Three different promoters control expression of the aromatase cytochrome p450 gene (cyp19) in mouse gonads and brain

Lipopolysaccharide alters CEBPβ signaling and reduces estradiol production in bovine granulosa cells

Background

Bacterial infection of the uterus in postpartum dairy cows limits ovarian follicle growth, reduces blood estradiol concentrations, and leads to accumulation of bacterial lipopolysaccharide (LPS) in ovarian follicular fluid. Although treating granulosa cells with LPS in vitro decreases the expression of the estradiol synthesis enzyme CYP19A1 and reduces estradiol secretion, the molecular mechanisms are unclear. The transcription factor CCAAT enhancer binding protein beta (CEBPβ) not only facilitates the transcription of LPS regulated cytokines, but also binds to the promoter region of CYP19A1 in humans, mice, and buffalo. We hypothesized that LPS alters CEBPβ signaling to reduce CYP19A1 expression, resulting in decreased estradiol secretion.

Methods

Bovine granulosa cells were isolated from small/medium or large follicles and treated with LPS in the presence of FSH and androstenedione for up to 24 h.

Results

Treatment with LPS increased CXCL8 and IL6 gene expression and reduced estradiol secretion in granulosa cells from both small/medium and large follicles. However, LPS only reduced CYP19A1 expression in granulosa cells from large follicles. Treatment with LPS increased CEBPB expression and reduced CEBPβ nuclear localization in granulosa cells from small/medium follicles, but not granulosa cells from large follicles.

Conclusions

Although LPS reduces estradiol synthesis in bovine granulosa cells, the effects of LPS on CYP19A1 and CEBPβ are dependent on follicle size.

Tau mRNA Metabolism in Neurodegenerative Diseases: A Tangle Journey

Tau proteins are known to be mainly involved in regulation of microtubule dynamics. Besides this function, which is critical for axonal transport and signal transduction, tau proteins also have other roles in neurons. Moreover, tau proteins are turned into aggregates and consequently trigger many neurodegenerative diseases termed tauopathies, of which Alzheimer’s disease (AD) is the figurehead. Such pathological aggregation processes are critical for the onset of these diseases. Among the various causes of tau protein pathogenicity, abnormal tau mRNA metabolism, expression and dysregulation of tau post-translational modifications are critical steps. Moreover, the relevance of tau function to general mRNA metabolism has been highlighted recently in tauopathies. In this review, we mainly focus on how mRNA metabolism impacts the onset and development of tauopathies. Thus, we intend to portray how mRNA metabolism of, or mediated by, tau is associated with neurodegenerative diseases.

Experimental models of endocrine responsive breast cancer: strengths, limitations, and use

Breast cancers characterized by expression of estrogen receptor-alpha (ER; ESR1) represent approximately 70% of all new cases and comprise the largest molecular subtype of this disease. Despite this high prevalence, the number of adequate experimental models of ER+ breast cancer is relatively limited. Nonetheless, these models have proved very useful in advancing understanding of how cells respond to and resist endocrine therapies, and how the ER acts as a transcription factor to regulate cell fate signaling. We discuss the primary experimental models of ER+ breast cancer including 2D and 3D cultures of established cell lines, cell line- and patient-derived xenografts, and chemically induced rodent models, with a consideration of their respective general strengths and limitations. What can and cannot be learned easily from these models is also discussed, and some observations on how these models may be used more effectively are provided. Overall, despite their limitations, the panel of models currently available has enabled major advances in the field, and these models remain central to the ability to study mechanisms of therapy action and resistance and for hypothesis testing that would otherwise be intractable or unethical in human subjects.

Genomic Structure of the Porcine CYP19 Locus and Expression of the CYP19A3 Paralog

Proper, tissue-specific regulation of CYP19, the gene encoding aromatase, the key enzyme of estrogen synthesis, is essential for reproductive processes. Here, we analyzed transcriptional regulation of the porcine CYP19 in female and male gonads and brain by 5'RACE and RT-PCR and comprehensively mapped the pig CYP19 locus by in silico analysis. Our data revealed that the complete locus, including three paralogous copies, CYP19A1, CYP19A2 and CYP19A3, spans approximately 330 kb of the porcine chromosome 1. The locus also harbors the first exon of the Gliomedin gene (GLDN) in reverse orientation. Only transcripts of the CYP19A3 paralog were substantially expressed in gonads and hypothalamus. We identified CYP19A3-associated untranslated exons approximately 160 kb and 50 kb distal from the first codon. The 5´ untranslated regions of transcripts were derived from either a proximal or from one of these distal untranslated exons. Transcripts including only untranslated exons could be amplified from testis, thus suggesting long non-coding transcripts. The data revealed an additional layer of complexity in the regulation of the porcine CYP19 locus. Tissue-specific expression is not only achieved by tissue- and stage-specific expression of the three different CYP19 paralogs, but also by directing the expression of CYP19A3 from different, proximal and distal promoter regions.

Human Cognitive Ability Is Modulated by Aromatase Availability in the Brain in a Sex-Specific Manner

The enzyme aromatase catalyzes the final step in estrogen biosynthesis, converting testosterone to estradiol, and is expressed in the brain of all mammals. Estrogens are thought to be important for maintenance of cognitive function in women, whereas testosterone is thought to modulate cognitive abilities in men. Here, we compare differences in cognitive performance in relation to brain aromatase availability in healthy men and women. Twenty-seven healthy participants were administered tests of verbal learning and memory and perceptual/abstract reasoning. In vivo images of brain aromatase availability were acquired in this sample using positron emission tomography (PET) with the validated aromatase radiotracer [¹¹C]vorozole. Regions of interest were placed bilaterally on the amygdala and thalamus where aromatase availability is highest in the human brain. Though cognitive performance and aromatase availability did not differ as a function of sex, higher availability of aromatase in the amygdala was associated with lower cognitive performance in men. No such relationship was found in women; and the corresponding regression slopes were significantly different between the sexes. Thalamic aromatase availability was not significantly correlated with cognitive performance in either sex. These findings suggest that the effects of brain aromatase on cognitive performance are both region- and sex-specific and may explain some of the normal variance seen in verbal and nonverbal cognitive abilities in men and women as well as sex differences in the trajectory of cognitive decline associated with Alzheimer’s disease.

Brain Aromatase and the Regulation of Sexual Activity in Male Mice

The biologically active estrogen estradiol has important roles in adult brain physiology and sexual behavior. A single gene, Cyp19a1, encodes aromatase, the enzyme that catalyzes the conversion of testosterone to estradiol in the testis and brain of male mice. Estradiol formation was shown to regulate sexual activity in various species, but the relative contributions to sexual behavior of estrogen that arises in the brain versus from the gonads remained unclear. To determine the role of brain aromatase in regulating male sexual activity, we generated a brain-specific aromatase knockout (bArKO) mouse. A newly generated whole-body total aromatase knockout mouse of the same genetic background served as a positive control. Here we demonstrate that local aromatase expression and estrogen production in the brain is partially required for male sexual behavior and sex hormone homeostasis. Male bArKO mice exhibited decreased sexual activity in the presence of strikingly elevated circulating testosterone. In castrated adult bArKO mice, administration of testosterone only partially restored sexual behavior; full sexual behavior, however, was achieved only when both estradiol and testosterone were administered together. Thus, aromatase in the brain is, in part, necessary for testosterone-dependent male sexual activity. We also found that brain aromatase is required for negative feedback regulation of circulating testosterone of testicular origin. Our findings suggest testosterone activates male sexual behavior in part via conversion to estradiol in the brain. These studies provide foundational evidence that sexual behavior may be modified through inhibition or enhancement of brain aromatase enzyme activity and/or utilization of selective estrogen receptor modulators.

Epigenetic regulation of gonadal and brain aromatase expression in a cichlid fish with environmental sex determination

A fit animal must develop testes or ovaries, with brain and physiology to match. In species with alternative male morphs this coordination of development across tissues operates within sexes as well as between. For Pelvicachromis pulcher, an African cichlid in which early pH exposure influences both sex and alternative male morph, we sequence both copies of aromatase (cyp19a1), a key gene for sex determination. We analyze gene expression and epigenetic state, comparing gonad and brain tissue from females, alternative male morphs, and fry. Relative to brain, we find elevated expression of the A-copy in the ovaries but not testes. Methylation analysis suggests strong epigenetic regulation, with one region specifying sex and another specifying tissue. We find elevated brain expression of the B-copy with no sex or male morph differences. B-copy methylation follows that of the A-copy rather than corresponding to B-copy expression. In 30-day old fry, we see elevated B-copy expression in the head, but we do not see the expected elevated A-copy expression in the trunk that would reflect ovarian development. Interestingly, the A-copy epialleles that distinguish ovaries from testes are among the most explanatory patterns for variation among fry, suggesting epigenetic marking of sex prior to differentiation and thus laying the groundwork for mechanistic studies of epigenetic regulation of sex and morph differentiation.

ERO1α inhibits cell apoptosis and regulates steroidogenesis in mouse granulosa cells

ER oxidoreduclin 1α (ERO1α), an oxidase that exists in the ER, participates in protein folding and secretion and inhibiting apoptosis, and regulates tumor progression, which is a novel factor of poor cancer prognosis. However, the other physiological functions of ERO1α remain undiscovered. Although our preliminary results of this study indicated that ERO1α revealed the robust expression in ovary, especially in granulosa cells, the role of ERO1α in follicular development is not well known. Therefore, the aims of the present study were to explore the role of ERO1α and the possible mechanisms in regulating cell apoptosis and steroidogenesis in ovarian granulosa cells. ERO1α was mainly localized in granulosa cells and oocytes in the adult ovary by immunohistochemistry. Western blot analysis showed that the expression of ERO1α was highest at oestrous stage during the estrous cycle. The effect of ERO1α on cell apoptosis and steroidogenesis was detected by transduction of ERO1α overexpression and knockdown lentiviruses into primary cultured granulosa cells. Flow cytometry analysis showed that ERO1α decreased granulosa cells apoptosis. Western bolt and RT-qPCR analysis found that ERO1α increased the ratio of BCL-2/BAX, and decreased BAD and Caspase-3 expression. ELISA analysis showed that ERO1α enhanced estrogen (E2) secretion. Western bolt and RT-qPCR analysis found that ERO1α increased StAR, CYP11A1, 3β-HSD, CYP17A1, and CYP19A1 expression, and decreased CYP1B1 expression. Furthermore, Western bolt analysis found that ERO1αincreased PDI and PRDX 4 expression, and activated the PI3K/AKT/mTOR signaling pathway through increasing the phosphorylation of AKT and P70 S6 kinase. In summary, these results suggested that ERO1α might play an anti-apoptotic role and regulate steroidogenesis in granulosa cells, at least partly, via activation of the PI3K/AKT/mTOR signaling pathway.

Functional Genetic Variation in the Anti-Müllerian Hormone Pathway in Women With Polycystic Ovary Syndrome

CONTEXT

Polycystic ovary syndrome (PCOS) is a highly heritable, common endocrine disorder characterized by hyperandrogenism, irregular menses, and polycystic ovaries. PCOS is often accompanied by elevated levels of anti-Müllerian hormone (AMH). AMH inhibits follicle maturation. AMH also inhibits steroidogenesis through transcriptional repression of CYP17A1. We recently identified 16 rare PCOS-specific pathogenic variants in AMH.

OBJECTIVE

To test whether additional members of the AMH signaling pathway also contribute to the etiology of PCOS.

PARTICIPANTS/DESIGN

Targeted resequencing of coding and regulatory regions of AMH and its specific type 2 receptor, AMHR2, was performed on 608 women affected with PCOS and 142 reproductively normal control women. Prediction tools of deleteriousness and in silico evidence of epigenetic modification were used to prioritize variants for functional evaluation. Dual-luciferase reporter assays and splicing assays were used to measure the impact of genetic variants on function.

RESULTS

We identified 20 additional variants in/near AMH and AMHR2 with significantly reduced signaling activity in in vitro assays. Collectively, from our previous study and as reported herein, we have identified a total of 37 variants with impaired activity in/near AMH and AMHR2 in 41 women affected with PCOS, or 6.7% of our PCOS cohort. Furthermore, no functional variants were observed in the 142 phenotyped controls. The functional variants were significantly associated with PCOS in our cohort of 608 women with PCOS and 142 controls (P = 2.3 × 10-5) and very strongly associated with PCOS relative to a larger non-Finnish European (gnomAD) population-based control cohort (P < 1 × 10-9).

CONCLUSION

The AMH signaling cascade plays an important role in PCOS etiology.

The challenges of modeling hormone receptor-positive breast cancer in mice

Estrogen receptor-positive (ER+) tumors account for 70-80% of all breast cancer (BC) cases and are characterized by estrogen dependency for their growth. Endocrine therapies using estrogen receptor antagonists or aromatase inhibitors represent a key component of the standard of care for these tumors. The occurrence of de novo or acquired resistance to estrogen withdrawal represents an important clinical problem, impacting on patient survival. In addition, despite an initially favorable outcome, a part of ER+ BC patients present with disease recurrence locally or at distant sites years or even decades after apparent remission. In vivo models that closely mimic human disease are urgently needed to study the biology of these tumors, investigate the molecular mechanisms underlying endocrine resistance and identify patients at risk of recurrence. Despite the similarities in the overall hormonal regulation of mammary gland development between mice and humans, the majority of the mammary carcinomas occurring in genetically engineered mouse models (GEMMs) are ER negative and most xenograft models are based on few ER+ cancer cell lines. We recently showed that the microenvironment is critical for ER+ cancer cells and discuss in this review the potential of intraductal xenograft model for basic and preclinical research.

Effect of (R)-(+) Pulegone on Ovarian Tissue; Correlation with Expression of Aromatase Cyp19 and Ovarian Selected Genes in Mice

Objective

Pulegone (PGN) is a monoterpene ketone, whose metabolites exert several cytotoxic effects in various tissues. The present study was conducted in order to evaluate the (R)-(+) PGN-induced alterations in ovarian aromatization, proto-oncogenes and estrogen receptorα (ERα) and ERβ receptors expressions.

Materials and Methods

In this experimental study, mature albino mice were divided into experimental (received 25 mg/kg, 50 mg/kg and 100 mg/kg PGN, orally for 35 days) and control (received 2% solution of Tween 80 as a PGN solvent, orally) groups. The mRNA levels of Erα, Erβ, p53, Bcl-2, and cytochrome p450 (Cyp19) as well as ovarian angiogenesis were analyzed through reverse transcription polymerase chain reaction and immunohistochemical techniques, respectively. Moreover, apoptosis of follicular cells, serum estrogen and progesterone levels and mRNA damage were investigated via using terminal transferase and biotin-16-dUTP staining, electrochemilunescence and fluorescent microscopy methods, respectively.

Results

The PGN reduced Erα, Erβ and Cyp19 expression at 50 mg/kg and 100 mg/kg doses, while significantly elevating p53 and reducing Bcl-2 expression. Finally, PGN impaired ovarian angiogenesis, increased apoptosis, elevated follicular atresia and reduced serum levels of estrogen and progesterone.

Conclusion

Chronic exposure to PGN (50 mg/kg and 100 mg/kg), severely affects ovarian aromatization, proto- oncogenes mRNA levels and expression of ERs.

Alternative promoter usage generates novel shorter MAPT mRNA transcripts in Alzheimer's disease and progressive supranuclear palsy brains

Alternative promoter usage is an important mechanism for transcriptome diversity and the regulation of gene expression. Indeed, this alternative usage may influence tissue/subcellular specificity, protein translation and function of the proteins. The existence of an alternative promoter for MAPT gene was considered for a long time to explain differential tissue specificity and differential response to transcription and growth factors between mRNA transcripts. The alternative promoter usage could explain partly the different tau proteins expression patterns observed in tauopathies. Here, we report on our discovery of a functional alternative promoter for MAPT, located upstream of the gene's second exon (exon 1). By analyzing genome databases and brain tissue from control individuals and patients with Alzheimer's disease or progressive supranuclear palsy, we identified novel shorter transcripts derived from this alternative promoter. These transcripts are increased in patients' brain tissue as assessed by 5'RACE-PCR and qPCR. We suggest that these new MAPT isoforms can be translated into normal or amino-terminal-truncated tau proteins. We further suggest that activation of MAPT's alternative promoter under pathological conditions leads to the production of truncated proteins, changes in protein localization and function, and thus neurodegeneration.

Influence of Tetrabromobisphenol A, with or without Concurrent Triclosan, upon Bisphenol A and Estradiol Concentrations in Mice

BACKGROUND

Humans are commonly exposed to multiple environmental chemicals, including tetrabromobisphenol A (TBBPA; a flame retardant), triclosan (an antimicrobial agent), and bisphenol A (BPA; polycarbonate plastics). These chemicals are readily absorbed and may interact with each other.

OBJECTIVES

We sought to determine whether TBBPA, given alone or in combination with triclosan, can modulate the concentrations of BPA and 17β-estradiol (E2).

METHODS

Female and male CF-1 mice were each given a subcutaneous injection of 0-27mg TBBPA, with or without concurrent 0.33mg triclosan, followed by dietary administration of 50μg/kg body weight ¹⁴C-BPA. Radioactivity was measured in blood serum and tissues through liquid scintillation counting. In subsequent experiments, female and male CF-1 mice were each given a subcutaneous injection of 0 or 1mg TBBPA and E2 was measured in urine 2-12 h after injection.

RESULTS

Doses as low as 1mg TBBPA significantly elevated ¹⁴C-BPA concentrations in the uterus and ovaries of females; in the testes, epididymides, vesicular-coagulating glands, and preputial glands of males; and in blood serum, heart, lungs, and kidneys of both sexes; urinary E2 concentrations were also elevated. Lower doses of TBBPA or triclosan that had no effects on their own elevated ¹⁴C-BPA concentrations when the two substances were given concurrently.

CONCLUSION

These data indicate that TBBPA, triclosan, and BPA interact in vivo, consistent with evidence that TBBPA and triclosan inhibit enzymes that are critical for BPA and E2 metabolism. https://doi.org/10.1289/EHP1329.

Estrogens in Male Physiology

Estrogens have historically been associated with female reproduction, but work over the last two decades established that estrogens and their main nuclear receptors (ESR1 and ESR2) and G protein-coupled estrogen receptor (GPER) also regulate male reproductive and nonreproductive organs. 17β-Estradiol (E2) is measureable in blood of men and males of other species, but in rete testis fluids, E2 reaches concentrations normally found only in females and in some species nanomolar concentrations of estrone sulfate are found in semen. Aromatase, which converts androgens to estrogens, is expressed in Leydig cells, seminiferous epithelium, and other male organs. Early studies showed E2 binding in numerous male tissues, and ESR1 and ESR2 each show unique distributions and actions in males. Exogenous estrogen treatment produced male reproductive pathologies in laboratory animals and men, especially during development, and studies with transgenic mice with compromised estrogen signaling demonstrated an E2 role in normal male physiology. Efferent ductules and epididymal functions are dependent on estrogen signaling through ESR1, whose loss impaired ion transport and water reabsorption, resulting in abnormal sperm. Loss of ESR1 or aromatase also produces effects on nonreproductive targets such as brain, adipose, skeletal muscle, bone, cardiovascular, and immune tissues. Expression of GPER is extensive in male tracts, suggesting a possible role for E2 signaling through this receptor in male reproduction. Recent evidence also indicates that membrane ESR1 has critical roles in male reproduction. Thus estrogens are important physiological regulators in males, and future studies may reveal additional roles for estrogen signaling in various target tissues.

Seasonal expression of P450arom and estrogen receptors in scented glands of muskrats (Ondatra zibethicus)

Male muskrats have one pair of scented glands that grow and involute annually. To investigate the annual changes in the scented gland, we measured the expressions of aromatase cytochrome P-450 (P450arom) and estrogen receptors (ERs) in the scented glands. P450arom was expressed in glandular cells and epithelial cells in the scented glands during the breeding season, and only in glandular cells during the nonbreeding season. ERα and ERβ were also detected in different types of cells in the scented gland during the breeding and nonbreeding seasons. Both mRNA and protein levels of P450arom, ERα, and ERβ were higher in the scented glandular tissues during the breeding season than those during the nonbreeding season. In addition, small RNA sequencing showed that the predicted targets of the significantly changed microRNAs might be the genes encoding P450arom and ERs. In conclusion, the seasonal changes in the expression of P450arom and ERs may be involved in the regulation of scented gland functions.

Dysregulation of Aromatase in Breast, Endometrial, and Ovarian Cancers: An Overview of Therapeutic Strategies

Aromatase is the rate-limiting enzyme in the biosynthesis of estrogens, which play crucial roles on a spectrum of developmental and physiological processes. The biological actions of estrogens are classically mediated by binding to two estrogen receptors (ERs), ERα and ERβ. Encoded by the cytochrome P450, family 19, subfamily A, polypeptide 1 (CYP19A1) gene, aromatase is expressed in a wide variety of tissues, as well as benign and malignant tumors, and is regulated in a pathway- and tissue-specific manner. Overexpression of aromatase, leading to elevated systemic levels of estrogen, is unequivocally linked to the pathogenesis and growth of a number malignancies, including breast, endometrium, and ovarian cancers. Aromatase inhibitors (AIs) are routinely used to treat estrogen-dependent breast cancers in postmenopausal women; however, their roles in endometrial and ovarian cancers remain obscure. While AI therapy is effective in hormone sensitive cancers, they diminish estrogen production throughout the body and, thus, generate undesirable side effects. Despite the effectiveness of AI therapy, resistance to endocrine therapy remains a major concern and is the leading cause of cancer death. Considerable advances, toward mitigating these issues, have evolved in conjunction with a number of histone deacetylase (HDAC) inhibitors for countering an assortment of diseases and cancers, including the aforesaid malignancies. HDACs are a family of enzymes that are frequently dysregulated in human tumors. This chapter will discuss the current understanding of aberrant regulation and expression of aromatase in breast, endometrial, and ovarian cancers, and potential therapeutic strategies for prevention and treatment of these life-threatening diseases.

Aromatase expression and regulation in breast and endometrial cancer

Long-term exposure to excess estrogen increases the risk of breast cancer and type 1 endometrial cancer. Most of the estrogen in premenopausal women is synthesized by the ovaries, while extraovarian subcutaneous adipose tissue is the predominant tissue source of estrogen after menopause. Estrogen and its metabolites can cause hyperproliferation and neoplastic transformation of breast and endometrial cells via increased proliferation and DNA damage. Several genetically modified mouse models have been generated to help understand the physiological and pathophysiological roles of aromatase and estrogen in the normal breast and in the development of breast cancers. Aromatase, the key enzyme for estrogen production, is comprised of at least ten partially tissue-selective and alternatively used promoters. These promoters are regulated by distinct signaling pathways to control aromatase expression and estrogen formation via recruitment of various transcription factors to their cis-regulatory elements. A shift in aromatase promoter use from I.4 to I.3/II is responsible for the excess estrogen production seen in fibroblasts surrounding malignant epithelial cells in breast cancers. Targeting these distinct pathways and/or transcription factors to modify aromatase activity may lead to the development of novel therapeutic remedies that inhibit estrogen production in a tissue-specific manner.

In vivo visualization of aromatase in animals and humans

Aromatase catalyzes the last and obligatory step in the biosynthesis of estrogens across species. In vivo visualization of aromatase can be performed using positron emission tomography (PET) with radiolabeled aromatase inhibitors such as [(11)C]vorozole. PET studies in rats, monkeys and healthy human subjects demonstrate widespread but heterogeneous aromatase availability in brain and body, which appears to be regulated in a species, sex and region-specific manner. Thus, aromatase availability is high in brain amygdala and in ovaries of all species examined to date, with males demonstrating higher levels than females in all comparable organs. However, the highest concentrations of aromatase in the human brain are found in specific nuclei of the thalamus while the highest levels in rats and monkeys are found in the amygdala. Regional brain aromatase availability is increased by androgens and inhibited by nicotine. Future studies may improve diagnosis and treatment in brain disorders and cancers overexpressing aromatase.

Weight gain and inflammation regulate aromatase expression in male adipose tissue, as evidenced by reporter gene activity

Obesity and white adipose tissue (WAT) inflammation are associated with enhanced aromatization in women, but little is known about the regulation of aromatase (CYP19A1) gene expression in male WAT. We investigated the impact of weight gain and WAT inflammation on the regulation of CYP19A1 in males, by utilizing the hARO-Luc aromatase reporter mouse model containing a >100-kb 5'-region of the human CYP19A1 gene. We show that hARO-Luc reporter activity is enhanced in WAT of mice with increased adiposity and inflammation. Dexamethasone and TNFα, as well as forskolin and phorbol 12-myristate 13-acetate, upregulate hARO-Luc activity, suggesting the involvement of promoters I.4 and I.3/II. Furthermore, we show that diet enriched with antioxidative plant polyphenols attenuates WAT inflammation and hARO-Luc activity in obese males. In conclusion, our data suggest that obesity-associated WAT inflammation leads to increased peripheral CYP19A1 expression in males, and that polyphenol-enriched diet may have the potential to attenuate excessive aromatization in WAT of obese men.

Activation of brain steroidogenesis and neurogenesis during the gonadal differentiation in protandrous black porgy, Acanthopagrus schlegelii

The early brain development, at the time of gonadal differentiation was investigated using a protandrous teleost, black porgy. This natural model of monosex juvenile fish avoids the potential complexity of sexual dimorphism. Brain neurogenesis was evaluated by histological analyses of the diencephalon, at the time of testicular differentiation (in fish between 90 and 150 days after hatching). Increases in the number of both Nissl-stained total brain cells, and Pcna-immunostained proliferative brain cells were observed in specific area of the diencephalon, such as ventromedialis thalami and posterior preoptic area, revealing brain cell proliferation. qPCR analyses showed significantly higher expression of the radial glial cell marker blbp and neuron marker bdnf. Strong immunohistochemical staining of Blbp and extended cellular projections were observed. A peak expression of aromatase (cyp19a1b), as well as an increase in estradiol (E2 ) content were also detected in the early brain. These data demonstrate that during gonadal differentiation, the early brain exhibits increased E2 synthesis, cell proliferation, and neurogenesis. To investigate the role of E2 in early brain, undifferentiated fish were treated with E2 or aromatase inhibitor (AI). E2 treatment upregulated brain cyp19a1b and blbp expression, and enhanced brain cell proliferation. Conversely, AI reduced brain cell proliferation. Castration experiment did not influence the brain gene expression patterns and the brain cell number. Our data clearly support E2 biosynthesis in the early brain, and that brain E2 induces neurogenesis. These peak activity patterns in the early brain occur at the time of gonad differentiation but are independent of the gonads.

Aromatase imaging with [N-methyl-11C]vorozole PET in healthy men and women

Aromatase, the last and obligatory enzyme catalyzing estrogen biosynthesis from androgenic precursors, can be labeled in vivo with (11)C-vorozole. Aromatase inhibitors are widely used in breast cancer and other endocrine conditions. The present study aimed to provide baseline information defining aromatase distribution in healthy men and women, against which its perturbation in pathologic situations can be studied.

METHODS

(11)C-vorozole (111-296 MBq/subject) was injected intravenously in 13 men and 20 women (age range, 23-67 y). PET data were acquired over a 90-min period. Each subject had 4 scans, 2 per day separated by 2-6 wk, including brain and torso or pelvis scans. Young women were scanned at 2 discrete phases of the menstrual cycle (midcycle and late luteal). Men and postmenopausal women were also scanned after pretreatment with a clinical dose of the aromatase inhibitor letrozole. Time-activity curves were obtained, and standardized uptake values (SUV) were calculated for major organs including brain, heart, lungs, liver, kidneys, spleen, muscle, bone, and male and female reproductive organs (penis, testes, uterus, ovaries). Organ and whole-body radiation exposures were calculated using OLINDA software.

RESULTS

Liver uptake was higher than uptake in any other organ but was not blocked by pretreatment with letrozole. Mean SUVs were higher in men than in women, and brain uptake was blocked by letrozole. Male brain SUVs were also higher than SUVs in any other organ (ranging from 0.48 ± 0.05 in lungs to 1.5 ± 0.13 in kidneys). Mean ovarian SUVs (3.08 ± 0.7) were comparable to brain levels and higher than in any other organ. Furthermore, ovarian SUVs in young women around the time of ovulation (midcycle) were significantly higher than those measured in the late luteal phase, whereas aging and cigarette smoking reduced (11)C-vorozole uptake.

CONCLUSION

PET with (11)C-vorozole is useful for assessing physiologic changes in estrogen synthesis capacity in the human body. Baseline levels in breasts, lungs, and bones are low, supporting further investigation of this tracer as a new tool for detection of aromatase-overexpressing primary tumors or metastases in these organs and optimization of treatment in cancer and other disorders in which aromatase inhibitors are useful.

Identification and characterization of methylation-dependent/independent DNA regulatory elements in the human SLC9B1 gene

The human NHEDC1 (hNHEDC1) protein is thought to be essential for sperm motility and fertility however the mechanisms regulating its gene expression are largely unknown. In this study we have identified multiple DNA regulatory elements in the 5' end of the gene encoding hNHEDC1 (SLC9B1) and have explored the role that DNA methylation at these elements plays in the regulation of its expression. We first show that the full-length hNHEDC1 protein is testis-specific for the tissues that we tested and that it localizes to the cells of the seminiferous tubules. In silico analysis of the SLC9B1 gene locus identified two putative promoters (P1 and P2) and two CpG islands - CpGI (overlapping with P1) and CpGII (intragenic) - at the 5' end of the gene. By deletion analysis of P1, we show that the region from -23 bp to +200 bp relative to the transcription start site (TSS) is sufficient for optimal promoter activity in a germ cell line. Additionally, in vitro methylation of the P1 (the -500 bp to +200 bp region relative to the TSS) abolishes its activity in germ cells and somatic cells strongly suggesting that DNA methylation at this promoter could regulate SLC9B1 expression. Furthermore, bisulfite-sequencing analysis of the P1/CpGI uncovered reduced methylation in the testis vs. lung whereas CpGII displayed no differences in methylation between these two tissues. Additionally, treatment of HEK 293 cells with 5-aza-2-Deoxycytidine led to upregulation of NHEDC1 transcript and reduced methylation in the promoter CpGI. Finally, we have uncovered both enhancer and silencer functions of the intragenic SLC9B1 CpGII. In all, our data suggests that SLC9B1 gene expression could be regulated via a concerted action of DNA methylation-dependent and independent mechanisms mediated by these multiple DNA regulatory elements.

Quantitative analysis of long-form aromatase mRNA in the male and female rat brain

In vitro studies show that estrogens acutely modulate synaptic function in both sexes. These acute effects may be mediated in vivo by estrogens synthesized within the brain, which could fluctuate more rapidly than circulating estrogens. For this to be the case, brain regions that respond acutely to estrogens should be capable of synthesizing them. To investigate this question, we used quantitative real-time PCR to measure expression of mRNA for the estrogen-synthesizing enzyme, aromatase, in different brain regions of male and female rats. Importantly, because brain aromatase exists in two forms, a long form with aromatase activity and a short form with unknown function, we targeted a sequence found exclusively in long-form aromatase. With this approach, we found highest expression of aromatase mRNA in the amygdala followed closely by the bed nucleus of the stria terminalis (BNST) and preoptic area (POA); we found moderate levels of aromatase mRNA in the dorsal hippocampus and cingulate cortex; and aromatase mRNA was detectable in brainstem and cerebellum, but levels were very low. In the amygdala, gonadal/hormonal status regulated aromatase expression in both sexes; in the BNST and POA, castration of males down-regulated aromatase, whereas there was no effect of estradiol in ovariectomized females. In the dorsal hippocampus and cingulate cortex, there were no differences in aromatase levels between males and females or effects of gonadal/hormonal status. These findings demonstrate that long-form aromatase is expressed in brain regions that respond acutely to estrogens, such as the dorsal hippocampus, and that gonadal/hormonal regulation of aromatase differs among different brain regions.

Estrogen receptor signaling during vertebrate development

Estrogen receptors are expressed and their cognate ligands produced in all vertebrates, indicative of important and conserved functions. Through evolution estrogen has been involved in controlling reproduction, affecting both the development of reproductive organs and reproductive behavior. This review broadly describes the synthesis of estrogens and the expression patterns of aromatase and the estrogen receptors, in relation to estrogen functions in the developing fetus and child. We focus on the role of estrogens for the development of reproductive tissues, as well as non-reproductive effects on the developing brain. We collate data from human, rodent, bird and fish studies and highlight common and species-specific effects of estrogen signaling on fetal development. Morphological malformations originating from perturbed estrogen signaling in estrogen receptor and aromatase knockout mice are discussed, as well as the clinical manifestations of rare estrogen receptor alpha and aromatase gene mutations in humans. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

Functional Importance of 1α,25(OH)2-Vitamin D3 and the Identification of Its Nongenomic and Genomic Signaling Pathways in the Testis

The 1α,25(OH)2-vitamin D3 (1,25-D3) is known by its classic effects on Ca2+ metabolism and regulation of cellular proliferation and differentiation. The hormone 1,25-D3 acts in the testis through nongenomic and genomic events being implicated in the success of spermatogenesis in rats and in human being. The aim of this review was to highlight the effect and intracellular pathways of 1,25-D3 to modulate the spermatogenesis. The pivotal role of 1,25-D3 in male reproduction is reinforced by the presence of VDR and 1α-hydroxylase in reproductive tract. Also, the marked expression of VDR and the VD metabolizing enzymes in human testis, ejaculatory tract, and mature spermatozoa implicates the 1,25-D3 in spermatogenesis and maturation of human spermatozoa. Among genomic events, 1,25-D3 influences the expression of calcium binding protein and stimulates aromatase gene expression through a nongenomic activation of the membrane-bound VDR receptor involving the PKA pathway in the testis. Also, 1,25-D3 stimulates amino acid transport and exocytosis in testis by nongenomic events coupled to ionic currents triggered at plasma membrane. All together, the demonstration that 1,25-D3 regulates both Sertoli cell and sperm function may be useful for the study and development of new therapeutic strategies for the male reproductive disorders.

Expression and localization of aromatase during fetal mouse testis development

BACKGROUND

Both androgens and estrogens are necessary to ensure proper testis development and function. Studies on endocrine disruptors have highlighted the importance of maintaining the balance between androgens and estrogens during fetal development, when testis is highly sensitive to environmental disturbances. This balance is regulated mainly through an enzymatic cascade that converts irreversibly androgens into estrogens. The most important and regulated component of this cascade is its terminal enzyme: the cytochrome p450 19A1 (aromatase hereafter). This study was conducted to improve our knowledge about its expression during mouse testis development.

FINDINGS

By RT-PCR and western blotting, we show that full-length aromatase is expressed as early as 12.5 day post-coitum (dpc) with maximal expression at 17.5 dpc. Two additional truncated transcripts were also detected by RT-PCR. Immunostaining of fetal testis sections and of gonocyte-enriched cell cultures revealed that aromatase is strongly expressed in fetal Leydig cells and at variable levels in gonocytes. Conversely, it was not detected in Sertoli cells.

CONCLUSIONS

This study shows for the first time that i) aromatase is expressed from the early stages of fetal testis development, ii) it is expressed in mouse gonocytes suggesting that fetal germ cells exert an endocrine function in this species and that the ratio between estrogens and androgens may be higher inside gonocytes than in the interstitial fluid. Furthermore, we emphasized a species-specific cell localization. Indeed, previous works found that in the rat aromatase is expressed both in Sertoli and Leydig cells. We propose to take into account this species difference as a new concept to better understand the changes in susceptibility to Endocrine Disruptors from one species to another.

Expression and sequence evolution of aromatase cyp19a1 and other sexual development genes in East African cichlid fishes

Sex determination mechanisms are highly variable across teleost fishes and sexual development is often plastic. Nevertheless, downstream factors establishing the two sexes are presumably conserved. Here, we study sequence evolution and gene expression of core genes of sexual development in a prime model system in evolutionary biology, the East African cichlid fishes. Using the available five cichlid genomes, we test for signs of positive selection in 28 genes including duplicates from the teleost whole-genome duplication, and examine the expression of these candidate genes in three cichlid species. We then focus on a particularly striking case, the A- and B-copies of the aromatase cyp19a1, and detect different evolutionary trajectories: cyp19a1A evolved under strong positive selection, whereas cyp19a1B remained conserved at the protein level, yet is subject to regulatory changes at its transcription start sites. Importantly, we find shifts in gene expression in both copies. Cyp19a1 is considered the most conserved ovary-factor in vertebrates, and in all teleosts investigated so far, cyp19a1A and cyp19a1B are expressed in ovaries and the brain, respectively. This is not the case in cichlids, where we find new expression patterns in two derived lineages: the A-copy gained a novel testis-function in the Ectodine lineage, whereas the B-copy is overexpressed in the testis of the speciest-richest cichlid group, the Haplochromini. This suggests that even key factors of sexual development, including the sex steroid pathway, are not conserved in fish, supporting the idea that flexibility in sexual determination and differentiation may be a driving force of speciation.

Glucocorticoid-induction of hypothalamic aromatase via its brain-specific promoter

In the brain, a 36-kb distal promoter (I.f) regulates the Cyp19a1 gene that encodes aromatase, the key enzyme for estrogen biosynthesis. Local estrogen production in the brain regulates critical functions such as gonadotropin secretion and sexual behavior. The mechanisms that control brain aromatase production are not well understood. Here we show that the glucocorticoid dexamethasone robustly increases aromatase mRNA and protein by up to 98-fold in mouse hypothalamic cell lines in a dose- and time-dependent fashion. Using deletion mutants of the brain-specific promoter I.f and chromatin immunoprecipitation-PCR, we isolated a distinct region (-500/-200 bp) which becomes enriched in bound glucocorticoid receptor upon dexamethasone stimulation. A glucocorticoid antagonist or siRNA based knockdown of glucocorticoid receptor ablated dexamethasone stimulation of aromatase expression. Our findings demonstrate how glucocorticoids alter aromatase expression in the hypothalamus and might indicate a mechanism whereby glucocorticoid action modifies gonadotropin pulses and the menstrual cycle.

A humanized pattern of aromatase expression is associated with mammary hyperplasia in mice

Aromatase is essential for estrogen production and is the target of aromatase inhibitors, the most effective endocrine treatment for postmenopausal breast cancer. Peripheral tissues in women, including the breast, express aromatase via alternative promoters. Female mice lack the promoters that drive aromatase expression in peripheral tissues; thus, we generated a transgenic humanized aromatase (Arom(hum)) mouse line containing a single copy of the human aromatase gene to study the link between aromatase expression in mammary adipose tissue and breast pathology. Arom(hum) mice expressed human aromatase, driven by the proximal human promoters II and I.3 and the distal promoter I.4, in breast adipose fibroblasts and myoepithelial cells. Estrogen levels in the breast tissue of Arom(hum) mice were higher than in wild-type mice, whereas circulating levels were similar. Arom(hum) mice exhibited accelerated mammary duct elongation at puberty and an increased incidence of lobuloalveolar breast hyperplasia associated with increased signal transducer and activator of transcription-5 phosphorylation at 24 and 64 wk. Hyperplastic epithelial cells showed remarkably increased proliferative activity. Thus, we demonstrated that the human aromatase gene can be expressed via its native promoters in a wide variety of mouse tissues and in a distribution pattern nearly identical to that of humans. Locally increased tissue levels, but not circulating levels, of estrogen appeared to exert hyperplastic effects on the mammary gland. This novel mouse model will be valuable for developing tissue-specific aromatase inhibition strategies.

Aromatase promoter I.f is regulated by progesterone receptor in mouse hypothalamic neuronal cell lines

Aromatase catalyzes the conversion of C(19) steroids to estrogens. Aromatase and progesterone, both of which function at different steps of steroidogenesis, are crucial for the sexually dimorphic development of the fetal brain and the regulation of gonadotropin secretion and sexual interest in adults. The aromatase gene (Cyp19a1) is selectively expressed in distinct neurons of the mouse hypothalamus through a distal brain-specific promoter, I.f, located ∼40 kb upstream of the coding region. However, the regulation of aromatase expression in the brain is not well understood. In this study, we investigated a short feedback effect of progesterone analogues on aromatase mRNA expression and enzyme activity in estrogen receptor α (Esr1)-positive or -negative mouse embryonic hypothalamic neuronal cell lines that express aromatase via promoter I.f. In a hypothalamic neuronal cell line that highly expresses aromatase, progesterone receptor (Pgr), and Esr1, a progesterone agonist, R5020, inhibited aromatase mRNA level and enzyme activity. The inhibitory effect of R5020 was reversed by its antagonist, RU486. Deletion mutants of promoter I.f suggested that inhibition of aromatase expression by progesterone is conferred by the nt -1000/-500 region, and R5020 enhanced binding of Pgr to the nt -800/-600 region of promoter I.f. Small interfering RNA knockdown of Pgr eliminated progesterone-dependent inhibition of aromatase mRNA and enzyme activity. Taken together, progesterone enhances recruitment of Pgr to specific regions of the promoter I.f of Cyp19a1 and regulates aromatase expression in hypothalamic neurons.

Unique distribution of aromatase in the human brain: in vivo studies with PET and [N-methyl-11C]vorozole

Aromatase catalyzes the last step in estrogen biosynthesis. Brain aromatase is involved in diverse neurophysiological and behavioral functions including sexual behavior, aggression, cognition, and neuroprotection. Using positron emission tomography (PET) with the radiolabeled aromatase inhibitor [N-methyl-(11)C]vorozole, we characterized the tracer distribution and kinetics in the living human brain. Six young, healthy subjects, three men and three women, were administered the radiotracer alone on two separate occasions. Women were scanned in distinct phases of the menstrual cycle. Specificity was confirmed by pretreatment with a pharmacological (2.5 mg) dose of the aromatase inhibitor letrozole. PET data were acquired over a 90-min period and regions of interest placed over selected brain regions. Brain and plasma time activity curves, corrected for metabolites, were used to derive kinetic parameters. Distribution volume (V(T)) values in both men and women followed the following rank order: thalamus > amygdala = preoptic area > medulla (inferior olive) > accumbens, pons, occipital and temporal cortex, putamen, cerebellum, and white matter. Pretreatment with letrozole reduced V(T) in all regions, though the size of the reduction was region-dependent, ranging from ∼70% blocking in thalamus andpreoptic area to ∼10% in cerebellum. The high levels of aromatase in thalamus and medulla (inferior olive) appear to be unique to humans. These studies set the stage for the noninvasive assessment of aromatase involvement in various physiological and pathological processes affecting the human brain.

Intrauterine growth restriction alters hippocampal expression and chromatin structure of Cyp19a1 variants

We evaluated the impact of uteroplacental insufficiency (UPI), and subsequent intrauterine growth restriction (IUGR), on serum testosterone and hippocampal expression of Cyp19a1 variants and aromatase in rats. Additionally, we determined UPI induced histone modification of the promoter regions of Cyp19a1 variants using chromatin immunoprecipitation. Cyp19a1 is the gene encoding the protein aromatase, that catalyzes the biosynthesis of estrogens from androgens and is necessary for masculinization of the brain. IUGR was induced via bilateral uterine artery. UPI increased serum testosterone in day of life 0 (D(0)) and day of life 21 (D(21)) IUGR males to 224% and 299% of control values, respectively. While there was no significant impact of UPI on testosterone in D(0) females, testosterone in D(21) IUGR females was 187% of controls. Cyp19a1 variant 1.f and variant II are expressed in the rat hippocampus at D(0) and D(21). UPI significantly reduced expression of Cyp19a1 variant 1.f in D(0) males, with no impact in females. Similarly at D(0), UPI reduced expression of aromatase, the protein encoded by Cyp19a1, in males. Dimethylation of H3K4 was increased in the promoter region of variant 1.f (P1.f) and trimethylation of H3K4 was decreased in the promoter region of variant II (PII). At D(21), dimethylation of H3K4 is significantly reduced in PII of IUGR males. We conclude that UPI increases serum testosterone and reduces Cyp19a1 variant 1.f expression in the hippocampus of D(0) IUGR males. Additionally, UPI alters the chromatin structure of CYP19a1 at both D(0) and D(21).

BAX-dependent and BAX-independent regulation of Kiss1 neuron development in mice

The Kiss1 gene and its product kisspeptin are important regulators of reproduction. In rodents, Kiss1 is expressed in the hypothalamic arcuate (ARC) and anteroventral periventricular (AVPV)/rostral periventricular (PeN) nuclei. In the AVPV/PeN, females have more Kiss1 and tyrosine hydroxylase (TH) neurons than males. We explored the ontogeny of the Kiss1 sex difference, and the role of cell death in establishing Kiss1 and TH cell number. We also determined whether Kiss1 cells in AVPV/PeN coexpress TH. AVPV/PeN Kiss1 neurons were first detected in both sexes on postnatal d 10, but the Kiss1 sex difference did not emerge until postnatal d 12. The role of BAX-mediated apoptosis in generating this sex difference was tested in adult Bax knockout (KO) and wild-type mice. Deletion of Bax did not diminish the sex difference in Kiss1 expression in the AVPV/PeN. TH expression was sexually dimorphic in the AVPV of both wild-type and Bax KO mice but, unlike Kiss1, was not sexually dimorphic in the PeN of either genotype. Double-label analysis determined that most Kiss1 neurons coexpress TH mRNA, but many TH neurons do not coexpress Kiss1, especially in the PeN. These findings suggest that several subpopulations of TH cells reside within the AVPV/PeN, only one of which coexpresses Kiss1. In the ARC, Kiss1 cell number was markedly increased in Bax KO mice of both sexes, indicating that although BAX-dependent apoptosis does not generate the sex difference in either Kiss1 or TH expression in AVPV/PeN, BAX does importantly regulate Kiss1 cell number in the ARC.

Oestrogens and spermatogenesis

The role of oestrogens in male reproductive tract physiology has for a long time been a subject of debate. The testis produces significant amounts of oestrogenic hormones, via aromatase, and oestrogen receptors (ERs)alpha (ESR1) and ERbeta (ESR2) are selectively expressed in cells of the testis as well as the epididymal epithelium, depending upon species. This review summarizes the current knowledge concerning the presence and activity of aromatase and ERs in testis and sperm and the potential roles that oestrogens may have in mammalian spermatogenesis. Data show that physiology of the male gonad is in part under the control of a balance of androgens and oestrogens, with aromatase serving as a modulator.

Localization and regulation of aromatase liver receptor homologue-1 in the developing rat testis

The enzyme aromatase converts androgens to estrogens, which have recently been postulated to be essential for testicular development and fertility. Understanding the mechanisms that regulate aromatase activity in the testis may therefore have implications for treatment of male infertility. Aromatase is encoded by the CYP19 gene, which uses multiple tissue-specific alternative promoters. In the testis, the proximal promoter PII drives aromatase expression. PII activity requires a nuclear receptor half-site, CAAGGTCA, to which two orphan receptors; SF-1 and LRH-1, have been shown to bind in vitro. The aim of this study was to investigate expression of aromatase and LRH-1 in the developing rat testis and define the ability of LRH-1 to induce aromatase expression in the testicular cells where both are expressed. We show that aromatase and LRH-1 are present throughout all stages of development of the rat testis, although the sites and levels of expression vary. The pattern of LRH-1 expression was broadly similar to that of aromatase. In adult animals higher levels of expression were observed in Leydig and germ cells. Over-expression of LRH-1 in primary rat Leydig and germ cells by adenoviral infection strongly increased endogenous aromatase mRNA levels, demonstrating the ability of LRH-1 to stimulate aromatase expression in vivo. We also observed binding of endogenous LRH-1 to the aromatase promoter II by chromatin immunoprecipitation. These data provide evidence that LRH-1 plays an important role in the regulation of testicular aromatase expression, and implicate LRH-1 as a regulator of rat spermatogenesis, in which estrogens are emerging as important mediators.

Differential involvement of insulin-like growth factor-I and estrogen on prolactin cells in the mouse anterior pituitary

Estrogen and insulin-like growth factor-I (IGF-I) stimulate prolactin (PRL) production, release and proliferation of PRL-producing cells (PRL cells) in the anterior pituitary. PRL cells in adult estrogen receptor alpha (ERalpha) knockout (alphaERKO) mice and IGF-I knockout (IGF-IKO) mice are decreased considerably in number. To investigate a correlation between 17beta-estradiol (E2) and IGF-I on PRL production, IGF-I wild-type (WT) or IGF-IKO mice were ovariectomized at day 8 and the number of PRL cells was examined at days 20 and 60. Although PRL cell number at day 20 and WT or IGF-IKO mice ovariectomized at day 8 was similar to that in intact WT or IGF-IKO mice, PRL cells in adult WT or IGF-IKO mice ovariectomized at day 8 were significantly decreased as compared with those in intact WT or IGF-IKO mice. Therefore, estrogen is essential for PRL cell differentiation between days 20 and 60, regardless of IGF-I. While PRL cells in WT ovariectomized mice increased from days 20 to 60, those in IGF-IKO ovariectomized mice did not increase, suggesting that IGF-I modified PRL cell differentiation after day 20. ICI 182,780 (anti-estrogen) treatment canceled an increase of PRL cells in 30-day-old ovariectomized WT mice, indicating that the presence of ERalpha is important. The number of PRL cells in alphaERKO mice was similar to that in WT mice at day 20; however, PRL cells in alphaERKO mice at day 60 were not increased in number from day 20, supporting the idea that estrogen is essential for PRL cell differentiation after day 20. Finally, the percentage of PRL cells in IGF-IKO mice was decreased as compared with that in WT mice at day 20; therefore, IGF-I affects PRL cells before day 20. In conclusion, PRL cell differentiation is differently regulated by E2 and IGF-I depending on the age.

Fish with thermolabile sex determination (TSD) as models to study brain sex differentiation

As fish are ectothermic animals, water temperature can affect their basic biological processes such as larval development, growth and reproduction. Similar to reptiles, the incubation temperature during early phases of development is capable to modify sex ratios in a large number of fish species. This phenomenon, known as thermolabile sex determination (TSD) was first reported in Menidia menidia, a species belonging to the family Atherinopsidae. Since then, an increasing number of fish have also been found to exhibit TSD. Traditionally, likewise in reptiles, several TSD patterns have been described in fish, however it has been recently postulated that only one, females at low temperatures and males at high temperatures, may represent the "real" or "true" TSD. Many studies regarding the influence of temperature on the final sex ratios have been focused on the expression and activity of gonadal aromatase, the enzyme involved in the conversion of androgens into estrogens and encoded by the cyp19a1a gene. In this regard, teleost fish, may be due to a whole genome duplication event, produce another aromatase enzyme, commonly named brain aromatase, encoded by the cyp19a1b gene. Contrary to what has been described in other vertebrates, fish exhibit very high levels of aromatase activity in the brain and therefore they synthesize high amounts of neuroestrogens. However, its biological significance is still not understood. In addition, the mechanism whereby temperature can induce the development of a testis or an ovary still remains elusive. In this context the present review is aimed to discuss several theories about the possible role of brain aromatase using fish as models. The relevance of brain aromatase and therefore of neuroestrogens as the possible cue for gonadal differentiation is raised. In addition, the possible role of brain aromatase as the way to keep the high levels of neurogenesis in fish is also considered. Several key examples of how teleosts and aromatase regulation can offer more insight into basic mechanisms of TSD are also reviewed.

The multiple roles of estrogens and the enzyme aromatase

Aromatase is the enzyme that catalyzes the last step of estrogen biosynthesis. It is expressed in many tissues such as the gonads, brain and adipose tissue. The regulation of the level and activity of aromatase determines the levels of estrogens that have endocrine, paracrine and autocrine effects on tissues. Estrogens play many roles in the body, regulating reproduction, metabolism and behavior. In the brain, cell survival and the activity of neurons are affected by estrogens and hence aromatase.

Aromatase promoter I.f is regulated by estrogen receptor alpha (ESR1) in mouse hypothalamic neuronal cell lines

Aromatase (CYP19A1) catalyzes the conversion of C(19) steroids to estrogens. Aromatase and its product estradiol (E(2)) are crucial for the sexually dimorphic development of the fetal brain and the regulation of gonadotropin secretion and sexual interest in adults. The regulation of aromatase expression in the brain is not well understood. The aromatase (Cyp19a1) gene is selectively expressed in distinct neurons of the hypothalamus through a distal brain-specific promoter I.f located approximately 36 kb upstream of the coding region. Here, we investigated a short feedback effect of E(2) on aromatase mRNA expression and enzyme activity using estrogen receptor alpha (ESR1; also known as ER alpha)-positive or ESR1-negative mouse embryonic hypothalamic neuronal cell lines that express aromatase via promoter I.f. Estradiol regulated aromatase mRNA expression and enzyme activity in a time- and dose-dependent manner, whereas an E(2) antagonist reversed these effects. The nucleotide -200/-1 region of promoter I.f conferred E(2) responsiveness. Two activator protein 1 (AP-1) elements in this region were essential for induction of promoter activity by E(2). ESR1 and JUN (c-Jun) bound to these AP-1 motifs in intact cells and under cell-free conditions. The addition of an ESR1 mutant that interacts with JUN but not directly with DNA enhanced E(2)-dependent promoter I.f activity. Independently, we demonstrated an interaction between ESR1 and JUN in hypothalamic cells. Knockdown of ESR1 abolished E(2)-induced aromatase mRNA and enzyme activity. Taken together, E(2) regulates Cyp19a1 expression via promoter I.f by enhanced binding of an ESR1/JUN complex to distinct AP-1 motifs in hypothalamic cells. We speculate that this mechanism may, in part, regulate gonadotropin secretion and sexual activity.

Alternative 5'-untranslated first exons of the mouse Cyp19A1 (aromatase) gene

The human aromatase gene (CYP19A1) has eleven tissue-specific untranslated first exons, while only three have been described in the mouse Cyp19A1 namely brain-, ovary- and testis-specific exons 1. The present study aims to elucidate the complete structure of the mouse Cyp19A1 gene. We detected aromatase transcripts in mouse bone, aorta, hypothalamus, adipose, gonads and placenta, but not nulliparous mammary fat pad. BestFit algorithm analysis against the human CYP19A1 has identified ten putative first exons upstream of mouse Cyp19A1. Based on these putative sequences, we were able to design specific primers for RT-PCR and detected for the first time, the presence of exons I.4 and I.3 in murine fat and gonads, respectively. These are novel 5'UTRs of mouse Cyp19A1. Using RT-PCR and 5' RACE, we confirmed the expression of exon 1f in the hypothalamus and proximal exon P2 in the ovary. The testis-specific exon 1 begins 217bp further upstream than previously reported. Putative exons 2a, I.5, I.7, I.6 and I.2 were not detected in mouse tissues. Therefore, we showed that mouse Cyp19A1 contains more tissue-specific first exons than previously thought and displays a similar genomic organization to human CYP19A1.

The proximal promoter governs germ cell-specific expression of the mouse glutathione transferase mGstm5 gene

To explain the tissue-selective expression patterns of a distinct subclass of glutathione S-transferase (GST), transgenic mice expressing EGFP under control of a 2 kb promoter sequence in the 5'-flanking region of the mGstm5 gene were produced. The intent of the study was to establish whether the promoter itself or whether posttranscriptional mechanisms, particularly at the levels of mRNA translation and stability or protein targeting, based on unique properties of mGSTM5, determine the restricted expression pattern. Indeed, the transgene expression was limited to testis as the reporter was not detected in somatic tissues such as brain, kidney or liver, indicating that the mGstm5 proximal promoter is sufficient to target testis-specific expression of the gene. EGFP expression was also more restricted vis-a-vis the natural mGstm5 gene and exclusively found in germ but not in somatic cells. Real-time quantitative PCR (qPCR) data were consistent with alternate transcription start sites in which the promoter region of the natural mGstm5 gene in somatic cells is part of exon 1 of the germ cell transcript. Thus, the primary transcription start site for mGstm5 is upstream of a TATA box in testis and downstream of this motif in somatic cells. The 5' flanking sequence of the mGstm5 gene imparts germ cell-specific transcription.

A novel promoter controls Cyp19a1 gene expression in mouse adipose tissue

BACKGROUND

Aromatase, the key enzyme in estrogen biosynthesis, is encoded by the Cyp19a1 gene. Thus far, 3 unique untranslated first exons associated with distinct promoters in the mouse Cyp19a1 gene have been described (brain, ovary, and testis-specific). It remains unknown whether aromatase is expressed in other mouse tissues via novel and tissue-specific promoters.

METHODS

Real-time PCR was used to examine the aromatase expression levels in various C57BL/6 mouse tissues. 5'-rapid amplification of cDNA ends (5'-RACE) was used to determine the transcriptional start sites of Cyp19a1 transcripts. Promoter activity was measured using serial deletion mutants of DNA fused to the luciferase reporter gene. Primary mouse adipose fibroblasts were isolated and cultured from 16-week-old mouse gonadal fat pads.

RESULTS

We systematically analyzed Cyp19a1 expression in a large number of mouse tissues, and demonstrated for the first time that aromatase was expressed in the male but not female gonadal fat pad. Subcutaneous and brown adipose tissue did not contain detectable Cyp19a1 mRNA. We used 5'-RACE to clone a novel gonadal fat-specific untranslated first exon, which is spliced onto a common junction 15 bp upstream of the translation start site. This adipose-specific first exon was mapped to approximately 75 kb upstream of the translation start site. Transfection of luciferase reporter gene plasmids containing the promoter region upstream of the adipose-specific first exon into murine 3T3-L1 adipose fibroblasts demonstrated significant basal promoter activity conferred primarily by the sequence located at -343/-1 bp. Dexamethasone significantly induced activity of this adipose-specific promoter region. Adipose-specific Cyp19a1 mRNA was expressed in primary mouse adipose fibroblasts and significantly induced by dexamethasone alone or serum plus dexamethasone.

CONCLUSION

Taken together, this research identified a novel, adipose-specific first exon of Cyp19a1 and its hormonally regulated promoter region in male murine gonadal fat. These results expand the known 5'-regulatory region of the murine Cyp19a1 gene to 75 kb upstream of the translation start site. Cyp19a1 expression in mouse adipose tissue may play an important role in reproductive biology and lipid metabolism.

Sexual differentiation of the rodent hypothalamus: hormonal and environmental influences

Brain sexual differentiation is a complex developmental phenomenon influenced by the genetic background, sex hormone secretions and environmental inputs, including pollution. The main hormonal drive to masculinize and defeminize the rodent brain is testosterone secreted by the testis. The hormone does not influence sex brain differentiation only in its native configuration, but it mostly needs local conversion into active metabolites (estradiol and DHT) through the action of specific enzymatic systems: the aromatase and 5alpha-reductase (5alpha-R), respectively. This allows the hormone to control target cell gene expression either through the estrogen (ER) or the androgen (AR) receptors. The developmental profile of testosterone metabolizing enzymes, different in the two sexes, is therefore of the utmost importance in affecting the bioavailability of the steroids active in brain differentiation. Widely diffused pollutants, like polychlorinated biphenyls (PCBs) are able to affect the production and/or action of testosterone metabolites, exerting detrimental influences on reproduction and sex behavior. The main studies performed in our and other laboratories concerning the pattern of expression and the control of the enzymatic systems involved in brain androgen action and metabolism are shortly reviewed. Some recent data on the influence exerted by PCBs on these metabolic systems are also reported.

Aromatase distribution in the monkey temporal neocortex and hippocampus

Numerous studies have shown that neuronal plasticity in the hippocampus and neocortex is regulated by estrogen and that aromatase, the key enzyme for estrogen biosynthesis, is present in cerebral cortex. Although the expression pattern of aromatase mRNA has been described in the monkey brain, its precise cellular distribution has not been determined. In addition, the degree to which neuronal aromatase is affected by gonadal estrogen has not been investigated. In this study, we examined the immunohistochemical distribution of aromatase in young ovariectomized female rhesus monkeys with or without long-term cyclic estradiol treatment. Both experimental groups showed that aromatase is localized in a large population of CA1-3 pyramidal cells, in granule cells of the dentate gyrus and in some interneurons in which it was co-expressed with the calcium-binding proteins calbindin, calretinin, and parvalbumin. Moreover, numerous pyramidal cells were immunoreactive for aromatase in the neocortex, whereas only small subpopulations of neocortical interneurons were immunoreactive for aromatase. The widespread expression of the protein in a large neuronal population suggests that local intraneuroral estrogen synthesis may contribute to estrogen-induced synaptic plasticity in monkey hippocampus and neocortex of female rhesus monkeys. In addition, the apparent absence of obvious differences in aromatase distribution between the two experimental groups suggests that these localization patterns are not dependent on plasma estradiol levels.

Molecular characterization of the injury-induced aromatase transcript in the adult zebra finch brain

In the zebra finch (Taeniopygia guttata), the aromatase gene is transcribed from one of two promoters resulting in two transcripts constitutively expressed in brain or ovary. These transcripts differ only in Exon 1 which lies in the 5' un-translated region (UTR). An inducible form of aromatase is expressed following brain injury in glia. Towards characterizing this transcript, we (a) examined the up-regulation of amplicons within the aromatase transcript using quantitative PCR (qPCR), (b) performed 5' and 3' rapid amplification of cDNA ends (RACE) on injured brain RNA and (c) sequenced the injury-induced aromatase transcript. qPCR suggested that inducible aromatase may contain a novel 3'UTR. However, neither 3' nor 5' RACE revealed novel UTRs in the injured telencephalon. We then sequenced aromatase from injured entopallium, a region that lacks detectable constitutive aromatase. Inducible aromatase was identical in sequence to the known neural aromatase transcript. These data suggest that injury-induced aromatase differs from ovarian, but is indistinguishable from neuronal aromatase. We suggest that an injury-specific signal in glia may modulate aromatase transcription. Alternatively, injury-induced aromatase transcription may be silenced under constitutive conditions. To the best of our knowledge, this is the first report that documents the sequence of inducible aromatase in any vertebrate.