Gene networks and the neuroendocrine regulation of puberty

Multi-tissue omics analyses reveal molecular regulatory networks for puberty in composite beef cattle

Puberty is a complex physiological event by which animals mature into an adult capable of sexual reproduction. In order to enhance our understanding of the genes and regulatory pathways and networks involved in puberty, we characterized the transcriptome of five reproductive tissues (i.e. hypothalamus, pituitary gland, ovary, uterus, and endometrium) as well as tissues known to be relevant to growth and metabolism needed to achieve puberty (i.e., longissimus dorsi muscle, adipose, and liver). These tissues were collected from pre- and post-pubertal Brangus heifers (3/8 Brahman; Bos indicus x 5/8 Angus; Bos taurus) derived from a population of cattle used to identify quantitative trait loci associated with fertility traits (i.e., age of first observed corpus luteum (ACL), first service conception (FSC), and heifer pregnancy (HPG)). In order to exploit the power of complementary omics analyses, pre- and post-puberty co-expression gene networks were constructed by combining the results from genome-wide association studies (GWAS), RNA-Seq, and bovine transcription factors. Eight tissues among pre-pubertal and post-pubertal Brangus heifers revealed 1,515 differentially expressed and 943 tissue-specific genes within the 17,832 genes confirmed by RNA-Seq analysis. The hypothalamus experienced the most notable up-regulation of genes via puberty (i.e., 204 out of 275 genes). Combining the results of GWAS and RNA-Seq, we identified 25 loci containing a single nucleotide polymorphism (SNP) associated with ACL, FSC, and (or) HPG. Seventeen of these SNP were within a gene and 13 of the genes were expressed in uterus or endometrium. Multi-tissue omics analyses revealed 2,450 co-expressed genes relative to puberty. The pre-pubertal network had 372,861 connections whereas the post-pubertal network had 328,357 connections. A sub-network from this process revealed key transcriptional regulators (i.e., PITX2, FOXA1, DACH2, PROP1, SIX6, etc.). Results from these multi-tissue omics analyses improve understanding of the number of genes and their complex interactions for puberty in cattle.

The POU factor ventral veins lacking/Drifter directs the timing of metamorphosis through ecdysteroid and juvenile hormone signaling

Although endocrine changes are known to modulate the timing of major developmental transitions, the genetic mechanisms underlying these changes remain poorly understood. In insects, two developmental hormones, juvenile hormone (JH) and ecdysteroids, are coordinated with each other to induce developmental changes associated with metamorphosis. However, the regulation underlying the coordination of JH and ecdysteroid synthesis remains elusive. Here, we examined the function of a homolog of the vertebrate POU domain protein, Ventral veins lacking (Vvl)/Drifter, in regulating both of these hormonal pathways in the red flour beetle, Tribolium castaneum (Tenebrionidae). RNA interference-mediated silencing of vvl expression led to both precocious metamorphosis and inhibition of molting in the larva. Ectopic application of a JH analog on vvl knockdown larvae delayed the onset of metamorphosis and led to a prolonged larval stage, indicating that Vvl acts upstream of JH signaling. Accordingly, vvl knockdown also reduced the expression of a JH biosynthesis gene, JH acid methyltransferase 3 (jhamt3). In addition, ecdysone titer and the expression of the ecdysone response gene, hormone receptor 3 (HR3), were reduced in vvl knockdown larvae. The expression of the ecdysone biosynthesis gene phantom (phm) and spook (spo) were reduced in vvl knockdown larvae in the anterior and posterior halves, respectively, indicating that Vvl might influence ecdysone biosynthesis in both the prothoracic gland and additional endocrine sources. Injection of 20-hydroxyecdysone (20E) into vvl knockdown larvae could restore the expression of HR3 although molting was never restored. These findings suggest that Vvl coordinates both JH and ecdysteroid biosynthesis as well as molting behavior to influence molting and the timing of metamorphosis. Thus, in both vertebrates and insects, POU factors modulate the production of major neuroendocrine regulators during sexual maturation.

Hormones play major roles in initiating major developmental transitions, such as puberty and metamorphosis. However, how organisms coordinate changes across multiple hormones remains unclear. In this study, we show that silencing the POU domain transcription factor Ventral veins lacking (Vvl)/Drifter in the red flour beetle Tribolium castaneum leads to precocious metamorphosis and an inability to molt. We show that Vvl regulates the biosynthesis and signaling of two key insect developmental hormones, juvenile hormone (JH) and ecdysteroids. Vvl therefore appears to act as a potential central regulator of developmental timing by influencing two major hormones. Because POU factors are known as a major regulator of the onset of puberty, POU factors play a major role during sexual maturation in both vertebrates and insects.

Molecular and gene network analysis of thyroid transcription factor 1 (TTF1) and enhanced at puberty (EAP1) genes in patients with GnRH-dependent pubertal disorders

BACKGROUND/AIM

TTF1 and EAP1 are transcription factors that modulate gonadotropin-releasing hormone expression. We investigated the contribution of TTF1 and EAP1 genes to central pubertal disorders.

PATIENTS AND METHODS

133 patients with central pubertal disorders were studied: 86 with central precocious puberty and 47 with normosmic isolated hypogonadotropic hypogonadism. The coding region of TTF1 and EAP1 were sequenced. Variations of polyglutamine and polyalanine repeats in EAP1 were analyzed by GeneScan software. Association of TTF1 and EAP1 to genes implicated in timing of puberty was investigated by meta-network framework GeneMANIA and Cytoscape software.

RESULTS

Direct sequencing of the TTF1 did not reveal any mutation or polymorphisms. Four EAP1 synonymous variants were identified with similar frequencies among groups. The most common EAP1 5'-distal polyalanine genotype was the homozygous 12/12, but the genotype 12/9 was identified in 2 central precocious puberty sisters without functional alteration in EAP1 transcriptional activity. TTF1 and EAP1 were connected, via genetic networks, to genes implicated in the control of menarche.

CONCLUSION

No TTF1 or EAP1 germline mutations were associated with central pubertal disorders. TTF1 and EAP1 may affect puberty by changing expression in response to other members of puberty-associated gene networks, or by differentially affecting the expression of gene components of these networks.

The kisspeptin-GnRH pathway in human reproductive health and disease

BACKGROUND

The discovery of kisspeptin as key central regulator of GnRH secretion has led to a new level of understanding of the neuroendocrine regulation of human reproduction. The related discovery of the kisspeptin-neurokinin B-dynorphin (KNDy) pathway in the last decade has further strengthened our understanding of the modulation of GnRH secretion by endocrine, metabolic and environmental inputs. In this review, we summarize current understanding of the physiological roles of these novel neuropeptides, and discuss the clinical relevance of these discoveries and their potential translational applications.

METHODS

A systematic literature search was performed using PUBMED for all English language articles up to January 2014. In addition, the reference lists of all relevant original research articles and reviews were examined. This review focuses mainly on published human studies but also draws on relevant animal data.

RESULTS

Kisspeptin is a principal regulator of the secretion of gonadotrophins, and through this key role it is critical for the onset of puberty, the regulation of sex steroid-mediated feedback and the control of adult fertility. Although there is some sexual dimorphism, both neuroanatomically and functionally, these functions are apparent in both men and women. Kisspeptin acts upstream of GnRH and, following paracrine stimulatory and inhibitory inputs from neurokinin B and dynorphin (KNDy neuropeptides), signals directly to GnRH neurones to control pulsatile GnRH release. When administered to humans in different isoforms, routes and doses, kisspeptin robustly stimulates LH secretion and LH pulse frequency. Manipulation of the KNDy system is currently the focus of translational research with the possibility of future clinical application to regulate LH pulsatility, increasing gonadal sex steroid secretion in reproductive disorders characterized by decreased LH pulsatility, including hypothalamic amenorrhoea and hypogonadotropic hypogonadism. Conversely there may be scope to reduce the activity of the KNDy system to reduce LH secretion where hypersecretion of LH adds to the phenotype, such as in polycystic ovary syndrome.

CONCLUSIONS

Kisspeptin is a recently discovered neuromodulator that controls GnRH secretion mediating endocrine and metabolic inputs to the regulation of human reproduction. Manipulation of kisspeptin signalling has the potential for novel therapies in patients with pathologically low or high LH pulsatility.

A systems biology approach using metabolomic data reveals genes and pathways interacting to modulate divergent growth in cattle

BACKGROUND

Systems biology enables the identification of gene networks that modulate complex traits. Comprehensive metabolomic analyses provide innovative phenotypes that are intermediate between the initiator of genetic variability, the genome, and raw phenotypes that are influenced by a large number of environmental effects. The present study combines two concepts, systems biology and metabolic analyses, in an approach without prior functional hypothesis in order to dissect genes and molecular pathways that modulate differential growth at the onset of puberty in male cattle. Furthermore, this integrative strategy was applied to specifically explore distinctive gene interactions of non-SMC condensin I complex, subunit G (NCAPG) and myostatin (GDF8), known modulators of pre- and postnatal growth that are only partially understood for their molecular pathways affecting differential body weight.

RESULTS

Our study successfully established gene networks and interacting partners affecting growth at the onset of puberty in cattle. We demonstrated the biological relevance of the created networks by comparison to randomly created networks. Our data showed that GnRH (Gonadotropin-releasing hormone) signaling is associated with divergent growth at the onset of puberty and revealed two highly connected hubs, BTC and DGKH, within the network. Both genes are known to directly interact with the GnRH signaling pathway. Furthermore, a gene interaction network for NCAPG containing 14 densely connected genes revealed novel information concerning the functional role of NCAPG in divergent growth.

CONCLUSIONS

Merging both concepts, systems biology and metabolomic analyses, successfully yielded new insights into gene networks and interacting partners affecting growth at the onset of puberty in cattle. Genetic modulation in GnRH signaling was identified as key modifier of differential cattle growth at the onset of puberty. In addition, the benefit of our innovative concept without prior functional hypothesis was demonstrated by data suggesting that NCAPG might contribute to vascular smooth muscle contraction by indirect effects on the NO pathway via modulation of arginine metabolism. Our study shows for the first time in cattle that integration of genetic, physiological and metabolomics data in a systems biology approach will enable (or contribute to) an improved understanding of metabolic and gene networks and genotype-phenotype relationships.

Metabolic programming of puberty: sexually dimorphic responses to early nutritional challenges

Body energy stores and metabolic cues influence the onset of puberty. However, the pubertal impact of early nutritional challenges has been only fragmentarily addressed. We evaluated here the consequences, in terms of pubertal timing and hormonal markers, of various nutritional manipulations during pre- or postnatal maturation in rats of both sexes. Males and females were submitted to gestational undernutrition (UNG) or peripubertal (SUB) subnutrition or were raised in large (LL; underfeeding) or small (SL; overfeeding) litters. In addition, groups of UNG, LL, and SL rats were fed on a high-fat diet (HFD) after weaning. Postnatal overfeeding resulted in higher body weights (BWs) during pubertal transition in both sexes, but only SL males displayed overtly advanced external signs of puberty. Postnatal underfeeding persistently decreased BW gain during puberty, yet the magnitude of pubertal delay was greater in LL males. In contrast, regardless of postnatal nutrition, HFD tended to advance the onset of puberty in females but did not alter pubertal timing in males. Likewise, SUB females displayed a marked delay in BW gain and puberty onset, whereas despite similar reduction in BW, SUB males showed normal timing of puberty. These sex divergences were also detected in various hormonal and metabolic indices so that postnatal overnutrition consistently increased LH, FSH, leptin, and insulin levels only in pubertal females, whereas HFD decreased gonadotropin levels in SL females but increased them in SL males. Notably, UNG rats did not show signs of delayed puberty but displayed a striking sex dimorphism in serum insulin/glucose levels, regardless of the diet, so that only UNG males had signs of presumable insulin resistance. Our data disclose important sex differences in the impact of various early nutritional challenges on the timing of puberty, which may help to explain the different trends of altered puberty and related comorbidities between sexes.

The kisspeptin system genes in teleost fish, their structure and regulation, with particular attention to the situation in Pleuronectiformes

It is well established that Kisspeptin regulates the onset of puberty in vertebrates through stimulation of the secretion of gonadotropin-releasing hormones. However, the function of kisspeptin in peripheral tissues and in other functions is still poorly understood. Recently, the evolution and distribution of kisspeptin genes in vertebrates has been clarified. In contrast to placental mammals, which have a single gene for the ligand (Kiss) and for the receptor (Kissr), fish may have up to three Kiss genes and up to four Kissr genes because of genome duplications. However, information on the genomic structure of the piscine kiss and kissr genes is still scarce. Furthermore, when data from several species is taken together, interspecific differences in the expression of kiss and kissr during the reproductive cycle are found. Here, we discuss data gathered from several fish species, but mainly from two flatfishes, the Senegalese sole and the Atlantic halibut, to address general questions on kiss gene structure, regulation and function. Flatfish are among the most derived fish species and the two species referred to above have only one ligand and one receptor, probably because of the genome reduction observed in Pleuronectiformes. However, gene analysis shows that both species have an alternative splicing mechanism based on intron retention, but the functions of the alternative isoforms are unclear. In the Senegalese sole, sex-related differences in the temporal and spatial expression of kiss and kissr were observed during a whole reproductive cycle. In addition, recent studies suggested that kisspeptin system gene expression is correlated to energy balance and reproduction. This suggests that kisspeptin signaling may involve different sources of information to synchronize important biological functions in vertebrates, including reproduction. We propose a set of criteria to facilitate the comparison of kiss and kissr gene expression data across species.

A system biology approach to identify regulatory pathways underlying the neuroendocrine control of female puberty in rats and nonhuman primates

This article is part of a Special Issue "Puberty and Adolescence". Puberty is a major developmental milestone controlled by the interaction of genetic factors and environmental cues of mostly metabolic and circadian nature. An increased pulsatile release of the decapeptide gonadotropin releasing hormone (GnRH) from hypothalamic neurosecretory neurons is required for both the initiation and progression of the pubertal process. This increase is brought about by coordinated changes that occur in neuronal and glial networks associated with GnRH neurons. These changes ultimately result in increased neuronal and glial stimulatory inputs to the GnRH neuronal network and a reduction of transsynaptic inhibitory influences. While some of the major players controlling pubertal GnRH secretion have been identified using gene-centric approaches, much less is known about the system-wide control of the overall process. Because the pubertal activation of GnRH release involves a diversity of cellular phenotypes, and a myriad of intracellular and cell-to-cell signaling molecules, it appears that the overall process is controlled by a highly coordinated and interactive regulatory system involving hundreds, if not thousands, of gene products. In this article we will discuss emerging evidence suggesting that these genes are arranged as functionally connected networks organized, both internally and across sub-networks, in a hierarchical fashion. According to this concept, the core of these networks is composed of transcriptional regulators that, by directing expression of downstream subordinate genes, provide both stability and coordination to the cellular networks involved in initiating the pubertal process. The integrative response of these gene networks to external inputs is postulated to be coordinated by epigenetic mechanisms.

Disruption of reproductive aging in female and male rats by gestational exposure to estrogenic endocrine disruptors

Polychlorinated biphenyls (PCBs) are industrial contaminants and known endocrine-disrupting chemicals. Previous work has shown that gestational exposure to PCBs cause changes in reproductive neuroendocrine processes. Here we extended work farther down the life spectrum and tested the hypothesis that early life exposure to Aroclor 1221 (A1221), a mixture of primarily estrogenic PCBs, results in sexually dimorphic aging-associated alterations to reproductive parameters in rats, and gene expression changes in hypothalamic nuclei that regulate reproductive function. Pregnant Sprague Dawley rats were injected on gestational days 16 and 18 with vehicle (dimethylsulfoxide), A1221 (1 mg/kg), or estradiol benzoate (50 μg/kg). Developmental parameters, estrous cyclicity (females), and timing of reproductive senescence were monitored in the offspring through 9 months of age. Expression of 48 genes was measured in 3 hypothalamic nuclei: the anteroventral periventricular nucleus (AVPV), arcuate nucleus (ARC), and median eminence (females only) by real-time RT-PCR. Serum LH, testosterone, and estradiol were assayed in the same animals. In males, A1221 had no effects; however, prenatal estradiol benzoate increased serum estradiol, gene expression in the AVPV (1 gene), and ARC (2 genes) compared with controls. In females, estrous cycles were longer in the A1221-exposed females throughout the life cycle. Gene expression was not affected in the AVPV, but significant changes were caused by A1221 in the ARC and median eminence as a function of cycling status. Bionetwork analysis demonstrated fundamental differences in physiology and gene expression between cycling and acyclic females independent of treatment. Thus, gestational exposure to biologically relevant levels of estrogenic endocrine-disrupting chemicals has sexually dimorphic effects, with an altered transition to reproductive aging in female rats but relatively little effect in males.

Precocious puberty in girls

Precocious puberty in girls can be due to number of factors of which idiopathic central precocious puberty is the most common etiology. Here, we describe 3 cases of precocious puberty where the first case had premature thelarche in the background history of mother with Type 2 Diabetes Mellitus, cases 2 and 3 had ovarian tumours with heterogeneity in presentation.

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.

Investigation of peripubertal expression of Lin28a and Lin28b in C57BL/6 female mice

Genome-wide association studies recently identified 32 loci that associate with the age at menarche (AAM) in humans. Because the locus most robustly associated with AAM is in/near LIN28B, the goal of this study was to investigate how the Lin28 pathway might modulate pubertal timing by examining expression of Lin28b, and its homologue, Lin28a, across the pubertal transition in female mice. Quantitative reverse-transcriptase PCR data indicate that, prior to the onset of puberty, expression of both Lin28b and Lin28a decreases in the ovary, while expression of only Lin28a decreases in the hypothalamus; the expression of Lin28a increases after the onset of puberty in the pituitary. Immunohistochemistry in ovarian tissue verified that Lin28a protein levels decreased in parallel with gene expression. Although these data do not demonstrate cause and effect, they do suggest that decreased expression of Lin28a/Lin28b may facilitate the transition into puberty, consistent with previous data showing that overexpression of Lin28a in transgenic mice leads to delayed puberty. In addition, although Lin28b and/or Lin28a expression significantly decreased prior to puberty, neither Let-7a nor Let-7g miRNA levels changed significantly, raising the possibility that some effects of Lin28b and Lin28a within the hypothalamic-pituitary-gonadal (HPG) axis may be Let-7 miRNA independent. Subsequent studies, such as tissue and age specific modulation of Lin28b and Lin28a expression, could determine whether the expression patterns observed are responsible for modulating the onset of puberty and delineate further the role of this pathway in the HPG axis.

Male pubertal development: are endocrine-disrupting compounds shifting the norms?

Endocrine-disrupting compounds (EDCs) are synthetic or natural compounds that interfere with endogenous endocrine action. The frequent use of chemicals with endocrine active properties in household products and contamination of soil, water, and food sources by persistent chemical pollutants result in ubiquitous exposures. Wildlife observations and animal toxicological studies reveal adverse effects of EDCs on reproductive health. In humans, a growing number of epidemiological studies report an association with altered pubertal timing and progression. While these data are primarily reported in females, this review will focus on the small number of studies performed in males that report an association of polychlorinated biphenyls with earlier sexual maturity rating and confirm subtle effects of lead, dioxins, and endosulfan on delaying pubertal onset and progression in boys. Recent studies have also demonstrated that EDC exposure may affect pubertal testosterone production without having a noticeable effect on sexual maturity rating. A limitation to understand the effects of EDCs in humans is the potential for confounding due to the long temporal lag from early-life exposures to adult outcomes. The complex interplay of multiple environmental exposures over time also complicates the interpretation of human studies. These studies have identified critical windows of vulnerability during development when exposures to EDCs alter critical pathways and affect postnatal reproductive health. Contemporaneous exposures can also disrupt the hypothalamic-pituitary-gonadal axis. This paper will review the normal process of puberty in males and summarize human data that suggest potential perturbations in pubertal onset and tempo with early-life exposures to EDCs.

Development and Aging of the Kisspeptin-GPR54 System in the Mammalian Brain: What are the Impacts on Female Reproductive Function?

The prominent role of the G protein coupled receptor GPR54 and its peptide ligand kisspeptin in the progression of puberty has been extensively documented in many mammalian species including humans. Kisspeptins are very potent gonadotropin-releasing hormone secretagogues produced by two main populations of neurons located in two ventral forebrain regions, the preoptic area and the arcuate nucleus. Within the last 2 years a substantial amount of data has accumulated concerning the development of these neuronal populations and their timely regulation by central and peripheral factors during fetal, neonatal, and peripubertal stages of development. This review focuses on the development of the kisspeptin-GPR54 system in the brain of female mice, rats, sheep, monkeys, and humans. We will also discuss the notion that this system represents a major target through which signals from the environment early in life can reprogram reproductive function.

Molecular profiling of postnatal development of the hypothalamus in female and male rats

Reproductive function is highly dynamic during postnatal developmental. Here, we performed molecular profiling of gene expression patterns in the hypothalamus of developing male and female rats to identify which genes are sexually dimorphic, to gain insight into a more complex network of hypothalamic genes, and to ascertain dynamic changes in their relationships with one another and with sex steroid hormones during development. Using a low-density PCR platform, we quantified mRNA levels in the preoptic area (POA) and medial basal hypothalamus (MBH), and assayed circulating estradiol, testosterone, and progesterone at six ages from birth through adulthood. Numerous genes underwent developmental change, particularly postnatal increases, decreases, or peaks/plateaus at puberty. Surprisingly, there were few sex differences; only Esr1, Kiss1, and Tac2 were dimorphic (higher in females). Cluster analysis of gene expression revealed sexually dimorphic correlations in the POA but not the MBH from P30 (Postnatal Day 30) to P60. Hormone measurements showed few sex differences in developmental profiles of estradiol; higher levels of progesterone in females only after P30; and a developmental pattern of testosterone with a nadir at P30 followed by a dramatic increase through P60 (males). Furthermore, bionetwork analysis revealed that hypothalamic gene expression profiles and their relationships to hormones undergo dynamic developmental changes that differ considerably from adults. These data underscore the importance of developmental stage in considering the effects of hormones on the regulation of neuroendocrine genes in the hypothalamus. Moreover, the finding that few neuroendocrine genes are sexually dimorphic highlights the need to consider postnatal development from a network approach that allows assessment of interactions and patterns of expression.

Deciphering puberty: novel partners, novel mechanisms

Puberty is a fascinating developmental phase that involves the attainment of reproductive capacity and the completion of sexual and somatic maturation. As a life-changing event, puberty onset is precisely controlled by interconnected regulatory pathways that are sensitive to numerous endogenous signals and environmental cues. The mechanisms of normal puberty and its potential deviations have been thoroughly studied in humans and model species. Yet, characterization of the neurobiological basis of puberty is still incomplete. Progress on this front is not only relevant from a physiological perspective but would also help to unravel the underlying causes for the observed changes in the timing of puberty in humans, with a trend for earlier puberty onset, especially in girls. In this review, we will provide a synoptic overview of some recent developments in the field that have deepened our understanding of the neuroendocrine and molecular basis for the control of puberty onset. These include not only the demonstration of the involvement of the hypothalamic Kiss1 system in the control of puberty and its modulation by metabolic cues but also the identification of the roles of other neuropeptide pathways and molecular mediators in the regulation of puberty. In addition, the potential contribution of novel regulatory mechanisms, such as epigenetics, in the central control of puberty will be briefly discussed. Characterization of these novel players and regulatory mechanisms will improve our understanding of the basis of normal puberty and its eventual alterations in various pathological conditions.

Perinatal exposure to low doses of tributyltin chloride advances puberty and affects patterns of estrous cyclicity in female mice

Tributyltin (TBT), a proven endocrine-disrupting chemical, is well known to induce imposex in female gastropods. Herein we demonstrate the effects of low doses of tributyltin chloride (TBTCl) on the female offspring of KM mice. Pregnant mice were administered by gavage with 0, 1, 10, or 100 μg TBTCl/kg body weight/day from day 6 of pregnancy through the period of lactation. TBTCl dramatically advanced the age of onset of vaginal opening (VO) and first vaginal estrus, and reduced body weights at VO and first estrus. Furthermore, perinatal treatment with TBTCl significantly reduced the number of days between VO and first estrus. In addition, female offspring from dams exposed to 10 and 100 μg kg(-1) TBTCl exhibited altered patterns of estrous cyclicity in adulthood. In conclusion, perinatal exposure to low doses TBTCl result in early puberty and impaired estrous cyclicity in female mice, which suggest that TBTCl might act as an estrogen agonist or/and a disruptor on hypothalamic-pituitary function in the present study.

The coordinated expression, interaction and evolution of the neuroendocrine genes

The neuroendocrine system is a complex biological system controlled by various neuropeptides and hormones. The evolution and network properties of neuroendocrine genes are analyzed along with their expression profiles. The neuroendocrine genes show very similar expression profiles and local network properties across a wide range of tissues consistent with the physiological roles of their proteins. Moreover, the coordinated evolution of 10 neuroendocrine genes involved in mammalian reproduction and homeostasis is demonstrated using several methods, such as correlated evolution, relative-rate test, relative-ratio test and codon usage bias. The neuroendocrine genes seem to evolve predominantly under similar selective strengths and regimes of purifying selection, which is well reflected in their evolutionary fingerprints. This result demonstrates for the first time a key role of natural selection in creating and maintaining a well-designed neuroendocrine system at the genomic level. It also indicates that component properties of a complex system at a higher physiological scale may determine component properties at a lower genomic scale and/or vice versa.

Gene network analyses of first service conception in Brangus heifers: use of genome and trait associations, hypothalamic-transcriptome information, and transcription factors

Measures of heifer fertility are economically relevant traits for beef production systems and knowledge of candidate genes could be incorporated into future genomic selection strategies. Ten traits related to growth and fertility were measured in 890 Brangus heifers (3/8 Brahman × 5/8 Angus, from 67 sires). These traits were: BW and hip height adjusted to 205 and 365 d of age, postweaning ADG, yearling assessment of carcass traits (i.e., back fat thickness, intramuscular fat, and LM area), as well as heifer pregnancy and first service conception (FSC). These fertility traits were collected from controlled breeding seasons initiated with estrous synchronization and AI targeting heifers to calve by 24 mo of age. The BovineSNP50 BeadChip was used to ascertain 53,692 SNP genotypes for ∼802 heifers. Associations of genotypes and phenotypes were performed and SNP effects were estimated for each trait. Minimally associated SNP (P < 0.05) and their effects across the 10 traits formed the basis for an association weight matrix and its derived gene network related to FSC (57.3% success and heritability = 0.06 ± 0.05). These analyses yielded 1,555 important SNP, which inferred genes linked by 113,873 correlations within a network. Specifically, 1,386 SNP were nodes and the 5,132 strongest correlations (|r| ≥ 0.90) were edges. The network was filtered with genes queried from a transcriptome resource created from deep sequencing of RNA (i.e., RNA-Seq) from the hypothalamus of a prepubertal and a postpubertal Brangus heifer. The remaining hypothalamic-influenced network contained 978 genes connected by 2,560 edges or predicted gene interactions. This hypothalamic gene network was enriched with genes involved in axon guidance, which is a pathway known to influence pulsatile release of LHRH. There were 5 transcription factors with 21 or more connections: ZMAT3, STAT6, RFX4, PLAGL1, and NR6A1 for FSC. The SNP that identified these genes were intragenic and were on chromosomes 1, 5, 9, and 11. Chromosome 5 harbored both STAT6 and RFX4. The large number of interactions and genes observed with network analyses of multiple sources of genomic data (i.e., GWAS and RNA-Seq) support the concept of FSC being a polygenic trait.

Mechanisms affecting neuroendocrine and epigenetic regulation of body weight and onset of puberty: potential implications in the child born small for gestational age (SGA)

Signaling peptides produced in peripheral tissues such as gut, adipose tissue, and pancreas communicate with brain centers, such as hypothalamus and hindbrain to manage energy homeostasis. These regulatory mechanisms of energy intake and storage have evolved during long periods of hunger in the evolution of man to protect the species from extinction. It is now clear that these circuitries are influenced by prenatal and postnatal environmental factors including endocrine disruptive chemicals. Hypothalamic appetite regulatory systems develop and mature in utero and early infancy, and involve signaling pathways that are important also for the regulation of puberty onset. Recent studies in humans and animals have shown that metabolic pathways involved in regulation of growth, body weight gain and sexual maturation are largely affected by epigenetic programming that can impact both current and future generations. In particular, intrauterine and early infantile developmental phases of high plasticity are susceptible to factors that affect metabolic programming that therefore, affect metabolic function throughout life. In children born small for gestational age, poor nutritional conditions during gestation can modify metabolic systems to adapt to expectations of chronic undernutrition. These children are potentially poorly equipped to cope with energy-dense diets and are possibly programmed to store as much energy as possible, leading to later obesity, metabolic syndrome, disturbed regulation of normal puberty and early onset of cardiovascular disease. Most cases of disturbed energy balance are likely a result of a combination of genetics, epigenetics and environment. This review will discuss potential mechanisms linking intrauterine growth retardation with changes in growth, energy homeostasis and sexual maturation.

Gonadotrophin secretion pattern in anorchid boys from birth to pubertal age: pathophysiological aspects and diagnostic usefulness

CONTEXT

The biphasic ontogeny of serum gonadotrophins observed in normal children also exists in girls with gonadal dysgenesis, although with higher levels. However, limited data exist in prepubertal boys with anorchia.

OBJECTIVE

To investigate whether the existence of testicular tissue is required for gonadotrophin downregulation in boys. Secondarily, we analysed the prevalence of high gonadotrophins and its diagnostic value to assess the presence or absence of testes in childhood.

STUDY DESIGN

In a retrospective, semi-longitudinal study, we compared serum gonadotrophin levels in 35 boys with anorchia aged 0-18 years, in 29 bilaterally cryptorchid boys with abdominal testes and in 236 normal boys.

RESULTS

In anorchid boys, follicle stimulating hormone (FSH) and luteinizing hormone (LH) were abnormally high in the first months after birth, then decreased progressively. LH decreased more readily than FSH and dropped to normal values in up to 70% of anorchid patients before the usual age of pubertal onset, when both gonadotrophins increased again to very high levels. In cryptorchid boys, FSH was elevated in a significantly (P < 0·0001) lower proportion of cases. Below the age of 6 years, FSH below 2 IU/l ruled out anorchia and LH above 5 IU/l confirmed anorchia with high accuracy. Between 6 and 11 years, FSH or LH levels above 5 IU/l were highly specific for the absence of testes.

CONCLUSIONS

The U-shaped pattern of serum gonadotrophins observed in normal males from birth to puberty was also found in anorchid boys, but with gonadotrophin levels considerably elevated. Serum gonadotrophin levels may normalize in anorchid boys during late childhood only to rise again at puberty. The presence of testicular tissue results in restrain of gonadotrophin secretion in most patients, even if the testes are cryptorchid.

Transcription of the human EAP1 gene is regulated by upstream components of a puberty-controlling Tumor Suppressor Gene network

Mammalian puberty is initiated by an increased pulsatile release of gonadotropin-releasing hormone (GnRH) from specialized neurons located in the hypothalamus. GnRH secretion is controlled by neuronal and glial networks, whose activity appears to be coordinated via transcriptional regulation. One of the transcription factors involved in this process is thought to be the recently described gene Enhanced at Puberty 1 (EAP1), which encodes a protein with dual transcriptional activity. In this study we used gene reporter and chromatin immunoprecipitation (ChIP) assays to examine the hypothesis that EAP1 expression is controlled by transcriptional regulators earlier postulated to serve as central nodes of a gene network involved in the neuroendocrine control of puberty. These regulators include Thyroid Transcription Factor 1 (TTF1), Yin Yang 1 (YY1), and CUX1, in addition to EAP1 itself. While TTF1 has been shown to facilitate the advent of puberty, YY1 (a zinc finger protein component of the Polycomb silencing complex) may play a repressive role. The precise role of CUX1 in this context is not known, but like EAP1, CUX1 can either activate or repress gene transcription. We observed that DNA segments of two different lengths (998 and 2744bp) derived from the 5'-flanking region of the human EAP1 gene display similar transcriptional activity. TTF1 stimulates transcription from both DNA segments with equal potency, whereas YY1, CUX1, and EAP1 itself, behave as transcriptional repressors. All four proteins are recruited in vivo to the EAP1 5'-flanking region. These observations suggest that EAP1 gene expression is under dual transcriptional regulation imposed by a trans-activator (TTF1) and two repressors (YY1 and CUX1) previously postulated to be upstream components of a puberty-controlling gene network. In addition, EAP1 itself appears to control its own expression via a negative auto-feedback loop mechanism. Further studies are needed to determine if the occupancy of the EAP1 promoter by these regulatory factors changes at the time of puberty.

The Buzz about anabolic androgenic steroids: electrophysiological effects in excitable tissues

Anabolic androgenic steroids (AAS) comprise a large and growing class of synthetic androgens used clinically to promote tissue-building in individuals suffering from genetic disorders, injuries, and diseases. Despite these beneficial therapeutic applications, the predominant use of AAS is illicit: these steroids are self-administered to promote athletic performance and body image. Hand in hand with the desired anabolic actions of the AAS are untoward effects on the brain and behavior. While the signaling routes by which the AAS impose both beneficial and harmful actions may be quite diverse, key endpoints are likely to include ligand-gated and voltage-dependent ion channels that govern the activity of electrically excitable tissues. Here, we review the known effects of AAS on molecular targets that play critical roles in controlling electrical activity, with a specific focus on the effects of AAS on neurotransmission mediated by GABA(A) receptors in the central nervous system.

Endocrine modulation of the adolescent brain: a review

Neurophysiological and behavioral development is particularly complex in adolescence. Youngsters experience strong emotions and impulsivity, reduced self-control, and preference for actions which offer immediate rewards, among other behavioral patterns. Given the growing interest in endocrine effects on adolescent central nervous system development and their implications on later stages of life, this article reviews the effects of gonadal steroid hormones on the adolescent brain. These effects are classified as organizational, the capacity of steroids to determine nervous system structure during development, and activational, the ability of steroids to modify nervous activity to promote certain behaviors. During transition from puberty to adolescence, steroid hormones trigger various organizational phenomena related to structural brain circuit remodelling, determining adult behavioral response to steroids or sensory stimuli. These changes account for most male-female sexual dimorphism. In this stage sex steroids are involved in the main functional mechanisms responsible for organizational changes, namely myelination, neural pruning, apoptosis, and dendritic spine remodelling, activated only during embryonic development and during the transition from puberty to adolescence. This stage becomes a critical organizational window when the appropriately and timely exerted functions of steroid hormones and their interaction with some neurotransmitters on adolescent brain development are fundamental. Thus, understanding the phenomena linking steroid hormones and adolescent brain organization is crucial in the study of teenage behavior and in later assessment and treatment of anxiety, mood disorders, and depression. Adolescent behavior clearly evidences a stage of brain development influenced for the most part by steroid hormones.

Physiology and Endocrinology Symposium: How single nucleotide polymorphism chips will advance our knowledge of factors controlling puberty and aid in selecting replacement beef females

The promise of genomic selection is accurate prediction of the genetic potential of animals from their genotypes. Simple DNA tests might replace low-accuracy predictions for expensive or lowly heritable measures of puberty and fertility based on performance and pedigree. Knowing with some certainty which DNA variants (e.g., SNP) affect puberty and fertility is the best way to fulfill the promise. Several SNP from the BovineSNP50 assay have tentatively been associated with reproductive traits including age at puberty, antral follicle count, and pregnancy observed on different sets of heifers. However, sample sizes are too small and SNP density is too sparse to definitively determine genomic regions harboring causal variants affecting reproductive success. Additionally, associations between individual SNP and similar phenotypes are inconsistent across data sets, and genomic predictions do not appear to be globally applicable to cattle of different breeds. Discrepancies may be a result of different QTL segregating in the sampled populations, differences in linkage disequilibrium (LD) patterns such that the same SNP are not correlated with the same QTL, and spurious correlations with phenotype. Several approaches can be used independently or in combination to improve detection of genomic factors affecting heifer puberty and fertility. Larger samples and denser SNP will increase power to detect real associations with SNP having more consistent LD with underlying QTL. Meta-analysis combining results from different studies can also be used to effectively increase sample size. High-density genotyping with heifers pooled by pregnancy status or early and late puberty can be a cost-effective means to sample large numbers. Networks of genes, implicated by associations with multiple traits correlated with puberty and fertility, could provide insight into the complex nature of these traits, especially if corroborated by functional annotation, established gene interaction pathways, and transcript expression. Example analyses are provided to demonstrate how integrating information about gene function and regulation with statistical associations from whole-genome SNP genotyping assays might enhance knowledge of genomic mechanisms affecting puberty and fertility, enabling reliable DNA tests to guide heifer selection decisions.

Hypothalamic glial-to-neuronal signaling during puberty: influence of alcohol

Mammalian puberty requires complex interactions between glial and neuronal regulatory systems within the hypothalamus that results in the timely increase in the secretion of luteinizing hormone releasing hormone (LHRH). Assessing the molecules required for the development of coordinated communication networks between glia and LHRH neuron terminals in the basal hypothalamus, as well as identifying substances capable of affecting cell-cell communication are important. One such pathway involves growth factors of the epidermal growth factor (EGF) family that bind to specific erbB receptors. Activation of this receptor results in the release of prostaglandin-E₂ (PGE₂) from adjacent glial cells, which then acts on the nearby LHRH nerve terminals to elicit release of the peptide. Another pathway involves novel genes which synthesize adhesion/signaling proteins responsible for the structural integrity of bi-directional glial-neuronal communication. In this review, we will discuss the influence of these glial-neuronal communication pathways on the prepubertal LHRH secretory system, and furthermore, discuss the actions and interactions of alcohol on these two signaling processes.

A single nucleotide polymorphism-derived regulatory gene network underlying puberty in 2 tropical breeds of beef cattle

Harsh tropical environments impose serious challenges on poorly adapted species. In beef cattle, tropical adaptation in the form of temperature and disease resistance, coupled with acclimatization to seasonal and limited forage, comes at a cost to production efficiency. Prominent among these costs is delayed onset of puberty, a challenging phenotype to manipulate through traditional breeding mechanisms. Recently, system biology approaches, including gene networks, have been applied to the genetic dissection of complex phenotypes. We aimed at developing and studying gene networks underlying cattle puberty. Our starting material comprises the association results of ~50,000 SNP on 22 traits, including age at puberty, and 2 cattle breed populations: Brahman (n = 843) and Tropical Composite (n = 866). We defined age at puberty as the age at first corpus luteum (AGECL). By capturing the genes harboring mutations minimally associated (P < 0.05) to AGECL or to a set of traits related with AGECL, we derived a gene network for each breed separately and a third network for the combined data set. At the intersection of the 3 networks, we identified candidate genes and pathways that were common to both breeds. Resulting from these analyses, we identified an enrichment of genes involved in axon guidance, cell adhesion, ErbB signaling, and glutamate activity, pathways that are known to affect pulsatile release of GnRH, which is necessary for the onset of puberty. Furthermore, we employed network connectivity and centrality parameters along with a regulatory impact factor metric to identify the key transcription factors (TF) responsible for the molecular regulation of puberty. As a novel finding, we report 5 TF (HIVEP3, TOX, EYA1, NCOA2, and ZFHX4) located in the network intersecting both breeds and interacting with other TF, forming a regulatory network that harmonizes with the recent literature of puberty. Finally, we support our network predictions with evidence derived from gene expression in hypothalamic tissue of adult cows.

Fibroblast growth factor signaling in the developing neuroendocrine hypothalamus

Fibroblast growth factor (FGF) signaling is pivotal to the formation of numerous central regions. Increasing evidence suggests FGF signaling also directs the development of the neuroendocrine hypothalamus, a collection of neuroendocrine neurons originating primarily within the nose and the ventricular zone of the diencephalon. This review outlines evidence for a role of FGF signaling in the prenatal and postnatal development of several hypothalamic neuroendocrine systems. The emphasis is placed on the nasally derived gonadotropin-releasing hormone neurons, which depend on neurotrophic cues from FGF signaling throughout the neurons' lifetime. Although less is known about neuroendocrine neurons derived from the diencephalon, recent studies suggest they also exhibit variable levels of dependence on FGF signaling. Overall, FGF signaling provides a broad spectrum of cues that ranges from genesis, cell survival/death, migration, morphological changes, to hormone synthesis in the neuroendocrine hypothalamus. Abnormal FGF signaling will deleteriously impact multiple hypothalamic neuroendocrine systems, resulting in the disruption of diverse physiological functions.

The transcriptional control of female puberty

The initiation of mammalian puberty requires a sustained increase in pulsatile release of gonadotrophin releasing hormone (GnRH) from the hypothalamus. This increase is brought about by coordinated changes in transsynaptic and glial-neuronal communication, consisting of an increase in neuronal and glial stimulatory inputs to the GnRH neuronal network and the loss of transsynaptic inhibitory influences. GnRH secretion is stimulated by transsynaptic inputs provided by excitatory amino acids (glutamate) and at least one peptide (kisspeptin), and by glial inputs provided by growth factors and small bioactive molecules. The inhibitory input to GnRH neurons is mostly transsynaptic and provided by GABAergic and opiatergic neurons; however, GABA has also been shown to directly excite GnRH neurons. There are many genes involved in the control of these cellular networks, and hence in the control of the pubertal process as a whole. Our laboratory has proposed the concept that these genes are arranged in overlapping networks internally organized in a hierarchical fashion. According to this concept, the highest level of intra-network control is provided by transcriptional regulators that, by directing expression of key subordinate genes, impose genetic coordination to the neuronal and glial subsets involved in initiating the pubertal process. More recently, we have begun to explore the concept that a more dynamic and encompassing level of integrative coordination is provided by epigenetic mechanisms.

WDR11, a WD protein that interacts with transcription factor EMX1, is mutated in idiopathic hypogonadotropic hypogonadism and Kallmann syndrome

By defining the chromosomal breakpoint of a balanced t(10;12) translocation from a subject with Kallmann syndrome and scanning genes in its vicinity in unrelated hypogonadal subjects, we have identified WDR11 as a gene involved in human puberty. We found six patients with a total of five different heterozygous WDR11 missense mutations, including three alterations (A435T, R448Q, and H690Q) in WD domains important for β propeller formation and protein-protein interaction. In addition, we discovered that WDR11 interacts with EMX1, a homeodomain transcription factor involved in the development of olfactory neurons, and that missense alterations reduce or abolish this interaction. Our findings suggest that impaired pubertal development in these patients results from a deficiency of productive WDR11 protein interaction.

Neurokinin B signaling in puberty: human and animal studies

Recent reports of humans who have normosmic idiopathic hypogonadotropic hypogonadism due to TAC3 or TACR3 (encoding neurokinin B and its receptor, NK3R, respectively) mutations provided compelling evidence for the involvement of neurokinin B (NKB) signaling in puberty. This apparently stimulated the field to understand the exact mechanism through which NKB signaling exerts its effects. With the important findings from these recent studies a sketch of GnRH pulse generator has emerged in which NKB signaling appears to play a key role. In this communication, NKB involvement in puberty is reviewed from the perspective of the fundamental question of "what controls puberty?"