CNS-specific ablation of steroidogenic factor 1 results in impaired female reproductive function

SF-1 Induces Nuclear PIP2

Metazoan cell nuclei contain non-membrane pools of the phosphoinositide lipid PI(4,5)P2 (PIP2), but how this hydrophobic lipid exists within the aqueous nucleoplasm remains unclear. Steroidogenic Factor-1 (NR5A1, SF-1) is a nuclear receptor that binds PIP2 in vitro, and a co-crystal structure of the complex suggests the acyl chains of PIP2 are hidden in the hydrophobic core of the SF-1 protein while the PIP2 headgroup is solvent-exposed. This binding mode explains how SF-1 can solubilize nuclear PIP2; however, cellular evidence that SF-1 expression associates with nuclear PIP2 has been lacking. Here, we examined if tetracycline induction of SF-1 expression would associate with nuclear accumulation of PIP2, using antibodies directed against the PIP2 headgroup. Indeed, tetracycline induction of wild-type SF-1 induced a signal in the nucleus of HEK cells that cross-reacts with PIP2 antibodies, but did not cross-react with antibodies against the lower abundance phosphoinositide PI(3,4,5)P3 (PIP3). The nuclear PIP2 signal co-localized with FLAG-tagged SF-1 in the nuclear compartment. To determine if the nuclear PIP2 signal was dependent on the ability of SF-1 to bind PIP2, we examined a "pocket mutant" of SF-1 (A270W, L345F) shown to be deficient in phospholipid binding by mass spectrometry. Tetracycline induction of this pocket mutant SF-1 in HEK cells failed to induce a detectable PIP2 antibody cross-reactive signal, despite similar Tet-induced expression levels of the wild-type and pocket mutant SF-1 proteins in these cells. Together, these data are the first to suggest that expression of SF-1 induces a PIP2 antibody cross-reactive signal in the nucleus, consistent with X-ray crystallographic and biochemical evidence suggesting SF-1 binds PIP2 in human cells.

Steroidogenic factor 1 (SF-1; Nr5a1) regulates the formation of the ovarian reserve

The ovarian follicle reserve, formed pre- or perinatally, comprises all oocytes for lifetime reproduction. Depletion of this reserve results in infertility. Steroidogenic factor 1 (SF-1; Nr5a1) and liver receptor homolog 1 (LRH-1; Nr5a2) are two orphan nuclear receptors that regulate adult endocrine function, but their role in follicle formation is unknown. We developed models of conditional depletion of SF-1 or LRH-1 from prenatal ovaries. Depletion of SF-1, but not LRH-1, resulted in dramatically smaller ovaries and fewer primordial follicles. This was mediated by increased oocyte death, resulting from increased ovarian inflammation and increased Notch signaling. Major dysregulated genes were Iroquois homeobox 3 and 5 and their downstream targets involved in the establishment of the ovarian laminin matrix and oocyte-granulosa cell gap junctions. Disruptions of these pathways resulted in follicles with impaired basement membrane formation and compromised oocyte-granulosa communication networks, believed to render them more prone to atresia. This study identifies SF-1 as a key regulator of the formation of the ovarian reserve.

Estrogenic regulation of reproduction and energy homeostasis by a triumvirate of hypothalamic arcuate neurons

Pregnancy is energetically demanding and therefore, by necessity, reproduction and energy balance are inextricably linked. With insufficient or excessive energy stores a female is liable to suffer complications during pregnancy or produce unhealthy offspring. Gonadotropin-releasing hormone neurons are responsible for initiating both the pulsatile and subsequent surge release of luteinizing hormone to control ovulation. Meticulous work has identified two hypothalamic populations of kisspeptin (Kiss1) neurons that are critical for this pattern of release. The involvement of the hypothalamus is unsurprising because its quintessential function is to couple the endocrine and nervous systems, coordinating energy balance and reproduction. Estrogens, more specifically 17β-estradiol (E₂ ), orchestrate the activity of a triumvirate of hypothalamic neurons within the arcuate nucleus (ARH) that govern the physiological underpinnings of these behavioral dynamics. Arising from a common progenitor pool, these cells differentiate into ARH kisspeptin, pro-opiomelanocortin (POMC), and agouti related peptide/neuropeptide Y (AgRP) neurons. Although the excitability of all these subpopulations is subject to genomic and rapid estrogenic regulation, Kiss1 neurons are the most sensitive, reflecting their integral function in female fertility. Based on the premise that E₂ coordinates autonomic functions around reproduction, we review recent findings on how Kiss1 neurons interact with gonadotropin-releasing hormone, AgRP and POMC neurons, as well as how the rapid membrane-initiated and intracellular signaling cascades activated by E₂ in these neurons are critical for control of homeostatic functions supporting reproduction. In particular, we highlight how Kiss1 and POMC neurons conspire to inhibit AgRP neurons and diminish food motivation in service of reproductive success.

Ventromedial Nucleus of the Hypothalamus Neurons Under the Magnifying Glass

The ventromedial nucleus of the hypothalamus (VMH) is a complex brain structure that is integral to many neuroendocrine functions, including glucose regulation, thermogenesis, and appetitive, social, and sexual behaviors. As such, it is of little surprise that the nucleus is under intensive investigation to decipher the mechanisms which underlie these diverse roles. Developments in genetic and investigative tools, for example the targeting of steroidogenic factor-1-expressing neurons, have allowed us to take a closer look at the VMH, its connections, and how it affects competing behaviors. In the current review, we aim to integrate recent findings into the literature and contemplate the conclusions that can be drawn.

Constitutive expression of Steroidogenic factor-1 (NR5A1) disrupts ovarian functions, fertility, and metabolic homeostasis in female mice

Steroid hormones regulate various aspects of physiology, from reproductive functions to metabolic homeostasis. Steroidogenic factor-1 (NR5A1) plays a central role in the development of steroidogenic tissues and their ability to produce steroid hormones. Inactivation of Nr5a1 in the mouse results in a complete gonadal and adrenal agenesis, absence of gonadotropes in the pituitary and impaired development of ventromedial hypothalamus, which controls glucose and energy metabolism. In this study, we set out to examine the consequences of NR5A1 overexpression (NR5A1+) in the NR5A1-positive cell populations in female mice. Ovaries of NR5A1+ females presented defects such as multi-oocyte follicles and an accumulation of corpora lutea. These females were hyperandrogenic, had irregular estrous cycles with persistent metestrus and became prematurely infertile. Furthermore, the decline in fertility coincided with weight gain, increased adiposity, hypertriglyceridemia, hyperinsulinemia, and impaired glucose tolerance, indicating defects in metabolic functions. In summary, excess NR5A1 expression causes hyperandrogenism, disruption of ovarian functions, premature infertility, and disorders of metabolic homeostasis. This NR5A1 overexpression mouse provides a novel model for studying not only the molecular actions of NR5A1, but also the crosstalk between endocrine, reproductive, and metabolic systems.

The Orphan Nuclear Receptors Steroidogenic Factor-1 and Liver Receptor Homolog-1: Structure, Regulation, and Essential Roles in Mammalian Reproduction

Nuclear receptors are intracellular proteins that act as transcription factors. Proteins with classic nuclear receptor domain structure lacking identified signaling ligands are designated orphan nuclear receptors. Two of these, steroidogenic factor-1 (NR5A1, also known as SF-1) and liver receptor homolog-1 (NR5A2, also known as LRH-1), bind to the same DNA sequences, with different and nonoverlapping effects on targets. Endogenous regulation of both is achieved predominantly by cofactor interactions. SF-1 is expressed primarily in steroidogenic tissues, LRH-1 in tissues of endodermal origin and the gonads. Both receptors modulate cholesterol homeostasis, steroidogenesis, tissue-specific cell proliferation, and stem cell pluripotency. LRH-1 is essential for development beyond gastrulation and SF-1 for genesis of the adrenal, sexual differentiation, and Leydig cell function. Ovary-specific depletion of SF-1 disrupts follicle development, while LRH-1 depletion prevents ovulation, cumulus expansion, and luteinization. Uterine depletion of LRH-1 compromises decidualization and pregnancy. In humans, SF-1 is present in endometriotic tissue, where it regulates estrogen synthesis. SF-1 is underexpressed in ovarian cancer cells and overexpressed in Leydig cell tumors. In breast cancer cells, proliferation, migration and invasion, and chemotherapy resistance are regulated by LRH-1. In conclusion, the NR5A orphan nuclear receptors are nonredundant factors that are crucial regulators of a panoply of biological processes, across multiple reproductive tissues.

Neuroanatomical Framework of the Metabolic Control of Reproduction

A minimum amount of energy is required for basic physiological processes, such as protein biosynthesis, thermoregulation, locomotion, cardiovascular function, and digestion. However, for reproductive function and survival of the species, extra energy stores are necessary. Production of sex hormones and gametes, pubertal development, pregnancy, lactation, and parental care all require energy reserves. Thus the physiological systems that control energy homeostasis and reproductive function coevolved in mammals to support both individual health and species subsistence. In this review, we aim to gather scientific knowledge produced by laboratories around the world on the role of the brain in integrating metabolism and reproduction. We describe essential neuronal networks, highlighting key nodes and potential downstream targets. Novel animal models and genetic tools have produced substantial advances, but critical gaps remain. In times of soaring worldwide obesity and metabolic dysfunction, understanding the mechanisms by which metabolic stress alters reproductive physiology has become crucial for human health.

Distinct temporal requirements for Sonic hedgehog signaling in development of the tuberal hypothalamus

Sonic hedgehog (Shh) plays well characterized roles in brain and spinal cord development, but its functions in the hypothalamus have been more difficult to elucidate owing to the complex neuroanatomy of this brain area. Here, we use fate mapping and conditional deletion models in mice to define requirements for dynamic Shh activity at distinct developmental stages in the tuberal hypothalamus, a brain region with important homeostatic functions. At early time points, Shh signaling regulates dorsoventral patterning, neurogenesis and the size of the ventral midline. Fate-mapping experiments demonstrate that Shh-expressing and -responsive progenitors contribute to distinct neuronal subtypes, accounting for some of the cellular heterogeneity in tuberal hypothalamic nuclei. Conditional deletion of the hedgehog transducer smoothened (Smo), after dorsoventral patterning has been established, reveals that Shh signaling is necessary to maintain proliferation and progenitor identity during peak periods of hypothalamic neurogenesis. We also find that mosaic disruption of Smo causes a non-cell autonomous gain in Shh signaling activity in neighboring wild-type cells, suggesting a mechanism for the pathogenesis of hypothalamic hamartomas, benign tumors that form during hypothalamic development.

Signaling through non-membrane nuclear phosphoinositide binding proteins in human health and disease

Phosphoinositide membrane signaling is critical for normal physiology, playing well-known roles in diverse human pathologies. The basic mechanisms governing phosphoinositide signaling within the nucleus, however, have remained deeply enigmatic owing to their presence outside the nuclear membranes. Over 40% of nuclear phosphoinositides can exist in this non-membrane state, held soluble in the nucleoplasm by nuclear proteins that remain largely unidentified. Recently, two nuclear proteins responsible for solubilizing phosphoinositides were identified, steroidogenic factor-1 (SF-1; NR5A1) and liver receptor homolog-1 (LRH-1; NR5A2), along with two enzymes that directly remodel these phosphoinositide/protein complexes, phosphatase and tensin homolog (PTEN; MMAC) and inositol polyphosphate multikinase (IPMK; ipk2). These new footholds now permit the assignment of physiological functions for nuclear phosphoinositides in human diseases, such as endometriosis, nonalcoholic fatty liver disease/steatohepatitis, glioblastoma, and hepatocellular carcinoma. The unique nature of nuclear phosphoinositide signaling affords extraordinary clinical opportunities for new biomarkers, diagnostics, and therapeutics. Thus, phosphoinositide biology within the nucleus may represent the next generation of low-hanging fruit for new drugs, not unlike what has occurred for membrane phosphatidylinositol 3-kinase drug development. This review connects recent basic science discoveries in nuclear phosphoinositide signaling to clinical pathologies, with the hope of inspiring development of new therapies.

SOCS3 expression in SF1 cells regulates adrenal differentiation and exercise performance

Many hormones/cytokines are secreted in response to exercise and cytokine signaling may play a pivotal role in the training adaptations. To investigate the importance of cytokine signaling during vertical ladder climbing, a resistance exercise model, we produced mice lacking SOCS3 protein exclusively in steroidogenic factor-1 (SF1) cells (SF1 Socs3 KO mice). SF1 expression is found in steroidogenic cells of the adrenal cortex and gonads, as well as in neurons of the ventromedial nucleus of the hypothalamus. Histological markers of the fetal adrenal zone (or X-zone in rodents) were still present in adult males and postpartum SF1 Socs3 KO females, suggesting a previously unrecognized effect of SOCS3 on the terminal differentiation of the adrenal gland. This change led to a distinct distribution of lipid droplets along the adrenal cortex. Under basal conditions, adult SF1 Socs3 KO mice exhibited similar adrenal weight, and plasma ACTH and corticosterone concentrations. Nonetheless, SF1 Socs3 KO mice exhibited a blunted ACTH-induced corticosterone secretion. The overall metabolic responses induced by resistance training remained unaffected in SF1 Socs3 KO mice, including changes in body adiposity, glucose tolerance and energy expenditure. However, training performance and glucose control during intense resistance exercise were impaired in SF1 Socs3 KO mice. Furthermore, a reduced counter-regulatory response to 2-deoxy-d-glucose was observed in mutant mice. These findings revealed a novel participation of SOCS3 regulating several endocrine and metabolic aspects. Therefore, cytokine signaling in SF1 cells exerts an important role to sustain training performance possibly by promoting the necessary metabolic adjustments during exercise.

Neuroendocrine integration of nutritional signals on reproduction

Reproductive function in mammals is energetically costly and therefore tightly regulated by nutritional status. To enable this integration of metabolic and reproductive function, information regarding peripheral nutritional status must be relayed centrally to the gonadotropin-releasing hormone (GNRH) neurons that drive reproductive function. The metabolically relevant hormones leptin, insulin and ghrelin have been identified as key mediators of this 'metabolic control of fertility'. However, the neural circuitry through which they act to exert their control over GNRH drive remains incompletely understood. With the advent of Cre-LoxP technology, it has become possible to perform targeted gene-deletion and gene-rescue experiments and thus test the functional requirement and sufficiency, respectively, of discrete hormone-neuron signaling pathways in the metabolic control of reproductive function. This review discusses the findings from these investigations, and attempts to put them in context with what is known from clinical situations and wild-type animal models. What emerges from this discussion is clear evidence that the integration of nutritional signals on reproduction is complex and highly redundant, and therefore, surprisingly difficult to perturb. Consequently, the deletion of individual hormone-neuron signaling pathways often fails to cause reproductive phenotypes, despite strong evidence that the targeted pathway plays a role under normal physiological conditions. Although transgenic studies rarely reveal a critical role for discrete signaling pathways, they nevertheless prove to be a good strategy for identifying whether a targeted pathway is absolutely required, critically involved, sufficient or dispensable in the metabolic control of fertility.

Development of the Neuroendocrine Hypothalamus

The neuroendocrine hypothalamus is composed of the tuberal and anterodorsal hypothalamus, together with the median eminence/neurohypophysis. It centrally governs wide-ranging physiological processes, including homeostasis of energy balance, circadian rhythms and stress responses, as well as growth and reproductive behaviours. Homeostasis is maintained by integrating sensory inputs and effecting responses via autonomic, endocrine and behavioural outputs, over diverse time-scales and throughout the lifecourse of an individual. Here, we summarize studies that begin to reveal how different territories and cell types within the neuroendocrine hypothalamus are assembled in an integrated manner to enable function, thus supporting the organism's ability to survive and thrive. We discuss how signaling pathways and transcription factors dictate the appearance and regionalization of the hypothalamic primordium, the maintenance of progenitor cells, and their specification and differentiation into neurons. We comment on recent studies that harness such programmes for the directed differentiation of human ES/iPS cells. We summarize how developmental plasticity is maintained even into adulthood and how integration between the hypothalamus and peripheral body is established in the median eminence and neurohypophysis. Analysis of model organisms, including mouse, chick and zebrafish, provides a picture of how complex, yet elegantly coordinated, developmental programmes build glial and neuronal cells around the third ventricle of the brain. Such conserved processes enable the hypothalamus to mediate its function as a central integrating and response-control mediator for the homeostatic processes that are critical to life. Early indications suggest that deregulation of these events may underlie multifaceted pathological conditions and dysfunctional physiology in humans, such as obesity.

Hypothalamic innate immune reaction in obesity

Findings from rodent and human studies show that the presence of inflammatory factors is positively correlated with obesity and the metabolic syndrome. Obesity-associated inflammatory responses take place not only in the periphery but also in the brain. The hypothalamus contains a range of resident glial cells including microglia, macrophages and astrocytes, which are embedded in highly heterogenic groups of neurons that control metabolic homeostasis. This complex neural-glia network can receive information directly from blood-borne factors, positioning it as a metabolic sensor. Following hypercaloric challenge, mediobasal hypothalamic microglia and astrocytes enter a reactive state, which persists during diet-induced obesity. In established mouse models of diet-induced obesity, the hypothalamic vasculature displays angiogenic alterations. Moreover, proopiomelanocortin neurons, which regulate food intake and energy expenditure, are impaired in the arcuate nucleus, where there is an increase in local inflammatory signals. The sum total of these events is a hypothalamic innate immune reactivity, which includes temporal and spatial changes to each cell population. Although the exact role of each participant of the neural-glial-vascular network is still under exploration, therapeutic targets for treating obesity should probably be linked to individual cell types and their specific signalling pathways to address each dysfunction with cell-selective compounds.

Patterning, specification, and differentiation in the developing hypothalamus

Owing to its complex structure and highly diverse cell populations, the study of hypothalamic development has historically lagged behind that of other brain regions. However, in recent years, a greatly expanded understanding of hypothalamic gene expression during development has opened up new avenues of investigation. In this review, we synthesize existing work to present a holistic picture of hypothalamic development from early induction and patterning through nuclear specification and differentiation, with a particular emphasis on determination of cell fate. We will also touch on special topics in the field including the prosomere model, adult neurogenesis, and integration of migratory cells originating outside the hypothalamic neuroepithelium, and how these topics relate to our broader theme.

An estrogen-responsive module in the ventromedial hypothalamus selectively drives sex-specific activity in females

Estrogen-receptor alpha (ERα) neurons in the ventrolateral region of the ventromedial hypothalamus (VMHVL) control an array of sex-specific responses to maximize reproductive success. In females, these VMHVL neurons are believed to coordinate metabolism and reproduction. However, it remains unknown whether specific neuronal populations control distinct components of this physiological repertoire. Here, we identify a subset of ERα VMHVL neurons that promotes hormone-dependent female locomotion. Activating Nkx2-1-expressing VMHVL neurons via pharmacogenetics elicits a female-specific burst of spontaneous movement, which requires ERα and Tac1 signaling. Disrupting the development of Nkx2-1(+) VMHVL neurons results in female-specific obesity, inactivity, and loss of VMHVL neurons coexpressing ERα and Tac1. Unexpectedly, two responses controlled by ERα(+) neurons, fertility and brown adipose tissue thermogenesis, are unaffected. We conclude that a dedicated subset of VMHVL neurons marked by ERα, NKX2-1, and Tac1 regulates estrogen-dependent fluctuations in physical activity and constitutes one of several neuroendocrine modules that drive sex-specific responses.

Regional specific regulation of steroid receptor coactivator-1 immunoreactivity by orchidectomy in the brain of adult male mice

Androgens including testosterone and dihydrotestosterone play important roles on brain structure and function, either directly through androgen receptor or indirectly through estrogen receptors, which need coactivators for their transcription activation. Steroid receptor coactivator-1 (SRC-1) has been shown to be multifunctional potentials in the brain, but how it is regulated by androgens in the brain remains unclear. In this study, we explored the effect of orchidectomy (ORX) on the expression of SRC-1 in the adult male mice using nickel-intensified immunohistochemistry. The results showed that ORX induced dramatic decrease of SRC-1 immunoreactivity in the olfactory tubercle, piriform cortex, ventral pallidum, most parts of the septal area, hippocampus, substantia nigra (compact part), pontine nuclei and nucleus of the trapezoid body (p<0.01). Significant decrease of SRC-1 was noticed in the dorsal and lateral septal nucleus, medial preoptical area, dorsomedial and ventromedial hypothalamic nucleus and superior paraolivary nucleus (p<0.05). Whereas in other regions examined, levels of SRC-1 immunoreactivity were not obviously changed by ORX (p>0.05). The above results demonstrated ORX downregulation of SRC-1 in specific regions that have been involved in sense of smell, learning and memory, cognition, neuroendocrine, reproduction and motor control, indicating that SRC-1 play pivotal role in the mediating circulating androgenic regulation on these important brain functions. It also indicates that SRC-1 may serve as a novel target for the central disorders caused by the age-related decrease of circulating androgens.

The hypothalamic neural-glial network and the metabolic syndrome

Despite numerous educational interventions and biomedical research efforts, modern society continues to suffer from obesity and its associated metabolic diseases, such as type 2 diabetes mellitus, and these diseases show little sign of abating. One reason for this is an incomplete understanding of the pathology of the metabolic syndrome, which obstructs the development of effective therapeutic strategies. While hypothalamic neuropathy is a potential candidate that may contribute to the pathogenesis of the metabolic syndrome, the specific causes of hypothalamic neuropathy remain largely unknown. During different stages of high-calorie diet-induced metabolic syndrome, the hypothalamus undergoes gliosis and angiogenesis, both of which potentially reflect ongoing inflammatory processes. This overview discusses current data suggesting a role for hypothalamic inflammation-like processes in diet-induced metabolic diseases and provides a perspective on how to unravel molecular mechanisms of "hypothalamic inflammation" in order to develop anti-obesity therapeutic strategies.

Estrogen replacement therapy regulation of energy metabolism in female mouse hypothalamus

Estrogens play an important role in the regulation of energy homeostasis in female mammals and a reduced ovarian function, due to natural aging or surgery, is associated with body weight increase and fat redistribution. This disruption of energy homeostasis may constitute a trigger for several pathologies known to be associated with climacterium; however, so far, limited attention has been devoted to the ability of estrogen replacement therapies (ERT) to reinstate the balanced energy metabolism characteristic of cycling female mammals. The purpose of the present study was to compare the efficacy of selected ERTs in reversing the ovariectomy-induced gain in body weight. To this aim female ERE-Luc mice were ovariectomized and, after 3 weeks, treated per os for 21 days with: conjugated estrogens, two selective estrogen receptor modulators (bazedoxifene and raloxifene), and the combination of bazedoxifene plus conjugated estrogens (tissue-selective estrogen complex, TSEC). The study shows that the therapy based on TSEC was the most efficacious in reducing the body weight accrued by ovariectomy (OVX). In addition, by means of in vivo imaging, the TSEC treatment was shown to increase estrogen receptor (ER) transcriptional activity selectively in the arcuate nucleus, which is a key area for the control of energy homeostasis. Finally, quantitative analysis of the mRNAs encoding orexigenic and anorexigenic peptides indicated that following ERT with TSEC there was a significant change in Agrp, NPY, and Kiss-1 mRNA accumulation in the whole hypothalamus. Considering that prior studies showed that ERT with TSEC was able to mimic the rhythm of ER oscillatory activity during the reproductive cycle and that such fluctuations were relevant for energy metabolism, the present observations further point to the ER tetradian oscillation as an important component of the ER signaling necessary for the full hormone action and therefore for an efficacious ERT.

Genetic labeling of steroidogenic factor-1 (SF-1) neurons in mice reveals ventromedial nucleus of the hypothalamus (VMH) circuitry beginning at neurogenesis and development of a separate non-SF-1 neuronal cluster in the ventrolateral VMH

The ventromedial nucleus of the hypothalamus (VMH) influences a wide variety of physiological responses. Here, using two distinct but complementary genetic tracing approaches in mice, we describe the development of VMH efferent projections, as marked by steroidogenic factor-1 (SF-1; NR5A1). SF-1 neurons were visualized by Tau-green fluorescent protein (GFP) expressed from the endogenous Sf-1 locus (Sf-1(TauGFP)) or by crossing the transgenic Sf1:Cre driver to a GFP reporter strain (Z/EG(Sf1:Cre)). Strikingly, VMH projections were visible early, at embryonic (E) 10.5, when few postmitotic SF1 neurons have been born, suggesting that formation of VMH circuitry begins at the onset of neurogenesis. At E14.5, comparison of these two reporter lines revealed that SF1-positive neurons in the ventrolateral VMH (VMH(vl)) persist in Z/EG(Sf1:Cre) embryos but are virtually absent in Sf-1(TauGFP). Therefore, although the entire VMH including the VMH(vl) shares a common lineage, the VMH(vl) further differentiates into a neuronal cluster devoid of SF-1. At birth, extensive VMH projections to broad regions of the brain were observed in both mouse reporter lines, matching well with those previously discovered by injection of axonal anterograde tracers in adult rats. In summary, our genetic tracing studies show that VMH efferent projections are highly conserved in rodents and are established far earlier than previously appreciated. Moreover, our results imply that neurons in the VMH(vl) adopt a distinct fate early in development, which might underlie the unique physiological functions associated with this VMH subregion.

Revisiting the Ventral Medial Nucleus of the Hypothalamus: The Roles of SF-1 Neurons in Energy Homeostasis

Obesity, diabetes, and other metabolic complications are growing concerns for public health and could lead to detrimental life-threatening conditions. Neurons whose activities are required for energy and glucose homeostasis are found in a number of hypothalamic nuclei. In the early twentieth century, the ventral medial nucleus of the hypothalamus (VMH) was the first site reported to play a prominent role in the regulation of energy homeostasis through control of food intake and energy expenditure. Recent studies using sophisticated genetic tools have further highlighted the importance of the VMH and have extended our understanding of the physiological role of the nucleus in regulation of energy homeostasis. These genetic studies were preceded by the identification of steroidogenic factor-1 (SF-1) as a marker of the VMH. This review focuses on the emerging homeostatic roles of the SF-1 neurons in the VMH discovered through the use of genetic models, particularly highlighting the control of energy, and glucose homeostasis.

Leptin signaling and circuits in puberty and fertility

Leptin is an adipocyte-derived hormone involved in a myriad of physiological process, including the control of energy balance and several neuroendocrine axes. Leptin-deficient mice and humans are obese, diabetic, and display a series of neuroendocrine and autonomic abnormalities. These individuals are infertile due to a lack of appropriate pubertal development and inadequate synthesis and secretion of gonadotropins and gonadal steroids. Leptin receptors are expressed in many organs and tissues, including those related to the control of reproductive physiology (e.g., the hypothalamus, pituitary gland, and gonads). In the last decade, it has become clear that leptin receptors located in the brain are major players in most leptin actions, including reproduction. Moreover, the recent development of molecular techniques for brain mapping and the use of genetically modified mouse models have generated crucial new findings for understanding leptin physiology and the metabolic influences on reproductive health. In the present review, we will highlight the new advances in the field, discuss the apparent contradictions, and underline the relevance of this complex physiological system to human health. We will focus our review on the hypothalamic circuitry and potential signaling pathways relevant to leptin’s effects in reproductive control, which have been identified with the use of cutting-edge technologies of molecular mapping and conditional knockouts.

Evidence that sex chromosome genes affect sexual differentiation of female sexual behavior

Female receptivity including the immobile hormone-dependent lordosis posture is essential for successful reproduction in rodents. It is well documented that lordosis is organized during the perinatal period when the actions of androgens decrease the males' ability to display this behavior in adulthood. Conversely the absence of androgens, and the presence of low levels of prepubertal estrogens, preserve circuitry that regulates this behavior in females. The current study set out to determine whether sex chromosomal genes are involved in the differentiation of this behavior. An agonadal mouse model was used to test this hypothesis. The SF-1 gene (Nr5a1) is required for development of gonads and adrenal glands, and knockout mice are consequently not exposed to endogenous gonadal steroids. Thus contributions of sex chromosome genes can be disassociated from the actions of estrogens. Use of this model reveals a direct genetic contribution from sex chromosomes in the display of lordosis and other female-typical sexual behavior patterns. It is likely that the concentrations of gonadal steroids present during normal male development modify the actions of sex chromosome genes on the potential to display female sexual behavior.

Steroidogenic factor 1 and the central nervous system

Steroidogenic factor 1 (SF-1; officially designated NR5a1) is a member of a nuclear receptor superfamily with important roles in the development of endocrine systems. Studies with global and tissue-specific (i.e. central nervous system) knockout mice have revealed several roles of SF-1 in brain. These include morphological effects on the development of the ventromedial nucleus of the hypothalamus and functional effects on body weight regulation through modulation of physical activity, anxiety-like behaviours and female sexual behaviours. Although such defects are almost certainly a result of the absence of SF-1 acting as a transcription factor in the hypothalamus, global SF-1 knockout mice also represent a model for studying the sex differences in the brain that develop in the absence of exposure to foetal sex steroid hormones as a result of the absence of gonads. In the present review, current knowledge of the roles of SF-1 protein in the central nervous system is discussed.

Distinct hypothalamic neurons mediate estrogenic effects on energy homeostasis and reproduction

Estrogens regulate body weight and reproduction primarily through actions on estrogen receptor-α (ERα). However, ERα-expressing cells mediating these effects are not identified. We demonstrate that brain-specific deletion of ERα in female mice causes abdominal obesity stemming from both hyperphagia and hypometabolism. Hypometabolism and abdominal obesity, but not hyperphagia, are recapitulated in female mice lacking ERα in hypothalamic steroidogenic factor-1 (SF1) neurons. In contrast, deletion of ERα in hypothalamic pro-opiomelanocortin (POMC) neurons leads to hyperphagia, without directly influencing energy expenditure or fat distribution. Further, simultaneous deletion of ERα from both SF1 and POMC neurons causes hypometabolism, hyperphagia, and increased visceral adiposity. Additionally, female mice lacking ERα in SF1 neurons develop anovulation and infertility, while POMC-specific deletion of ERα inhibits negative feedback regulation of estrogens and impairs fertility in females. These results indicate that estrogens act on distinct hypothalamic ERα neurons to regulate different aspects of energy homeostasis and reproduction.

Cooperation of sex chromosomal genes and endocrine influences for hypothalamic sexual differentiation

There is little debate that mammalian sexual differentiation starts from the perspective of two primary sexes that correspond to differential sex chromosomes (X versus Y) that lead to individuals with sex typical characteristics. Sex steroid hormones account for most aspects of brain sexual differentiation, however, a growing literature has raised important questions about the role of sex chromosomal genes separate from sex steroid actions. Several important model animals are being used to address these issues and, in particular, they are taking advantage of molecular genetic approaches using different mouse strains. The current review examines the cooperation of genetic and endocrine influences from the perspective of behavioral and morphological hypothalamic sexual differentiation, first in adults and then in development. In the final analysis, there is an ongoing need to account for the influence of hormones in the context of underlying genetic circumstances and null hormone conditions.

Sex differences in the neural circuit that mediates female sexual receptivity

Female sexual behavior in rodents, typified by the lordosis posture, is hormone-dependent and sex-specific. Ovarian hormones control this behavior via receptors in the hypothalamic ventromedial nucleus (VMH). This review considers the sex differences in the morphology, neurochemistry and neural circuitry of the VMH to gain insights into the mechanisms that control lordosis. The VMH is larger in males compared with females, due to more synaptic connections. Another sex difference is the responsiveness to estradiol, with males exhibiting muted, and in some cases reverse, effects compared with females. The lack of lordosis in males may be explained by differences in synaptic organization or estrogen responsiveness, or both, in the VMH. However, given that damage to other brain regions unmasks lordosis behavior in males, a male-typical VMH is unlikely the main factor that prevents lordosis. In females, key questions remain regarding the mechanisms whereby ovarian hormones modulate VMH function to promote lordosis.

Cross-Talk between Metabolism and Reproduction: The Role of POMC and SF1 Neurons

Energy homeostasis and reproduction require tight coordination, but the mechanisms underlying their interaction are not fully understood. Two sets of hypothalamic neurons, namely pro-opiomelanocortin (POMC) neurons in the arcuate nucleus and steroidogenic factor-1 (SF1) neurons in the ventromedial hypothalamic nucleus, are emerging as critical nodes where metabolic and reproductive signals communicate. This view is supported by recent genetic studies showing that disruption of metabolic signals (e.g., leptin and insulin) or reproductive signals (e.g., estradiol) in these neurons leads to impaired regulation of both energy homeostasis and fertility. In this review, we will examine the potential mechanisms of neuronal communication between POMC, SF1, and gonadotropin-releasing hormone neurons in the regulation of metabolism and reproduction.

Hypothalamic sites of leptin action linking metabolism and reproduction

A critical amount of energy reserve is necessary for puberty initiation, for normal sexual maturation and maintenance of cyclicity and fertility in females of most species. Therefore, the existence of circulating metabolic cues which directly modulate the hypothalamus-pituitary-gonad axis is predictable. The adipocyte-derived hormone leptin is one of these cues having been studied extensively in the context of regulating the reproductive physiology. Humans and mice lacking leptin (ob/ob) or leptin receptor (LepR, db/db) are infertile. Leptin administration to leptin-deficient subjects and ob/ob mice induces puberty and restores fertility. LepR is expressed in brain, pituitary gland and gonads, but studies using genetically engineered mouse models determined that the brain plays a major role. Recently, it has been made clear that leptin acts indirectly on gonadotropin-releasing hormone (GnRH)-secreting cells via actions on interneurons. However, the exact site(s) of leptin action has been difficult to determine. In this review, we discuss the recent advances in the field focused on the identification of potential site(s) or specific neuronal populations involved in leptin's effects in the neuroendocrine reproductive axis.

Location of glutamatergic/aspartatergic neurons projecting to the hypothalamic ventromedial nucleus studied by autoradiography of retrogradely transported [³H]D-aspartate

The hypothalamic ventromedial nucleus is a prominent cell group, which is involved in the control of feeding, sexual behavior and cardiovascular function as well as having other functions. The nucleus receives inputs from various forebrain structures and has a dense glutamatergic innervation. The aim of the present investigations was to reveal the location of glutamatergic neurons in the telencephalon and diencephalon projecting to this hypothalamic cell group. [(3)H]d-aspartate retrograde autoradiography was used injecting the tracer into the ventromedial nucleus. We detected radiolabeled neurons in telencephalic structures including the lateral septum, bed nucleus of the stria terminalis and the amygdala, and in various diencephalic regions, such as the medial preoptic area, hypothalamic paraventricular nucleus, periventricular nucleus, anterior hypothalamic area, ventral premamillary nucleus, thalamic paraventricular and parataenial nuclei and in the hypothalamic ventromedial nucleus itself. Our observations are the first data on the location of glutamatergic neurons terminating in the hypothalamic ventromedial nucleus. The findings indicate that glutamatergic innervation of the ventromedial nucleus is very complex.