Effects of estradiol on kisspeptin neurons during puberty

Aspartame Intake Delayed Puberty Onset in Female Offspring Rats and Girls

SCOPE

The disturbance of the hypothalamic-pituitary-gonadal (HPG) axis, gut microbiota (GM) community, and short-chain fatty acids (SCFAs) is a triggering factor for pubertal onset. The study investigates the effects of the long-term intake of aspartame on puberty and GM in animals and humans.

METHODS AND RESULTS

Aspartame-fed female offspring rats result in vaginal opening time prolongation, serum estrogen reduction, and serum luteinizing hormone elevation. , 60 mg kg-1 aspartame treatment decreases the mRNA levels of gonadotropin-releasing hormone (GnRH), Kiss1, and G protein-coupled receptor 54 (GPR54), increases the mRNA level of RFamide-related peptide-3 (RFRP-3), and decreases the expression of GnRH neurons in the hypothalamus. Significant differences in relative bacterial abundance at the genus levels and decreased fecal SCFA levels are noted by 60 mg kg-1 aspartame treatment. Among which, Escherichia-Shigella is negatively correlated with several SCFAs. In girls, high-dose aspartame consumption decreases the risk of precocious puberty.

CONCLUSIONS

Aspartame reduces the chance of puberty occurring earlier than usual in female offspring and girls. Particularly, 60 mg kg-1 aspartame-fed female offspring delays pubertal onset through the dysregulation of HPG axis and GM composition by inhibiting the Kiss1/GPR54 system and inducing the RFRP-3. An acceptable dose of aspartame should be recommended during childhood.

Deciphering the Roles & Regulation of Estradiol Signaling during Female Mini-Puberty: Insights from Mouse Models

Mini-puberty of infancy is a short developmental phase occurring in humans and other mammals after birth. In females, it corresponds to transient and robust activation of the hypothalamo-pituitary-ovarian (HPO) axis revealed by high levels of gonadotropin hormones, follicular growth, and increased estradiol production by the ovary. The roles of estradiol signaling during this intriguing developmental phase are not yet well known, but accumulating data support the idea that it aids in the implementation of reproductive function. This review aims to provide in-depth information on HPO activity during this particular developmental phase in several mammal species, including humans, and to propose emerging hypotheses on the putative effect of estradiol signaling on the development and function of organs involved in female reproduction.

Growth variations with opposite clinical outcomes and the emerging role of IGF-1

Normal growth pattern variations [i.e., constitutional advancement and constitutional delay of growth and puberty (CAGP and CDGP)] are the mirror image of each other and are associated with early puberty (EP) and delayed puberty (DP), respectively. Differences between CAGP and CDGP relate not only to auxological characteristics (height, weight) but also to insulin-like growth factor-1 (IGF-1). IGF-1 levels in CAGP are above average whereas in CDGP they are below average, suggesting a role for IGF-1 in the induction of these growth patterns. Herein, we provide data suggesting that early activation of the growth hormone (GH)/IGF-1 axis induces the growth pattern of CAGP. Moreover, we suggest that IGF-1 is a decisive factor for the release of the gonadotropin-releasing hormone (GnRH) inhibition brake that occurs in prepuberty. It is therefore crucial for puberty onset.

Effects of Fuyou Formula on GnRH Secretion and Related Gene Expression in Treating Precocious Puberty

The Fuyou (Fy) formula is an in-hospital preparation consisting of traditional Chinese medicine (TCM) that has been used for treating precocious puberty (PP) for more than 20 years. In this study, we aimed to clarify the effect of the Fy formula and its major components on PP. To confirm the effect of the Fy formula on the release of hypothalamic gonadotropin-releasing hormone (GnRH), GT1-7 cells were treated with estrogen to build the model group and subsequently treated with the Fy formula and its major components to explore their effects on the secretion of GnRH. The level of GnRH in GT1-7 cells was determined using enzyme-linked immunosorbent assay. The results illustrated that, compared to the model group, the Fy formula inhibited the release of GnRH. In addition, the expression levels of proteins related to GnRH secretion, including GnRH, gonadotropin-releasing hormone receptor (GnRHR), Kiss-1 metastasis-suppressor (Kiss1), G-protein coupled receptor 54 (GPR54), estrogen receptor α (ERα), insulin-like growth factor-1 (IGF-1), and insulin-like growth factor-1 receptor (IGF-1R), were detected by real-time polymerase chain reaction (RT-qPCR). The results demonstrated that the Fy formula significantly reduced the level of GnRH secretion in the GT1-7 cell lines compared with the model group. Moreover, it significantly downregulated the expression of GnRH, GnRHR, Kiss1, GPR54, ERα, IGF-1, and IGF-1R. In summary, our results indicate that the Fy formula and its major components may inhibit the effects of estrogen, which alleviates PP through transcriptional regulation of target genes.

Interplay of KNDy and nNOS neurons: A new possible mechanism of GnRH secretion in the adult brain

Reproduction in mammals is favoured when there is sufficient energy available to permit the survival of offspring. Neuronal nitric oxide synthase expressing neurons produce nitric oxide in the proximity of the gonadotropin-releasing hormone neurons in the preoptic region. nNOS neurons are an integral part of the neuronal network controlling ovarian cyclicity and ovulation. Nitric oxide can directly regulate the activity of the GnRH neurons and play a vital role neuroendocrine axis. Kisspeptin neurons are essential for the GnRH pulse and surge generation. The anteroventral periventricular nucleus (AVPV), kisspeptin neurons are essential for GnRH surge generation. KNDy neurons are present in the hypothalamus's arcuate nucleus (ARC), co-express NKB and dynorphin, essential for GnRH pulse generation. Kisspeptin-neurokinin B-dynorphin (KNDy) neuroendocrine molecules of the hypothalamus are key components in the central control of GnRH secretion. The hypothalamic neurons kisspeptin, KNDy, nitric oxide synthase (NOS), and other mediators such as leptin, adiponectin, and ghrelin, play an active role in attaining puberty. Kisspeptin signalling is mediated by NOS, which further results in the secretion of GnRH. Neuronal nitric oxide is critical for attaining puberty, but its direct role in adult GnRH secretion is poorly understood. This review mainly focuses on the role of nNOS and its interplay with KNDy neurons in the hormonal regulation of reproduction.

The Traditional Chinese Medicine Fuyou Formula Alleviates Precocious Puberty by Inhibiting GPR54/GnRH in the Hypothalamus

The purpose of this study was to explore the effect of the traditional Chinese medicine Fuyou formula on precocious puberty (PP). The Fy formula may exert an effect in female rats with PP and GT-7 cells through the GPR54/GnRH signaling pathway. To confirm the effect of the Fy formula on PP through the GPR54/GnRH signaling pathway, we first treated GT1-7 cells with the Fy formula and observed changes in the expression of related genes and proteins and in GnRH secretion. Then, we randomly divided young female Sprague-Dawley rats into the control group, model group, leuprorelin group and the Fy formula group. A PP model was established by injection of danazol on postnatal day 5, and the Fy formula was administered on PND15. The time of vaginal opening, the wet weights of the ovary and uterus, serum hormone levels and the expression of hypothalamic-related genes were observed. We found that the Fy formula delayed vaginal opening, decreased the wet weights and coefficients of the ovary and uterus, decreased the levels of serum hormones (E2, follicle-stimulating hormone and luteinizing hormone) and the cellular GnRH level, and downregulated the gene expression of Kiss1, GPR54 and GnRH in the hypothalamus and the gene and protein expression of GPR54 and GnRH in GT1-7 cells. In conclusion, the Fy formula may alleviate PP via the GPR54/GnRH signaling pathway.

Age-dependent vulnerability of the ovary to AhR-mediated TCDD action before puberty: Evidence from mouse models

In female mammals, puberty and fertility are regulated by the synthesis of estradiol (E2) by the ovaries at the infantile stage and at the approach of puberty, a process which may be affected by endocrine disrupting chemicals (EDC)s acting through the Aryl hydrocarbon receptor (AhR). However, there is no information on AhR-mediated regulation of ovarian estrogenic activity during these developmental periods. Here, we assessed in mouse models, the intrinsic and exogenous ligand-induced AhR action on E2 synthesis at the infantile stage (14 days postnatal (dpn)) and at the approach of puberty (28 dpn). Intrinsic AhR pathway became activated in the ovary at the approach of puberty, as suggested by the decreased intra-ovarian expression in prototypical and steroidogenesis-related AhR targets and E2 contents in Ahr knockout (Ahr^-/-) mice versus Ahr^+/+ mice exclusively at 28 dpn. Accordingly, AhR nuclear localization in granulosa cells, reflecting its activity in cells responsible for E2 synthesis, was much lower at 14 dpn than at 28 dpn in C57BL/6 mice. However, AhR signaling could be activated by exogenous ligands at both ages, as revealed by FICZ- and TCDD-induced Ahrr and Cyp1a1 expression in C57BL/6 mice. Nevertheless, TCDD impacted ovarian estrogenic activity only at 28 dpn. This age-related AhR action may be ligand-dependent, since FICZ had no effect on E2 synthesis at 28 dpn. In conclusion, AhR would not regulate ovarian estrogenic activity before the approach of puberty. Its activation by EDCs may be more detrimental to reproductive health at this stage than during infancy.

Role of Kisspeptin and NKB in Puberty in Nonhuman Primates: Sex Differences

To understand the roles of kisspeptin and neurokinin B (NKB) in puberty and sex differences in their involvement, we conducted a series of experiments measuring the release of gonadotropin-releasing hormone (GnRH) and kisspeptin in the median eminence of the hypothalamus in male and female monkeys throughout sexual development. Results indicate that kisspeptin-10 and the NKB agonist, senktide, stimulated GnRH release in males and females at the prepubertal and pubertal stages, but females are much more sensitive to kisspeptin signaling than males. Moreover, throughout the progress of puberty, major remodeling of kisspeptin and NKB signaling pathways for the regulation of GnRH release takes place. In females during puberty, reciprocal pathways (i.e., kisspeptin signaling mediated through NKB neurons and NKB signaling mediated through kisspeptin neurons) are established, to provide powerful and flexible mechanisms for GnRH neurosecretory activity necessary for complex female reproductive function in adulthood. By contrast, during puberty in males, reciprocal pathways are consolidated to a simpler kisspeptin-dominant signaling pathway. Nevertheless, in primates, both kisspeptin and NKB signaling are contributing factors for the pubertal increase in GnRH release, rather than initiating puberty.

Using 17β-estradiol heparin-poloxamer thermosensitive hydrogel to enhance the endometrial regeneration and functional recovery of intrauterine adhesions in a rat model

Mechanical damage or infection to the endometrium can lead to the formation of adhesions in the uterine cavity, which may result in reduced reproductive outcome and/or pregnancy complications. The prognosis of this disease is poor due to few effective treatments and the complex environment of endometrium. Heparin-Poloxamer Hydrogel (HP hydrogel) is a nontoxic and biodegradable biomaterial, which has been commonly used as a sustained-release delivery system. In this study, we applied a mini-endometrial curette to scrape the endometrium of rats to mimic the process of curettage in patients. After the establishment of IUA model in rats, we injected the thermo-sensitive hydrogel(E₂-HP hydrogel) into the injured uterine cavity and evaluated the therapeutic effect of E₂-HP hydrogel on the recovery of IUA. Our results showed that E₂-HP hydrogel can significantly facilitate the regeneration of injured endometrium along with inhibiting the cell apoptosis in IUA model. Furthermore, we revealed that E₂-HP hydrogel on the recovery of IUA was closely associated with the upregulation of kisspeptin through activating the ERK1/2 and MAPKs p38 pathways. In conclusion, E₂-HP hydrogel can effectively transfer E₂ into the injured endometrium and it can be considered as a promising therapeutic method for the women with intrauterine adhesions.

Adolescence as a Biocultural Life History Transition

While the categories of adolescence and puberty are often treated as one, the existence of two distinct terms points to different kinds of maturation in humans. Puberty refers to a period of coordinated somatic growth and reproductive maturation that shifts individuals from nonreproductive juvenility to reproductive maturity. Adolescence includes the behavioral and social assumption of adult roles. Life history theory offers powerful tools for understanding why puberty occurs later in humans than in other primates, including the benefits of delayed reproduction as part of a cooperation-intensive life history strategy. It also sheds light on the ways that pubertal timing responds to environmental variation. I review the mechanisms of maturation in humans and propose biocultural approaches to integrate life historical understandings of puberty with a broader definition of environment to encompass the concept of adolescence.

Neonatal and juvenile exposure to perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS): Advance puberty onset and kisspeptin system disturbance in female rats

Perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) are widespread and persistent chemicals in the environment, and limited data about their effects on puberty development are available. In order to explore the effects of neonatal and juvenile PFOA/PFOS exposure on puberty maturation, female rats were injected with PFOA or PFOS at 0.1, 1 and 10 mg/kg/day during postnatal day (PND) 1-5 or 26-30. The day of vaginal opening (VO) and first estrus were significantly advanced in 10 mg/kg PFOA, 1 and 10 mg/kg PFOS groups after neonatal and juvenile exposure. Besides, neonatal PFOA/PFOS exposure increased body weight and anogenital distance (AGD) in a non-dose-dependent manner. Estradiol and luteinizing hormone levels were also increased with more frequent occurrences of irregular estrous cycles in 0.1 and 1 mg/kg PFOA/PFOS exposure groups. Although no altered ovarian morphology was observed, follicles numbers were reduced in neonatal groups. Kiss1, Kiss1r and ERα mRNA expressions were downregulated after two periods' exposure in the hypothalamic anteroventral periventricular (AVPV) and arcuate (ARC) nuclei. PFOA/PFOS exposure also suppressed kisspeptin fiber intensities, especially at the high dose. In conclusion, neonatal and juvenile are critical exposure periods, during which puberty maturation may be vulnerable to environmental exposure of PFOA/PFOS, and kisspeptin system plays a key role during these processes.

Role of Kisspeptin and Neurokinin B Signaling in Male Rhesus Monkey Puberty

Despite the well-established concept that an increase in pulsatile GnRH release triggers puberty, the precise signaling mechanism responsible for the pubertal increase in GnRH release remains unclear. A recent study indicates that developmental changes in the network formation between kisspeptin and neurokinin B (NKB) signaling greatly contribute to the pubertal increase in GnRH release in female monkeys. It is, however, unknown whether similar developmental changes in the kisspeptin and NKB network are involved in male puberty. In the current study, we first characterized the pubertal stages in male rhesus monkeys by assessing physiological and hormonal changes during sexual development. Subsequently, we examined the role of the kisspeptin and NKB signaling network in the pubertal increase in GnRH release. Results suggest that while collaborative kisspeptin and NKB signaling to GnRH neurons was active before puberty onset, after initiation of puberty the role of NKB signaling in GnRH neurons diminished and kisspeptin signaling assumed the primary stimulatory role in the regulation of GnRH release in male monkeys. These findings in males differ from those seen in females.

Prepubertal exposure to an oestrogenic mycotoxin zearalenone induces central precocious puberty in immature female rats through the mechanism of premature activation of hypothalamic kisspeptin-GPR54 signaling

Sporadic epidemics and several researches in rodents indicated that zearalenone (ZEA) and its metabolites, the prevailing oestrogenic mycotoxins in foodstuffs, were a triggering factor for true precocious puberty development in girls. Nevertheless, the neuroendocrine mechanism through which ZEA mycoestrogens advance puberty onset is not fully understood. To elucidate this issue, hypothalamic kisspeptin-G-protein coupled receptor-54 (GPR54) signaling pathway that regulates the onset of puberty was focused on in the present study. Immature female SD rats were given a daily intragastric administration of corn oil (vehicle control), 50 μg/kg body weight (bw) of 17β-estradiol (E2, positive control), and 3 doses (0.2, 1 and 5 mg/kg bw) of ZEA for consecutive 5 days starting from postnatal day 15, respectively. Puberty onset was evaluated by detecting the physiological and hormonal responses, and hypothalamic kisspeptin-GPR54 pathway was determined to reveal the neuroendocrine mechanism. As the markers of puberty onset, vaginal opening was significantly accelerated and uterine weight was increased in both E2 and 5 mg/kg ZEA groups. Serum levels of follicle stimulating hormone, luteinizing hormone and estradiol were also markedly elevated by E2 and 5 mg/kg ZEA, which is compatible with the changes in peripheral reproductive organs. The mRNA and protein expressions of hypothalamic gonadotropin-releasing hormone (GnRH) were both obviously elevated by E2 and 5 mg/kg ZEA. GnRH expression changes occurred in parallel with increased expressions of hypothalamic Kiss1 and its receptor GPR54 at both mRNA and protein levels. Most of these changes were also noted in 1 mg/kg ZEA group, but none in 0.2 mg/kg group. Therefore, within the context of this study, the No Observed Adverse Effect Level (NOAEL) for ZEA in terms of oestrogenic activity and puberty-promoting effect in immature female rats was considered to be 0.2 mg/kg bw per day, and the Lowest Observed Adverse Effect Level (LOAEL) was 1 mg/kg bw per day. In conclusion, prepubertal exposure to dietary relevant levels of ZEA induced central precocious puberty in female rats by premature activation of hypothalamic kisspeptin-GPR54-GnRH signaling pathway, followed by the stimulation of gonadotropins release at an earlier age, resulting in the advancement of vaginal opening and enlargement of uterus at periphery.

Actions of sex steroids on kisspeptin expression and other reproduction-related genes in the brain of the teleost fish European sea bass

Kisspeptins are well known as mediators of the coordinated communication between the brain-pituitary axis and the gonads in many vertebrates. To test the hypothesis that gonadal steroids regulate kiss1 and kiss2 mRNA expression in European sea bass (a teleost fish), we examined the brains of gonad-intact (control) and castrated animals, as well as castrated males (GDX) and ovariectomized females (OVX) that received testosterone (T) and estradiol (E₂) replacement, respectively, during recrudescence. In GDX males, low expression of kiss1 mRNA is observed by in situ hybridization in the caudal hypothalamus (CH) and the mediobasal hypothalamus (MBH), although hypothalamic changes in kiss1 mRNA levels were not statistically different among the groups, as revealed by real-time PCR. However, T strongly decreased kiss2 expression levels in the hypothalamus, which was documented in the MBH and the nucleus of the lateral recess (NRLd) in GDX T-treated sea bass males. Conversely, it appears that E₂ evokes low kiss1 mRNA in the CH, while there were cells expressing kiss2 in the MBH and NRLd in these OVX females. These results demonstrate that kisspeptin neurons are presumably sensitive to the feedback actions of sex steroids in the sea bass, suggesting that the MBH represents a major site for sex steroid actions on kisspeptins in this species. Also, recent data provide evidence that both positive and negative actions occur in key factors involved in sea bass reproductive function, including changes in the expression of gnrh-1/gonadotropin, cyp19b, er and ar genes and sex steroid and gonadotropin plasma levels in this teleost fish.

Oestrogenic action of neonatal tamoxifen on the hypothalamus and reproductive system in female mice

Tamoxifen, a selective oestrogen receptor modulator, is widely used for both the treatment and prevention of breast cancer in women; however, it is known to have adverse effects in the female reproductive system. Growing evidence suggests that oestrogen-sensitive neuron populations of the anteroventral periventricular (AVPV) nucleus and arcuate (ARC) nucleus, especially kisspeptin neurons, play a pivotal role in the timing of puberty onset and reproductive function. The aim of the present study was to evaluate whether neonatal exposure to tamoxifen affects oestrogenic actions in the brain and reproductive function in mice. On 1 to 5 postnatal days, female pups were injected subcutaneously with sesame oil (sham), oestradiol benzoate (EB; 20 µg kg-1), tamoxifen (0.4 mg kg-1) or EB+tamoxifen. Control mice received no treatment. Mice in the EB, tamoxifen and tamoxifen+EB groups exhibited advanced vaginal opening, disrupted oestrous cycles and a decreased follicular pool. Conversely, in these groups, there was a reduction in kisspeptin (Kiss1) mRNA expression, the neuronal density of AVPV and ARC nuclei and LH and oestradiol concentrations in the serum. The results of the present study confirm oestrogenic actions of tamoxifen in the brain and reproductive system. In addition, we show, for the first time, that tamoxifen has oestrogenic effects on the oestrogen-sensitive hypothalamic AVPV and ARC nuclei controlling the reproductive axis in female mice.

Xenoestrogens Ethinyl Estradiol and Zearalenone Cause Precocious Puberty in Female Rats via Central Kisspeptin Signaling

Xenoestrogens from synthetic or natural origin represent an increasing risk of disrupted endocrine functions including the physiological activity of the hypothalamo-pituitary-gonad axis. Ethinyl estradiol (EE2) is a synthetic estrogen used in contraceptive pills, whereas zearalenone (ZEA) is a natural mycoestrogen found with increasing prevalence in various cereal crops. Both EE2 and ZEA are agonists of estrogen receptor-α and accelerate puberty. However, the neuroendocrine mechanisms that are responsible for this effect remain unknown. Immature female Wistar rats were treated with EE2 (10 μg/kg), ZEA (10 mg/kg), or vehicle for 10 days starting from postnatal day 18. As a marker of puberty, the vaginal opening was recorded and neuropeptide and related transcription factor mRNA levels were measured by quantitative real time PCR and in situ hybridization histochemistry. Both ZEA and EE2 accelerated the vaginal opening, increased the uterine weight and the number of antral follicles in the ovary, and resulted in the increased central expression of gnrh. These changes occurred in parallel with an earlier increase of kiss1 mRNA in the anteroventral and rostral periventricular hypothalamus and an increased kisspeptin (KP) fiber density and KP-GnRH appositions in the preoptic area. These changes are compatible with a mechanism in which xenoestrogens overstimulate the developmentally unprepared reproductive system, which results in an advanced vaginal opening and an enlargement of the uterus at the periphery. Within the hypothalamus, ZEA and EE2 directly activate anteroventral and periventricular KP neurons to stimulate GnRH mRNA. However, GnRH and gonadotropin release and ovulation are disrupted due to xenoestrogen-mediated inhibitory KP signaling in the arcuate nucleus.

Delayed pubertal onset and prepubertal Kiss1 expression in female mice lacking central oestrogen receptor beta

Ovarian oestradiol is essential for pubertal maturation and adult physiology of the female reproductive axis. It acts at central and peripheral sites through two main oestrogen receptors (ER) α and β. Here we investigate the role of ERβ on central effects of oestradiol, by generating a mouse line specifically lacking the ERβ gene in neuronal and glial cells. Central ERβ deletion delays the age at vaginal opening and first oestrous and reduces uterine weight without affecting body growth. Analysis of factors necessary for pubertal progression shows reduced levels of Kiss1 transcripts at postnatal (P) day 25 in the preoptic area, but not in the mediobasal hypothalamus (MBH) of mutant females. In agreement with these data, the number of kisspeptin-immunoreactive neurons was decreased by 57-72% in the three subdivisions of the rostral periventricular area of the third ventricle (RP3V), whereas the density of kisspeptin-immunoreactive fibres was unchanged in the arcuate nucleus of mutant mice. These alterations do not involve changes in ERα mRNAs in the preoptic area and protein levels in the RP3V. The number and distribution of GnRH-immunoreactive cells were unaffected, but gonadotropin-releasing hormone (GnRH) transcript levels were higher in the P25 preoptic area of mutants. At adulthood, mutant females have normal oestrous cyclicity, kisspeptin system and exhibit unaltered sexual behaviour. They display, however, reduced ovary weight and increased anxiety-related behaviour during the follicular phase. This argues for the specific involvement of central ERβ in the regulation of pubertal onset in female reproduction, possibly through prepubertal induction of kisspeptin expression in the RP3V.

Relative Importance of the Arcuate and Anteroventral Periventricular Kisspeptin Neurons in Control of Puberty and Reproductive Function in Female Rats

Kisspeptin plays a critical role in pubertal timing and reproductive function. In rodents, kisspeptin perikarya within the hypothalamic arcuate (ARC) and anteroventral periventricular (AVPV) nuclei are thought to be involved in LH pulse and surge generation, respectively. Using bilateral microinjections of recombinant adeno-associated virus encoding kisspeptin antisense into the ARC or AVPV of female rats at postnatal day 10, we investigated the relative importance of these two kisspeptin populations in the control of pubertal timing, estrous cyclicity, and LH surge and pulse generation. A 37% knockdown of kisspeptin in the AVPV resulted in a significant delay in vaginal opening and first vaginal estrous, abnormal estrous cyclicity, and reduction in the occurrence of spontaneous LH surges, although these retained normal amplitude. This AVPV knockdown had no effect on LH pulse frequency, measured after ovariectomy. A 32% reduction of kisspeptin in the ARC had no effect on the onset of puberty but resulted in abnormal estrous cyclicity and decreased LH pulse frequency. Additionally, the knockdown of kisspeptin in the ARC decreased the amplitude but not the incidence of LH surges. These results might suggest that the role of AVPV kisspeptin in the control of pubertal timing is particularly sensitive to perturbation. In accordance with our previous studies, ARC kisspeptin signaling was critical for normal pulsatile LH secretion in female rats. Despite the widely reported role of AVPV kisspeptin neurons in LH surge generation, this study suggests that both AVPV and ARC populations are essential for normal LH surges and estrous cyclicity.

Specialized subpopulations of kisspeptin neurons communicate with GnRH neurons in female mice

The neuropeptide kisspeptin is a potent stimulator of GnRH neurons and has been implicated as a major regulator of the hypothalamus-pituitary-gonadal axis. There are mainly two anatomically segregated populations of neurons that express kisspeptin in the female hypothalamus: one in the anteroventral periventricular nucleus (AVPV) and the other in the arcuate nucleus (ARC). Distinct roles have been proposed for AVPV and ARC kisspeptin neurons during reproductive maturation and in mediating estrogen feedback on the hypothalamus-pituitary-gonadal axis in adults. Despite their pivotal role in the regulation of reproductive physiology, little is known about kisspeptin neuron connectivity. Although previous data suggest heterogeneity within the AVPV and ARC kisspeptin neuron populations, how many and which of these potential kisspeptin neuron subpopulations are actually communicating with GnRH neurons is not known. Here we used a combinatorial genetic transsynaptic tracing strategy to start to analyze the connectivity of individual kisspeptin neurons with the GnRH neuron population in female mice with a single-cell resolution. We find that only subsets of AVPV and ARC kisspeptin neurons are synaptically connected with GnRH neurons. We demonstrate that the majority of kisspeptin neurons within the AVPV and ARC does not communicate with GnRH neurons. Furthermore, we show that all kisspeptin neurons within the AVPV connected to GnRH neurons are estrogen sensitive and that most of these express tyrosine hydroxylase. Our data demonstrate functional specialization within the two kisspeptin neuron populations.

Association of aromatase (TTTA)n repeat polymorphisms with central precocious puberty in girls

OBJECTIVE

Precocious puberty is characterized by early activation of the pituitary-gonadal axis. Oestrogen is the final key factor to start the onset of puberty. The cytochrome P450 19A1 (CYP19A1) gene encodes an aromatase that is responsible for the conversion of androgens to oestrogen, which is a key step in oestrogen biosynthesis. The aim of this study was to identify CYP19A1 gene mutations or polymorphisms in girls with central precocious puberty (CPP).

METHODS

We evaluated the frequency of allelic variants of the CYP19A1 exons and the tetranucleotide tandem repeat (TTTA)n in intron 4 in 203 idiopathic central precocious puberty (CPP) girls and 101 normal healthy women.

RESULTS

The genotype analysis of the CYP19A1 (TTTA)n polymorphism revealed six different alleles ranging from seven to 13 repeats. Among the six different repeat alleles detected in this study, the (TTTA)₁₃ repeat allele was only detected in the patient group and carriers of the (TTTA)₁₃ allele were significantly associated with an increased risk of CPP (OR = 1·509, 95% CI = 1·425-1·598, P = 0·033). Carriers of the (TTTA)₁₃ repeat allele were significantly younger at pubertal onset and had higher levels of oestrogen than noncarriers of the (TTTA)₁₃ repeat allele. Although nine polymorphisms were detected in exons of the CYP19A1 gene, no clinical significance was observed.

CONCLUSION

In this study, carriers of a higher repeat (TTTA)₁₃ polymorphism in intron 4 of the CYP19A1 gene had higher levels of oestrogen. Those carrying the (TTTA)₁₃ repeat allele may have a higher risk of developing CPP.

Murine arcuate nucleus kisspeptin neurons communicate with GnRH neurons in utero

Puberty is a transition period of reproductive development from juvenile stages to adulthood and depends upon the activity of gonadotropin-releasing hormone (GnRH) neurons. GnRH neurons are initially activated in utero but remain quiescent throughout the juvenile period. Premature reactivation of GnRH neurons results in precocious puberty in mice and humans, but the mechanisms underlying developmental control of GnRH neuron activity remain unknown. The neuropeptide kisspeptin, a potent activator of GnRH neurons that is implicated as a critical permissive signal triggering puberty and a major regulator of the adult female hypothalamus-pituitary-gonadal axis, is paradoxically produced by neurons in the developing brain well before puberty onset. Thus, the neural circuits controlling the timing of reproductive maturation remain elusive. Here, we delineate the underlying neural circuitry using conditional genetic transsynaptic tracing in female mouse embryos. We find that kisspeptin-producing neurons in the arcuate nucleus (ARC) already communicate with a specific subset of GnRH neurons in utero. We show that ARC kisspeptin neurons are upstream of GnRH neurons, and that GnRH neuron connectivity to ARC kisspeptin neurons does not depend on their spatial position in the brain. Furthermore, we demonstrate that the neural circuits between ARC kisspeptin and GnRH neurons are fully established and operative before birth. Finally, we find that most GnRH neurons express the kisspeptin receptor GPR54 upon circuit formation, suggesting that the signaling system implicated in gatekeeping puberty becomes operative in the embryo.

An alternative transcription start site yields estrogen-unresponsive Kiss1 mRNA transcripts in the hypothalamus of prepubertal female rats

The importance of the Kiss1 gene in the control of reproductive development is well documented. However, much less is known about the transcriptional regulation of Kiss1 expression in the hypothalamus. Critical for these studies is an accurate identification of the site(s) where Kiss1 transcription is initiated. Employing 5'-RACE PCR, we detected a transcription start site (TSS1) used by the hypothalamus of rats, mice, nonhuman primates and humans to initiate Kiss1 transcription. In rodents, an exon 1 encoding 5'-untranslated sequences is followed by an alternatively spliced second exon, which encodes 5'-untranslated regions of two different lengths and contains the translation initiation codon (ATG). In nonhuman primates and humans, exon 2 is not alternatively spliced. Surprisingly, in rat mediobasal hypothalamus (MBH), but not preoptic area (POA), an additional TSS (TSS2) located upstream from TSS1 generates an exon 1 longer (377 bp) than the TSS1-derived exon 1 (98 bp). The content of TSS1-derived transcripts increased at puberty in the POA and MBH of female rats. It also increased in the MBH after ovariectomy, and this change was prevented by estrogen. In contrast, no such changes in TSS2-derived transcript abundance were detected. Promoter assays showed that the proximal TSS1 promoter is much more active than the putative TSS2 promoter, and that only the TSS1 promoter is regulated by estrogen. These differences appear to be related to the presence of a TATA box and binding sites for transcription factors activating transcription and interacting with estrogen receptor-α in the TSS1, but not TSS2, promoter.