The initiation and maintenance of gonadotropin-releasing hormone neuron identity in congenital hypogonadotropic hypogonadism.

Neurons that secrete gonadotropin-releasing hormone (GnRH) drive vertebrate reproduction. Genetic lesions that disrupt these neurons in humans lead to congenital hypogonadotropic hypogonadism (CHH) and reproductive failure. Studies on CHH have largely focused on the disruption of prenatal GnRH neuronal migration and postnatal GnRH secretory activity. However, recent evidence suggests a need to also focus on how GnRH neurons initiate and maintain their identity during prenatal and postnatal periods. This review will provide a brief overview of what is known about these processes and several gaps in our knowledge, with an emphasis on how disruption of GnRH neuronal identity can lead to CHH phenotypes.

Reagents for Mass Cytometry.

Mass cytometry (cytometry by time-of-flight detection [CyTOF]) is a bioanalytical technique that enables the identification and quantification of diverse features of cellular systems with single-cell resolution. In suspension mass cytometry, cells are stained with stable heavy-atom isotope-tagged reagents, and then the cells are nebulized into an inductively coupled plasma time-of-flight mass spectrometry (ICP-TOF-MS) instrument. In imaging mass cytometry, a pulsed laser is used to ablate ca. 1 µm2 spots of a tissue section. The plume is then transferred to the CyTOF, generating an image of biomarker expression. Similar measurements are possible with multiplexed ion bean imaging (MIBI). The unit mass resolution of the ICP-TOF-MS detector allows for multiparametric analysis of (in principle) up to 130 different parameters. Currently available reagents, however, allow simultaneous measurement of up to 50 biomarkers. As new reagents are developed, the scope of information that can be obtained by mass cytometry continues to increase, particularly due to the development of new small molecule reagents which enable monitoring of active biochemistry at the cellular level. This review summarizes the history and current state of mass cytometry reagent development and elaborates on areas where there is a need for new reagents. Additionally, this review provides guidelines on how new reagents should be tested and how the data should be presented to make them most meaningful to the mass cytometry user community.

Mind-Body Health Benefits of Traditional Chinese Qigong on Women: A Systematic Review of Randomized Controlled Trials.

Most women live with an inactive lifestyle, which suggests a need for preference-based choices to promote their participation in physical activity. This systematic review synthesized key findings on the health benefits of Qigong among women. We conducted a systematic search of randomized controlled trials (RCTs) of Qigong among women according to the PRISMA guidelines using the following databases from their inception through March 2021: PubMed/MEDLINE, Web of Science, Cochrane Library, and US National Library of Medicine. The risk of bias was examined using the Cochrane Collaboration's tool for assessing the risk of bias in randomized trials. Altogether, 18 RCTs were included for final review. Results showed that Qigong was a feasible exercise in improving health outcomes, particularly depressive symptoms (63% of trials), quality of life (43%), and fatigue (29%), among general women, intimate partner violence survivors, and women with chronic conditions (e.g., breast cancer patients or survivors). Almost 90% (7/8) of trials reported high adherence rates ranging from 73 to 95% for supervised group training and 63 to 80% for home self-practice. Thus far, there was no evidence of serious adverse effects from performing Qigong. For the risk of bias across trials, a lack of allocation concealment (72% of trials), no blinding of participants and personnel (67%), and incomplete outcome data (67%) were the major sources. In summary, Qigong is a safe, feasible, and beneficial exercise for general women, abused sufferers, and health-compromised women. However, given the potential risk of bias found in many studies, improved rigor of study design in future trials will be imperatively required.

Absolute Quantification of Phosphorylated ERß Amino Acids in the Hippocampus of Women and in A Rat Model of Menopause.

The rapid decline of circulating 17ß-estradiol (E2) at menopause leads to negative neurological consequences, although hormone therapy paradoxically has both harmful and positive effects depending on the age at which it is delivered. The inconsistent response to E2 suggests unappreciated regulatory mechanisms for estrogen receptors (ERs), and we predicted it could be due to age-related differences in ERß phosphorylation. We assessed ERß phosphorylation using a sensitive mass spectrometry approach that provides absolute quantification (AQUA-MS) of individually phosphorylated residues. Specifically, we quantified phosphorylated ERß in the hippocampus of women (aged 21-83 years) and in a rat model of menopause at 4 residues with conserved sequence homology between the 2 species: S105, S176, S200, and Y488. Phosphorylation at these sites, which spanned all domains of ERß, were remarkably consistent between the 2 species, showing high levels of S105 phosphorylation (80%-100%) and low levels of S200 (20%-40%). Further, S200 phosphorylation decreased with aging in humans and loss of E2 in rats. Surprisingly, Y488 phosphorylation, which has been linked to ERß ligand-independent actions, exhibited approximately 70% phosphorylation, unaltered by species, age, or E2, suggesting ERß's primary mode of action may not require E2 binding. We further show phosphorylation at 2 sites directly altered ERß DNA-binding efficiency, and thus could affect its transcription factor activity. These findings provide the first absolute quantification of ERß phosphorylation in the human and rat brain, novel insights into ERß regulation, and a critical foundation for providing more targeted therapeutic options for menopause in the future.

Patterns of Sedentary Behavior among Older Adults in Care Facilities: A Scoping Review.

Understanding the sedentary patterns can guide the design of strategies to engage older adults in physical activity. This scoping review aimed to synthesize available evidence on sedentary behaviors in care facilities. We searched PubMed/MEDLINE and Web of Science for studies published from inception through October 2020. Eighteen studies were included and reviewed according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Data obtained were analyzed based on levels of care provided. Overall, daily sedentary time was higher among residents in high level care facilities (e.g., nursing homes) (11.6 h/day) than intermediate/mixed level care facilities (e.g., assisted living) (9.5 h/day). In intermediate/mixed level care facilities, television (TV) viewing was the most common sedentary activity (2.5-2.9 h/day; 26% of daily sedentary time), while napping was the most favorite sedentary activity (4.7 h/day; 36% of waking hours) in high level care facilities. Sex differences in daily patterns of sedentary behavior (sedentary time, uninterrupted bouts, and bout durations) were commonly observed in intermediate/mixed level care facilities, as exemplified by men being more sedentary by 0.7-1.1 h/day. In summary, this study highlights distinctive sedentary patterns among older adults residing in different levels of care facilities, addressing a pressing need for customized interventions to engage care facility residents in physical activity.

Epigenomic control of gonadotrophin-releasing hormone neurone development and hypogonadotrophic hypogonadism.

Mammalian reproductive success depends on gonadotrophin-releasing hormone (GnRH) neurones to stimulate gonadotrophin secretion from the anterior pituitary and activate gonadal steroidogenesis and gametogenesis. Genetic screening studies in patients diagnosed with Kallmann syndrome (KS), a congenital form of hypogonadotrophic hypogonadism (CHH), identified several causal mutations, including those in the fibroblast growth factor (FGF) system. This signalling pathway regulates neuroendocrine progenitor cell proliferation, fate specification and cell survival. Indeed, the GnRH neurone system was absent or abrogated in transgenic mice with reduced (ie, hypomorphic) Fgf8 and/or Fgf receptor (Fgfr) 1 expression, respectively. Moreover, we found that GnRH neurones were absent in the embryonic olfactory placode of Fgf8 hypomorphic mice, the putative birthplace of GnRH neurones. These observations, together with those made in human KS/CHH patients, indicate that the FGF8/FGFR1 signalling system is a requirement for the ontogenesis of the GnRH neuronal system and function. In this review, we discuss how epigenetic factors control the expression of genes such as Fgf8 that are known to be critical for GnRH neurone ontogenesis, fate specification, and the pathogenesis of KS/CHH.

Neurodevelopmental wiring deficits in the Ts65Dn mouse model of Down syndrome.

Down syndrome is the most common genetic cause of intellectual disability and occurs due to the trisomy of human chromosome 21. Adolescent and adult brains from humans with Down syndrome exhibit various neurological phenotypes including a reduction in the size of the corpus callosum, hippocampal commissure and anterior commissure. However, it is unclear when and how these interhemispheric connectivity defects arise. Using the Ts65Dn mouse model of Down syndrome, we examined interhemispheric connectivity in postnatal day 0 (P0) Ts65Dn mouse brains. We find that there is no change in the volume of the corpus callosum or anterior commissure in P0 Ts65Dn mice. However, the volume of the hippocampal commissure is significantly reduced in P0 Ts65Dn mice, and this may contribute to the impaired learning and memory phenotype of this disorder. Interhemispheric connectivity defects that arise during development may be due to disrupted axon growth. In line with this, we find that developing hippocampal neurons display reduced axon length in vitro, as compared to neurons from their euploid littermates. This study is the first to report the presence of defective interhemispheric connectivity at the time of birth in Ts65Dn mice, providing evidence that early therapeutic intervention may be an effective time window for the treatment of Down syndrome.

TET1 regulates fibroblast growth factor 8 transcription in gonadotropin releasing hormone neurons.

Fibroblast growth factor 8 (FGF8) is a potent morphogen that regulates the ontogenesis of gonadotropin-releasing hormone (GnRH) neurons, which control the hypothalamus-pituitary-gonadal (HPG) axis, and therefore reproductive success. Indeed, FGF8 and FGFR1 deficiency severely compromises vertebrate reproduction in mice and humans and is associated with Kallmann Syndrome (KS), a congenital disease characterized by hypogonadotropic hypogonadism associated with anosmia. Our laboratory demonstrated that FGF8 signaling through FGFR1, both of which are KS-related genes, is necessary for proper GnRH neuron development in mice and humans. Here, we investigated the possibility that non-genetic factors, such as the epigenome, may contribute to KS onset. For this purpose, we developed an embryonic explant model, utilizing the mouse olfactory placode (OP), the birthplace of GnRH neurons. We show that TET1, which converts 5-methylcytosine residues (5mC) to 5-hydroxymethylated cytosines (5hmC), controls transcription of Fgf8 during GnRH neuron ontogenesis. Through MeDIP and ChIP RT-qPCR we found that TET1 bound to specific CpG islands on the Fgf8 promoter. We found that the temporal expression of Fgf8 correlates with not only TET1 binding, but also with 5hmC enrichment. siRNA knockdown of Tet1 reduced Fgf8 and Fgfr1 mRNA expression. During this time period, Fgf8 also switched histone status, most likely via recruitment of EZH2, a major component of the polycomb repressor complex-2 (PRC2) at E13.5. Together, these studies underscore the significance of epigenetics and chromatin modifications to temporally regulated genes involved in KS.

Tetralogy of Fallot with concurrent patent foramen ovale and tricuspid valve dysplasia in a dog.

The echocardiographic findings of a young Pomeranian-cross dog with tetralogy of Fallot, patent foramen ovale, and tricuspid valve dysplasia are described. Ongoing medical management of hypoxemia and erythrocytosis was carried out and the dog survived to 2 years of age. Treatment options for tetralogy of Fallot are discussed.

Tétralogie de Fallot avec persistance du foramen ovale et dysplasie de la valve tricuspide concomitante chez un chien. Les constatations écho-cardiographiques chez un chien Poméranien de race croisée atteint de la tétralogie de Fallot, de la persistance du foramen ovale et d'une dysplasie de la valve tricuspide sont décrites. Une gestion médicale constante de l'hypoxémie et de l'érythrocytose a été réalisée et le chien a survécu jusqu'à l'âge de 2 ans. Les options de traitement pour la tétralogie de Fallot sont discutées.(Traduit par Isabelle Vallières).

The Regulation and Function of Fibroblast Growth Factor 8 and Its Function during Gonadotropin-Releasing Hormone Neuron Development.

Over the last few years, numerous studies solidified the hypothesis that fibroblast growth factor (FGF) signaling regulates neuroendocrine progenitor cell proliferation, fate specification, and cell survival and, therefore, is critical for the regulation and maintenance of homeostasis of the body. One important example that underscores the involvement of FGF signaling during neuroendocrine cell development is gonadotropin-releasing hormone (GnRH) neuron ontogenesis. Indeed, transgenic mice with reduced olfactory placode (OP) Fgf8 expression do not have GnRH neurons. This observation indicates the requirement of FGF8 signaling for the emergence of the GnRH neuronal system in the embryonic OP, the putative birth place of GnRH neurons. Mammalian reproductive success depends on the presence of GnRH neurons to stimulate gonadotropin secretion from the anterior pituitary, which activates gonadal steroidogenesis and gametogenesis. Together, these observations are critical for understanding the function of GnRH neurons and their control of the hypothalamus-pituitary-gonadal (HPG) axis to maintain fertility. Taken together, these studies illustrate that GnRH neuron emergence and hence HPG function is vulnerable to genomic and molecular signals that abnormally modify Fgf8 expression in the developing mouse OP. In this short review, we focus on research that is aimed at unraveling how androgen, all-trans retinoic acid, and how epigenetic factors modify control mouse OP Fgf8 transcription in the context of GnRH neuronal development and mammalian reproductive success.

Perinatal midline astrocyte development is impaired in fibroblast growth factor 8 hypomorphic mice.

Our previous studies showed that Fgf8 mutations can cause Kallmann syndrome (KS), a form of congenital hypogonadotropic hypogonadism, in which patients do not undergo puberty and are infertile. Interestingly, some KS patients also have agenesis of the corpus callosum (ACC) suggesting that KS pathology is not limited to reproductive function. Here, we asked whether FGF8 dysfunction is the underlying cause of ACC in some KS patients. Indeed, early studies in transgenic mice with Fgf8 mutations reported the presence of failed or incomplete corpus callosum formation. Additional studies in transgenic mice showed that FGF8 function most likely prevents the prenatal elimination of glial fibrillary acidic protein (GFAP)-immunoreactive (IR) glial cells in the indusium griseum (IG) and midline zipper (MZ), two anterior-dorsal midline regions required for corpus callosum formation (i.e., between embryonic days (E) 15.5-18.5). Here, we tested the hypothesis that FGF8 function is critical for the survival of the GFAP-IR midline glial cells. First, we measured the incidence of apoptosis in the anterior-dorsal midline region in Fgf8 hypomorphic mice during embryonic corpus callosum formation. Second, we quantified the GFAP expression in the anterior-dorsal midbrain region during pre- and postnatal development, in order to study: 1) how Fgf8 hypomorphy disrupts prenatal GFAP-IR midline glial cell development, and 2) whether Fgf8 hypomorphy continues to disrupt postnatal GFAP-IR midline glial cell development. Our results indicate that perinatal FGF8 signaling is important for the timing of the onset of anterior-dorsal Gfap expression in midline glial cells suggesting that FGF8 function regulates midline GFAP-IR glial cell development, which when disrupted by Fgf8 deficiency prevents the formation of the corpus callosum. These studies provide an experimentally-based mechanistic explanation as to why corpus callosum formation may fail in KS patients with deficits in FGF signaling.

Fibroblast Growth Factor 8 Expression in GT1-7 GnRH-Secreting Neurons Is Androgen-Independent, but Can Be Upregulated by the Inhibition of DNA Methyltransferases.

Fibroblast growth factor 8 (FGF8) is a potent morphogen that regulates the embryonic development of hypothalamic neuroendocrine cells. Indeed, using Fgf8 hypomorphic mice, we showed that reduced Fgf8 mRNA expression completely eliminated the presence of gonadotropin-releasing hormone (GnRH) neurons. These findings suggest that FGF8 signaling is required during the embryonic development of mouse GnRH neurons. Additionally, in situ hybridization studies showed that the embryonic primordial birth place of GnRH neurons, the olfactory placode, is highly enriched for Fgf8 mRNA expression. Taken together these data underscore the importance of FGF8 signaling for GnRH emergence. However, an important question remains unanswered: How is Fgf8 gene expression regulated in the developing embryonic mouse brain? One major candidate is the androgen receptor (AR), which has been shown to upregulate Fgf8 mRNA in 60-70% of newly diagnosed prostate cancers. Therefore, we hypothesized that ARs may be involved in the regulation of Fgf8 transcription in the developing mouse brain. To test this hypothesis, we used chromatin-immunoprecipitation (ChIP) assays to elucidate whether ARs interact with the 5'UTR region upstream of the translational start site of the Fgf8 gene in immortalized mouse GnRH neurons (GT1-7) and nasal explants. Our data showed that while AR interacts with the Fgf8 promoter region, this interaction was androgen-independent, and that androgen treatment did not affect Fgf8 mRNA levels, indicating that androgen signaling does not induce Fgf8 transcription. In contrast, inhibition of DNA methyltransferases (DNMT) significantly upregulated Fgf8 mRNA levels indicating that Fgf8 transcriptional activity may be dependent on DNA methylation status.

Fibroblast growth factor 8 regulates postnatal development of paraventricular nucleus neuroendocrine cells.

BACKGROUND: Fibroblast growth factors (FGFs) are crucial signaling molecules that direct the development of the vertebrate brain. FGF8 gene signaling in particular, may be important for the development of the hypothalamus-pituitary-adrenal (HPA)-axis. Indeed, newborn Fgf8 hypomorphic mice harbor a major reduction in the number of vasopressin (VP) neurons in the paraventricular nucleus (PVN), the central output component of the HPA-axis. Additionally, recent studies indicated that adult heterozygous ((+/neo)) Fgf8 hypomorphic mice exhibit more anxiety-like behaviors than wildtype (WT) mice. These studies led us to investigate whether Fgf8 hypomorphy abrogated VP and/or corticotropin-releasing hormone (CRH) neuronal development in the postnatal day (PN) 21 and adult mouse PVN. Furthermore, we studied whether Fgf8 hypomorphy disrupted HPA responsiveness in these mice. METHODS: Using immunohistochemistry, we examined the development of VP and CRH neurons located in the PVN of PN 21 and adult Fgf8 (+/neo) mice. Moreover, we used a restraint stress (RS) paradigm and measured corticosterone levels with enzyme immunoassays in order to assess HPA axis activation. RESULTS: The number of VP neurons in the PVN did not differ between WT and Fgf8 (+/neo) mice on PN 21 and in adulthood. In contrast, CRH immunoreactivity was much higher in Fgf8 (+/neo) mice than in WT mice on PN 21, this difference was no longer shown in adult mice. RS caused a higher increase in corticosterone levels in adult Fgf8 (+/neo) mice than in WT mice after 15 min, but no difference was seen after 45 min. CONCLUSIONS: First, Fgf8 hypomorphy did not eliminate VP and CRH neurons in the mouse PVN, but rather disrupted the postnatal timing of neuropeptide expression onset in PVN neurons. Second, Fgf8 hypomorphy may, in part, be an explanation for affective disorders involving hyperactivity of the HPA axis, such as anxiety.

Ontogenesis of gonadotropin-releasing hormone neurons: a model for hypothalamic neuroendocrine cell development.

The vertebrate hypothalamo-pituitary-gonadal axis is the anatomical framework responsible for reproductive competence and species propagation. Essential to the coordinated actions of this three-tiered biological system is the fact that the regulatory inputs ultimately converge on the gonadotropin-releasing hormone (GnRH) neuronal system, which in rodents primarily resides in the preoptic/hypothalamic region. In this short review we will focus on: (1) the general embryonic temporal and spatial development of the rodent GnRH neuronal system, (2) the origin(s) of GnRH neurons, and (3) which transcription - and growth factors have been found to be critical for GnRH neuronal ontogenesis and cellular fate-specification. Moreover, we ask the question whether the molecular and cellular mechanisms involved in GnRH neuronal development may also play a role in the development of other hypophyseal secreting neuroendocrine cells in the hypothalamus.

Mutations in FGF17, IL17RD, DUSP6, SPRY4, and FLRT3 are identified in individuals with congenital hypogonadotropic hypogonadism.

Congenital hypogonadotropic hypogonadism (CHH) and its anosmia-associated form (Kallmann syndrome [KS]) are genetically heterogeneous. Among the >15 genes implicated in these conditions, mutations in FGF8 and FGFR1 account for ~12% of cases; notably, KAL1 and HS6ST1 are also involved in FGFR1 signaling and can be mutated in CHH. We therefore hypothesized that mutations in genes encoding a broader range of modulators of the FGFR1 pathway might contribute to the genetics of CHH as causal or modifier mutations. Thus, we aimed to (1) investigate whether CHH individuals harbor mutations in members of the so-called "FGF8 synexpression" group and (2) validate the ability of a bioinformatics algorithm on the basis of protein-protein interactome data (interactome-based affiliation scoring [IBAS]) to identify high-quality candidate genes. On the basis of sequence homology, expression, and structural and functional data, seven genes were selected and sequenced in 386 unrelated CHH individuals and 155 controls. Except for FGF18 and SPRY2, all other genes were found to be mutated in CHH individuals: FGF17 (n = 3 individuals), IL17RD (n = 8), DUSP6 (n = 5), SPRY4 (n = 14), and FLRT3 (n = 3). Independently, IBAS predicted FGF17 and IL17RD as the two top candidates in the entire proteome on the basis of a statistical test of their protein-protein interaction patterns to proteins known to be altered in CHH. Most of the FGF17 and IL17RD mutations altered protein function in vitro. IL17RD mutations were found only in KS individuals and were strongly linked to hearing loss (6/8 individuals). Mutations in genes encoding components of the FGF pathway are associated with complex modes of CHH inheritance and act primarily as contributors to an oligogenic genetic architecture underlying CHH.

MicroRNAs in the aging female brain: a putative mechanism for age-specific estrogen effects.

Menopause is characterized by the rapid age-related decline of circulating 17ß-estradiol (E(2)) levels in women, which can sometimes result in cognitive disorders such as impaired memory and increased anxiety. Hormone therapy (HT) is a widely used treatment for the adverse effects associated with menopause; however, evidence suggests that HT administered to postmenopausal women age 65 years and over can lead to increased risks for cognitive disorders. We hypothesized that these age-related changes in E(2) action are due to posttranscriptional gene regulation by microRNAs (miRNAs). miRNAs are a class of small noncoding RNAs that regulate gene expression by binding to the 3'-untranslated region of target mRNAs and subsequently target these transcripts for degradation. In the present study, 3- and 18-month-old female rats were oophorectomized (OVX) and treated 1 week after surgery with 2.5 µg E(2) once per day for 3 days. Total RNA was isolated from the ventral and dorsal hippocampus, central amygdala, and paraventricular nucleus. Our results showed that E(2) differentially altered miRNA levels in an age- and brain region-dependent manner. Multiple miRNA target prediction algorithms revealed putative target genes that are important for memory and stress regulation, such as BDNF, glucocorticoid receptor, and SIRT-1. Indeed, quantitative RT-PCR analyses of some of the predicted targets, such as SIRT1, showed that the mRNA expression levels were the inverse of the targeting miRNA, thereby confirming the prediction algorithms. Taken together, these data show that E(2) regulates miRNA expression in an age- and E(2)-dependent manner, which we hypothesize results in differential gene expression and consequently altered neuronal function.

Gender differences in neurodevelopment and epigenetics.

The concept that the brain differs in make-up between males and females is not new. For example, it is well established that anatomists in the nineteenth century found sex differences in human brain weight. The importance of sex differences in the organization of the brain cannot be overstated as they may directly affect cognitive functions, such as verbal skills and visuospatial tasks in a sex-dependent fashion. Moreover, the incidence of neurological and psychiatric diseases is also highly dependent on sex. These clinical observations reiterate the importance that gender must be taken into account as a relevant possible contributing factor in order to understand the pathogenesis of neurological and psychiatric disorders. Gender-dependent differentiation of the brain has been detected at every level of organization--morphological, neurochemical, and functional--and has been shown to be primarily controlled by sex differences in gonadal steroid hormone levels during perinatal development. In this review, we discuss howthe gonadal steroid hormone testosterone and its metabolites affect downstream signaling cascades, including gonadal steroid receptor activation, and epigenetic events in order to differentiate the brain in a gender-dependent fashion.

Opposite-sex housing reactivates the declining GnRH system in aged transgenic male mice with FGF signaling deficiency.

The continued presence of gonadotropin-releasing hormone (GnRH) neurons is required for a healthy reproductive lifespan, but factors that maintain postnatal GnRH neurons have not been identified. To begin to understand these factors, we investigated whether 1) fibroblast growth factor (FGF) signaling and 2) interactions with the opposite sex are involved in the maintenance of the postnatal GnRH system. A transgenic mouse model (dnFGFR mouse) with the targeted expression of a dominant-negative FGF receptor (dnFGFR) in GnRH neurons was used to examine the consequence of FGF signaling deficiency on postnatal GnRH neurons. Male dnFGFR mice suffered a significant loss of postnatal GnRH neurons within the first 100 days of life. Interestingly, this loss was reversed after cohabitation with female, but not male, mice for 300-550 days. Along with a rescue in GnRH neuron numbers, opposite-sex housing in dnFGFR males also increased hypothalamic GnRH peptide levels, promoted a more mature GnRH neuronal morphology, facilitated litter production, and enhanced testicular morphology. Last, mice hypomorphic for FGFR3 exhibited a similar pattern of postnatal GnRH neuronal loss as dnFGFR males, suggesting FGF signaling acts, in part, through FGFR3 to enhance the maintenance of the postnatal GnRH system. In summary, we have shown that FGF signaling is required for the continued presence of postnatal GnRH neurons. However, this requirement is not absolute, since sexual interactions can compensate for defects in FGFR signaling, thereby rescuing the declining GnRH system. This suggests the postnatal GnRH system is highly plastic and capable of responding to environmental stimuli throughout adult life.

Maternal behavior in transgenic mice with reduced fibroblast growth factor receptor function in gonadotropin-releasing hormone neurons.

BACKGROUND: Fibroblast growth factors (FGFs) and their receptors (FGFRs) are necessary for the proper development of gonadotropin-releasing hormone (GnRH) neurons, which are key activators of the hypothalamo-pituitary-gonadal axis. Transgenic mice that have the targeted expression of a dominant negative FGFR (dnFGFR) in GnRH neurons (dnFGFR mice) have a 30% decrease of GnRH neurons. Additionally, only 30-40% of the pups born to the transgenic dams survive to weaning age. These data raised the possibility that FGFR defects in GnRH neurons could adversely affect maternal behavior via novel mechanisms. METHODS: We first determined if defective maternal behavior in dnFGFR mothers may contribute to poor pup survival by measuring pup retrieval and a battery of maternal behaviors in primiparous control (n=10-12) and dnFGFR (n=13-14) mothers. Other endocrine correlates of maternal behaviors, including plasma estradiol levels and hypothalamic pro-oxyphysin and GnRH transcript levels were also determined using enzyme-linked immunoassay and quantitative reverse transcription polymerase chain reaction, respectively. RESULTS: Maternal behaviors (% time crouching with pups, time off pups but not feeding, time feeding, and total number of nesting bouts) were not significantly different in dnFGFR mice. However, dnFGFR dams were more likely to leave their pups scattered and took significantly longer to retrieve each pup compared to control dams. Further, dnFGFR mothers had significantly lower GnRH transcripts and circulating E2, but normal pro-oxyphysin transcript levels. CONCLUSIONS: Overall, this study suggests a complex scenario in which a GnRH system compromised by reduced FGF signaling leads to not only suboptimal reproductive physiology, but also suboptimal maternal behavior.

Fibroblast growth factor signaling deficiencies impact female reproduction and kisspeptin neurons in mice.

Fibroblast growth factor (FGF) signaling is essential for the development of the gonadotropin-releasing hormone (GnRH) system. Mice harboring deficiencies in Fgf8 or Fgf receptor 1 (Fgfr1) suffer a significant loss of GnRH neurons, but their reproductive phenotypes have not been examined. This study examined if female mice hypomorphic for Fgf8, Fgfr1, or both (compound hypomorphs) exhibited altered parameters of pubertal onset, estrous cyclicity, and fertility. Further, we examined the number of kisspeptin (KP)-immunoreactive (ir) neurons in the anteroventral periventricular/periventricular nuclei (AVPV/PeV) of these mice to assess if changes in the KP system, which stimulates the GnRH system, could contribute to the reproductive phenotypes. Single hypomorphs (Fgfr1(+/-) or Fgf8(+/-)) had normal timing for vaginal opening (VO) but delayed first estrus. However, after achieving the first estrus, they underwent normal expression of estrous cycles. In contrast, the compound hypomorphs underwent early VO and normal first estrus, but had disorganized estrous cycles that subsequently reduced their fertility. KP immunohistochemistry on Postnatal Day 15, 30, and 60 transgenic female mice revealed that female compound hypomorphs had significantly more KP-ir neurons in the AVPV/PeV compared to their wild-type littermates, suggesting increased KP-ir neurons may drive early VO but could not maintain the cyclic changes in GnRH neuronal activity required for female fertility. Overall, these data suggest that Fgf signaling deficiencies differentially alter the parameters of female pubertal onset and cyclicity. Further, these deficiencies led to changes in the AVPV/PeV KP-ir neurons that may have contributed to the accelerated VO in the compound hypomorphs.