The expression of a functional cDNA encoding the chicken cytochrome P-450arom (aromatase) that catalyzes the formation of estrogen from androgen

Sex-specific transcriptome of the chicken chorioallantoic membrane

Dimorphism between male and female embryos has been demonstrated in many animal species, including chicken species. Likewise, extraembryonic membranes such as the chorioallantoic membrane (CAM) are likely to exhibit a sex-specific profile. Analysis of the previously published RNA-seq data of the chicken CAM sampled at two incubation times, revealed 783 differentially expressed genes between the CAM of male and female embryos. The expression of some of these genes is sex-dependant only at one or other stage of development, while 415 genes are sex-dependant at both developmental stages. These genes include well-known sex-determining and sex-differentiation genes (DMRT1, HEGM, etc.), and are mainly located on sex chromosomes. This study provides evidence that gene expression of extra-embryonic membranes is differentially regulated between male and female embryos. As such, a better characterisation of associated mechanisms should facilitate the identification of new sex-specific biomarkers.

Neuropeptidergic control of neurosteroids biosynthesis

Neurosteroids are steroids synthesized within the central nervous system either from cholesterol or by metabolic reactions of circulating steroid hormone precursors. It has been suggested that neurosteroids exert pleiotropic activities within the central nervous system, such as organization and activation of the central nervous system and behavioral regulation. It is also increasingly becoming clear that neuropeptides exert pleiotropic activities within the central nervous system, such as modulation of neuronal functions and regulation of behavior, besides traditional neuroendocrinological functions. It was hypothesized that some of the physiological functions of neuropeptides acting within the central nervous system may be through the regulation of neurosteroids biosynthesis. Various neuropeptides reviewed in this study possibly regulate neurosteroids biosynthesis by controlling the activities of enzymes that catalyze the production of neurosteroids. It is now required to thoroughly investigate the neuropeptidergic control mechanisms of neurosteroids biosynthesis to characterize the physiological significance of this new neuroendocrinological phenomenon.

Molecular characterization, expression profile and transcriptional regulation of the CYP19 gene in goose ovarian follicles

Cytochrome P450 Family 19 (CYP19) is a crucial enzyme to catalyze the conversion of androgens to estrogens. However, the regulatory mechanism of goose CYP19 gene remains poorly understood. The present study attempted to obtain the full-length coding sequence (CDS) and 5'-flanking sequence of CYP19 gene, to investigate its expression and distribution profiles in different sized follicles, and to analyze the transcriptional regulatory mechanism of CYP19 gene in goose. Results showed that its CDS consisted of 1512 nucleotides and the encoded amino acid sequence contained a classical P450 structural domain. Homology analysis showed that there were high homologies of nucleotide and amino acid sequences between goose and other avian species. Its promoter sequence spanned from -1925 bp to the transcription start site (ATG) and several transcriptional factors were predicted in this region. Further analysis from luciferase assay showed that the luciferase activity was the highest spanning from -118 to -1 bp by constructing deletion promoter reporter vector. In addition, result from quantitative real-time polymerase chain reaction indicated that the mRNA level of CYP19 gene were highly expressed in theca layer of the fifth largest follicle, and the cellular location was in the theca externa cells by immunohistochemistry. Taken together, it could be concluded that the transcription activity of CYP19 gene was activated by transcriptional factors in its proximal region of promoter to promote the synthesis of estrogens, regulating the selection of pre-hierarchical into hierarchical follicle in goose.

History of Estrogen: Its Purification, Structure, Synthesis, Biologic Actions, and Clinical Implications

This mini-review summarizes key points from the Clark Sawin Memorial Lecture on the History of Estrogen delivered at Endo 2018 and focuses on the rationales and motivation leading to various discoveries and their clinical applications. During the classical period of antiquity, incisive clinical observations uncovered important findings; however, extensive anatomical dissections to solidify proof were generally lacking. Initiation of the experimental approach followed later, influenced by Claude Bernard's treatise "An Introduction to the Study of Experimental Medicine." With this approach, investigators began to explore the function of the ovaries and their "internal secretions" and, after intensive investigations for several years, purified various estrogens. Clinical therapies for hot flashes, osteoporosis, and dysmenorrhea were quickly developed and, later, methods of hormonal contraception. Sophisticated biochemical methods revealed the mechanisms of estrogen synthesis through the enzyme aromatase and, after discovery of the estrogen receptors, their specific biologic actions. Molecular techniques facilitated understanding of the specific transcriptional and translational events requiring estrogen. This body of knowledge led to methods to prevent and treat hormone-dependent neoplasms as well as a variety of other estrogen-related conditions. More recently, the role of estrogen in men was uncovered by prismatic examples of estrogen deficiency in male patients and by knockout of the estrogen receptor and aromatase in animals. As studies became more extensive, the effects of estrogen on nearly every organ were described. We conclude that the history of estrogen illustrates the role of intellectual reasoning, motivation, and serendipity in advancing knowledge about this important sex steroid.

RNA-Seq Profile Reveals Th-1 and Th-17-Type of Immune Responses in Mice Infected Systemically with Aspergillus fumigatus

With the increasing numbers of immunocompromised hosts, Aspergillus fumigatus emerges as a lethal opportunistic fungal pathogen. Understanding innate and acquired immunity responses of the host is important for a better therapeutic strategy to deal with aspergillosis patients. To determine the transcriptome in the kidneys in aspergillosis, we employed RNA-Seq to obtain single 76-base reads of whole-genome transcripts of murine kidneys on a temporal basis (days 0; uninfected, 1, 2, 3 and 8) during invasive aspergillosis. A total of 6284 transcripts were downregulated, and 5602 were upregulated compared to baseline expression. Gene ontology enrichment analysis identified genes involved in innate and adaptive immune response, as well as iron binding and homeostasis, among others. Our results showed activation of pathogen recognition receptors, e.g., β-defensins, C-type lectins (e.g., dectin-1), Toll-like receptors (TLR-2, TLR-3, TLR-8, TLR-9 and TLR-13), as well as Ptx-3 and C-reactive protein among the soluble receptors. Upregulated transcripts encoding various differentiating cytokines and effector proinflammatory cytokines, as well as those encoding for chemokines and chemokine receptors, revealed Th-1 and Th-17-type immune responses. These studies form a basic dataset for experimental prioritization, including other target organs, to determine the global response of the host against Aspergillus infection.

Celebrating 75 years of oestradiol

Oestrogens exert important effects on the reproductive as well as many other organ systems in both men and women. The history of the discovery of oestrogens, the mechanisms of their synthesis, and their therapeutic applications are very important components of the fabric of endocrinology. These aspects provide the rationale for highlighting several key components of this story. Two investigators, Edward Doisy and Alfred Butenandt, purified and crystalized oestrone nearly simultaneously in 1929, and Doisy later discovered oestriol and oestradiol. Butenandt won the Nobel Prize for this work and Doisy's had to await his purification of vitamin K. Early investigators quickly recognized that oestrogens must be synthesized from androgens and later investigators called this process aromatization. The aromatase enzyme was then characterized, its mechanism determined, and its structure identified after successful crystallization. With the development of knock-out methodology, the precise effects of oestrogen in males and females were defined and clinical syndromes of deficiency and excess described. Their discovery ultimately led to the development of oral contraceptives, treatment of menopausal symptoms, therapies for breast cancer, and induction of fertility, among others. The history of the use of oestrogens for postmenopausal women to relieve symptoms has been characterized by cyclic periods of enthusiasm and concern. The individuals involved in these studies, the innovative thinking required, and the detailed understanding made possible by evolving biologic and molecular techniques provide many lessons for current endocrinologists.

Molecular cloning and characterization of brain and ovarian cytochrome P450 aromatase genes in the catfish Heteropneustes fossilis: Sex, tissue and seasonal variation in, and effects of gonadotropin on gene expression

Cytochrome P450 aromatase (Cyp19arom) is the rate-limiting enzyme controlling estrogen biosynthesis, coded by Cyp19a1 in most gnathostomes. Most teleosts have two forms expressed differentially in ovary (cyp19a1a) and neural tissue (cyp19a1b). In this study, full length cDNAs of 2006 bp and 1913 bp with ORFs of 1575 bp and 1488 bp were isolated from the brain and ovary, respectively, of the catfish Heteropneustes fossilis, an air-breathing species with high aquaculture potential. The ORFs encode predicted proteins of 495 and 524 amino acid residues, respectively. The proteins show 62% identity with each other and cluster in two distinct clades (the brain type and ovary type) in the teleost taxon, separated from the tetrapod type. In the in situ localization study, both cyp19a1a and cyp19a1b transcripts were localized in the brain but the signal intensity was higher for the brain type paralog. The transcript signals were observed in the radial glial cells and in neuronal populations of the dorso-lateral region of the telencephalon, pre-tectum, hypothalamus and medulla oblongata. In the ovary, both paralogs were expressed in the follicular layer with a high signal intensity of the ovarian type (cyp19a1a). The differential expression of the gene paralogs was evident from qPCR analysis. Cyp19a1b has relatively a high abundance in the female brain, followed by other peripheral tissues (gonads, liver, gill, kidney and muscle). On the other hand, cyp19a1a has relatively a high transcript abundance in the ovary and female brain, followed by the testis and male brain, and female liver and muscle. The expression was low in male liver and muscle, and the lowest in the gill and kidney. The expression of the two paralogs exhibit brain regional differences; both types have relatively a high transcript abundance in telencephalon-preoptic area with the cyp19a1b expression higher in females than males. In hypothalamus, the expression of both types is higher in males than females. In medulla, the expression of the cyp19a1b is higher than cyp19a1a, and the transcript abundance of the ovarian type is higher in females than males. The expression of the gene paralogs elicits significant seasonal variations in the ovary and brain. In both tissues, the expression increases from the resting to preparatory phases, and decreases through the prespawning phase to low levels in spawning phase. In vivo and/or in vitro treatments with human chorionic gonadotropin (hCG) stimulated the expression of the gene paralogs in the brain and ovary, time-dependently. In conclusion, both paralogs have an overlapping distribution at different levels of the brain-pituitary-gonad axis and may function as a single functional unit as far as the estrogen synthesis is concerned.

Review: neuroestrogen regulation of socio-sexual behavior of males

It is thought that estrogen (neuroestrogen) synthesized by the action of aromatase in the brain from testosterone activates male socio-sexual behaviors, such as aggression and sexual behavior in birds. We recently found that gonadotropin-inhibitory hormone (GnIH), a hypothalamic neuropeptide, inhibits socio-sexual behaviors of male quail by directly activating aromatase and increasing neuroestrogen synthesis in the preoptic area (POA). The POA is thought to be the most critical site of aromatization and neuroestrogen action for the regulation of socio-sexual behavior of male birds. We concluded that GnIH inhibits socio-sexual behaviors of male quail by increasing neuroestrogen concentration beyond its optimal concentration in the brain for expression of socio-sexual behavior. On the other hand, it has been reported that dopamine and glutamate, which stimulate male socio-sexual behavior in birds and mammals, inhibit the activity of aromatase in the POA. Multiple studies also report that the activity of aromatase or neuroestrogen is negatively correlated with changes in male socio-sexual behavior in fish, birds, and mammals including humans. Here, we review previous studies that investigated the role of neuroestrogen in the regulation of male socio-sexual behavior and reconsider the hypothesis that neuroestrogen activates male socio-sexual behavior in vertebrates. It is considered that basal concentration of neuroestrogen is required for the maintenance of male socio-sexual behavior but higher concentration of neuroestrogen may inhibit male socio-sexual behavior.

Genes encoding aromatases in teleosts: evolution and expression regulation

Cytochrome P450 aromatases, encoded by cyp19a1 genes, catalyzes the conversion of androgens to estrogens and plays important roles in the reproduction of vertebrates. Vertebrate cyp19a1 genes showed high synteny in chromosomal locations and conservation in sequences during evolution. However, amphioxus cyp19a1 does not show synteny to vertebrate cyp19a1. Teleost fish possess two copies of the cyp19a1 gene, which were postulated to result from a fish-specific genome duplication. The duplicated copies of fish cyp19a1 genes evolved into the brain and ovarian forms of cytochrome P450 aromatase genes, cyp19a1a and cyp19a1b, respectively, with different regulatory mechanisms of expression, through subfunctionalization under long-term selective pressure. In addition to the estradiol (E2) auto-regulatory loop, there may be other mechanisms responsible for the high expression of aromatase in the teleost brain. The study of the two cyp19a1 copies in teleost fish will shed light on the general evolution, function, and regulation of vertebrate cyp19a1.

Overexpression of aromatase alone is sufficient for ovarian development in genetically male chicken embryos

Estrogens play a key role in sexual differentiation of both the gonads and external traits in birds. The production of estrogen occurs via a well-characterised steroidogenic pathway, which is a multi-step process involving several enzymes, including cytochrome P450 aromatase. In chicken embryos, the aromatase gene (CYP19A1) is expressed female-specifically from the time of gonadal sex differentiation. To further explore the role of aromatase in sex determination, we ectopically delivered this enzyme using the retroviral vector RCASBP in ovo. Aromatase overexpression in male chicken embryos induced gonadal sex-reversal characterised by an enlargement of the left gonad and development of ovarian structures such as a thickened outer cortex and medulla with lacunae. In addition, the expression of key male gonad developmental genes (DMRT1, SOX9 and Anti-Müllerian hormone (AMH)) was suppressed, and the distribution of germ cells in sex-reversed males followed the female pattern. The detection of SCP3 protein in late stage sex-reversed male embryonic gonads indicated that these genetically male germ cells had entered meiosis, a process that normally only occurs in female embryonic germ cells. This work shows for the first time that the addition of aromatase into a developing male embryo is sufficient to direct ovarian development, suggesting that male gonads have the complete capacity to develop as ovaries if provided with aromatase.

Effects of estrogen on estrogen receptor expression in the bursal cells of chick embryos and steroidogenic enzymes gene expression in the bursa: relevance of estrogen receptor and estrogen synthesis in the bursa of chick embryos

Estrogen has been reported to act on B cell genesis in the bursa of Fabricius of chick embryos. In this study, we attempted to demonstrate the hypothesis that B cell genesis is controlled by estrogen receptor (ER) in the bursal cells and steroidogenic enzymes synthesized in the bursa. We previously reported the presence of estrogen receptor α (ERα) in the bursa during the late stage of embryogenesis and an increase in the expression of ERα messenger RNA (mRNA) between the 13th day and 16th day. The number of ER-positive cells was maximal on the 16th day. In the present study, ER-positive cells in the bursa during the late stage of embryogenesis increased 4 h after β-estradiol treatment on the 14th to 18th day. The concentration of β-estradiol in the embryonic bursa increased. These results suggest that this stage of embryogenesis is critical in B cell development in the bursa in connection with the effect of estrogen treatment. Our findings also showed that the mRNA expression of five steroidogenic enzymes occurred in the bursa of chick embryos. These results suggest that estrogen is synthesized in the embryonic bursa and estrogen acts on the bursal cells in a paracrine fashion.

Comparative transcriptomic analysis of follicle-enclosed oocyte maturational and developmental competence acquisition in two non-mammalian vertebrates

BACKGROUND

In vertebrates, late oogenesis is a key period during which the oocyte acquires its ability to resume meiosis (i.e. maturational competence) and to develop, once fertilized, into a normal embryo (i.e. developmental competence). However, the molecular mechanisms involved in these key biological processes are far from being fully understood. In order to identify key mechanisms conserved among teleosts and amphibians, we performed a comparative analysis using ovarian tissue sampled at successive steps of the maturational competence acquisition process in the rainbow trout (Oncorhynchus mykiss) and in the clawed toad (Xenopus laevis). Our study aimed at identifying common differentially expressed genes during late oogenesis in both species. Using an existing transcriptomic analysis that had previously been carried out in rainbow trout, candidate genes were selected for subsequent quantitative PCR-based comparative analysis.

RESULTS

Among the 1200 differentially expressed clones in rainbow trout, twenty-six candidate genes were selected for further analysis by real-time PCR in both species during late oogenesis. Among these genes, eight had similar expression profiles in trout and Xenopus. Six genes were down-regulated during oocyte maturation (cyp19a1, cyp17a1, tescalcin, tfr1, cmah, hsd11b3) while two genes exhibited an opposite pattern (apoc1, star). In order to document possibly conserved molecular mechanisms, four genes (star, cyp19a1, cyp17a1 and hsd11b3) were further studied due to their known or suspected role in steroidogenesis after characterization of the orthology relationships between rainbow trout and Xenopus genes. Apoc1 was also selected for further analysis because of its reported function in cholesterol transport, which may modulate steroidogenesis by regulating cholesterol bioavailability in the steroidogenic cells.

CONCLUSIONS

We have successfully identified orthologous genes exhibiting conserved expression profiles in the ovarian follicle during late oogenesis in both trout and Xenopus. While some identified genes were previously uncharacterized during Xenopus late oogenesis, the nature of these genes has pointed out molecular mechanisms possibly conserved in amphibians and teleosts. It should also be stressed that in addition to the already suspected importance of steroidogenesis in maturational competence acquisition, our approach has shed light on other regulatory pathways which may be involved in maturational and developmental competence acquisitions that will require further studies.

Behavioral effects of brain-derived estrogens in birds

In birds as in other vertebrates, estrogens produced in the brain by aromatization of testosterone have widespread effects on behavior. Research conducted with male Japanese quail demonstrates that effects of brain estrogens on all aspects of sexual behavior, including appetitive and consummatory components as well as learned aspects, can be divided into two main classes based on their time course. First, estrogens via binding to estrogen receptors regulate the transcription of a variety of genes involved primarily in neurotransmission. These neurochemical effects ultimately result in the activation of male copulatory behavior after a latency of a few days. Correlatively, testosterone and its aromatized metabolites increase the transcription of the aromatase mRNA, resulting in an increased concentration and activity of the enzyme that actually precedes behavioral activation. Second, recent studies with quail demonstrate that brain aromatase activity can also be modulated within minutes by phosphorylation processes regulated by changes in intracellular calcium concentration, such as those associated with glutamatergic neurotransmission. The rapid upregulations or downregulations of brain estrogen concentration (presumably resulting from these changes in aromatase activity) affect, by nongenomic mechanisms with relatively short latencies (frequency increases or decreases respectively within 10-15 min), the expression of male sexual behavior in quail and also in rodents. Brain estrogens thus affect behavior on different time scales by genomic and nongenomic mechanisms similar to those of a hormone or a neurotransmitter.

History of aromatase: saga of an important biological mediator and therapeutic target

Aromatase is the enzyme that catalyzes the conversion of androgens to estrogens. Initial studies of its enzymatic activity and function took place in an environment focused on estrogen as a component of the birth control pill. At an early stage, investigators recognized that inhibition of this enzyme could have major practical applications for treatment of hormone-dependent breast cancer, alterations of ovarian and endometrial function, and treatment of benign disorders such as gynecomastia. Two general approaches ultimately led to the development of potent and selective aromatase inhibitors. One targeted the enzyme using analogs of natural steroidal substrates to work out the relationships between structure and function. The other approach initially sought to block adrenal function as a treatment for breast cancer but led to the serendipitous finding that a nonsteroidal P450 steroidogenesis inhibitor, aminoglutethimide, served as a potent but nonselective aromatase inhibitor. Proof of the therapeutic concept of aromatase inhibition involved a variety of studies with aminoglutethimide and the selective steroidal inhibitor, formestane. The requirement for even more potent and selective inhibitors led to intensive molecular studies to identify the structure of aromatase, to development of high-sensitivity estrogen assays, and to "mega" clinical trials of the third-generation aromatase inhibitors, letrozole, anastrozole, and exemestane, which are now in clinical use in breast cancer. During these studies, unexpected findings led investigators to appreciate the important role of estrogens in males as well as in females and in multiple organs, particularly the bone and brain. These studies identified the important regulatory properties of aromatase acting in an autocrine, paracrine, intracrine, neurocrine, and juxtacrine fashion and the organ-specific enhancers and promoters controlling its transcription. The saga of these studies of aromatase and the ultimate utilization of inhibitors as highly effective treatments of breast cancer and for use in reproductive disorders serves as the basis for this first Endocrine Reviews history manuscript.

Potential effects of environmental contaminants on P450 aromatase activity and DNA damage in swallows from the Rio Grande and Somerville, Texas

Cliff swallows (Petrochelidon pyrrhonota) and cave swallows (P. fulva) were sampled during the breeding season at several locations in the Rio Grande, Texas, to evaluate the potential effects of environmental contaminants on P450 aromatase activity in brain and gonads and DNA damage in blood cells. The tritiated water-release aromatase assay was used to measure aromatase activity and flow cytometry was used to measure DNA damage in nucleated blood cells. There were no significant differences in brain and gonadal aromatase activities or in estimates of DNA damage (HPCV values) among cave swallow colonies from the Lower Rio Grande Valley (LRGV) and Somerville. However, both brain and gonadal aromatase activities were significantly higher (P < 0.05) in male cliff swallows from Laredo than in those from Somerville. Also, DNA damage estimates were significantly higher (P < 0.05) in cliff swallows (males and females combined) from Laredo than in those from Somerville. Contaminants of current high use in the LRGV, such as atrazine, and some of the highly persistent organochlorines, such as toxaphene and DDE, could be potentially associated with modulation of aromatase activity in avian tissues. Previous studies have indicated possible DNA damage in cliff swallows. We did not observe any differences in aromatase activity or DNA damage in cave swallows that could be associated with contaminant exposure. Also, the differences in aromatase activity and DNA damage between male cliff swallows from Laredo and Somerville could not be explained by contaminants measured at each site in previous studies. Our study provides baseline information on brain and gonadal aromatase activity in swallows that could be useful in future studies.

Regulation of P450 oxidoreductase by gonadotropins in rat ovary and its effect on estrogen production

BACKGROUND

P450 oxidoreductase (POR) catalyzes electron transfer to microsomal P450 enzymes. Its deficiency causes Antley-Bixler syndrome (ABS), and about half the patients with ABS have ambiguous genitalia and/or impaired steroidogenesis. POR mRNA expression is up-regulated when mesenchymal stem cells (MSCs) differentiate into steroidogenic cells, suggesting that the regulation of POR gene expression is important for steroidogenesis. In this context we examined the regulation of POR expression in ovarian granulosa cells by gonadotropins, and its possible role in steroidogenesis.

METHODS

Changes in gene expression in MSCs during differentiation into steroidogenic cells were examined by DNA microarray analysis. Changes in mRNA and protein expression of POR in the rat ovary or in granulosa cells induced by gonadotropin treatment were examined by reverse transcription-polymerase chain reaction and western blotting. Effects of transient expression of wild-type or mutant (R457H or V492E) POR proteins on the production of estrone in COS-7 cells were examined in vitro. Effects of POR knockdown were also examined in estrogen producing cell-line, KGN cells.

RESULTS

POR mRNA was induced in MSCs following transduction with the SF-1 retrovirus, and was further increased by cAMP treatment. Expression of POR mRNA, as well as Cyp19 mRNA, in the rat ovary were induced by equine chorionic gonadotropin and human chorionic gonadotropin. POR mRNA and protein were also induced by follicle stimulating hormone in primary cultured rat granulosa cells, and the induction pattern was similar to that for aromatase. Transient expression of POR in COS-7 cells, which expressed a constant amount of aromatase protein, greatly increased the rate of conversion of androstenedione to estrone, in a dose-dependent manner. The expression of mutant POR proteins (R457H or V492E), such as those found in ABS patients, had much less effect on aromatase activity than expression of wild-type POR proteins. Knockdown of endogenous POR protein in KGN human granulosa cells led to reduced estrone production, indicating that endogenous POR affected aromatase activity.

CONCLUSION

We demonstrated that the expression of POR, together with that of aromatase, was regulated by gonadotropins, and that its induction could up-regulate aromatase activity in the ovary, resulting in a coordinated increase in estrogen production.

The effect of heat stress on ovarian function of laying hens

Reproductive failure associated with heat stress is a well-known phenomenon. The mechanism involved in this failure is not clearly understood. In order to test a possible direct effect of heat stress on ovarian function, 36 White Leghorn laying hens were housed in individual cages in 2 temperature- and light-controlled rooms (n = 18). At 31 wk of age, one group was exposed daily for 12 h to high temperature (42 +/- 3 degrees C), and the second group was maintained under thermoneutral conditions (24 to 26 degrees C) and served as control. Body temperature, feed intake, egg production, and egg weight were recorded daily; heparinized blood samples were drawn every 3 d for plasma hormonal level of luteinizing hormone, follicular stimulating hormone, progesterone, 17beta-estradiol, and testosterone. Six days after exposure half of the birds in each group were killed, and the ovary and oviduct were weighed and preovulatory follicles removed and extracted for mRNA of Cytochrome P 450 aromatase, 17-alpha hydroxylase. The same procedure was repeated 9 d later with the rest of the birds. Short and long heat exposure caused significant hyperthermia and reduction of egg production, egg weight, ovarian weight, and the number of large follicles. In addition, a significant reduction in plasma progesterone and testosterone was detected 2 d after exposing the birds to heat stress, and plasma 17beta-estradiol was significantly reduced 14 d after initiation of heat stress. Short exposure to heat stress caused significant reduction in mRNA expression of cytochrome P450 17-alpha hydroxylase, exposing the birds to long-term heat stress caused significant reduction in expression of mRNA of both steroidogenic enzymes. No significant change was found in plasma luteinizing hormone and follicular stimulating hormone levels during the entire experimental period. We suggest a possible direct effect of heat stress on ovarian function.

Regulation of aromatase expression in estrogen-responsive breast and uterine disease: from bench to treatment

A single gene encodes the key enzyme for estrogen biosynthesis termed aromatase, inhibition of which effectively eliminates estrogen production. Aromatase inhibitors successfully treat breast cancer and endometriosis, whereas their roles in endometrial cancer, uterine fibroids, and aromatase excess syndrome are less clear. Ovary, testis, adipose tissue, skin, hypothalamus, and placenta express aromatase normally, whereas breast and endometrial cancers, endometriosis, and uterine fibroids overexpress aromatase and produce local estrogen that exerts paracrine and intracrine effects. Tissue-specific promoters distributed over a 93-kilobase regulatory region upstream of a common coding region alternatively control aromatase expression. A distinct set of transcription factors regulates each promoter in a signaling pathway- and tissue-specific manner. Three mechanisms are responsible for aromatase overexpression in a pathologic tissue versus its normal counterpart. First, cellular composition is altered to increase aromatase-expressing cell types that use distinct promoters (breast cancer). Second, molecular alterations in stromal cells favor binding of transcriptional enhancers versus inhibitors to a normally quiescent aromatase promoter and initiate transcription (breast/endometrial cancer, endometriosis, and uterine fibroids). Third, heterozygous mutations, which cause the aromatase coding region to lie adjacent to constitutively active cryptic promoters that normally transcribe other genes, result in excessive estrogen formation owing to the overexpression of aromatase in many tissues.

The genomic environment around the Aromatase gene: evolutionary insights

Background

The cytochrome P450 aromatase (CYP19), catalyses the aromatisation of androgens to estrogens, a key mechanism in vertebrate reproductive physiology. A current evolutionary hypothesis suggests that CYP19 gene arose at the origin of vertebrates, given that it has not been found outside this clade. The human CYP19 gene is located in one of the proposed MHC-paralogon regions (HSA15q). At present it is unclear whether this genomic location is ancestral (which would suggest an invertebrate origin for CYP19) or derived (genomic location with no evolutionary meaning). The distinction between these possibilities should help to clarify the timing of the CYP19 emergence and which taxa should be investigated.

Results

Here we determine the "genomic environment" around CYP19 in three vertebrate species Homo sapiens, Tetraodon nigroviridis and Xenopus tropicalis. Paralogy studies and phylogenetic analysis of six gene families suggests that the CYP19 gene region was structured through "en bloc" genomic duplication (as part of the MHC-paralogon formation). Four gene families have specifically duplicated in the vertebrate lineage. Moreover, the mapping location of the different paralogues is consistent with a model of "en bloc" duplication. Furthermore, we also determine that this region has retained the same gene content since the divergence of Actinopterygii and Tetrapods. A single inversion in gene order has taken place, probably in the mammalian lineage. Finally, we describe the first invertebrate CYP19 sequence, from Branchiostoma floridae.

Conclusion

Contrary to previous suggestions, our data indicates an invertebrate origin for the aromatase gene, given the striking conservation pattern in both gene order and gene content, and the presence of aromatase in amphioxus. We propose that CYP19 duplicated in the vertebrate lineage to yield four paralogues, followed by the subsequent loss of all but one gene in vertebrate evolution. Finally, we suggest that agnathans and lophotrocozoan protostomes should be investigated for the presence of aromatase.

Molecular cloning of P450 aromatase from the leopard gecko and its expression in the ovary

In this study, we identified the cDNA of P450 aromatase in the leopard gecko, a lizard with temperature-dependent sex determination. The cDNA encodes a putative protein of 505 amino acids. The deduced amino acid sequence of leopard gecko aromatase cDNA showed 80% identity with that of turtles, 70% with humans and 77% with chickens. This is the first report of the identification of P450 aromatase cDNA in squamata species. It has been reported that this gene is expressed in different layers of cells in the ovary of mammalian species and avian species. Thus, we also investigated cells expressing the mRNA of this gene in the ovary of the leopard gecko by RT-PCR and in situ hybridization. The mRNA expression of leopard gecko P450 aromatase was localized in both the thecal and granulosa cell layers in the ovary. The expression in thecal and granulosa cell layers was examined in the largest follicle, second largest follicle and third largest follicle by RT-PCR. A higher level of mRNA expression was observed in the granulosa cell layer of the second largest follicle than in other cell layers. This result may reflect the characteristics of follicles in species with automonochronic ovulation.

Two types of aromatase with different encoding genes, tissue distribution and developmental expression in Nile tilapia (Oreochromis niloticus)

We isolated a novel type of aromatase cDNA from a Nile tilapia (Oreochromis niloticus) ovary cDNA library. Because this aromatase is phylogenetically related to brain aromatase (CYP19b) of goldfish, zebrafish and sea bass, we named it tilapia CYP19b (tCYP19b). tCYP19b encodes a protein that is predicted to consist of 495 residues and have 63.8% homology with the aromatase (tCYP19a) we previously isolated from the same source. In vitro transient transfection of cultured COS7 cells demonstrated that tCYP19b codes a functional protein to catalyze estrogen production from an androgen substrate. RT-PCR and Northern hybridization analysis showed that tCYP19b was expressed at a high level in the brain and at a low level in a wide variety of other tissues, whereas tCYP19a was mainly present in the ovary and its level significantly increased during the vitellogenic stage. RT-PCR also detected tCYP19b expression in brain and gonad tissues of both female and male tilapia during sex differentiation, but tCYP19a was only found in the ovary of the fry at that period. These results suggest that tCYP19a plays a key role in sex differentiation and ovarian development. We also isolated genes of two tilapia aromatases. Based on the location of the transcription initiation site, we predicted that there is one promoter for tCYP19a and three promoters for tCYP19b. Although the two aromatase isoforms have similar gene structures in the coding region, we found that the binding regions of SF-1/Ad4 BP region, WT1-KTS and SRY, which are sex-determining factors in mammals, are present in the 5' flank region of tCYP19a but not tCYP19b. A similar situation is present in promoters of zebrafish and goldfish aromatase isoforms. This data indicates that CYP19a plays a decisive role in sex differentiation of those species. The unique presence of the ERE motif in the tCYP19b promoter and the high expression of tCYP19b in the brain support that CYP19b is mainly involved in estrogen-mediated neural estrogen synthesis.

Preoptic aromatase modulates male sexual behavior: slow and fast mechanisms of action

In many species, copulatory behavior and appetitive (anticipatory/motivational) aspects of male sexual behavior are activated by the action in the preoptic area of estrogens locally produced by testosterone aromatization. Estrogens bind to intracellular receptors, which then act as transcription factors to activate the behavior. Accordingly, changes in aromatase activity (AA) result from slow steroid-induced modifications of enzyme transcription. More recently, rapid nongenomic effects of estrogens have been described and evidence has accumulated indicating that AA can be modulated by rapid (minutes to hour) nongenomic mechanisms in addition to the slower transcriptional changes. Hypothalamic AA is rapidly down-regulated in conditions that enhance protein phosphorylation, in particular, increases in the intracellular calcium concentration, such as those triggered by neurotransmitter (e.g., glutamate) activity. Fast changes in brain estrogens can thus be caused by aromatase phosphorylation as a result of changes in neurotransmission. In parallel, recent studies demonstrate that the pharmacological blockade of AA by specific inhibitors rapidly (within 15-45 min) down-regulates motivational and consummatory aspects of male sexual behavior in quail while injections of estradiol can rapidly increase the expression of copulatory behavior. These data collectively support an emerging concept in neuroendocrinology, namely that estrogen, locally produced in the brain, regulates male sexual behavior via a combination of genomic and nongenomic mechanisms. Rapid and slower changes of brain AA match well with these two modes of estrogen action and provide temporal variations in the estrogen's bioavailability that can support the entire range of established effects for this steroid.

Cloning and developmental expression of the cytochrome P450 aromatase gene (CYP19) in the European eel (Anguilla anguilla)

To characterize the involvement of the aromatase gene during the process of sex determination in the European eel (Anguilla anguilla), the expression of its gonadal form was determined during various developmental stages. The cloned cDNA from the European eel gonad (EeCYP19) contains an open reading frame of 1539 bp, encoding a deduced protein of 513 residues. The predicted amino acid sequence shows 97% identity with that of the Japanese eel, and 59-69% of identity with those of the CYP19 gonadal and brain forms of other teleost fish. Two potential initiation sites (ATG) were found downstream of the first ATG codon. A fluorescent-based method of real-time PCR was developed to quantify EeCYP19 expression. The expression levels of EeCYP19 in the gonads of adult males were approximately 12- and 30-fold lower than the levels in adult females and juvenile eels previously treated with E2, respectively. Expression of aromatase was found only in a single specimen in the control group. In contrast, no difference was found among sexes in the aromatase expression in the brain. Treatment with aromatase inhibitor (AI) of juvenile eel resulted in the total loss of aromatase expression in the gonads and brains. The results of this work revealed that AI treatment not only reduces the synthesis of estradiol, but reduces the expression levels of EeCYP19 as well. No evidence for the presence of a distinct extra-gonadal (brain) form of aromatase in the European eel could be provided.

Effect of Non-Steroidal Aromatase Inhibitor on Blood Plasma Ovarian Steroid and Thyroid Hormones in Laying Hen (Gallus domesticus)

HyLine Brown laying hens at 30 weeks of age were treated twice daily with Fadrozole, a non-steroidal aromatase inhibitor (AI; 1 mg/kg body weight; i.m.) for six consecutive days; control hens received saline. Blood was collected every day 0.5 h after oviposition, i.e. just before AI treatment. Ovarian steroids: progesterone (P4), testosterone (T) and estradiol (E2), and iodothyronines: thyroxine (T4), triiodothyronine (T3) and reverse-triiodothyronine (rT3) were measured in blood plasma by radioimmunoassay methods. In AI-treated hens a gradual delay in oviposition time was observed. AI significantly decreased P4 and E2 levels, maximally by 43% on day 4 and by 74% on day 5, respectively, and elevated T level, maximally by 248% on day 4. Simultaneously, the increases in T4 and T3 levels with no changes in rT3 levels were observed. The maximal effect of AI on T4 and T3 levels was found on day 4 (60% increase) and day 5 (312% increase), respectively. Moreover, statistically significant, negative coefficient of correlation between E2 and T3 (r = -0.51), and positive coefficient of correlation between T and T3 (r = 0.42) in AI-treated hens were found. The results obtained indicate that in mature laying hens there is a strong relationship between ovarian steroids and thyroid hormones, and suppression of E2 synthesis not only disrupts ovarian function but also affects the activity of the thyroid gland and peripheral metabolism of thyroid hormones.

Profiles of mRNA expression of genes related to sex differentiation of the gonads in the chicken embryo

Sex is determined genetically in birds. The homogametic sex is male (ZZ), whereas the heterogametic sex is female (ZW). According to the genetic sex, gonads develop into testes or ovary. In this study, we performed experiments to reveal mRNA expression patterns in the gonad between d 5.5 and 8.5 of incubation and examined a possible role of Dss-Ahc critical region on the X chromosome 1 (Dax1), Steroidogenic factor 1 (Sf1), P450aromatase (P450arom), Estrogen receptor alpha (ER alpha), doublesex and mab3 related transcription factor 1 (Dmrt1), Sry-related HMG box gene 9 (Sox9), Gata binding protein 4 (Gata4), and anti-müllerian hormone (Amh) in sex differentiation in chicken embryonic gonads using RNase protection assay. In embryonic chicken gonads, Dax1 mRNA was expressed in both sexes but was higher in females than in males at d 6.5 and 7.5 of incubation. The Sf1 mRNA was expressed in both sexes, but it was expressed more in males at d 5.5 than in females but more in females than in males at d 7.5 and 8.5 of incubation. The P450arom mRNA was expressed only in female gonads from d 5.5 of incubation. The ER alpha mRNA was expressed in both sexes, but it did not show a sex difference. On the other hand, the Dmrt1 mRNA was expressed in both sexes, but it showed a male-specific expression pattern. The male-specific expression pattern was observed in Sox9 mRNA, but it was not expressed in female gonads. The Gata4 mRNA was expressed in both sexes, and sex differences were not revealed throughout the observational period. Amh mRNA was expressed in both sexes, but it had male-specific mRNA expression pattern at d 6.5 to 8.5 of incubation. These results indicate that Dax1, Sf1, and P450arom have possible roles in ovary formation, whereas Dmrt1, Sox9, and Amh are related to testis formation in differentiating chicken gonads at d 5.5 to 8.5 of incubation.

Multiple mechanisms control brain aromatase activity at the genomic and non-genomic level

Evidence has recently accumulated indicating that aromatase activity in the preoptic area is modulated in parallel by both slow (hours to days) genomic and rapid (minutes to hours) non-genomic mechanisms. We review here these two types of control mechanisms and their potential contribution to various aspects of brain physiology in quail. High levels of aromatase mRNA, protein and activity (AA) are present in the preoptic area of this species where the transcription of aromatase is controlled mainly by steroids. Estrogens acting in synergy with androgens play a key role in this control and both androgen and estrogen receptors (ER; alpha and beta subtypes) are present in the preoptic area even if they are not necessarily co-localized in the same cells as aromatase. Steroids have more pronounced effects on aromatase transcription in males than in females and this sex difference could be caused, in part, by a sexually differentiated expression of the steroid receptor coactivator 1 in this area. The changes in aromatase concentration presumably control seasonal variations as well as sex differences in brain estrogen production. Aromatase activity in hypothalamic homogenates is also rapidly (within minutes) down-regulated by exposure to conditions that enhance protein phosphorylation such as the presence of high concentrations of calcium, magnesium and ATP. Similarly, pharmacological manipulations such as treatment with thapsigargin or stimulation of various neurotransmitter receptors (alpha-amino-3-hydroxy-methyl-4-isoxazole propionic acid (AMPA), kainate, and N-methyl-D-aspartate (NMDA)) leading to enhanced intracellular calcium concentrations depress within minutes the aromatase activity measured in quail preoptic explants. The effects of receptor stimulation are presumably direct: electrophysiological data confirm the presence of these receptors in the membrane of aromatase-expressing cells. Inhibitors of protein kinases interfere with these processes and Western blotting experiments on brain aromatase purified by immunoprecipitation confirm that the phosphorylations regulating aromatase activity directly affect the enzyme rather than another regulatory protein. Accordingly, several phosphorylation consensus sites are present on the deduced amino acid sequence of the recently cloned quail aromatase. Fast changes in the local availability of estrogens in the brain can thus be caused by aromatase phosphorylation so that estrogen could rapidly regulate neuronal physiology and behavior. The rapid as well as slower processes of local estrogen production in the brain thus match well with the genomic and non-genomic actions of steroids in the brain. These two processes potentially provide sufficient temporal variation in the bio-availability of estrogens to support the entire range of established effects for this steroid.

Estrogen excess associated with novel gain-of-function mutations affecting the aromatase gene

BACKGROUND

Gynecomastia of prepubertal onset may result from increased estrogen owing to excessive aromatase activity in extraglandular tissues. A gene in chromosome 15q21.2 encodes aromatase, the key enzyme for estrogen biosynthesis. Several physiologic tissue-specific promoters regulate the expression of aromatase, giving rise to messenger RNA (mRNA) species with an identical coding region but tissue-specific 5'-untranslated regions in placenta, gonads, brain, fat, and skin.

METHODS

We studied skin, fat, and blood samples from a 36-year-old man, his 7-year-old son, and an unrelated 17-year-old boy with severe gynecomastia of prepubertal onset and hypogonadotropic hypogonadism caused by elevated estrogen levels.

RESULTS

Aromatase activity and mRNA levels in fat and skin and whole-body aromatization of androstenedione were severely elevated. Treatment with an aromatase inhibitor decreased serum estrogen levels and normalized gonadotropin and testosterone levels. The 5'-untranslated regions of aromatase mRNA contained the same sequence (FLJ) in the father and son and another sequence (TMOD3) in the unrelated boy; neither sequence was found in control subjects. These 5'-untranslated regions normally make up the first exons of two ubiquitously expressed genes clustered in chromosome 15q21.2-3 in the following order (from telomere to centromere): FLJ, TMOD3, and aromatase. The aromatase gene is normally transcribed in the direction opposite to that of TMOD3 and FLJ. Two distinct heterozygous inversions reversed the direction of the TMOD3 or FLJ promoter in the patients.

CONCLUSIONS

Heterozygous inversions in chromosome 15q21.2-3, which caused the coding region of the aromatase gene to lie adjacent to constitutively active cryptic promoters that normally transcribe other genes, resulted in severe estrogen excess owing to the overexpression of aromatase in many tissues.

Molecular characterization and expression of equine testicular cytochrome P450 aromatase

We characterized testicular equine aromatase and its expression. A 2707 bp cDNA was isolated, it encoded a polypeptide of 503 residues with a deduced molecular mass of 57.8 kDa. The sequence features were those of a cytochrome P450 aromatase, with a 78% polypeptide identity with the human counterpart. The gene has a minimal length of 74 kb comprising at least 9 exons and expresses a 2.8 kb mRNA in the testis. Transient cDNA transfections in E293 cells and in vitro translations in a reticulocyte lysate system allowed aromatase protein and activity detections. The activity increased with androstenedione as substrate in a dose-dependent manner. The isolation of testicular aromatase by a new immunoaffinity method demonstrated that the protein could exist either glycosylated or not with a 2 kDa difference. All these results taken together allow new structural studies to progress in the understanding of this cytochrome P450.

Characterization of a cDNA encoding P-450 aromatase (CYP19) from Japanese eel ovary and its expression in ovarian follicles during induced ovarian development

A cDNA encoding P450 aromatase (CYP19) was isolated from a Japanese eel (Anguilla japonica) ovarian cDNA library. This cDNA contains a complete open reading frame encoding 511 amino acid residues. The deduced amino acid sequence is 59% and 65% identical to the catfish and rainbow trout forms, respectively, and 52-54% to mammalian and chicken forms. Non-steroidogenic COS-7 cells transfected with the eel CYP19 cDNA converted exogenous androstenedione to estrone, thus verifying its identity. Northern blot analysis indicated that there was a single 2.1 kb transcript in the ovary. A 2.1 kb transcript was also found in the brain but not in the spleen, head kidney, kidney, or liver. Throughout ovarian development induced by weekly injections of salmon pituitary homogenate (SPH, 20 microg/g body weight), the 2.1 kb transcript was barely or not detectable in the ovaries. However, signals greatly increased in intensity in oocytes in the migratory nucleus stage and then decreased slightly in the post-ovulatory ovary. These changes in transcript levels are consistent with the changes in aromatase activity of ovarian follicles, suggesting that aromatase activity in ovarian follicles is mainly regulated at the transcriptional level. In addition, fadrozole was found to significantly inhibit aromatase activity in a heterologous expression system using COS-7 cells, which indicates that fadrozole treatment could be useful to control E(2) production during artificial maturation of eels.

Interactions between aromatase (estrogen synthase) and dopamine in the control of male sexual behavior in quail

In male quail, like in other vertebrates including rodents, testosterone acting especially through its estrogenic metabolites is necessary for the activation of male sexual behavior. Also, the administration of dopamine agonists and antagonists profoundly influences male sexual behavior. How the steroid-sensitive neural network and dopamine interact physiologically, remains largely unknown. It is often implicitly assumed that testosterone or its metabolite estradiol, stimulates male sexual behavior via the modification of dopaminergic transmission. We have now identified in quail two possible ways in which dopamine could potentially affect sexual behavior by modulating the aromatization of testosterone into an estrogen. One is a long-acting mechanism that presumably involves the modification of dopaminergic transmission followed by the alteration of the genomic expression of aromatase. The other is a more rapid mechanism that does not appear to be dopamine receptor-mediated and may involve a direct interaction of dopamine with aromatase (possibly via substrate competition). We review here the experimental data supporting the existence of these controls of aromatase activity by dopamine and discuss the possible contribution of these controls to the activation of male sexual behavior.

Phosphorylation processes mediate rapid changes of brain aromatase activity

The enzyme aromatase (also called estrogen synthase) that catalyzes the transformation of testosterone (T) into estradiol plays a key limiting role in the action of T on many aspects of reproduction. The distribution and regulation of aromatase in the quail brain has been studied by radioenzyme assays on microdissected brain areas, immunocytochemistry, RT-PCR and in situ hybridization. High levels of aromatase activity (AA) characterize the sexually dimorphic, steroid-sensitive medial preoptic nucleus (POM), a critical site of T action and aromatization for the activation of male sexual behavior. The boundaries of the POM are clearly outlined by a dense population of aromatase-containing cells as visualized by both immunocytochemistry and in situ hybridization histochemistry. Aromatase synthesis in the POM is controlled by T and its metabolite estradiol, but estradiol receptors alpha (ERalpha) are not normally co-localized with aromatase in this brain area. Estradiol receptor beta (ERbeta) has been recently cloned in quail and localized in POM but we do not yet know whether ERbeta occurs in aromatase cells. It is therefore not known whether estrogens regulate aromatase synthesis directly or by affecting different inputs to aromatase cells as is the case with the gonadotropin releasing hormone neurons. The presence of aromatase in presynaptic boutons suggests that locally formed estrogens may exert part of their effects by non-genomic mechanisms at the membrane level. Rapid effects of estrogens in the brain that presumably take place at the neuronal membrane level have been described in other species. If fast transduction mechanisms for estrogen are available at the membrane level, this will not necessarily result in rapid changes in brain function if the availability of the ligand does not also change rapidly. We demonstrate here that AA in hypothalamic homogenates is rapidly down-regulated by exposure to conditions that enhance protein phosphorylation (addition of Ca2+, Mg2+, ATP). This inhibition is blocked by kinase inhibitors which supports the notion that phosphorylation processes are involved. A rapid (within minutes) and reversible regulation of AA is also observed in hypothalamic explants incubated in vitro and exposed to high Ca2+ levels (K+-induced depolarization, treatment by thapsigargin, by kainate, AMPA or NMDA). The local production and availability of estrogens in the brain can therefore be rapidly changed by Ca2+ based on variation in neurotransmitter activity. Locally-produced estrogens are as a consequence available for non-genomic regulation of neuronal physiology in a manner more akin to the action of a neuropeptide/neurotransmitter than previously thought.

The 5'-flanking regions of CYP19A1 and CYP19A2 in zebrafish

This report describes the structure of the 5'-flanking regions of both the CYP19A1 and A2 genes that were isolated from the genome of the zebrafish (Danio rerio). Consensus sequences of three cAMP-responsive elements (CRE), an aryl hydrocarbon-responsive element (AhR/Arnt), a steroidogenic factor 1 (SF-1) site, and a TATA box were observed in the 5'-flanking region of CYP19A1. In contrast, the 5'-flanking region of CYP19A2 was located upstream of an untranslated exon and possessed consensus sequences of a single CRE, an estrogen-responsive element (ERE), a peroxisome proliferator-activated receptor alpha/retinoid X receptor alpha heterodimer-responsive element (PPARalpha/RXRalpha), and a TATA box. Primer extension analysis revealed that the predominant transcription initiation sites for CYP19A1 and A2 transcripts were 28 and 91 bp upstream from the putative translation initiation codon, respectively. These analyses indicate that substantially different regulators, including a variety of environmental xenobiotics, control the expression the two CYP19 genes.

The control of preoptic aromatase activity by afferent inputs in Japanese quail

This review summarizes current knowledge on the mechanisms that control aromatase activity in the quail preoptic area, a brain region that plays a key role in the control of reproduction. Aromatase and aromatase mRNA synthesis in the preoptic area are enhanced by testosterone and its metabolite estradiol, but estradiol receptors of the alpha subtype are not regularly colocalized with aromatase. Estradiol receptors of the beta subtype are present in the preoptic area but it is not yet known whether these receptors are colocalized with aromatase. The regulation by estrogen of aromatase activity may be, in part, trans-synaptically mediated, in a manner that is reminiscent of the ways in which steroids control the activity of gonadotropic hormone releasing hormone neurons. Aromatase-immunoreactive neurons are surrounded by dense networks of vasotocin-immunoreactive and tyrosine hydroxylase-immunoreactive fibers and punctate structures. These inputs are in part steroid-sensitive and could therefore mediate the effects of steroids on aromatase activity. In vivo pharmacological experiments indicate that catecholaminergic depletions significantly affect aromatase activity presumably by modulating aromatase transcription. In addition, in vitro studies on brain homogenates or on preoptic-hypothalamic explants show that aromatase activity can be rapidly modulated by a variety of dopaminergic compounds. These effects do not appear to be mediated by the membrane dopamine receptors and could involve changes in the phosphorylation state of the enzyme. Together, these results provide converging evidence for a direct control of aromatase activity by catecholamines consistent with the anatomical data indicating the presence of a catecholaminergic innervation of aromatase cells. These dopamine-induced changes in aromatase activity are observed after several hours or days and presumably result from changes in aromatase transcription but rapid non-genomic controls have also been identified. The potential significance of these processes for the physiology of reproduction is critically evaluated.

Correlation between messenger RNA expression of cytochrome P450 aromatase and its enzyme activity during oocyte development in the red seabream (Pagrus major)

In teleosts, estradiol-17beta (E2) is an important hormone responsible for oocyte development. To elucidate the molecular mechanisms underlying E2 biosynthesis, we characterized the structure of red seabream (Pagrus major) cytochrome P450 aromatase (P450(arom)) that is directly involved in E2 biosynthesis and found changes in mRNA levels of P450(arom) during oocyte development induced by implantation of gonadotropin-releasing hormone analogue. A cDNA clone encoding P450(arom) is 1779 base pairs in length and encodes a protein of 519 amino acids in length, with a calculated molecular weight of 58.9 kDa. Northern blot analysis showed that P450(arom) mRNA levels increased gradually from Day 8, when oocytes reached the secondary yolk globule stage, and were maintained at high levels at the day of spawning (Day 15). The P450(arom) mRNA levels increased in association with an increase of the gonadosomatic index (gonad weight/body weight x 100%), serum E2, and P450(arom) enzyme activity (in vitro conversion of testosterone to E2 in the ovarian fragments). Furthermore, an increase in mRNA levels of the LHbeta, but not FSHbeta, correlated with increased P450(arom) mRNA levels during the course of ovarian development. In addition, the levels of P450(arom) mRNA increased in isolated ovarian follicles during the course of vitellogenic oocyte growth and became undetectable in follicles at the migratory nucleus and the mature stages. These findings, together with those of the previous studies, suggest that LH, not FSH, may regulate E2 biosynthesis via increased levels of P450(arom) mRNA during oocyte development of red seabream.

An overview of factors influencing sex determination and gonadal development in birds

The morphological development of the embryonic gonads is very similar in birds and mammals, and recent evidence suggests that the genes involved in this process are conserved between these classes of vertebrates. The genetic mechanism by which sex is determined in birds remains to be elucidated, although recent studies have reinforced the contention that steroids may play an important role in the structural development of the testes and ovaries in birds. So far, few genes have been assigned to the avian sex chromosomes, but it is known that the Z and W chromosomes do not share significant homology with the mammalian X and Y chromosomes. The commercial importance of poultry breeding has motivated considerable investment in developing physical and genetic maps of the chicken genome. These efforts, in combination with modern molecular approaches to analyzing gene expression, should help to elucidate the sex-determining mechanism in birds in the near future.

Follicle-stimulating hormone regulates steroidogenic enzymes in cultured cells of the chick embryo ovary

This investigation addresses the potential regulation of enzymes involved in the biosynthesis of steroid hormones during early stages of gonadal development by follicle-stimulating hormone (FSH). Gonadal cells of 10-day-old chick embryo and cells of the left ovary of 18-day-old chick embryo were cultured for 60 h in a defined medium with or without the addition of FSH (2.0 IU/ml). At the end of the culture, cells were recovered and evaluated by biotransformation of tritiated steroid precursors and mRNA levels were evaluated by RT-PCR. The production of estrone from androstenedione was increased in the FSH-treated cells, both human FSH (hFSH) and recombinant human FSH (rhFSH), indicating a stimulatory effect on aromatase (P450arom). Similarly, the intensity of the band corresponding to P450arom mRNA was higher in hFSH and rhFSH than in control and chorionic gonadotropin (hCG) groups. The P450arom stimulation was observed in the ovary of 10- and 18-day-old chick embryo. The transformation of dehydroepiandrosterone to androstenedione was taken as evidence of 3beta-hydroxysteroid dehydrogenase function. This enzyme was stimulated in the cultured ovarian cells of 18-day-old chick embryos treated with hFSH and rhFSH compared with controls. The production of pregnenolone in the mitocondrial fraction of 18-day-old chick embryo ovary was increased when cultured with hFSH and rhFSH. This observation together with the increase in the band intensity corresponding to mRNA of P450 cholesterol side-chain cleavage indicates stimulation by FSH treatment; hCG produced a similar effect. Somatic cells of the medullary cords are proposed to be FSH target cells in the ovary of the chick embryo.

Distinct cytochrome P450 aromatase isoforms in zebrafish (Danio rerio) brain and ovary are differentially programmed and estrogen regulated during early development

As a first step toward understanding estrogen's role in neurodevelopment, a PCR cloning strategy was used to isolate complementary DNAs encoding two distinct cytochrome P450 aromatase isoforms in adult zebrafish (Danio rerio) brain and ovary (termed P450aromB and P450aromA, respectively). Sequence and phylogenetic analysis showed that the zebrafish P450arom forms are orthologs of previously identified cyp19b and cyp19a genes in goldfish. On Northern blots, a single 4.4-kb transcript of the P450aromB subtype was identified in brain, and a 2.1-kb transcript of the P450aromA subtype in ovary, but RT-PCR showed a degree of overlapping expression. Both messenger RNA (mRNA) forms were detected in unfertilized eggs and 1.5 hpf (cleavage stage) embryos but declined by 12 hpf, indicating maternal transfer. A secondary rise in mRNAs between 12-24 hpf indicated the onset of embryonic cyp19b and -a transcription. Both mRNA species accumulated progressively to 120 hpf (early larval stage), but the relative magnitude and pattern of change was isoform specific. Estradiol (E(2,) 1 microM) advanced and amplified the developmentally programmed accumulation of P450aromB mRNA, and ICI164.384 decreased expressed levels, implying blockade of an endogenous estrogen mediated regulatory component. Conversely, E(2) had no effect or decreased P450aromA mRNA. The early embryonic expression of P450aromB and P450aromA isoforms, and differences in developmental programming and estrogen regulation, imply independent regulatory mechanisms and unique functions during major morphogenetic and differentiative events.

Characterization of gonadal and extra-gonadal forms of the cDNA encoding the Atlantic stingray (Dasyatis sabina) cytochrome P450 aromatase (CYP19)

Cytochrome P450 aromatase (P450arom; CYP19) mediates the conversion of androgens to estrogens and its activity has been found in all vertebrates studied to date. This study describes the full-length cDNA encoding the ovarian form of P450arom and the differences in the 5'-untranslated region (5'-UTR) of the extra-gonadal P450arom transcript expressed by the Atlantic stingray (Dasyatis sabina). Elasmobranchs (cartilaginous fishes such as sharks, rays and skates) diverged from the other vertebrates more than 350 million years ago, therefore the stingray P450arom cDNA may represent an ancient form of this gene. Northern blot analysis showed that the ovarian follicle expressed transcripts of 3.1 and 1.7 kb in size which correspond to the clones isolated from a stingray ovarian follicle cDNA library. Both transcripts consisted of an identical 1.5 kb coding region and a 41 bp 5'-UTR, however the 3'-UTRs differed in the use of the most proximate and the most distal of four polyadenylation signals. COS cells transfected with the 1.7 kb cDNA had twice the aromatase activity as cells transfected with the 3.1 kb cDNA. The coding region of the cDNA predicted a 58.5 kDa protein which consisted of 511 residues. Alignment of the stingray protein indicates that the P450arom is equally identical (53-59%) to all other vertebrate forms of P450arom characterized to date, thus indicating a common ancestry. The evolutionary relationship of the stingray form of P450arom clearly predates the other forms and belongs to a unique lineage. Transcripts of P450arom were expressed in ovarian follicles (of all sizes), the testis, the pituitary, in all sections of the brain, and in the kidney. The extra-gonadal transcripts appear to encode a protein identical to the ovarian form, however, the 5'-UTR was 657 bp longer presumably due to the transcription of an untranslated 'first exon' as seen in the mammalian form of this gene.

Expression of five steroidogenic genes including aromatase gene at early developmental stages of chicken male and female embryos

In the course of avian embryo development, estrogen has been indicated to play a key role in gonadal differentiation by the inhibition of aromatase (P-450arom) that synthesizes estrogen from androgen. Biosynthesis of estrogen requires not only P-450arom but also other enzymes for a steroidogenic pathway. To elucidate gonadal differentiation, the steroidogenic pathway should be studied comprehensively in the early developmental stages including that of sex differentiation. Therefore, in the present study, the expressions of the steroidogenic genes, P-450scc, 3beta-HSD, P-450c17, 17beta-HSD and P-450arom, were measured at the developmental stages (days 2-9 of incubation) of chicken embryos by quantitative RT-PCR. Transcripts for all the genes studied, except for P-450arom were detected in all the developmental stages examined, indicating that mRNAs for the steroidogenic enzymes required to convert cholesterol to androgens are present in the avian embryo before gonadal differentiation. In contrast, P-450arom mRNA was detected in female embryos during days 5-9 of incubation but not in male embryos throughout incubation. The onset of P-450arom gene expression at day 5 coincides with the stage of gonadal differentiation, corroborating the role of estrogen in the process of gonadal differentiation in chicken.

Changes in testosterone metabolism associated with the evolution of placental and gonadal isozymes of porcine aromatase cytochrome P450

Differences in the catalytic activity of the placental and gonadal isozymes of porcine aromatase cytochrome P450 (P450arom) were examined in cell lines exhibiting stable expression of recombinant enzyme. Cell lines were selected that expressed high, but similar, immunodetectable levels of each isozyme based on Western analysis. Aromatase activity varied with growth in culture, decreasing at confluence from a peak reached between 50-80% cell density. Cells expressing the placental isozyme had 3-5 times higher catalytic activity (per mg protein) than those expressing the gonadal isozyme. The P450arom inhibitor fadrazole (1 microM) inhibited more than 97% of this activity, whereas another imidazole, etomidate (1 microM), selectively inhibited gonadal P450arom activity by 92%. Estrogen synthesis from androstenedione and testosterone was determined by RIA and confirmed by HPLC analysis, which also identified the accumulation of the 19-hydroxy and 19-oxo intermediates of the respective substrates. There was no evidence of other steroid metabolites accumulating in the media of cell lines expressing either isozyme. Tritiated water formed during aromatization of substrates 3H labeled at the C1 and C2 positions was stereo-selective for the beta orientation, but less so for testosterone than androstenedione during metabolism by the porcine placental (and human) isozyme than the gonadal isozyme. Testosterone showed a higher affinity for the porcine placental P450arom than the gonadal P450arom, but both isozymes had similar affinities for androstenedione. Testosterone was also aromatized more slowly than androstenedione by the porcine gonadal P450arom. These data suggest that catalytic differences have arisen in the substrate binding pocket during the evolution of isozymes of porcine P450arom that affect androgen metabolism, particularly the aromatization of testosterone. The physiological significance of these differences to the reproductive biology of the pig remains to be determined.

The cDNA cloning and transient expression of an ovary-specific 17beta-hydroxysteroid dehydrogenase of chickens

A cDNA clone, pc17bHSD, was obtained from the chicken ovarian cDNA library by its partial homology to the cDNA sequence of the rat 17beta-hydroxysteroid dehydrogenase (17beta-HSD). The cDNA insert of pc17bHSD is 979bp long and contains an open reading frame (ORF) of 906bp. The deduced amino acid sequence of the ORF shows 48 and 50% overall identity with those of the rat and the human type-1 17beta-HSD, respectively. Five sequence regions common to the short-chain alcohol dehydrogenase superfamily are well conserved, including the YxxxK sequence motif at the active site. Northern blot hybridization detected a transcript of about 1kb only in ovaries of both sexually immature and mature female chickens. The 17beta-HSD activity, which was highly specific to the interconversion between estrone and estradiol-17beta, was detected in the cytoplasmic fraction of human 293 cells transfected transiently with an expression vector carrying the c17bHSD cDNA sequence, pcDNAI/c17bHSD. From these results, it is concluded that the pc17bHSD is the cDNA clone for the ovary-specific molecular species of 17beta-HSD in chickens.

Steroid metabolising enzymes in the determination of brain gender

The neurotrophic effects of oestrogen formed in the brain are important in brain sexual differentiation of the central nervous system and behaviour. Aromatase, converting testosterone to oestradiol-17beta, is a key enzyme involved in brain development. In primary cell cultures of foetal hypothalamus, we have found that male neurones consistently have higher aromatase activity than in the female. Using a specific antibody to the mouse aromatase, immunoreactivity was localized in the neural soma and neurites in hypothalamic cultures. Additionally more male foetal hypothalamus neurones express aromatase than in the female. Testosterone increases aromatase activity in parallel with a greater number of aromatase-immunoreactive neurones. Testosterone also increases soma size, neurite length, and branching of cultured hypothalamic neurones. The neuronal aromatase activity appears to be sensitive to the inductive effects of androgen only during the later stages of foetal development. Endogenous inhibitors of the aromatase are also likely to have a regulatory role. This work suggests that regulation of a network of aromatase neurones, sensitive to the hormonal environment of the hypothalamus, may determine when oestrogens are available for neurotrophic effects underlying brain differentiation.

A steroidogenic factor-1-binding site and cyclic adenosine 3',5'-monophosphate response element-like elements are required for the activity of the rat aromatase promoter in rat Leydig tumor cell lines

Although transcription initiation within CYP19 (cytochrome P450 aromatase) occurs immediately 5' to the initiator methionine (proximal promoter) in two rat Leydig tumor cell lines (R2C and H540) that express high aromatase activity and in rat ovary, the patterns of aromatase expression in the two cell types are distinctive. To define mechanisms controlling different patterns of expression of the rat aromatase proximal promoter, we performed transient transfection and gel mobility shift assays. Transfection experiments using different sized promoter fragments fused to a reporter gene were used to identify regions that are functionally important for transcriptional regulation in steroidogenic cell lines [R2C, H540, and Y1 (mouse adrenocortical cells that express low aromatase activity)]. These experiments indicate that the cAMP response element (CRE) at -231 and the steroidogenic factor-1 (SF1) motif are both required for expression of the reporter gene in each steroidogenic cell line and that the CRE at -169 is similarly required in R2C cells. Gel mobility shift assays confirm binding of nuclear proteins from the steroidogenic cell lines to the SF1 motif and to CRE (-231). Leydig tumor cells also contain nuclear proteins that bind to the CRE (-169), but nuclear extracts from R2C cells produce a uniquely shifted band compared with H540 cells. These results suggest that differences in proteins that bind to distinct elements within the rat aromatase promoter may be responsible for different patterns and levels of aromatase expression in these steroidogenic cell lines.