X of males than of females. The number of AR expressing cells in N. IX-X decreases following gonadectomy in both sexes, and dihydrotestosterone (DHT) treatment for 1 month reverses this effect. Increased expression of AR mRNA in the brain of DHT treated animals is also apparent in nuclease protection assays. Sex differences in number of AR expressing cells and hormone regulation of AR mRNA expression in motor nuclei may influence neuromuscular systems devoted to sexually differentiated behaviors.

Preferential stimulation of human progesterone receptor B expression by estrogen in T-47D human breast cancer cells

Human progesterone receptor (PR) expression is controlled by two promoter regions giving rise to transcripts encoding PR A and B proteins. It is unknown whether estrogen and progesterone, the major physiological modulators of PR expression, exert their effects equally on the PR promoters. The aim of this study was to analyze estrogen and progestin effects on PR promoters, PR-encoding transcripts, and PR A and B proteins in T-47D human breast cancer cells. The progestin ORG 2058 caused a prolonged decrease in transcription of the PR gene and also abrogated estrogen stimulation of PR transcription. Estradiol (E2) treatment increased the activity of the B but not the A promoter transfected into T-47D cells. ORG 2058 had no effect on the basal or E2-stimulated activity of either promoter. E2 caused a preferential increase in transcripts derived from promoter B, whereas progestins decreased the levels of all PR transcripts. E2 preferentially increased the concentration of the PR B protein and caused a decrease in the PR A/B ratio. This demonstration that estrogen and progestin independently control the synthesis of transcripts arising from the PR promoters and that estrogen alters the cellular PR A/B ratio provides possible mechanisms underlying the cell and tissue specificity of PR regulation.

Sexual differentiation and hormonal regulation of the laryngeal synapse in Xenopus laevis

In Xenopus laevis frogs, sex differences in adult laryngeal synapses contribute to sex differences in vocal behavior. This study explores the development of sex differences in types of neuromuscular synapses and the development and hormone regulation of sex differences in transmitter release. Synapses in the juvenile larynx have characteristics not found in adults: juvenile muscle fibers can produce subthreshold or suprathreshold potentials in response to the same strength of nerve stimulation and can also produce multiple spikes to a single nerve stimulus. Juvenile laryngeal muscle also contains the same synapse types (I, II, and III) as are found in adult laryngeal muscle. The distribution of laryngeal synapse types in juveniles is less sexually dimorphic than the distribution in adults. Analysis of quantal content indicates that laryngeal synapses characteristically release low amounts of transmitter prior to sexual differentiation. Quantal content values from male and female juveniles are similar to values for adult males and are lower than values for adult females. When juveniles are gonadectomized and treated with exogenous estrogen, quantal content values increase significantly, suggesting that this hormone may increase transmitter release at laryngeal synapses during development. Gonadectomy alone does not affect quantal content of laryngeal synapses in either sex. Androgen treatment decreases quantal content in juvenile females but not males; the effect is opposite to and smaller than that of estrogen. Thus, muscle fiber responses to nerve stimulation and transmitter release are not sexually dimorphic in juvenile larynges. Transmitter release is strengthened, or feminized, by the administration of estradiol, an ovarian steroid hormone.

Androgen directs sexual differentiation of laryngeal innervation in developing Xenopus laevis

In adult Xenopus laevis, innervation of the vocal organ is more robust in males than in females. This sex difference originates during tadpole development; at stage 56, when the gonads first differentiate, the number of axons entering the larynx is the same in the sexes, but by stage 62, innervation is greater in males. To determine if androgen secretion establishes sex differences in axon number, we treated tadpoles with antiandrogen or androgen beginning at stage 48 or 54 and counted laryngeal nerve axons at stage 62 using electron microscopy. When male tadpoles were treated with the antiandrogen hydroxyflutamide, axon numbers were reduced to female-typical values; axon numbers in females were unaffected by antiandrogen treatment. When female tadpoles were treated with the androgen DHT (dihydrotestosterone), axon numbers were increased to male-like values. These findings suggest that endogenous androgen secretion during late tadpole stages in males is required for the sexual differentiation of laryngeal innervation observed from stage 62 on. Because androgen treatment and laryngeal innervation affect myogenesis in postmetamorphic frogs, numbers of laryngeal dilator muscle fibers were determined for hormonally manipulated tadpoles. At stage 62, vehicle-treated males had more laryngeal axons than females; laryngeal muscle fiber numbers did not, however, differ in the sexes. Both male and female tadpoles, treated from stage 54 with DHT, had more muscle fibers at stage 62 than vehicle-treated controls. Thus, while endogenous androgen secretion during late tadpole stages is subthreshold for the establishment of masculinized muscle fiber numbers, laryngeal myogenesis is androgen sensitive at this time and can be increased by suprathreshold provision of exogenous DHT. A subgroup of tadpoles, DHT treated from stage 54 to 62, was allowed to survive, untreated, until postmetamorphic stage 2 (PM2: 5 months after metamorphosis is complete). Androgen treatment between tadpole stages 54 and 62 does not prevent the ontogenetic decrease in axon numbers characteristic of laryngeal development. In addition, the elevation in stage 62 axon numbers produced by DHT-treatment at late tadpole stages was not associated with elevated numbers of laryngeal muscle fibers at PM2. Juvenile males normally maintain elevated axon numbers (relative to final adult values) through PM2 and the presence of these additional axons may result from--rather than contribute directly to--laryngeal muscle fiber addition.