Programming of GnRH feedback controls timing puberty and adult reproductive activity

Birth weight, growth indices, and seminal parameters in male offspring are resilient features to maternal pre-conceptional dietary manipulation in sheep

Gestational diet manipulation can lead to inadequate fetal nutrient supply resulting in low birth weight, limited postnatal growth, and consequently, reduced reproductive performance in the progeny. However, effects of short-term maternal pre-conceptional dietary manipulation on postnatal growth and reproductive parameters of male offspring in large animals remains unexplored. To determine these consequences, female crossbred (Polypay x Dorset) sheep were allocated to three groups (n = 33/group) of dietary manipulation for 21 days prior to mating under the following conditions: (1) control at 100 % of maintenance energy requirements (40 Kcal of metabolizable energy/kg body weight [BW]), (2) undernutrition (UN) at 50 % of Control intake, and (3) overnutrition (ON) at 200 % of maintenance energy. Singleton ram lambs (UN:9; C:12; ON:6) were monitored from birth until 8 months of age, including birth weight, weekly weights, weight gain, body mass index (BMI), and circulating testosterone. After weaning, monthly scrotal circumference and subcutaneous fat depth were measured. Semen morphology and motility were evaluated at 7 and 8 months of age. Birth weight, weight gain, and BMI at birth and weaning were not significantly different among nutritional treatments. None of the pre-conceptional diets affected body weight change from weaning until 36 weeks of age, BMI, fat depth, or scrotal circumference across the experiment. A sustained rise in plasma testosterone concentrations was detected when ram lambs were, on average, 82 days old and 37 kg. Both testosterone concentrations and scrotal circumference were positively correlated to body weight regardless of treatment group. In addition, seminal parameters did not differ among treatments, but a transient increase in plasma testosterone at 18 weeks of age was observed in ON ram lambs compared to control rams. In conclusion, birth weight, growth indices, and seminal parameters in singleton rams are resilient features in the progeny upon maternal pre-conceptional dietary manipulation in sheep.

Systematic review of hormonal strategies to improve fertility in rams

Reviewing the current state of knowledge on reproductive performance and productive traits in rams has many advantages. First, the compilation of this information will serve as a literature resource for scientists conducting research around the world and will contribute to the understanding of the data collected and interpreted by researchers on the different hormonal strategies used to improve reproductive performance in rams. Second, it will allow scientists to identify current knowledge gaps and set future research priorities in ram reproduction. Rams play an important role in the global flock economy, but their reproductive analysis has been limited in the use of hormonal technologies to increase the productivity of sheep flocks. In this review, we cite the most important works on six hormones that, in one way or another, modify the hypothalamus-pituitary-gonadal axis, at different doses, in and out of the reproductive season, breeds, application methods, among other factors. The overall aim is to increase the reproductive efficiency of rams in different scenarios and, in some cases, of other species due to the lack of limited information on rams.

Female scent accelerates growth of juvenile male mice

Exposing female house mice (Mus musculus) to male urinary scent accelerates their sexual development (Vandenbergh effect). Here, we tested whether exposing juvenile male mice to females' urine similarly influences male growth and size of their sexual organs. We exposed three-week old male house mice to female urine or water (control) for ca. three months. We found that female-exposed males grew significantly faster and gained more body mass than controls, despite all males being reared on a controlled diet, but we detected no differences in males' muscle mass or sexual organs. In contrast, exposing juvenile males to male urine had no effect their growth. We tested whether the males' accelerated growth imposed functional trade-offs on males' immune resistance to an experimental infection. We challenged the same male subjects with an avirulent bacterial pathogen (Salmonella enterica), but found no evidence that faster growth impacted their bacterial clearance, body mass or survival during infection compared to controls. Our results provide the first evidence to our knowledge that juvenile male mice accelerate their growth when exposed to the urine of adult females, though we found no evidence that increased growth had negative trade-offs on immune resistance to infectious disease.

Exploring differentially expressed genes in hypothalamic, pars tuberalis and pineal gland transcriptomes in different sexual behavior phenotypes in rams using RNA-Seq

Reproductive seasonality is a limiting factor in sheep production. Sexual behavior is a key element in reproductive efficiency, and this function is regulated by the hypothalamus-pituitary-gonadal (HPG) axis. To understand the mechanisms of sexual behavior, transcriptomic sequencing technology was used to identify differentially expressed genes (DEGs) in the hypothalamus (HT), pars tuberalis (PT) and pineal gland (PG) in Rasa Aragonesa rams with different sexual behavior. Bioinformatics analysis of the 16,401 identified genes by RNA-Seq revealed 103 and 12 DEGs in the HT and the PG, respectively, at a false discovery rate (FDR) of 5% with an absolute value of expression ≥ 1 (log2FC). However, no DEGs were found in the PT. Functional annotation and pathway enrichment analysis showed that DEGs of HT were enriched mainly in neuroactive ligand-receptor interactions and signaling pathways, including notable candidate genes such as MTNR1A, CHRNA2, FSHB, LHB, GNRHR, AVP, PRL, PDYN, CGA, GABRD, and TSHB, which play a crucial role in sexual behavior. The GnRH and cAMP signaling pathways were also highlighted. In addition, gene set enrichment analysis (GSEA) identified potential pathways, dominated mainly by biological process category, that could be responsible for the differences in sexual behavior observed in rams. The intracellular protein transport and pattern specification process were enriched within the PT and the transcription factor binding and protein ubiquitination pathways for the PG. Thus, these pathways together may play an important role in the regulation of the sexual behavior in Rasa Aragonesa rams through the hypothalamic-pituitary-gonadal axis. The validation of 5 DEGs using reverse transcription quantitative polymerase chain reaction (RT-qPCR) showed expression patterns like the found with RNA-Seq. Overall, these results contribute to understanding the genomic basis of sexual behavior in rams. Our study demonstrates that multiple networks and pathways orchestrate sexual behavior in sheep.

Circadian Rhythms in the Neuronal Network Timing the Luteinizing Hormone Surge

For billions of years before electric light was invented, life on Earth evolved under the pattern of light during the day and darkness during the night. Through evolution, nearly all organisms internalized the temporal rhythm of Earth's 24-hour rotation and evolved self-sustaining biological clocks with a ~24-hour rhythm. These internal rhythms are called circadian rhythms, and the molecular constituents that generate them are called molecular circadian clocks. Alignment of molecular clocks with the environmental light-dark rhythms optimizes physiology and behavior. This phenomenon is particularly true for reproductive function, in which seasonal breeders use day length information to time yearly changes in fertility. However, it is becoming increasingly clear that light-induced disruption of circadian rhythms can negatively impact fertility in nonseasonal breeders as well. In particular, the luteinizing hormone surge promoting ovulation is sensitive to circadian disruption. In this review, we will summarize our current understanding of the neuronal networks that underlie circadian rhythms and the luteinizing hormone surge.

Effects of lighting patterns in pubertal development and metabolism of female wistar rats

Modern lifestyle is characterized by constant exposure to artificial light, which is associated with alterations in biological rhythms, abnormalities to reproductive cycles and metabolic changes. In this study, we aimed to evaluate the effects of four different lighting patterns on puberty timing and on possible metabolic changes in female Wistar rats. Additionally, we developed a machine learning algorithm to automatically classify the stages of the estrous cycle. Adult Wistar rats mated during a week at a photoperiod station where they were exposed to combined red-green-blue lights (RGB) during the photoperiod that varied its spectral composition (i.e., variable color temperature) during the day (RGB-v; N = 14), RGB during the photoperiod with a fixed light color temperature (RGB-f; N = 13) during the whole photoperiod; constant darkness (DD; N = 13) and constant fixed light (LL; N = 15). Experiments were performed only on female litters from postnatal day (PND) 22 to 50. Body weight, puberty onset, estrous cyclicity and serum metabolic parameters were measured. We also collected pictures of vaginal smears to create a dataset of 15,936 images to construct an automatic classifier based on convolutional neural networks. No significant differences were found in the age of vaginal opening; however, the RGB-v group showed a significantly lower number of complete and consecutives cycles. Also, the RGB-f group showed the first complete estrous cycle significantly earlier than the RGB-v group. Female rats housed in LL condition presented significantly lower mean body weight from PND 33 to PDN 47 compared to the other groups. Furthermore, higher levels of plasma triglycerides were found in the DD group compared to RGB-f and RGB-v. HDL levels were significantly lower in RGB-v compared to RGB-f and LL groups. Total cholesterol was significantly lower in RGB-v compared to all groups. Visceral fat was significantly higher in RGB-f compared to the LL group. These results suggest that both changes in photoperiod and lighting quality affect pubertal development and alter lipid profiles and visceral fat accumulation.

Developmental programming: prenatal testosterone-induced epigenetic modulation and its effect on gene expression in sheep ovary†

Maternal perturbations or sub-optimal conditions during fetal development can predispose the offspring to diseases in adult life. Animal and human studies show that prenatal androgen excess may be an underlying cause of polycystic ovary syndrome (PCOS) later in life. In women, PCOS is a common fertility disorder with comorbid metabolic dysfunction. Here, using a sheep model of PCOS phenotype, we elucidate the epigenetic changes induced by prenatal (30-90 day) testosterone (T) treatment and its effect on gene expression in fetal day 90 (D90) and adult year 2 (Y2) ovaries. RNA-seq study shows 65 and 99 differentially regulated genes in prenatal T-treated fetal and adult ovaries, respectively. Interestingly, there were no differences in gene inducing histone marks H3K27ac, H3K9ac, and H3K4me3 or in gene silencing marks, H3K27me3 and H3K9me3 in the fetal D90 ovaries of control and excess T-exposed fetuses. In contrast, except for H3K4me3 and H3K27me3, all the other histone marks were upregulated in the prenatal T-treated adult Y2 ovary. Chromatin immunoprecipitation (ChIP) studies in adult Y2 ovaries established a direct relationship between the epigenetic modifications with the upregulated and downregulated genes obtained from RNA-seq. Results show increased gene inducing marks, H3K27ac and H3K9ac, on the promoter region of upregulated genes while gene silencing mark, H3K9me3, was also significantly increased on the downregulated genes. This study provides a mechanistic insight into prenatal T-induced developmental programming and its effect on ovarian gene expression that may contribute to reproductive dysfunction and development of PCOS in adult life.

Efficacy and safety of pulsatile gonadotropin-releasing hormone therapy in patients with congenital hypogonadotropic hypogonadism: a multicentre clinical study

Background

Pulsatile gonadotropin-releasing hormone (GnRH) therapy may restore function of the hypothalamus-pituitary-gonad axis and induce spermatogenesis in male patients with congenital hypogonadotropic hypogonadism (CHH). The study sought to test the reliability of a newly developed Innopump^® hormone pump, and to confirm the efficacy and safety of pulsatile GnRH therapy (by Innopump^® hormone pump) in CHH patients.

Methods

From November 2017 to November 2018, 28 male patients with CHH were treated with pulsatile GnRH at Peking Union Medical College Hospital, Beijing Chaoyang Hospital, and Shandong Provincial Hospital. A prospective, self-controlled, 7-day clinical trial was conducted. The primary outcome measures were the efficacy and safety of pulsatile GnRH therapy (which was administered via the Innopump^® hormone pump). The secondary outcome measures included total serum testosterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels.

Results

All of the patients participated the clinical study. For 7 days, a dosage prescribed by doctors was accurately administered by the Innopump^® hormone pump, and recorded by the pump. During the treatment, LH and FSH levels gradually increased to 2.66±1.74 and 5.05±3.03 IU/L, respectively. Upper respiratory tract infection in 1 patient and slight nausea in another patient were reported, which were confirmed to be unrelated to the pulsatile GnRH therapy.

Conclusions

The Innopump^® hormone pump was found to be reliable in drug administration, and to have an accurate alarming system. It effectively and safely treated patients with CHH. Pulsatile GnRH therapy may produce a physiological pattern of GnRH secretion, and re-establish pituitary-gonad axis function by increasing gonadotropin levels.

Selective effects of protein 4.1N deficiency on neuroendocrine and reproductive systems

Protein 4.1N, a member of the protein 4.1 family, is highly expressed in the brain. But its function remains to be fully defined. Using 4.1N^−/− mice, we explored the function of 4.1N in vivo. We show that 4.1N^−/− mice were born at a significantly reduced Mendelian ratio and exhibited high mortality between 3 to 5 weeks of age. Live 4.1N^−/− mice were smaller than 4.1N^+/+ mice. Notably, while there were no significant differences in organ/body weight ratio for most of the organs, the testis/body and ovary/body ratio were dramatically decreased in 4.1N^−/− mice, demonstrating selective effects of 4.1N deficiency on the development of the reproductive systems. Histopathology of the reproductive organs showed atrophy of both testis and ovary. Specifically, in the testis there is a lack of spermatogenesis, lack of leydig cells and lack of mature sperm. Similarly, in the ovary there is a lack of follicular development and lack of corpora lutea formation, as well as lack of secretory changes in the endometrium. Examination of pituitary glands revealed that the secretory granules were significantly decreased in pituitary glands of 4.1N^−/− compared to 4.1N^+/+. Moreover, while GnRH was expressed in both neuronal cell body and axons in the hypothalamus of 4.1N^+/+ mice, it was only expressed in the cell body but not the axons of 4.1N^-/- mice. Our findings uncover a novel role for 4.1N in the axis of hypothalamus-pituitary gland-reproductive system.

Role of core circadian clock genes in hormone release and target tissue sensitivity in the reproductive axis

Precise timing in hormone release from the hypothalamus, the pituitary and ovary is critical for fertility. Hormonal release patterns of the reproductive axis are regulated by a feedback loop within the hypothalamic-pituitary-gonadal (HPG) axis. The timing and rhythmicity of hormone release and tissue sensitivity in the HPG axis is regulated by circadian clocks located in the hypothalamus (suprachiasmatic nucleus, kisspeptin and GnRH neurons), the pituitary (gonadotrophs), the ovary (theca and granulosa cells), the testis (Leydig cells), as well as the uterus (endometrium and myometrium). The circadian clocks integrate environmental and physiological signals to produce cell endogenous rhythms generated by a transcriptional-translational feedback loop of transcription factors that are collectively called the "molecular clock". This review specifically focuses on the contribution of molecular clock transcription factors in regulating hormone release patterns in the reproductive axis, with an emphasis on the female reproductive system. Specifically, we discuss the contributions of circadian rhythms in distinct neuronal populations of the female hypothalamus, the molecular clock in the pituitary and its overall impact on female and male fertility.

Deficient melanocortin-4 receptor causes abnormal reproductive neuroendocrine profile in female mice

Deletion of the melanocortin-4-receptor (Mc4r) gene in mice causes hyperphagia, followed by hyperinsulinemia, obesity and progressive infertility. Evidence shows that the number of developed corpora lutea is reduced in obese MC4R-knockout (MC4R KO) female mice, but the mechanism is unclear. The effect of hyperphagia and obesity by MC4R KO on pulsatile luteinizing hormone (LH) secretion and ovulation remains unknown. In MC4R KO mice and wild-type littermates (WT LM) during the diestrus period throughout different ages, we examined and monitored their metabolic status, pulsatile LH profiles, follicular morphology and the number of corpora lutea. MC4R KO mice were hyperphagic, obese, hyperglycemic, hyperinsulinemic and demonstrated insulin resistance and hepatic steatosis. Irregular estrous cycles and significant changes in the LH secretion profiles were observed in sexually matured 16- to 28-week MC4R KO mice, without any difference in testosterone levels. In addition, MC4R KO mice at 16 weeks of age had significantly fewer corpora lutea than same age WT LM mice. The ovary examinations of MC4R KO mice at 28 weeks of age showed predominantly antral and preovulatory follicles with no corpora lutea. These findings were consistent with the decrease in total, pulsatile, mass and basal LH releases in MC4R KO mice. The characteristics of hormone profiles in obese MC4R KO mice indicate that MC4R plays an important role in regulating LH release, ovulation and reproductive ability probably via hyperphagia-induced obesity. Further study of correlation between metabolic and reproductive regulatory hormones is warranted to dissect the pathological mechanism underlying obesity-induced infertility.Free Chinese abstract: A Chinese translation of this abstract is freely available at http://www.reproduction-online.org/content/153/3/267/suppl/DC1.

Metals, hormones and sexual maturation in Flemish adolescents in three cross-sectional studies (2002-2015)

Sex hormone levels and timing of sexual maturation are considered important markers for health status of adolescents in puberty, and previous research suggests they might be influenced by metal exposure. In three campaigns of the Flemish Environment and Health Study (FLEHS I 2002-2006; FLEHS II 2007-2011 and FLEHS III 2012-2015), data were collected on internal exposure to metals (Cd, Cu, Pb, Cr, Mn, Tl, Ni, Sb, Hg, As and As species) and sexual maturation in 2671 14-15years old adolescents. All metals were measured in blood and/or urine, except total- and methylmercury which were measured in hair samples. Sex hormone levels were measured in blood serum of adolescent males of the cohorts of FLEHS I and FLESH II. The use of a uniform methodology in successive campaigns allows to confirm associations between exposure and health in different cohorts and over time. Furthermore, mathematical and statistical density correction methods using creatinine or specific gravity were tested for urinary markers. Significant associations between sex hormones and maturity markers were observed in the FLEHS I and II campaigns, when both were assessed together. Regardless of the applied correction method, creatinine correction systematically introduced bias due to associations of creatinine with sex hormones and maturation markers, especially in adolescent males, while this is not the case for specific gravity. A series of exposure-response associations were found, but several involving Cd, Pb, As, Tl and Cu persisted in different FLEHS campaigns. The effects of Pb and Cu on luteinizing hormone, (free) testosterone, (free) oestradiol and maturation support a xenoestrogenic agonistic action on the feedback of oestradiol to the hypothalamus-pituitary-gonadal axis. Our results suggest that specific care should be taken when selecting urine density correction for investigating associations with hormonal and maturation markers in adolescent males. Furthermore, the possibility of xenoestrogenic effects of certain metals in environmentally exposed adolescents warrants further investigation.

GnRH-mediated olfactory and visual inputs promote mating-like behaviors in male zebrafish

The engagement of sexual behaviors is regulated by a number of factors which include gene expression, hormone circulation, and multi-sensory information integration. In zebrafish, when a male and a female are placed in the same container, they show mating-like behaviors regardless of whether they are kept together or separated by a net. No mating-like behaviors are observed when same-sex animals are put together. Through the olfacto-visual centrifugal pathway, activation of the terminalis nerve in the olfactory bulb increases GnRH signaling in the brain and triggers mating-like behaviors between males. In zebrafish mutants or wild-type fish in which the olfacto-visual centrifugal pathway is impaired or chemically ablated, in response to odor stimulation the mating-like behaviors between males are no longer evident. Together, the data suggest that the combination of olfactory and visual signals alter male zebrafish's mating-like behaviors via GnRH signaling.

Developmental programming: postnatal estradiol modulation of prenatally organized reproductive neuroendocrine function in sheep

Gestational testosterone (TS) excess, acting via both the androgenic and estrogenic pathways, advances puberty and disrupts the neuroendocrine estradiol (E2) feedback and periovulatory hormonal dynamics in female sheep. These prenatally programmed defects may be subject to postnatal modifications by continued organizational and/or activational effects of steroids. This study investigated (1) the organizational contribution of prenatal estrogen excess and (2) the impact of postnatal exposure to E2 in modulating the effects of prenatal androgen excess (TS and dihydrotestosterone (DHT)) on puberty, neuroendocrine feedback mechanisms, and periovulatory hormonal dynamics in sheep. Pregnant Suffolk sheep were treated with TS, DHT, E2, or E2 plus DHT (ED) from days 30 to 90 of gestation. A subset of the control (C), TS, and DHT female offspring received a constant-release E2 implant postnatally. Findings revealed that (1) prenatal E2-treatment failed to reproduce the neuroendocrine disruptions predicted to be programmed by the estrogenic pathway and (2) prenatal E2D-treatment did not adequately replicate the reproductive neuroendocrine defects induced by prenatal TS excess. More importantly, continuous postnatal E2-treatment, while delaying the onset of puberty and reducing the inhibitory effects of E2 on tonic luteinizing hormone (LH) release, failed to amplify the E2-positive feedback and periovulatory defects induced by prenatal TS-treatment. Our results indicate that disruptions in E2-positive feedback mechanisms and periovulatory gonadotropin secretion induced by prenatal TS-treatment are programmed predominantly during the prenatal life with postnatal exposure to E2 excess not contributing further to these disruptions.

Developmental Exposure to Ethinylestradiol Affects Reproductive Physiology, the GnRH Neuroendocrine Network and Behaviors in Female Mouse

During development, environmental estrogens are able to induce an estrogen mimetic action that may interfere with endocrine and neuroendocrine systems. The present study investigated the effects on the reproductive function in female mice following developmental exposure to pharmaceutical ethinylestradiol (EE2), the most widespread and potent synthetic steroid present in aquatic environments. EE2 was administrated in drinking water at environmentally relevant (ENVIR) or pharmacological (PHARMACO) doses [0.1 and 1 μg/kg (body weight)/day respectively], from embryonic day 10 until postnatal day 40. Our results show that both groups of EE2-exposed females had advanced vaginal opening and shorter estrus cycles, but a normal fertility rate compared to CONTROL females. The hypothalamic population of GnRH neurons was affected by EE2 exposure with a significant increase in the number of perikarya in the preoptic area of the PHARMACO group and a modification in their distribution in the ENVIR group, both associated with a marked decrease in GnRH fibers immunoreactivity in the median eminence. In EE2-exposed females, behavioral tests highlighted a disturbed maternal behavior, a higher lordosis response, a lack of discrimination between gonad-intact and castrated males in sexually experienced females, and an increased anxiety-related behavior. Altogether, these results put emphasis on the high sensitivity of sexually dimorphic behaviors and neuroendocrine circuits to disruptive effects of EDCs.

Development of a methodology for and assessment of pulsatile luteinizing hormone secretion in juvenile and adult male mice

Current methodology to monitor pulsatile LH release in mice is limited by inadequate assay sensitivity, resulting in the need for collection of large blood volumes. Thus, assessment of pulsatile LH secretion in mice remains highly challenging, and observations are limited to adult mice. To address this, we developed a highly sensitive ELISA for assessment of mouse LH concentrations in small fractions of whole blood. We demonstrate that this assay is capable of reliably detecting LH down to a theoretical limit of 0.117 ng/mL in a 2-μL fraction of whole blood. Using an established frequent blood collection procedure, we validated the accuracy of this method by determining the pulsatile LH secretion in early-adult (10 weeks old) C57BL6/J male mice. Data demonstrate regular pulsatile release of LH, with peaks in LH secretion rarely exceeding 3 ng/mL. Moreover, assessment of LH release in Gpr54 knockout mice demonstrates the lack of pulsatile LH release after the loss of kisspeptin-mediated pubertal maturation. We next determined age-associated changes in pulsatile LH secretion by assessment of LH secretion in prepubertal (28 days old) C57BL6/J male mice and repeated assessment in the same mice in adulthood (120 days old). Data demonstrate that the rise in total LH secretion in mice after pubertal maturation occurs along with an overall rise in the pulsatile LH secretion rate. This was coupled with a significant increase in the number of LH secretory events (number of pulses). In addition, we observed a decrease in the clearance (increased half-life) and a decrease in the regularity (approximate entropy) of LH release. This method will be of wide general utility within the field of reproductive biology.

Early postnatal immunisation against gonadotrophin-releasing hormone induces a high but differential immune response in heifer calves

The aim of this study was to evaluate endocrinological and immunological effects of early postnatal immunisation against gonadotrophin-releasing hormone (GnRH) in heifer calves, as similar treatment in sheep provokes long-term immunocastration. Heifer calves were injected with either a construct of GnRH - bovine herpes virus 1 glycoprotein D (BHV1 gD; n=9) or saline (n=9) at 2, 6 and 13.5 weeks of age. Antibody (GnRH and carrier) and endocrine responses to immunisation were measured twice monthly (FSH and progesterone) or during intensive sampling regimes (LH). Early postnatal immunisation against GnRH induced a high, but variable, antibody response against both GnRH and carrier. Based on antibody responses, animals were divided into high-titre (HT, n=5) and low-titre (LT, n=4). Occurring mainly in HT, a further peak in anti-GnRH antibodies, stimulated independently of the carrier, was observed at 23 weeks of age, with antibody titres ≥ 10% binding for ≈ 9 weeks post-peak. Conversely immunisation had only temporary, reversible effects on reproductive function, not affecting age at puberty. We hypothesise that the newly generated antibody measured 10 weeks after the final immunisation resulted from antigenic stimulation and immunological memory cell activation to an endogenous GnRH release. This outcome offers an opportunity for further manipulation of reproductive function based on modulation of GnRH secretion and activity where long-term immunological memory may contribute to durable endocrine effects.

Gonad differentiation and puberty onset in the zebrafish: evidence for the dependence of puberty onset on body growth but not age in females

Puberty is the period in the vertebrate life cycle that marks the transition from sexual immaturity to maturity, enabling an animal to acquire adult reproductive functions. Puberty, an important point in vertebrate reproductive life, has been under extensive study in the past decades. It has been known for a long time that the initiation of puberty in mammals is closely associated with body growth and metabolism; however, there has been no equivalent report in small model teleosts such as the zebrafish. Using morphological and histological analysis, this study was undertaken to examine the timing of gonad differentiation and female maturation (puberty) in the zebrafish, with particular emphasis on the potential impact of body growth on the onset of puberty. Our data showed that gonad differentiation in the zebrafish completed around 35 days post-fertilization (dpf) in females and 45 dpf in males. Puberty in females is initiated at around 45 dpf. Our experiments provided clear evidence that the initiation of puberty in female zebrafish was strongly correlated with body size but not age, supporting the importance of the growth axis in the onset of puberty. This study provides essential information on basic characteristics of growth and reproduction in zebrafish.

Developmental programming: postnatal steroids complete prenatal steroid actions to differentially organize the GnRH surge mechanism and reproductive behavior in female sheep

In female sheep, estradiol (E2) stimulates the preovulatory GnRH/LH surge and receptive behavior, whereas progesterone blocks these effects. Prenatal exposure to testosterone disrupts both the positive feedback action of E2 and sexual behavior although the mechanisms remain unknown. The current study tested the hypothesis that both prenatal and postnatal steroids are required to organize the surge and sex differences in reproductive behavior. Our approach was to characterize the LH surge and mating behavior in prenatally untreated (Control) and testosterone-treated (T) female sheep subsequently exposed to one of three postnatal steroid manipulations: endogenous E2, excess E2 from a chronic implant, or no E2 due to neonatal ovariectomy (OVX). All females were then perfused at the time of the expected surge and brains processed for estrogen receptor and Fos immunoreactivity. None of the T females exposed postnatally to E2 exhibited an E2-induced LH surge, but a surge was produced in five of six T/OVX and all Control females. No surges were produced when progesterone was administered concomitantly with E2. All Control females were mounted by males, but significantly fewer T females were mounted by a male, including the T/OVX females that exhibited LH surges. The percentage of estrogen receptor neurons containing Fos was significantly influenced in a brain region-, developmental stage-, and steroid-specific fashion by testosterone and E2 treatments. These findings support the hypothesis that the feedback controls of the GnRH surge are sensitive to programming by prenatal and postnatal steroids in a precocial species.

Control of puberty: genetics, endocrinology, and environment

PURPOSE OF REVIEW

The aim of this review is to summarize recent advances regarding the genetic components of the complex and coordinated process of puberty, an update of the genes implicated in disorders of puberty, the endocrinologic changes of puberty, and influences of environment in the light of our current understanding of the mechanism of the onset of puberty.

RECENT FINDINGS

The timing of puberty varies greatly in the general population among ethnic groups throughout the world, suggesting the genetic control of puberty. Several studies on the pathological conditions of pubertal onset provide unique information about the interactions of either the genetic susceptibility of or environmental influences on hypothalamic control of pubertal onset. However, these findings suggested that no isolated pathway or external factor is solely responsible for the neuroendocrine control of puberty.

SUMMARY

Puberty is initiated by gonadotropin-releasing hormone from the hypothalamus followed by a complex sequence of endocrine changes and is regulated by both genetic and environmental factors. New attempts to use genetics and genomics might enhance our understanding of the spectrum of pubertal development.

The development of kisspeptin circuits in the Mammalian brain

The neuropeptide kisspeptin, encoded by the Kiss1 gene, is required for mammalian puberty and fertility. Examining the development of the kisspeptin system contributes to our understanding of pubertal progression and adult reproduction and sheds light on possible mechanisms underlying the development of reproductive disorders, such as precocious puberty or hypogonadotropic hypogonadism. Recent work, primarily in rodent models, has begun to study the development of kisspeptin neurons and their regulation by sex steroids and other factors at early life stages. In the brain, kisspeptin is predominantly expressed in two areas of the hypothalamus, the anteroventral periventricular nucleus and neighboring periventricular nucleus (pre-optic area in some species) and the arcuate nucleus. Kisspeptin neurons in these two hypothalamic regions are differentially regulated by testosterone and estradiol, both in development and in adulthood, and also display differences in their degree of sexual dimorphism. In this chapter, we discuss what is currently known and not known about the ontogeny, maturation, and sexual differentiation of kisspeptin neurons, as well as their regulation by sex steroids and other factors during development.

Mutual influences between the main olfactory and vomeronasal systems in development and evolution

The sense of smell plays a crucial role in the sensory world of animals. Two chemosensory systems have been traditionally thought to play-independent roles in mammalian olfaction. According to this, the main olfactory system (MOS) specializes in the detection of environmental odorants, while the vomeronasal system (VNS) senses pheromones and semiochemicals produced by individuals of the same or different species. Although both systems differ in their anatomy and function, recent evidence suggests they act synergistically in the perception of scents. These interactions include similar responses to some ligands, overlap of telencephalic connections and mutual influences in the regulation of olfactory-guided behavior. In the present work, we propose the idea that the relationships between systems observed at the organismic level result from a constant interaction during development and reflects a common history of ecological adaptations in evolution. We review the literature to illustrate examples of developmental and evolutionary processes that evidence these interactions and propose that future research integrating both systems may shed new light on the mechanisms of olfaction.

Developmental programming: prenatal androgen exposure alters the gonadotroph population of the ovine pituitary gland

In utero exposure of the female foetus to androgens during development disrupts the reproductive axis and results in hypersecretion of luteinising hormone (LH) (but not follicle-stimulating hormone) in postnatal life. Abnormalities in the neural circuits controlling hypothalamic gonadotrophin-releasing hormone have been documented; however, androgens could also programme abnormalities in the pituitary gland. Ovine foetuses were exposed to either testosterone propionate or the non-aromatisable androgen dihydro-testosterone from days 30-90 of gestation (term 147 days) and the effects on the functional morphology of the pituitary were determined. Exogenous testosterone propionate exposure resulted in pituitary glands in adult male and female sheep that were 40% heavier than controls. Because this effect was not observed in the dihydro-testosterone-exposed animals, these actions are mediated via the oestrogen receptor (ER). No significant differences were apparent in 90- or 140-day foetuses. There was no difference between control and androgen-exposed animals in the density of LHβ or ERα immunoreactive cells in the pituitary although the density of follicle-stimulating hormone-β immunoreactive cells was lower in the testosterone-treated animals. The percentage of cells co-localising LHβ and ERα was lower in the testosterone-treated ewes and this may, in part, explain a reduced ability to respond to steroid feedback. Thus, enlargement of the pituitary gland, coupled with a reduced sensitivity to oestrogen negative-feedback, may contribute to the hyper-secretion of LH observed in animals that have been exposed to excess androgens during foetal life.

Beyond overweight: nutrition as an important lifestyle factor influencing timing of puberty

Early onset of puberty may confer adverse health consequences. Thus, modifiable factors influencing the timing of puberty are of public health interest. Childhood overweight as a factor in the earlier onset of menarche has been supported by prospective evidence; nonetheless, its overall contribution may have been overemphasized, since secular trends toward a younger age at menarche have not been a universal finding during the recent obesity epidemic. Current observational studies suggest notable associations between dietary intakes and pubertal timing beyond contributions to an energy imbalance: children with the highest intakes of vegetable protein or animal protein experience pubertal onset up to 7 months later or 7 months earlier, respectively. Furthermore, girls with high isoflavone intakes may experience the onset of breast development and peak height velocity approximately 7-8 months later. These effect sizes are on the order of those observed for potentially neuroactive steroid hormones. Thus, dietary patterns characterized by higher intakes of vegetable protein and isoflavones and lower intakes of animal protein may contribute to a lower risk of breast cancer or a lower total mortality.

Kisspeptin-10 stimulates the release of luteinizing hormone and testosterone in pre- and post-pubertal male goats

The aims of the present study were to clarify the effect of kisspeptin-10 (Kp10) on the secretion of luteinizing hormone (LH) and testosterone (T) in pre-pubertal and post-pubertal male ruminants. Four male goats (Shiba goats) were given an intravenous (i.v.) injection of Kp10 (5 µg/kg body weight (b.w.)), gonadotoropin-releasing hormone (GnRH, 1 µg/kg b.w.), or 2 mL of saline as a control at the ages of 3 (pre-pubertal) and 6 (post-pubertal) months. A single i.v. injection of Kp10 significantly stimulated the release of LH and T in both groups. The area under the response curve (AUC) of LH for a 60-min period after the i.v. injection of Kp10 was significantly greater in the pre-pubertal goats (P < 0.05). The AUC of T for a 120 min period post-injection did not differ between the two age groups. A single i.v. injection of GnRH also significantly stimulated the release of LH and T in both groups (P < 0.05). The secretory pattern of LH and T in response to GnRH resembled that in response to Kp10. These results show that the LH-releasing response to Kp10 is greater in pre-pubertal than post-pubertal male goats. They also show that Kp10, as well as GnRH, is able to stimulate the release of T in male goats.

Prenatal programming by testosterone of hypothalamic metabolic control neurones in the ewe

Ewes treated prenatally with testosterone develop metabolic deficits, including insulin resistance, in addition to reproductive dysfunctions that collectively mimic polycystic ovarian syndrome (PCOS), a common endocrine disease in women. We hypothesised that metabolic deficits associated with prenatal testosterone excess involve alterations in arcuate nucleus (ARC) neurones that contain either agouti-related peptide (AgRP) or pro-opiomelanocortin (POMC). Characterisation of these neurones in the ewe showed that immunoreactive AgRP and POMC neurones were present in separate populations in the ARC, that AgRP and POMC neurones co-expressed either neuropeptide Y or cocaine- and amphetamine-regulated transcript, respectively, and that each population had a high degree of co-localisation with androgen receptors. Examination of the effect of prenatal testosterone exposure on the number of AgRP and POMC neurones in adult ewes showed that prenatal testosterone excess significantly increased the number of AgRP but not POMC neurones compared to controls; this increase was restricted to the middle division of the ARC, was mimicked by prenatal treatment with dihydrotestosterone, a non-aromatisable androgen, and was blocked by co-treatment of prenatal testosterone with the anti-androgen, flutamide. The density of AgRP fibre immunoreactivity in the preoptic area, paraventricular nucleus, lateral hypothalamus and dorsomedial hypothalamic nucleus was also increased by prenatal testosterone exposure. Thus, ewes that were exposed to androgens during foetal life showed alterations in the number of AgRP-immunoreactive neurones and the density of fibre immunoreactivity in their projection areas, suggestive of permanent prenatal programming of metabolic circuitry that may, in turn, contribute to insulin resistance and an increased risk of obesity in this model of PCOS.

Endogenously elevated androgens alter the developmental programming of the hypothalamic-pituitary axis in male mice

Transgenic male mice that express human chorionic gonadotropin (hCG) α and β subunits constitutively hypersecrete hCG and produce elevated levels of androgens. The aim of this study was to characterize the hypothalamic-pituitary function of these transgenic (hCGαβ+) males by focusing on FSH regulation. Serum FSH levels and pituitary mRNA expression of Fshb, Lhb, Cga, Gnrhr and Esr1 were reduced, whereas Fst expression was increased in prepubertal hCGαβ+ males as compared with wild-type. In the hypothalamus, Cyp19a1 expression, GnRH concentration and ex-vivo GnRH pulsatility were elevated in prepubertal hCGαβ+ mice, whereas Kiss1 expression was decreased prepubertally and Gad67 expression was elevated neonatally. The effect of androgens on the developmental programming of the hypothalamic-pituitary axis of hCGαβ+ males was evaluated by perinatal and prepubertal antiandrogen (flutamide) administration. Our studies identified a critical window between gestational day 18 and postnatal day 14, during which chronically elevated androgens and/or their locally produced metabolites activate the hypothalamus and concomitantly shut-down the gonadotropin axis.

Developmental programming: insulin sensitizer treatment improves reproductive function in prenatal testosterone-treated female sheep

Prenatal testosterone (T) excess causes reproductive and metabolic disruptions including insulin resistance, attributes of women with polycystic ovary syndrome. This study tested the hypothesis that insulin resistance contributes toward severity of reproductive disruptions in prenatally T-treated females. Pregnant sheep were injected im with 100 mg of T-propionate semiweekly from d 30-90 of gestation. Immediately after the first breeding season, a subset of controls and prenatal T-treated (TR) sheep were administered an insulin sensitizer (rosiglitazone; 8 mg/d) orally for 8 months. Untreated control and prenatal T-treated females (T group) were studied in parallel. Biochemical analyses revealed rosiglitazone to be safe for use in sheep. Glucose tolerance tests performed before and after the insulin sensitizer treatment found that insulin sensitizer decreased cumulative insulin, cumulative insulin/glucose ratio, and insulin area under the curve by about 50% and increased the insulin sensitivity index by about 70% in the TR compared with the T group. Twenty percent of TR females showed a reduced number of cycles in the second relative to first breeding season as opposed to 80% of T group females showing such deterioration. Insulin sensitizer treatment also decreased the number of aberrant cycles (>/=18 d) during the second breeding season in the TR group relative to the first as opposed to the T group females showing an increase in the second breeding season relative to the first. These findings provide evidence that insulin sensitizer treatment prevents further deterioration of the reproductive axis in prenatal T-treated sheep, a finding of translational relevance to women with polycystic ovary syndrome.

Gonadal and nongonadal regulation of sex differences in hypothalamic Kiss1 neurones

The brains of males and females differ anatomically and physiologically, including sex differences in neurone size or number, synapse morphology and specific patterns of gene expression. Brain sex differences may underlie critical sex differences in physiology or behaviour, including several aspects of reproduction, such as the timing of sexual maturation (earlier in females than males) and the ability to generate a preovulatory gonadotrophin surge (in females only). The reproductive axis is controlled by afferent pathways that converge upon forebrain gonadotrophin-releasing hormone (GnRH) neurones, but GnRH neurones are not sexually dimorphic. Although most reproductive sex differences probably reflect sex differences in the upstream circuits and factors that regulate GnRH secretion, the key sexually-dimorphic factors that influence reproductive status have remained poorly defined. The recently-identified neuropeptide kisspeptin, encoded by the Kiss1 gene, is an important regulator of GnRH secretion, and Kiss1 neurones in rodents are sexually dimorphic in specific hypothalamic populations, including the anteroventral periventricular nucleus-periventricular nucleus continuum (AVPV/PeN) and the arcuate nucleus (ARC). In the adult AVPV/PeN, Kiss1 neurones are more abundant in females than males, representing a sex difference that is regulated by oestradiol signalling during critical periods of postnatal and pubertal development. By contrast, Kiss1 neurones in the ARC are not sexually differentiated in adult rodents but, in mice, the regulation of ARC Kiss1 cells by gonadal hormone-independent factors is sexually dimorphic during prepubertal development. These various sex differences in hypothalamic Kiss1 neurones may relate to known sex differences in reproductive physiology, such as puberty onset and positive feedback.

Proliferative and transcriptional identity of distinct classes of neural precursors in the mammalian olfactory epithelium

Neural precursors in the developing olfactory epithelium (OE) give rise to three major neuronal classes - olfactory receptor (ORNs), vomeronasal (VRNs) and gonadotropin releasing hormone (GnRH) neurons. Nevertheless, the molecular and proliferative identities of these precursors are largely unknown. We characterized two precursor classes in the olfactory epithelium (OE) shortly after it becomes a distinct tissue at midgestation in the mouse: slowly dividing self-renewing precursors that express Meis1/2 at high levels, and rapidly dividing neurogenic precursors that express high levels of Sox2 and Ascl1. Precursors expressing high levels of Meis genes primarily reside in the lateral OE, whereas precursors expressing high levels of Sox2 and Ascl1 primarily reside in the medial OE. Fgf8 maintains these expression signatures and proliferative identities. Using electroporation in the wild-type embryonic OE in vitro as well as Fgf8, Sox2 and Ascl1 mutant mice in vivo, we found that Sox2 dose and Meis1 - independent of Pbx co-factors - regulate Ascl1 expression and the transition from lateral to medial precursor state. Thus, we have identified proliferative characteristics and a dose-dependent transcriptional network that define distinct OE precursors: medial precursors that are most probably transit amplifying neurogenic progenitors for ORNs, VRNs and GnRH neurons, and lateral precursors that include multi-potent self-renewing OE neural stem cells.

Developmental programming: impact of prenatal testosterone excess and postnatal weight gain on insulin sensitivity index and transfer of traits to offspring of overweight females

Polycystic ovary syndrome (PCOS) is the most common endocrinopathy of reproductive-aged women and is exacerbated by obesity. Exposure of ewes to excess testosterone (T) from d 30-90 of gestation culminates in anovulation, functional hyperandrogenism, LH excess, and polyfollicular ovaries, features similar to those of women with PCOS, with some reproductive defects programmed by androgenic actions of T and others not. Excess weight gain during postnatal life increases the severity of these reproductive defects. Prenatal T-treated ewes also manifest reduced insulin sensitivity, a feature found in more than 70% of PCOS women. We tested the hypotheses that reduced insulin sensitivity of prenatal T-treated ewes is programmed by androgenic actions of T, and excess postnatal weight gain exaggerates this defect. In addition, we tested whether disruptive effects of excess weight gain on insulin sensitivity index are transferred to female offspring. Insulin sensitivity was assessed using iv glucose tolerance tests. Results revealed that disruptive effects of prenatal T excess on insulin sensitivity were programmed by androgenic action of T and postnatal overfeeding-impaired insulin sensitivity in both T-treated and controls and that prenatal T-treated sheep tend to manifest such overfeeding impairments earlier than controls. Importantly, offspring of overweight controls also manifest defects in insulin dynamics supportive of intergenerational transfer of obesity-related traits. The findings are of relevance in the context of developmental programming of insulin resistance by prenatal steroids and excess weight gain.

Sex differences in the regulation of Kiss1/NKB neurons in juvenile mice: implications for the timing of puberty

In mammals, puberty onset typically occurs earlier in females than in males, but the explanation for sexual differentiation in the tempo of pubertal development is unknown. Puberty in both sexes is a brain-dependent phenomenon and involves alterations in the sensitivity of neuronal circuits to gonadal steroid feedback as well as gonadal hormone-independent changes in neuronal circuitry. Kisspeptin, encoded by the Kiss1 gene, plays an essential but ill-defined role in pubertal maturation. Neurokinin B (NKB) is coexpressed with Kiss1 in the arcuate nucleus (ARC) and is also important for puberty. We tested whether sex differences in the timing of pubertal development are attributable to sexual differentiation of gonadal hormone-independent mechanisms regulating hypothalamic Kiss1/NKB gene expression. We found that, in juvenile females, gonadotropin secretion and expression of Kiss1 and NKB in the ARC increased immediately following ovariectomy, suggesting that prepubertal females have negligible gonadal hormone-independent restraint on their reproductive axis. In contrast, in similarly aged juvenile males, no changes occurred in LH levels or Kiss1 or NKB expression following castration, suggesting that gonadal hormone-independent mechanisms restrain kisspeptin/NKB-dependent activation of the male reproductive axis before puberty. Notably, adult mice of both sexes showed comparable rapid increases in Kiss1/NKB expression and LH secretion following gonadectomy, signifying that sex differences in the regulation of ARC Kiss1/NKB neurons are manifest only during peripubertal development. Our findings demonstrate that the mechanisms controlling pubertal activation of reproduction in mice are different between the sexes and suggest that gonadal hormone-independent central restraint on pubertal timing involves Kiss1/NKB neurons in the ARC.

Effects of nutritional quality during early development on body weight and reproductive maturation of guinea pigs (Cavia aperea f. porcellus)

In many species, somatic and reproductive maturation are sensitive to seasonally-fluctuating environmental conditions such as food quality. The protein content of the diet during early development has been considered to be particularly important, a low-protein diet during gestation and lactation typically delaying growth and reproductive onset. To investigate the effects of maternal and early postnatal diet quality on body weight and puberty of male and female domestic guinea pigs, we fed F0-mothers either a low-protein (14%, LQ-group) or a high-protein diet (23%, HQ-group) during gestation and lactation. Their male and female offspring received the same respective diets until six weeks of age; afterward they were switched to an intermediate control diet. Body weight of F1-subjects was significantly affected by the dietary treatment. Reproductive parameters were only affected in F1-females but not in F1-males. We conclude that in guinea pigs, growth is sensitive to the quality of the maternal and early postnatal diet, and that reproductive maturation is more sensitive in females.

Estrogen receptor immunoreactivity in late-gestation fetal lambs

Prenatal androgens masculinize postnatal reproductive neuroendocrine function and behavior in sheep. Testosterone treatment of pregnant ewes during midgestation masculinizes sexual behavior and luteinizing hormone secretion in female lambs, presumably in part via aromatization and estrogen receptor (ESR) binding in the brain. We hypothesized that male and female sheep also differ in the number and distribution of ESR-containing neurons. If so, ESR expression should be sensitive to prenatal hormones delivered exogenously or in situ. ESR alpha (ESR1) was compared by immunocytochemistry in male and female lambs at the end of gestation, as well as in fetal females exposed prenatally to testosterone or dihydrotestosterone. ESR1-positive neurons were abundant in the posteromedial bed nucleus of the stria terminalis (BSTpm), medial preoptic area (MPOA), posterior medial amygdaloid nucleus (MeP), amygdalohippocampal area (AHi), ventromedial hypothalamic nuclei (VMH), and arcuate hypothalamic nuclei (ARC). In females, the ARC had the largest number of stained cells (mean +/- SEM, 475.6 +/- 57.4 cells/0.173 mm(2)), while staining intensity was greatest in the MPOA (mean +/- SEM gray level, 31.3 +/- 5.3). The mean +/- SEM integrated gray level (IGL) was high in the ARC (0.63 +/- 0.13) and in the MPOA (0.51 +/- 0.08). The mean +/- SEM IGL was low in the MeP (0.31 +/- 0.10) and in the BSTpm (0.21 +/- 0.06), while it was intermediate in the AHi (0.36 +/- 0.10) and in the VMH (0.37 +/- 0.07). ESR immunostaining was not significantly different in male and female fetal lambs, nor in females fetuses exposed prenatally to androgens (P > 0.05). However, ESR1 staining was significantly increased in the ARC, MPOA, and AHi of adult rams vs. adult ewes. These results suggest that brain ESR immunoreactivity in fetal lambs is unlikely to account for postnatal sex differences in reproductive function. Instead, sex differences in ESR emerge postnatally.

Prenatal testosterone excess reduces sperm count and motility

The reproductive system is extremely susceptible to insults from exposure to exogenous steroids during development. Excess prenatal testosterone exposure programs neuroendocrine, ovarian, and metabolic deficits in the female, features seen in women with polycystic ovary disease. The objective of this study was to determine whether prenatal testosterone excess also disrupts the male reproductive system, using sheep as a model system. The extent of reproductive disruption was tested by assessing sperm quantity and quality as well as Leydig cell responsiveness to human chorionic gonadotropin. Males born to mothers treated with 30 mg testosterone propionate twice weekly from d 30 to 90 and with 40 mg testosterone propionate from d 90 to 120 of pregnancy (T-males) showed a significant reduction (P < 0.05) in body weight, scrotal circumference, and sperm count compared with control males. Mean straight line velocity of sperms was also lower in T-males (P < 0.05). Circulating testosterone levels in response to the human chorionic gonadotropin did not differ between groups. These findings demonstrate that exposure to excess testosterone during fetal development has a negative impact on reproductive health of the male offspring, raising concerns relative to unintended human exposure to steroidal mimics in the environment.

Sexual differentiation of the external genitalia and the timing of puberty in the presence of an antiandrogen in sheep

Testicular steroids during midgestation sexually differentiate the steroid feedback mechanisms controlling GnRH secretion in sheep. To date, the actions of the estrogenic metabolites in programming neuroendocrine function have been difficult to study because exogenous estrogens disrupt maternal uterine function. We developed an approach to study the prenatal actions of estrogens by coadministering testosterone (T) and the androgen receptor antagonist flutamide, and tested the hypothesis that prenatal androgens program estradiol inhibitory feedback control of GnRH secretion to defeminize (advance) the timing of the pubertal increase in LH. Pregnant sheep were either untreated or treated with T, dihydrotestosterone (DHT) (a nonaromatizable androgen), or T plus flutamide from d 30-90 of gestation. To study the postnatal response to steroid negative feedback, lambs were gonadectomized and estradiol-replaced, and concentrations of LH were monitored in twice-weekly blood samples. Although T and DHT produced penile and scrotal development in females, the external genitalia of T plus flutamide offspring remained phenotypically female, regardless of genetic sex. Untreated females and females and males treated with T plus flutamide exhibited a pubertal increase in circulating LH at 26.4+/-0.5, 26.0+/-0.7, and 22.4+/-1.6 wk of age, respectively. In females exposed to prenatal androgens, the LH increase was advanced (T: 12.0+/-2.6 wk; DHT: 15.0+/-2.6 wk). These results demonstrate the usefulness of combining T and antiandrogen treatments as an approach to increasing prenatal exposure to estradiol. Importantly, the findings support our hypothesis that prenatal androgens program sensitivity to the negative feedback actions of estradiol and the timing of neuroendocrine puberty.

Prenatal origins of adult disease

PURPOSE OF REVIEW

Human epidemiological and animal studies show that many chronic adult conditions have their antecedents in compromised fetal and early postnatal development. Developmental programming is defined as the response by the developing mammalian organism to a specific challenge during a critical time window that alters the trajectory of development with resulting persistent effects on phenotype. Mammals pass more biological milestones before birth than any other time in their lives. Each individual's phenotype is influenced by the developmental environment as much as their genes. A better understanding is required of gene-environment interactions leading to adult disease.

RECENT FINDINGS

During development, there are critical periods of vulnerability to suboptimal conditions when programming may permanently modify disease susceptibility. Programming involves structural changes in important organs; altered cell number, imbalance in distribution of different cell types within the organ, and altered blood supply or receptor numbers. Compensatory efforts by the fetus may carry a price. Effects of programming may pass across generations by mechanisms that do not necessarily involve structural gene changes. Programming often has different effects in males and females.

SUMMARY

Developmental programming shows that epigenetic factors play major roles in development of phenotype and predisposition to disease in later life.

Modulation of estrogen receptors during development inhibits neurogenesis of precursors to GnRH-1 neurones: in vitro studies with explants of ovine olfactory placode

The aim of the present study was to explore the putative effects of agonists and antagonists of the estradiol receptor on the early phase of GnRH-1 neuron development. To address this question we used an in vitro model of GnRH-1 neurons using cultured olfactory placode from sheep embryos on day 26 of gestation. Previous studies on this model have shown that in vitro the development of GnRH-1 neurons mimics in vivo development up to the start of pulsatile GnRH-1 secretion, To address the effects of modulating the estrogen receptor, cultures were treated with the endogenous and synthetic ligands of estradiol receptors: 17beta-estradiol, 17alpha-estradiol and tamoxifen. Neurogenesis was measured by incorporation of [(3)H]-thymidine. Morphometric parameters were evaluated by image analysis. The main results are that antagonism of estradiol receptors induced an important decrease in neurogenesis but had little effect on morphometric parameters, suggesting that during this early phase of development, maternal estrogens are important to achieve correct development of the GnRH-1 neuronal network.

Diversity of actions of GnRHs mediated by ligand-induced selective signaling

Geoffrey Wingfield Harris' demonstration of hypothalamic hormones regulating pituitary function led to their structural identification and therapeutic utilization in a wide spectrum of diseases. Amongst these, Gonadotropin Releasing Hormone (GnRH) and its analogs are widely employed in modulating gonadotropin and sex steroid secretion to treat infertility, precocious puberty and many hormone-dependent diseases including endometriosis, uterine fibroids and prostatic cancer. While these effects are all mediated via modulation of the pituitary gonadotrope GnRH receptor and the G(q) signaling pathway, it has become increasingly apparent that GnRH regulates many extrapituitary cells in the nervous system and periphery. This review focuses on two such examples, namely GnRH analog effects on reproductive behaviors and GnRH analog effects on the inhibition of cancer cell growth. For both effects the relative activities of a range of GnRH analogs is distinctly different from their effects on the pituitary gonadotrope and different signaling pathways are utilized. As there is only a single functional GnRH receptor type in man we have proposed that the GnRH receptor can assume different conformations which have different selectivity for GnRH analogs and intracellular signaling proteins complexes. This ligand-induced selective-signaling recruits certain pathways while by-passing others and has implications in developing more selective GnRH analogs for highly specific therapeutic intervention.

The genetic basis for the timing of human puberty

Puberty is a complex, coordinated biological process with multiple levels of regulation. Epidemiological observations suggest that the timing of pubertal events is a heritable trait, although environmental factors can modulate such genetic influence. The study of pathological states of early and late puberty has provided valuable insight into those genes that regulate gonadotrophin-releasing hormone (GnRH) activity. The development of pulsatile release of GnRH secretion mediated through kisspeptin-1 activation of G-protein coupled receptor-54 appears to be a central event at the onset and during progression of puberty. Stimulating and restraining influences (e.g. in the form of glutamatergic and GABAergic neuronal inputs) are likely to influence the timing of this process. The study of extreme variants of 'normality', such as constitutional delay of growth and puberty and early puberty, may lead to the recognition of additional genes and pathways that can modulate both the timing of pubertal onset and its tempo.

Developmental programming: follicular persistence in prenatal testosterone-treated sheep is not programmed by androgenic actions of testosterone

Testosterone (T) treatment during early-midgestation (30-90 d; term is 147 d) leads to reproductive cycle defects. Daily ultrasonography in prenatal T-treated female sheep during the first two breeding seasons revealed an increase in the number of large follicles and follicular persistence. The objective of this study was to determine whether follicular persistence in prenatal T-treated females was programmed by the androgenic actions of T. Pregnant Suffolk ewes were injected with 100 mg (im; twice weekly) of T propionate or dihydrotestosterone (DHT, a nonaromatizable androgen) in cottonseed oil from d 30 to d 90 of gestation. Prior to daily transrectal ovarian ultrasonography, estrus was synchronized with two injections of 20 mg of prostaglandin F2alpha (PGF2alpha) given 11 d apart in two consecutive years. In yr 1 ultrasonography began 14 d after PGF2alpha, during the presumptive luteal phase, and continued until subsequent ovulation and corpora lutea were detected (10-13 d). In yr 2, ultrasonography began 2 d before the last PGF2alpha injection and concluded 25 d after the last PGF2alpha injection. Daily changes in appearance and disappearance of ovarian follicles and follicular sizes were assessed. Prenatal DHT, but not prenatal T, treatment increased the total number of follicles by increasing the number of small follicles. Prenatal T, but not DHT, treatment increased (P<0.05) the number of large follicles with the majority of prenatal T-treated females manifesting follicular persistence. The data indicate that occurrence of large-sized follicles and follicular persistence in prenatal T-treated females are not programmed by androgenic actions but likely are programmed by estrogenic actions stemming from aromatization of T to estradiol.

Polycystic ovary syndrome and its developmental origins

The prenatal testosterone (T)-treated adult female rhesus monkey is one animal model of polycystic ovary syndrome (PCOS) in women, with early prenatal T excess programming a permanent PCOS-like phenotype characterized by luteinizing hormone (LH) hypersecretion from reduced hypothalamic sensitivity to steroid negative feedback and relative insulin excess from increased abdominal adiposity. These combined reproductive and metabolic abnormalities are associated with ovarian hyperandrogenism and follicular arrest in adulthood, as well as premature follicle differentiation and impaired embryo development during gonadotropin therapy for in vitro fertilization (IVF). A second animal model for PCOS, the prenatal T-treated sheep also is characterized by LH hypersecretion from reduced hypothalamic sensitivity to steroid negative feedback, persistent follicles and insulin resistance, but also is associated with intrauterine growth retardation and compensatory growth after birth. The ability of prenatal T excess in both species to alter the developmental trajectory of multiple organ systems in utero provides evidence that the hormonal environment of intrauterine life programs target tissue differentiation, raising the possibility that T excess in human fetal development promotes PCOS in adulthood. Such a hypothesis must include data from clinical studies of PCOS women to clarify the homology between these PCOS-like animal models and PCOS per se in reproductive and metabolic function. Future studies should develop new clinical strategies that improve pregnancy outcome and minimize pregnancy loss in women with disorders of insulin action, including PCOS, obesity and diabetes mellitus as well as minimize transgenerational susceptibility to adult PCOS and its metabolic derangements in male close relatives.