Effects of embryonic treatment with fadrozole on phenotype of gonads, syrinx, and neural song system in zebra finches

Intracranial administration of the G-protein coupled estrogen receptor 1 antagonist, G-15, selectively affects dimorphic characteristics of the song system in zebra finches (Taeniopygia guttata)

In zebra finches (Taeniopygia guttata), estradiol contributes to sexual differentiation of the song system but the receptor(s) underlying its action are not exactly known. Whereas mRNA and/or protein for nuclear estrogen receptors ERα and ERβ are minimally expressed, G-protein coupled estrogen receptor 1 (GPER1) has a much greater distribution within neural song regions and the syrinx. At present, however, it is unclear if this receptor contributes to dimorphic development of the song system. To test this, the specific GPER1 antagonist, G-15, was intracranially administered to zebra finches for 25 days beginning on the day of hatching. In males, G-15 significantly decreased nuclear volumes of HVC and Area X. It also decreased the muscle fiber sizes of ventralis and dorsalis in the syrinx. In females, G-15 had no effect on measures within the brain, but did increase fiber sizes of both muscle groups. In sum, these data suggest that GPER1 can have selective and opposing influences on dimorphisms within the song system, but since not all features were affected additional factors are likely involved. © 2018 Wiley Periodicals, Inc. Develop Neurobiol, 2018.

Cognitive Effects of Aromatase and Possible Role in Memory Disorders

Diverse cognitive functions in many vertebrate species are influenced by local conversion of androgens to 17β-estradiol (E2) by aromatase. This enzyme is highly expressed in various brain regions across species, with some inter-species variation in terms of regional brain expression. Since women with breast cancer and men and women with other disorders are often treated with aromatase inhibitors (AI), these populations might be especially vulnerable to cognitive deficits due to low neuroE2 synthesis, i.e., synthesis of E2 directly within the brain. Animal models have been useful in deciphering aromatase effects on cognitive functions. Consequences of AI administration at various life cycle stages have been assessed on auditory, song processing, and spatial memory in birds and various aspects of cognition in rodent models. Additionally, cognitive deficits have been described in aromatase knockout (ArKO) mice that systemically lack this gene throughout their lifespan. This review will consider evidence to date that AI treatment in male and female rodent models, birds, and humans results in cognitive impairments. How brain aromatase regulates cognitive function throughout the lifespan, and gaps in current knowledge will be considered, along with future directions to better define how aromatase might guide learning and memory from early development through the geriatric period. Better understanding the importance of E2 synthesis on neurobehavioral responses at various ages will likely aid in the discovery of therapeutic strategies to prevent potential cognitive deficits, including Alzheimer's Disease, in individuals treated with AI or those possessing CYP19 gene polymorphisms, as well as cognitive effects of normal aging that may be related to changes in brain aromatase activity.

Evidence for parallel evolution of a gene involved in the regulation of spermatogenesis

PHD finger protein 7 (Phf7) is a male germline specific gene in Drosophila melanogaster that can trigger the male germline sexual fate and regulate spermatogenesis, and its human homologue can rescue fecundity defects in male flies lacking this gene. These findings prompted us to investigate conservation of reproductive strategies through studying the evolutionary origin of this gene. We find that Phf7 is present only in select species including mammals and some insects, whereas the closely related G2/M-phase specific E3 ubiquitin protein ligase (G2e3) is in the genome of most metazoans. Interestingly, phylogenetic analyses showed that vertebrate and insect Phf7 genes did not evolve from a common Phf7 ancestor but rather through independent duplication events from an ancestral G2e3 This is an example of parallel evolution in which a male germline factor evolved at least twice from a pre-existing template to develop new regulatory mechanisms of spermatogenesis.

Sex differences and rapid estrogen signaling: A look at songbird audition

The actions of estrogens have been associated with brain differentiation and sexual dimorphism in a wide range of vertebrates. Here we consider the actions of brain-derived 'neuroestrogens' in the forebrain and the accompanying differences and similarities observed between males and females in a variety of species. We summarize recent evidence showing that baseline and fluctuating levels of neuroestrogens within the auditory forebrain of male and female zebra finches are largely similar, and that neuroestrogens enhance auditory representations in both sexes. With a comparative perspective we review evidence that non-genomic mechanisms of neuroestrogen actions are sexually differentiated, and we propose a working model for nonclassical estrogen signaling via the MAPK intracellular signaling cascade in the songbird auditory forebrain that is informed by the way sex differences may be compensated. This view may lead to a more comprehensive understanding of how sex influences estradiol-dependent modulation of sensorimotor representations.

Modelling inhibition of avian aromatase by azole pesticides

The potential effects of pesticides and their metabolites on the endocrine system are of major concern to wildlife and human health. In this context, the azole pesticides have earned special attention due to their cytochrome P450 aromatase inhibition potential. Cytochrome P450 aromatase (CYP19) catalyses the conversion of androstenedione and testosterone into oestrone and oestradiol, respectively. Thus, aromatase modulates the oestrogenic balance essential not only for females, but also for male physiology, including gonadal function. Its inhibition affects reproductive organs, fertility and sexual behaviour in humans and wildlife species. Several studies have shown that azole pesticides are able to inhibit human and fish aromatases but the information on birds is lacking. Consequently, it appeared to be of interest to estimate the aromatase inhibition of azoles in three different avian species, namely Gallus gallus, Coturnix coturnix japonica and Taeniopygia guttata. In the absence of the crystal structure of the aromatase enzyme in these bird species, homology models for the individual avian species were constructed using the crystal structure of human aromatase (hAr) (pdb: 3EQM) that showed high sequence similarity for G. gallus (82.0%), T. guttata (81.9%) and C. japonica (81.2%). A homology model with Oncorhynchus mykiss (81.9%) was also designed for comparison purpose. The homology-modelled aromatase for each avian and fish species and crystal structure of human aromatase were selected for docking 46 structurally diverse azoles and related compounds. We showed that the docking behaviour of the chemicals on the different aromatases was broadly the same. We also demonstrated that there was an acceptable level of correlation between the binding score values and the available aromatase inhibition data. This means that the homology models derived on bird and fish species can be used to approximate the potential inhibitory effects of azoles on their aromatase.

Dynamic variation in forebrain estradiol levels during song learning

Estrogens shape brain circuits during development, and the capacity to synthesize estrogens locally has consequences for both sexual differentiation and the acute modulation of circuits during early learning. A recently optimized method to detect and quantify fluctuations in brain estrogens in vivo provides a direct means to explore how brain estrogen production contributes to both differentiation and neuromodulation during development. Here, we use this method to test the hypothesis that neuroestrogens are sexually differentiated as well as dynamically responsive to song tutoring (via passive video/audio playback) during the period of song learning in juvenile zebra finches. Our results show that baseline neuroestradiol levels in the caudal forebrain do not differ between males and females during an early critical masculinization window. Instead, we observe a prominent difference between males and females in baseline neuroestradiol that emerges during the subadult stage as animals approach sexual maturity. Second, we observe that fluctuating neuroestradiol levels during periods of passive song tutoring exhibit a markedly different profile in juveniles as compared to adults. Specifically, neuroestrogens in the caudal forebrain are elevated following (rather than during) tutor song exposure in both juvenile males and females, suggesting an important role for the early consolidation of tutor song memories. These results further reveal a circadian influence on the fluctuations in local neuroestrogens during sensory/cognitive tasks. Taken together, these findings uncover several unexpected features of brain estrogen synthesis in juvenile animals that may have implications for secondary masculinization as well as the consolidation of recent sensory experiences.

Genome-brain-behavior interdependencies as a framework to understand hormone effects on learned behavior

Hormones have profound effects on the maturation and function of the zebra finch song system. Hormones often signal through receptors that directly or indirectly regulate transcription. In this way, hormones and the genome are functionally connected. Genome-brain-behavior interdependencies are often studied on evolutionary timescales but we can now apply and test these relationships on short timescales, relevant to an individual. Here, we begin to place patterns of hormone-related gene expression into the timeframe of an individual's lifespan to consider how hormones contribute to organization of neural systems necessary for learned behavior, and how they might signal during experience in ways that affect future behavior. This framework illustrates both how much investigations into genome and hormone function are intertwined, and how much we still need to learn.

Activation of estrogen receptor alpha disrupts differentiation of the reproductive organs in chicken embryos

Gonadal estrogen plays an important role in the differentiation of a female phenotype in birds. Exogenous compounds that interfere with estrogen signaling, for instance by binding to the estrogen receptors alpha and beta (ERα and ERβ), are therefore potential disruptors of sexual differentiation in birds. The ERα agonist propyl-pyrazole-triol (PPT), the ERα antagonist methyl piperidino pyrazole (MPP) and the ERβ agonist diarylproprionitrile (DPN) were used in the present study to explore the roles of the ERs in normal and disrupted sex differentiation in the chicken embryo. Activation of ERα by PPT caused disturbed differentiation of the reproductive organs in both sexes. In male embryos, PPT caused left-side ovotestis formation and retention of the Müllerian ducts. In female embryos, PPT caused retention of the right Müllerian duct (which normally regresses) and malformation of both Müllerian ducts. PPT also induced hepatic expression of mRNA for the estrogen-regulated egg yolk protein apoVLDL II. Notably, none of these effects were observed following treatment with DPN. ERα-inactivation by MPP counteracted the action of PPT but had little effect by its own. Our results indicate that ERα plays an important role in sex differentiation of the reproductive tract in female chicken embryos and show that ERα can mediate xenoestrogen-induced disturbances of sex differentiation.

Neural expression and post-transcriptional dosage compensation of the steroid metabolic enzyme 17beta-HSD type 4

Background

Steroids affect many tissues, including the brain. In the zebra finch, the estrogenic steroid estradiol (E₂) is especially effective at promoting growth of the neural circuit specialized for song. In this species, only the males sing and they have a much larger and more interconnected song circuit than females. Thus, it was surprising that the gene for 17β-hydroxysteroid dehydrogenase type 4 (HSD17B4), an enzyme that converts E₂ to a less potent estrogen, had been mapped to the Z sex chromosome. As a consequence, it was likely that HSD17B4 was differentially expressed in males (ZZ) and females (ZW) because dosage compensation of Z chromosome genes is incomplete in birds. If a higher abundance of HSD17B4 mRNA in males than females was translated into functional enzyme in the brain, then contrary to expectation, males could produce less E₂ in their brains than females.

Results

Here, we used molecular and biochemical techniques to confirm the HSD17B4 Z chromosome location in the zebra finch and to determine that HSD17B4 mRNA and activity were detectable in the early developing and adult brain. As expected, HSD17B4 mRNA expression levels were higher in males compared to females. This provides further evidence of the incomplete Z chromosome inactivation mechanisms in birds. We detected HSD17B4 mRNA in regions that suggested a role for this enzyme in the early organization and adult function of song nuclei. We did not, however, detect significant sex differences in HSD17B4 activity levels in the adult brain.

Conclusions

Our results demonstrate that the HSD17B4 gene is expressed and active in the zebra finch brain as an E₂ metabolizing enzyme, but that dosage compensation of this Z-linked gene may occur via post-transcriptional mechanisms.

The specific estrogen receptor antagonist ICI 182,780 masculinizes development of the zebra finch syrinx

In zebra finches, the vocal organ (syrinx) is larger in males compared to females. The exact mechanism responsible for this sex difference is not known, but it may be related to steroid hormones. Previous studies have demonstrated that treatment with estradiol feminizes the mass as well as fiber size of the two largest syrinx muscles (ventralis and dorsalis) in males. Treating females with the aromatase inhibitor fadrozole, however, does not induce masculinization. As an alternative approach to further clarify this paradoxical effect of estrogens on syrinx development, we administered the specific estrogen receptor antagonist ICI 182,780 during the first 25 days post-hatching. Daily injections of this drug significantly increased ventralis and dorsalis muscle fiber size in both sexes. Data also demonstrate that in males, the ventralis muscle makes an earlier contribution to the sex difference in syrinx mass by becoming dimorphic prior to dorsalis. Taken together, these data suggest that estrogens can influence development of the syrinx by feminizing morphology of this tissue. However, the lack of reported sex differences during development in steroid receptors, plasma steroid levels, and aromatase enzyme, indicate that hormones are not solely responsible for sex differences in this organ. Thus, similar to the neural forebrain regions that control song, complete sexual differentiation of the zebra finch syrinx likely involves additional factors.

Steroidogenic enzymes along the ventricular proliferative zone in the developing songbird brain

Neural development requires regulation and coordination of the differentiation, migration, and survival of newly divided cells, most of which derive from the region surrounding the lateral ventricles. While many factors are involved in these maturational processes, studies of cell proliferation and neurogenesis in songbirds indicate that sex steroids may provide crucial cues to newly divided cells and may be fundamental to the organization of a specific neural circuit, the song system. In the case of the zebra finch, steroids that impact song system masculinization are most likely not synthesized from the gonads but from the brain, and evidence is mounting that both developing and adult zebra finches have the capacity for neurosteroidogenesis. Therefore, we hypothesized that during early development, all of the genes required for de novo sex steroid synthesis would be expressed in regions that would indicate a role for neurosteroids in neural organization. We found that the genes necessary for de novo neurosteroid synthesis at posthatch day 1 (P1) and P5 show a broad expression distribution. Most strikingly, the spatial distribution of expression for all of the genes necessary for androgen synthesis is similar to the previously described pattern of proliferating neuronal precursors along the lateral border of the lateral ventricle. Due to the increasing evidence for neurosteroid action on multiple cell traits, it may be that locally synthesized neurosteroids impact cells along the proliferative zone to influence early events in neural development generally and song system masculinization specifically.

Widespread capacity for steroid synthesis in the avian brain and song system

Steroids exert powerful effects on the brains and behavior of many species, but measures and manipulations of endocrine physiology in songbirds often reveal unexplained connections between steroids and the brain. The zebra finch song system, a sensorimotor neural circuit sensitive to steroids throughout life, organizes and functions largely in apparent independence from gonadally derived steroids. We tested the hypothesis that the zebra finch brain has the capacity for de novo steroidogenesis and that neurally synthesized steroids, neurosteroids, may impact the song system. Using multiple techniques, we demonstrate that the steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage (CYP11A1), and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase, the first three factors in the steroidogenic pathway, are expressed in both developing and adult zebra finch brain. Detailed expression mapping at posthatch d 20 (P20) and adult reveals widespread area-specific expression and coexpression patterns for steroidogenic acute regulatory protein, CYP11A1, and 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase, which suggest neurosteroids may modulate multiple brain functions, including sensory and motor systems. Notably, whereas expression of other steroidogenic genes such as aromatase has been essentially absent from the song system, each of the major song nuclei express at least a subset of steroidogenic genes described here, establishing the song system as a potential steroidogenic circuit.

Brain aromatase: new lessons from non-mammalian model systems

This review highlights recent studies of the anatomical and functional implications of brain aromatase (estrogen synthase) expression in two vertebrate lineages, teleost fishes and songbirds, that show remarkably high levels of adult brain aromatase activity, protein and gene expression compared to other vertebrate groups. Teleosts and birds have proven to be important neuroethological models for investigating how local estrogen synthesis leads to changes in neural phenotypes that translate into behavior. Region-specific patterns of aromatase expression, and thus estrogen synthesis, include the vocal and auditory circuits that figure prominently into the life history adaptations of vocalizing teleosts and songbirds. Thus, by targeting, for example, vocal motor circuits without inappropriate steroid exposure to other steroid-dependent circuits, such as those involved in either copulatory or spawning behaviors, the neuroendocrine system can achieve temporal and spatial specificity in its modulation of neural circuits that lead to the performance of any one behavior.

Sexual differentiation of the zebra finch song system

The song system of zebra finches (Taeniopygia gutatta) is highly sexually dimorphic. Only males sing, and the brain regions and muscles controlling song are much larger in males than in females. Development of the song system is highly sensitive to steroid hormones. However, unlike similar sexually dimorphic systems in other animal models, masculinization of song system structure and function is most likely not induced by testosterone secreted from the testes. Instead, sex-specific development of the neural song system appears to be regulated by factors intrinsic to the brain, probably by the expression of sex chromosome gene(s) that influence the levels of estradiol synthesized in the brain and/or the responses of brain tissue to estradiol. However, the existing data are complex and in some cases contradictory. More work is required to identify the critical genes and their relationships with steroid hormones.

Effects of estrogens during embryonal development on crowing in the domestic fowl

In the domestic fowl, crowing is typically a male-specific vocal behavior while the females normally do not crow. These sex differences in vocalization may result from organizational actions of estrogens during specific periods of embryonic development. To further investigate the role of estrogens in differentiation of crowing and development of the acoustic characteristics of crow calls, male domestic fowls were treated on Incubation Day 8 with estradiol benzoate (EB) or either oil or saline vehicles. On the same incubation day, the female fowls were treated with an aromatase inhibitor, fadrozole, or saline vehicle. An adulthood vocalization of cocks and hens was recorded during corresponding tests of sexual behavior. The exposure to EB or fadrozole had no effect on sexual differentiation of the gonads and all fadrozole-treated hens laid eggs at a rate similar to the control hens that received saline. While the levels of plasma testosterone at adulthood did not differ in treated and untreated cocks, the incidence of crowing rate was significantly lower in cocks that were exposed to estradiol. Acoustic analysis revealed a considerable reduction in duration and acoustic energy of calls while the main frequency characteristics were not changed. Four out of the seven tested fadrozole-treated hens demonstrated regularly crow-like vocalization with shorter duration and lower energy of calls in comparison to crows of the control males. These findings point out to a role for estradiol in organization of crowing behavior and a specific temporal pattern of the crowing call.

Cloning of the zebra finch androgen synthetic enzyme CYP17: a study of its neural expression throughout posthatch development

Male zebra finches develop a robust neural song system that supports singing, but females have a minimal song circuit and do not sing. Estrogens masculinize the song circuit and are especially potent during the first 3 weeks of posthatch development. The gonads do not seem to supply the masculinizing steroids, implying that another tissue synthesizes steroids. Evidence suggests that the brain is capable of synthesizing neurosteroids, which in developing zebra finches may be required for song system differentiation. Aromatase, the enzyme that synthesizes estrogen from androgen, is equally abundant in male and female brains. To investigate further the potential for neurosteroidogenesis in the zebra finch brain, we cloned and examined the expression of 17alpha-hydroxylase/17,20 lyase (CYP17), the enzyme that synthesizes the androgenic substrate for aromatase. We used Northern blots, reverse transcription-polymerase chain reaction, and in situ hybridization to show that CYP17 is transcribed in developing and adult brains. CYP17 is transcribed at developmental stages and in brain areas potentially important to aspects of the developing song system, although no sex difference was detected in mRNA levels. Our results support the hypothesis that neurosteroids may act to influence brain organization and function in the zebra finch.

Male Japanese quails with female brains do not show male sexual behaviors

During embryonic development, gonadal steroid hormones (androgens and estrogens) are thought to organize the sexual differentiation of the brain in the heterogametic sexes of higher vertebrates (males in mammals, females in birds). Brain differentiation of the homogametic sexes is thought to proceed by default, not requiring sex hormones for sex-specific organization. In gallinaceous birds such as the Japanese quail, female brain organization is thought to develop via estrogen-dependent demasculinization of a default male brain phenotype. We performed male donor-to-female host (MF), female-to-male (FM), male-to-male (MM), and female-to-female (FF) isotopic, isochronic transplantation of the forebrain primordium in Japanese quail embryos before gonadal differentiation had occurred; brain chimeras had a forebrain (including the hypothalamus) originating exclusively from donor cells. MM, FF, and MF chimeras all showed sexual behavior governed by the genetic sex of the host. In contrast, FM chimeras (genetically female forebrain, all other tissues genetically male) showed no mounting and only rudimentary crowing behavior. Although MM, FF, MF, and FM chimeras all showed host-typical production of steroid hormones during embryonic life, only FM chimeras were hypogonadal, had atypical low levels of circulating testosterone in adulthood, and showed reduction (crowing) or absence (mounting) of reproductive behaviors. Morphological features of the medial preoptic nucleus (a sexually dimorphic brain area) also were not male-like in FM males. These data demonstrate a brain-intrinsic, genetically determined component that organizes the sex-typical production of gonadal hormones in adulthood and call for a reevaluation of the mechanisms underlying brain sexual differentiation in other higher-vertebrate species.

Expression of androgen receptor mRNA in the late embryonic and early posthatch zebra finch brain

Zebra finch males sing and females do not, and the underlying neural circuitry in males is more developed than that in females. Sex steroid hormones influence the development of sex differences in this circuitry, including differences in androgen receptor (AR) expression, although the role of androgens has been controversial. We isolated a cDNA encoding a portion of the zebra finch AR and used in situ hybridization to examine the spatiotemporal pattern of AR mRNA expression in the brain during late embryonic development and at hatching. We detected AR mRNA in all the major subdivisions of the brain as early as embryonic day 10. No qualitative sex differences in AR mRNA expression patterns were observed. Cells lining the ventral arm of the lateral telencephalic ventricles expressed AR mRNA on embryonic day 11 and posthatching day 1, as did cells lining the third ventricle at all three developmental stages examined, suggesting that androgens may play a role in early stages of cellular proliferation, migration, or differentiation. AR mRNA was also detected in the hippocampus, neostriatum, septum, ventromedial archistriatum, hypothalamic regions, dorsal mesencephalon, and in and around the brainstem nucleus tracheosyringealis. Our results suggested that androgens act early in neural development and therefore may contribute to the process of sexual differentiation.

Antiandrogen blocks estrogen-induced masculinization of the song system in female zebra finches

Song behavior and the neural song system that serves it are sexually dimorphic in zebra finches. In this species, males sing and females normally do not. The sex differences in the song system include sex differences in the proportion of neurons that express androgen receptors, which is higher in specific brain regions of males. Estradiol (E2) administered in early development profoundly masculinizes the song system of females, including the proportion of neurons expressing androgen receptors. We examined whether or not the expression of these androgen receptors was causally related to the E2-induced masculinization of this system by co-administering Flutamide, which blocks androgen action at the receptor, along with E2 at hatching. E2 alone had its usual masculinizing effect on the female song system, measured in adulthood: increasing the size of song nuclei, the size of neurons in HVC, RA, and 1MAN, and the number of neurons in HVC. E2's masculinizing action, however, was significantly diminished on all measures by co-administering Flutamide. Indeed, females receiving both E2 and Flutamide were never significantly more masculine than controls on any measure. Flutamide alone had no effect. Our results strongly suggest that the activation of androgen receptors is necessary for the E2-induced masculinization of the song system in females.

Zebra finch sexual differentiation: the aromatization hypothesis revisited

Zebra finches have emerged as an outstanding model system for the investigation of the mechanisms regulating brain and behavior. Their song system has proven especially useful, as the function of discrete anatomical regions have been identified, and striking parallels exist between the morphology of these regions and the level of their function in males and females. That is, the structures are substantially more developed in males, who sing, compared to females, who do not. These parallels extend from higher (telencephalic) centers to the brainstem motor nucleus that innervates the muscles of the vocal organ. Other dimorphic aspects of reproduction in the zebra finch, such as copulatory behaviors and sexual partner preference, however, are not associated with known sex differences in anatomy. In many species, sex differences in neural and peripheral structures and behavior are regulated by secretions from the gonads, which of course are sexually dimorphic themselves. In birds, sex differences at all of these levels (gonad, brain, and behavior) can be mediated by steroid hormones. However, it is not entirely clear that gonadal secretions normally participate at all of the levels. This paper reviews the evidence relating to the role of gonadal steroids in the sexual differentiation of reproductive behaviors and the central and peripheral structures known to regulate them in zebra finches, with a focus on estradiol, which has been most extensively studied in the masculinization of song system morphology and function.

The expression of the sex steroid-synthesizing enzymes CYP11A1, 3beta-HSD, CYP17, and CYP19 in gonads and adrenals of adult and developing zebra finches

Songbirds have emerged as important animal models for understanding how sex steroids influence brain and behavior, particularly how they direct the sexually dimorphic development of the neural circuits controlling song and then activate adult song behavior. Presumably, sex steroids synthesized in the gonads are responsible for these actions on brain. However, experiments do not always reveal a direct relationship between gonadal function, circulating sex steroids, and activation and/or organization of song. Thus, it is critical that we understand more about the sites and mechanisms of sex steroid synthesis in this group of birds. Toward this end, we have established the use in zebra finches of chicken cDNA probes to the principal androgen synthetic enzymes, CYP11A1, 3beta-HSD, and CYP17. On Northern blots, these probes recognized bands of the appropriate size and in tissues similar to those seen in chickens. With these probes, and a probe to CYP19 specific to the zebra finch, we used in situ hybridization to examine the cellular expression of these enzymes in gonads and adrenals of adult and developing zebra finches (1 to 20 days posthatching). In adults, we identified significant expression of CYP11A1 and CYP17 in large ovarian follicles, particularly the thecal cell layer and over the testicular interstitial area. 3beta-HSD was expressed by both theca and granulosa and in testicular interstitial and seminiferous tubular cells. In adrenals, CYP11A1 and 3beta-HSD are abundant with lesser amounts of CYP17. Developmentally, we identified high expression of CYP11A1 and 3beta-HSD in the adrenals, CYP17 in both testes and ovaries, and CYP19 in ovaries only. These results suggest that the ovaries but not the testes may secrete estrogen developmentally and the adrenals may contribute precursors for gonadal steroidogensis.