Targeted disruption of the pituitary glycoprotein hormone alpha-subunit produces hypogonadal and hypothyroid mice

Role of microRNAs in pituitary gonadotrope cells

The gonadotrope cells within the pituitary control vital processes of reproduction by producing follicle stimulating hormone (FSH) and luteinizing hormone (LH). Both external stimuli and internal regulatory factors contribute to the regulation of gonadotrope development and function. In recent years, growing evidences indicate that microRNAs (miRNAs), which regulate gene expression post-transcriptionally, play critical roles in multiple processes of gonadotrope development and function, including the syntheses of α or β subunits of FSH and LH, the secretion of LH, the regulation of GnRH signaling, and the maintenance of gonadotrope cell kinetics. Here, we review recent advances of miRNAs' expression, functions and mechanisms approached by using miRNA knockout mouse models, in silico analysis and the in vitro cultures of primary pituitary cells and gonadotrope-derived cell lines. By summarizing and discussing different roles of miRNAs in gonadotropes, this minireview helps to gain insights into the complex molecular network in gonadotropes and reproduction.

Novel Aspects of cAMP-Response Element Modulator (CREM) Role in Spermatogenesis and Male Fertility

Spermatogenesis is a very complex process with an intricate transcriptional regulation. The transition from the diploid to the haploid state requires the involvement of specialized genes in meiosis, among other specific functions for the formation of the spermatozoon. The transcription factor cAMP-response element modulator (CREM) is a key modulator that triggers the differentiation of the germ cell into the spermatozoon through the modification of gene expression. CREM has multiple repressor and activator isoforms whose expression is tissue-cell-type specific and tightly regulated by various factors at the transcriptional, post-transcriptional and post-translational level. The activator isoform CREMτ controls the expression of several relevant genes in post-meiotic stages of spermatogenesis. In addition, exposure to xenobiotics negatively affects CREMτ expression, which is linked to male infertility. On the other hand, antioxidants could have a positive effect on CREMτ expression and improve sperm parameters in idiopathically infertile men. Therefore, CREM expression could be used as a biomarker to detect and even counteract male infertility. This review examines the importance of CREM as a transcription factor for sperm production and its relevance in male fertility, infertility and the response to environmental xenobiotics that may affect CREMτ expression and the downstream regulation that alters male fertility. Also, some health disorders in which CREM expression is altered are discussed.

Genetic variants of gonadotrophins and their receptors: Impact on the diagnosis and management of the infertile patient

This narrative review is concerned with genetic variants of the genes encoding gonadotrophin subunits and their receptors, as well as their implications into the diagnosis and treatment of infertility. We first review briefly the basics of molecular biology and biochemistry of gonadotrophin and gonadotrophin receptor structure and function, then describe the phenotypic effects of polymorphisms and mutations of these genes, followed by diagnostic aspects. We will then summarise the information that inactivating gonadotrophin receptor mutations have provided about the controversial topic of extragonadal gonadotrophin action. Finally, we will close with the current and future therapeutic approaches on patients with gonadotrophin and their receptor mutations.

Role of microRNAs in etiology of azoospermia and their application as non-invasive biomarkers in diagnosis of azoospermic patients

Azoospermia is a common cause of male infertility without any sperm in the semen and consists of ∼1% of all males and ∼15% of infertile ones. Currently, no accurate non-invasive diagnostic method exists for patients with azoospermia and testis biopsy is mandatory to determine if any spermatozoa exist in the testes. Studies have clarified that the expression of some distinct microRNAs shows alterations in azoospermic patients. MicroRNAs play critical roles during spermatogenesis and their dysregulation can defect this process. Here, we review studied microRNAs involved in the pathogenesis of azoospermia and their target genes. Moreover, we will imply the utility of seminal plasma microRNAs as non-invasive diagnostic biomarkers for azoospermia. We hope such studies could help patients with azoospermia in both diagnosis and treatment, in order that they could father their own biological children.

Specific Transcriptomic Signatures and Dual Regulation of Steroidogenesis Between Fetal and Adult Mouse Leydig Cells

Leydig cells (LC) are the main testicular androgen-producing cells. In eutherian mammals, two types of LCs emerge successively during testicular development, fetal Leydig cells (FLCs) and adult Leydig cells (ALCs). Both display significant differences in androgen production and regulation. Using bulk RNA sequencing, we compared the transcriptomes of both LC populations to characterize their specific transcriptional and functional features. Despite similar transcriptomic profiles, a quarter of the genes show significant variations in expression between FLCs and ALCs. Non-transcriptional events, such as alternative splicing was also observed, including a high rate of intron retention in FLCs compared to ALCs. The use of single-cell RNA sequencing data also allowed the identification of nine FLC-specific genes and 50 ALC-specific genes. Expression of the corticotropin-releasing hormone 1 (Crhr1) receptor and the ACTH receptor melanocortin type 2 receptor (Mc2r) specifically in FLCs suggests a dual regulation of steroidogenesis. The androstenedione synthesis by FLCs is stimulated by luteinizing hormone (LH), corticotrophin-releasing hormone (CRH), and adrenocorticotropic hormone (ACTH) whereas the testosterone synthesis by ALCs is dependent exclusively on LH. Overall, our study provides a useful database to explore LC development and functions.

Unconventional Actions of Glycoprotein Hormone Subunits: A Comprehensive Review

The glycoprotein hormones (GPH) are heterodimers composed of a common α subunit and a specific β subunit. They act by activating specific leucine-rich repeat G protein-coupled receptors. However, individual subunits have been shown to elicit responses in cells devoid of the receptor for the dimeric hormones. The α subunit is involved in prolactin production from different tissues. The human chorionic gonadotropin β subunit (βhCG) plays determinant roles in placentation and in cancer development and metastasis. A truncated form of the thyrotropin (TSH) β subunit is also reported to have biological effects. The GPH α- and β subunits are derived from precursor genes (gpa and gpb, respectively), which are expressed in most invertebrate species and are still represented in vertebrates as GPH subunit paralogs (gpa2 and gpb5, respectively). No specific receptor has been found for the vertebrate GPA2 and GPB5 even if their heterodimeric form is able to activate the TSH receptor in mammals. Interestingly, GPA and GPB are phylogenetically and structurally related to cysteine-knot growth factors (CKGF) and particularly to a group of antagonists that act independently on any receptor. This review article summarizes the observed actions of individual GPH subunits and presents the current hypotheses of how these actions might be induced. New approaches are also proposed in light of the evolutionary relatedness with antagonists of the CKGF family of proteins.

S100a4-Cre-mediated deletion of Patched1 causes hypogonadotropic hypogonadism: role of pituitary hematopoietic cells in endocrine regulation

Hormones produced by the anterior pituitary gland regulate an array of important physiological functions, but pituitary hormone disorders are not fully understood. Herein we report that genetically-engineered mice with deletion of the hedgehog signaling receptor Patched1 by S100a4 promoter-driven Cre recombinase (S100a4-Cre;Ptch1fl/fl mutants) exhibit adult-onset hypogonadotropic hypogonadism and multiple pituitary hormone disorders. During the transition from puberty to adult, S100a4-Cre;Ptch1fl/fl mice of both sexes develop hypogonadism coupled with reduced gonadotropin levels. Their pituitary glands also display severe structural and functional abnormalities, as revealed by transmission electron microscopy and expression of key genes regulating pituitary endocrine functions. S100a4-Cre activity in the anterior pituitary gland is restricted to CD45+ cells of hematopoietic origin, including folliculo-stellate cells and other immune cell types, causing sex-specific changes in the expression of genes regulating the local microenvironment of the anterior pituitary. These findings provide in vivo evidence for the importance of pituitary hematopoietic cells in regulating fertility and endocrine function, in particular during sexual maturation and likely through sexually dimorphic mechanisms. These findings support a previously unrecognized role of hematopoietic cells in causing hypogonadotropic hypogonadism and provide inroads into the molecular and cellular basis for pituitary hormone disorders in humans.

The gonadotropin system, lessons from animal models and clinical cases

This review article centers upon family of gonadotropin hormones which consists of two pituitary hormones - follicle-stimulating hormone (FSH) and luteinizing hormone (LH) as well as one non-pituitary hormone - human chorionic gonadotropin (hCG) secreted by placenta, and their receptors. Gonadotropins play an essential role in proper sexual development, puberty, gametogenesis, maintenance of pregnancy and male sexual differentiation during the fetal development. They belong to the family of glycoprotein hormones thus they constitute heterodimeric proteins built of common α subunit and hormone-specific β-subunit. Hitherto, several mutations in genes encoding both gonadotropins and their receptors have been identified in humans. Their occurrence resulted in a number of different phenotypes including delayed puberty, primary amenorrhea, hermaphroditism, infertility and hypogonadism. In order to understand the effects of mutations on the phenotype observed in affected patients, detailed molecular studies are required to map the relationship between the structure and function of gonadotropins and their receptors. Nonetheless, in vitro assays are often insufficient to understand physiology. Therefore, several animal models have been developed to unravel the physiological roles of gonadotropins and their receptors.

Regulation of Pituitary Progenitor Differentiation by β-Catenin

The pituitary gland is a critical organ that is necessary for many physiological processes, including growth, reproduction, and stress response. The secretion of pituitary hormones from specific cell types regulates these essential processes. Pituitary hormone cell types arise from a common pool of pituitary progenitors, and mutations that disrupt the formation and differentiation of pituitary progenitors result in hypopituitarism. Canonical WNT signaling through CTNNB1 (β-catenin) is known to regulate the formation of the POU1F1 lineage of pituitary cell types. When β-catenin is deleted during the initial formation of the pituitary progenitors, Pou1f1 is not transcribed, which leads to the loss of the POU1F1 lineage. However, when β-catenin is deleted after lineage specification, there is no observable effect. Similarly, the generation of a β-catenin gain-of-function allele in early pituitary progenitors or stem cells results in the formation of craniopharyngiomas, whereas stimulating β-catenin in differentiated cell types has no effect. PROP1 is a pituitary-specific transcription factor, and the peak of PROP1 expression coincides with a critical time point in pituitary organogenesis-that is, after pituitary progenitor formation but before lineage specification. We used a Prop1-cre to conduct both loss- and gain-of-function studies on β-catenin during this critical time point. Our results demonstrate that pituitary progenitors remain sensitive to both loss and gain of β-catenin at this time point, and that either manipulation results in hypopituitarism.

Mouse models for the analysis of gonadotropin secretion and action

Gonadotropins are pituitary gonadotrope-derived glycoprotein hormones. They act by binding to G-protein coupled receptors on gonads. Gonadotropins play critical roles in reproduction by regulating both gametogenesis and steroidogenesis. Although biochemical and physiological studies provided a wealth of knowledge, gene manipulation techniques using novel mouse models gave new insights into gonadotropin synthesis, secretion and action. Both gain of function and loss of function mouse models for understanding gonadotropin action in a whole animal context have already been generated. Moreover, recent studies on gonadotropin actions in non-gonadal tissues challenged the central dogma of classical gonadotropin actions in gonads and revealed new signaling pathways in these non-gonadal tissues. In this Chapter, we have discussed our current understanding of gonadotropin synthesis, secretion and action using a variety of genetically engineered mouse models.

Role of androgens in the ovary

It has been well established for decades that androgens, namely testosterone (T) plays an important role in female reproductive physiology as the precursor for oestradiol (E₂). However, in the last decade a direct role for androgens, acting via the androgen receptor (AR), in female reproductive function has been confirmed. Deciphering the specific roles of androgens in ovarian function has been hindered as complete androgen resistant females cannot be generated by natural breeding. In addition, androgens can be converted into estrogens which has caused confusion when interpreting findings from pharmacological studies, as observed effects could have been mediated via the AR or estrogen receptor. The creation and analysis of genetic mouse models with global and cell-specific disruption of the Ar gene, the sole mediator of pure androgenic action, has now allowed the elucidation of a role for AR-mediated androgen actions in the regulation of normal and pathological ovarian function. This review aims to summarize findings from clinical, animal, pharmacological and novel genetic AR mouse models to provide an understanding of the important roles androgens play in the ovary, as well as providing insights into the human implications of these roles.

Molecular regulation of follicle-stimulating hormone synthesis, secretion and action

Follicle-stimulating hormone (FSH) plays fundamental roles in male and female fertility. FSH is a heterodimeric glycoprotein expressed by gonadotrophs in the anterior pituitary. The hormone-specific FSHβ-subunit is non-covalently associated with the common α-subunit that is also present in the luteinizing hormone (LH), another gonadotrophic hormone secreted by gonadotrophs and thyroid-stimulating hormone (TSH) secreted by thyrotrophs. Several decades of research led to the purification, structural characterization and physiological regulation of FSH in a variety of species including humans. With the advent of molecular tools, availability of immortalized gonadotroph cell lines and genetically modified mouse models, our knowledge on molecular mechanisms of FSH regulation has tremendously expanded. Several key players that regulate FSH synthesis, sorting, secretion and action in gonads and extragonadal tissues have been identified in a physiological setting. Novel post-transcriptional and post-translational regulatory mechanisms have also been identified that provide additional layers of regulation mediating FSH homeostasis. Recombinant human FSH analogs hold promise for a variety of clinical applications, whereas blocking antibodies against FSH may prove efficacious for preventing age-dependent bone loss and adiposity. It is anticipated that several exciting new discoveries uncovering all aspects of FSH biology will soon be forthcoming.

Foxo1 Is Required for Normal Somatotrope Differentiation

The etiology for half of congenital hypopituitarism cases is unknown. Our long-term goal is to expand the molecular diagnoses for congenital hypopituitarism by identifying genes that contribute to this condition. We have previously shown that the forkhead box transcription factor, FOXO1, is present in approximately half of somatotropes at embryonic day (e) 18.5, suggesting it may have a role in somatotrope differentiation or function. To elucidate the role of FOXO1 in somatotrope differentiation and function, Foxo1 was conditionally deleted from the anterior pituitary (Foxo1^Δpit). Uncommitted progenitor cells are maintained and able to commit to the somatotrope lineage normally based on the expression patterns of Sox2, a marker of uncommitted pituitary progenitors, and Pou1f1 (also known as Pit1), which marks committed progenitors. Interestingly, Foxo1^Δpit embryonic mice exhibit delayed somatotrope differentiation as evidenced by an almost complete absence of GH immunoreactivity at e16.5 and reduced expression of Gh at e18.5 and postnatal day (P) 3. Consistent with this conclusion, expression of GHRH receptor, a marker of terminally differentiated somatotropes, is significantly reduced at e18.5 and P3 in the absence of FOXO1. The mechanism of FOXO1 regulation of somatotrope differentiation may involve the basic helix-loop-helix transcription factor, Neurod4, which has been implicated in somatotrope differentiation and is significantly reduced in Foxo1^Δpit mice. Foxo1^Δpit mice do not exhibit growth defects, and at P21 their pituitary glands exhibit a normal distribution of somatotropes. These studies demonstrate that FOXO1 is important for initial somatotrope specification embryonically but is dispensable for postnatal somatotrope expansion and growth.

Mouse Models for the Study of Synthesis, Secretion, and Action of Pituitary Gonadotropins

Gonadotropins play fundamental roles in reproduction. More than 30years ago, Cga transgenic mice were generated, and more than 20years ago, the phenotypes of Cga null mice were reported. Since then, numerous mouse strains have been generated and characterized to address several questions in reproductive biology involving gonadotropin synthesis, secretion, and action. More recently, extragonadal expression, and in some cases, functions of gonadotropins in nongonadal tissues have been identified. Several genomic and proteomic approaches including novel mouse genome editing tools are available now. It is anticipated that these and other emerging technologies will be useful to build an integrated network of gonadotropin signaling pathways in various tissues. Undoubtedly, research on gonadotropins will continue to provide new knowledge and allow us transcend from benchside to the bedside.

Gene Expression in Mouse Thyrotrope Adenoma: Transcription Elongation Factor Stimulates Proliferation

Thyrotrope hyperplasia and hypertrophy are common responses to primary hypothyroidism. To understand the genetic regulation of these processes, we studied gene expression changes in the pituitaries of Cga(-/-) mice, which are deficient in the common α-subunit of TSH, LH, and FSH. These mice have thyrotrope hypertrophy and hyperplasia and develop thyrotrope adenoma. We report that cell proliferation is increased, but the expression of most stem cell markers is unchanged. The α-subunit is required for secretion of the glycoprotein hormone β-subunits, and mutants exhibit elevated expression of many genes involved in the unfolded protein response, consistent with dilation and stress of the endoplasmic reticulum. Mutants have elevated expression of transcription factors that are important in thyrotrope function, such as Gata2 and Islet 1, and those that stimulate proliferation, including Nupr1, E2f1, and Etv5. We characterized the expression and function of a novel, overexpressed gene, transcription elongation factor A (SII)-like 5 (Tceal5). Stable expression of Tceal5 in a pituitary progenitor cell line is sufficient to increase cell proliferation. Thus, Tceal5 may act as a proto-oncogene. This study provides a rich resource for comparing pituitary transcriptomes and an analysis of gene expression networks.

Growth Arrest Specific-1 (GAS1) Is a C/EBP Target Gene That Functions in Ovulation and Corpus Luteum Formation in Mice

Ovulation and luteinization are initiated in preovulatory follicles by the luteinizing hormone (LH) surge; however, the signaling events that mediate LH actions in these follicles remain incompletely defined. Two key transcription factors that are targets of LH surge are C/EBPalpha and C/EBPbeta, and their depletion in granulosa cells results in complete infertility. Microarray analyses of these mutant mice revealed altered expression of a number of genes, including growth arrest specific-1 (Gas1). To investigate functions of Gas1 in ovulation- and luteinization-related processes, we crossed Cyp19a1-Cre and Gas1^flox/flox mice to conditionally delete Gas1 in granulosa and cumulus cells. While expression of Gas1 is dramatically increased in granulosa and cumulus cells around 12–16 h post-human chorionic gonadotropin (hCG) stimulation in wild-type mice, this increase is abolished in Cebpa/b double mutant and in Gas1 mutant mice. GAS1 is also dynamically expressed in stromal cells of the ovary independent of C/EBPalpha/beta. Female Gas1 mutant mice are fertile, exhibit enhanced rates of ovulation, increased fertility, and higher levels of Areg and Lhcgr mRNA in granulosa cells. The morphological appearance and vascularization of corpora lutea appeared normal in these mutant females. Interestingly, levels of mRNA for a number of genes (Cyp11a1, Star, Wnt4, Prlr, Cd52, and Sema3a) associated with luteinization are decreased in corpora lutea of Gas1 mutant mice as compared with controls at 24 h post-hCG; these differences were no longer detectable by 48 h post-hCG. The C/EBP target Gas1 is induced in granulosa cells and is associated with ovulation and luteinization.

ISL1 Is Necessary for Maximal Thyrotrope Response to Hypothyroidism

ISLET1 is a homeodomain transcription factor necessary for development of the pituitary, retina, motor neurons, heart, and pancreas. Isl1-deficient mice (Isl1(-/-)) die early during embryogenesis at embryonic day 10.5 due to heart defects, and at that time, they have an undersized pituitary primordium. ISL1 is expressed in differentiating pituitary cells in early embryogenesis. Here, we report the cell-specific expression of ISL1 and assessment of its role in gonadotropes and thyrotropes. Isl1 expression is elevated in pituitaries of Cga(-/-) mice, a model of hypothyroidism with thyrotrope hypertrophy and hyperplasia. Thyrotrope-specific disruption of Isl1 with Tshb-cre is permissive for normal serum TSH, but T4 levels are decreased, suggesting decreased thyrotrope function. Inducing hypothyroidism in normal mice causes a reduction in T4 levels and dramatically elevated TSH response, but mice with thyrotrope-specific disruption of Isl1 have a blunted TSH response. In contrast, deletion of Isl1 in gonadotropes with an Lhb-cre transgene has no obvious effect on gonadotrope function or fertility. These results show that ISL1 is necessary for maximal thyrotrope response to hypothyroidism, in addition to its role in development of Rathke's pouch.

Role of androgens in normal and pathological ovarian function

Androgens mediate their actions via the androgen receptor (AR), a member of the nuclear receptor superfamily. AR-mediated androgen action is essential in male reproductive development and function; however, only in the last decade has the suspected but unproven role for AR-mediated actions in female reproduction been firmly established. Deciphering the specific roles and precise pathways by which AR-mediated actions regulate ovarian function has been hindered by confusion on how to interpret results from pharmacological studies using androgens that can be converted into oestrogens, which exert actions via the oestrogen receptors. The generation and analysis of global and cell-specific femaleArknockout mouse models have deduced a role for AR-mediated actions in regulating ovarian function, maintaining female fertility, and have begun to unravel the mechanisms by which AR-mediated androgen actions regulate follicle health, development and ovulation. Furthermore, observational findings from human studies and animal models provide substantial evidence to support a role for AR-mediated effects not only in normal ovarian function but also in the development of the frequent ovarian pathological disorder, polycystic ovarian syndrome (PCOS). This review focuses on combining the findings from observational studies in humans, pharmacological studies and animal models to reveal the roles of AR-mediated actions in normal and pathological ovarian function. Together these findings will enable us to begin understanding the important roles of AR actions in the regulation of female fertility and ovarian ageing, as well as providing insights into the role of AR actions in the androgen-associated reproductive disorder PCOS.

Morphological and functional maturation of Leydig cells: from rodent models to primates

BACKGROUND

Leydig cells (LC) are the sites of testicular androgen production. Development of LC occurs in the testes of most mammalian species as two distinct growth phases, i.e. as fetal and pubertal/adult populations. In primates there are indications of a third neonatal growth phase. LC androgen production begins in embryonic life and is crucial for the intrauterine masculinization of the male fetal genital tract and brain, and continues until birth after which it rapidly declines. A short post-natal phase of LC activity in primates (including human) termed 'mini-puberty' precedes the period of juvenile quiescence. The adult population of LC evolves, depending on species, in mid- to late-prepuberty upon reawakening of the hypothalamic-pituitary-testicular axis, and these cells are responsible for testicular androgen production in adult life, which continues with a slight gradual decline until senescence. This review is an updated comparative analysis of the functional and morphological maturation of LC in model species with special reference to rodents and primates.

METHODS

Pubmed, Scopus, Web of Science and Google Scholar databases were searched between December 2012 and October 2014. Studies published in languages other than English or German were excluded, as were data in abstract form only. Studies available on primates were primarily examined and compared with available data from specific animal models with emphasis on rodents.

RESULTS

Expression of different marker genes in rodents provides evidence that at least two distinct progenitor lineages give rise to the fetal LC (FLC) population, one arising from the coelomic epithelium and the other from specialized vascular-associated cells along the gonad-mesonephros border. There is general agreement that the formation and functioning of the FLC population in rodents is gonadotrophin-responsive but not gonadotrophin-dependent. In contrast, although there is in primates some controversy on the role of gonadotrophins in the formation of the FLC population, there is consensus about the essential role of gonadotrophins in testosterone production. Like the FLC population, adult Leydig cells (ALC) in rodents arise from stem cells, which have their origin in the fetal testis. In contrast, in primates the ALC population is thought to originate from FLC, which undergo several cycles of regression and redifferentiation before giving rise to the mature ALC population, as well as from differentiation of stem cells/precursor cells. Despite this difference in origin, both in primates and rodents the formation of the mature and functionally active ALC population is critically dependent on the pituitary gonadotrophin, LH. From studies on rodents considerable knowledge has emerged on factors that are involved besides LH in the regulation of this developmental process. Whether the same factors also play a role in the development of the mature primate LC population awaits further investigation.

CONCLUSION

Distinct populations of LC develop along the life span of males, including fetal, neonatal (primates) and ALC. Despite differences in the LC lineages of rodents and primates, the end product is a mature population of LC with the main function to provide androgens necessary for the maintenance of spermatogenesis and extra-gonadal androgen actions.

Mammalian COPII coat component SEC24C is required for embryonic development in mice

COPII-coated vesicles mediate the transport of newly synthesized proteins from the endoplasmic reticulum to the Golgi. SEC24 is the COPII component primarily responsible for recruitment of protein cargoes into nascent vesicles. There are four Sec24 paralogs in mammals, with mice deficient in SEC24A, -B, and -D exhibiting a wide range of phenotypes. We now report the characterization of mice with deficiency in the fourth Sec24 paralog, SEC24C. Although mice haploinsufficient for Sec24c exhibit no apparent abnormalities, homozygous deficiency results in embryonic lethality at approximately embryonic day 7. Tissue-specific deletion of Sec24c in hepatocytes, pancreatic cells, smooth muscle cells, and intestinal epithelial cells results in phenotypically normal mice. Thus, SEC24C is required in early mammalian development but is dispensable in a number of tissues, likely as a result of compensation by other Sec24 paralogs. The embryonic lethality resulting from loss of SEC24C occurs considerably later than the lethality previously observed in SEC24D deficiency; it is clearly distinct from the restricted neural tube phenotype of Sec24b null embryos and the mild hypocholesterolemic phenotype of adult Sec24a null mice. Taken together, these results demonstrate that the four Sec24 paralogs have developed unique functions over the course of vertebrate evolution.

Genetic Models for the Study of Luteinizing Hormone Receptor Function

The luteinizing hormone/chorionic gonadotropin receptor (LHCGR) is essential for fertility in men and women. LHCGR binds luteinizing hormone (LH) as well as the highly homologous chorionic gonadotropin. Signaling from LHCGR is required for steroidogenesis and gametogenesis in males and females and for sexual differentiation in the male. The importance of LHCGR in reproductive physiology is underscored by the large number of naturally occurring inactivating and activating mutations in the receptor that result in reproductive disorders. Consequently, several genetically modified mouse models have been developed for the study of LHCGR function. They include targeted deletion of LH and LHCGR that mimic inactivating mutations in hormone and receptor, expression of a constitutively active mutant in LHCGR that mimics activating mutations associated with familial male-limited precocious puberty and transgenic models of LH and hCG overexpression. This review summarizes the salient findings from these models and their utility in understanding the physiological and pathological consequences of loss and gain of function in LHCGR signaling.

Sirt1-deficient mice have hypogonadotropic hypogonadism due to defective GnRH neuronal migration

Hypogonadatropic hypogonadism (HH) can be acquired through energy restriction or may be inherited as congenital hypogonadotropic hypogonadism and its anosmia-associated form, Kallmann's syndrome. Congenital hypogonadotropic hypogonadism is associated with mutations in a group of genes that impact fibroblast growth factor 8 (FGF8) function. The Sirt1 gene encodes a nicotinamide adenine dinucleotide-dependent histone deacetylase that links intracellular metabolic stress to gene expression. Herein Sirt1(-/-) mice are shown to have HH due to failed GnRH neuronal migration. Sirtuin-1 (Sirt1) catalytic function induces GnRH neuronal migration via binding and deacetylating cortactin. Sirt1 colocalized with cortactin in GnRH neurons in vitro. Sirt1 colocalization with cortactin was regulated in an FGF8/fibroblast growth factor receptor-1 dependent manner. The profound effect of Sirt1 on the hormonal status of Sirt1(-/-) mice, mediated via defective GnRH neuronal migration, links energy metabolism directly to the hypogonadal state. Sirt1-cortactin may serve as the distal transducer of neuronal migration mediated by the FGF8 synexpression group of genes that govern HH.

Pituitary gonadotrophic hormone synthesis, secretion, subunit gene expression and cell structure in normal and follicle-stimulating hormone β knockout, follicle-stimulating hormone receptor knockout, luteinising hormone receptor knockout, hypogonadal and ovariectomised female mice

To investigate the relationship between gonadotroph function and ultrastructure, we have compared, in parallel in female mice, the effects of several different mutations that perturb the hypothalamic-pituitary-gonadal axis. Specifically, serum and pituitary gonadotrophin concentrations, gonadotrophin gene expression, gonadotroph structure and number were measured. Follicle-stimulating hormone β knockout (FSHβKO), follicle-stimulating hormone receptor knockout (FSHRKO), luteinising hormone receptor knockout (LuRKO), hypogonadal (hpg) and ovariectomised mice were compared with control wild-type or heterozygote female mice. Serum levels of LH were elevated in FSHβKO and FSHRKO compared to heterozygote females, reflecting the likely decreased oestrogen production in KO females, as demonstrated by the threadlike uteri and acyclicity. As expected, there was no detectable FSH in the serum or pituitary and an absence of expression of the FSHβ subunit gene in FSHβKO mice. However, there was a significant increase in expression of the FSHβ and LHβ subunit genes in FSHRKO female mice. The morphology of FSHβKO and FSHRKO gonadotrophs was not significantly different from the control, except that secretory granules in FSHRKO gonadotrophs were larger in diameter. In LuRKO and ovariectomised mice, stimulation of LHβ and FSHβ mRNA, as well as serum protein concentrations, were reflected in subcellular changes in gonadotroph morphology, including more dilated rough endoplasmic reticula and fewer, larger secretory granules. In the gonadotophin-releasing hormone deficient hpg mouse, gonadotrophin mRNA and protein levels were significantly lower than in control mice and gonadotrophs were correspondingly smaller with less abundant endoplasmic reticula and reduced numbers of secretory granules. In summary, major differences in pituitary content and serum concentrations of the gonadotrophins LH and FSH were found between control and mutant female mice. These changes were associated with changes in expression of the gonadotrophin subunit genes and were reflected in the cellular structure and secretory granule appearance within the gonadotroph cells.

Mouse models of altered gonadotrophin action: insight into male reproductive disorders

The advent of technologies to genetically manipulate the mouse genome has revolutionised research approaches, providing a unique platform to study the causality of reproductive disorders in vivo. With the relative ease of generating genetically modified (GM) mouse models, the last two decades have yielded multiple loss-of-function and gain-of-function mutation mouse models to explore the role of gonadotrophins and their receptors in reproductive pathologies. This work has provided key insights into the molecular mechanisms underlying reproductive disorders with altered gonadotrophin action, revealing the fundamental roles of these pituitary hormones and their receptors in the hypothalamic–pituitary–gonadal axis. This review will describe GM mouse models of gonadotrophins and their receptors with enhanced or diminished actions, specifically focusing on the male. We will discuss the mechanistic insights gained from these models into male reproductive disorders, and the relationship and understanding provided into male human reproductive disorders originating from altered gonadotrophin action.

Anti-mullerian hormone deficiency in girls with congenital multiple pituitary hormone deficiency

CONTEXT

Anti-Mullerian hormone (AMH) is believed to validly reflect the ovarian reserve. We wanted to test whether congenital absence of gonadotropin stimulation of the ovaries affects AMH production.

OBJECTIVE

The objective of the study was to test the validity of AMH as a marker for the ovarian reserve in females with congenital multiple pituitary hormone deficiency (MPHD; deficiency of three or more axes).

DESIGN

This was a retrospective laboratory study.

SETTING

The study was conducted in the Department of Pediatric Endocrinology in a tertiary center.

PATIENTS

The AMH serum levels were assessed in females with congenital (n = 16; median age 12.5 y, range 0.7-31 y) or acquired (n = 20; 18.5 y, range 2-33 y) MPHD and in controls with short stature (n = 100; 9.7 y, range 2-17 y).

MAIN OUTCOME MEASURE

AMH was measured by AMH Gen II ELISA from Beckmann Coulter.

RESULTS

In the controls, AMH ranged between 1.8 (P3) and 67.8 pmol/L (P97). Three patients with a severe form of congenital MPHD were AMH deficient, whereas the other 33 patients with MPHD had normal AMH levels. There was significantly more AMH deficiency in congenital than in acquired MPHD (P < .05).

CONCLUSIONS

Most girls with MPHD have normal serum AMH levels. However, some females with severe congenital MPHD are AMH deficient. This deficiency might be the result of the total absence of gonadotropins. In these females, AMH is unlikely to be an accurate prognostic parameter of the efficacy of fertility treatment.

Dioxin-induced retardation of development through a reduction in the expression of pituitary hormones and possible involvement of an aryl hydrocarbon receptor in this defect: a comparative study using two strains of mice with different sensitivities to dioxin

We have previously revealed that treating pregnant rats with 2,3,7,8-tetracholorodibenzo-p-dioxin (TCDD) reduces the expression of gonadotropins and growth hormone (GH) in the fetal and neonatal pituitary. A change in gonadotropin expression impairs the testicular expression of steroidogenic proteins in perinatal pups, and imprint defects in sexual behavior after reaching maturity. In this study, we examined whether TCDD also affects the expression of gonadotropin and GH in mice using C57BL/6J and DBA/2J strains which express the aryl hydrocarbon receptor (Ahr) exhibiting a different affinity for TCDD. When pregnant C57BL/6J mice at gestational day (GD) 12 were given oral TCDD (0.2-20 μg/kg), all doses significantly attenuated the pituitary expression of gonadotropin mRNAs in fetuses at GD18. On the other hand, in DBA/2J mice, a much higher dose of TCDD (20 μg/kg) was needed to produce a significant attenuation. Such reduction in the C57BL/6J strain continued until at least postnatal day (PND) 4. In agreement with this, TCDD reduced the testicular expression of steroidogenic proteins in C57BL/6J neonates at PND2 and 4, although the same did not occur in the fetal testis and ovary. Furthermore, TCDD reduced the perinatal expression of GH, litter size and the body weight of newborn pups only in the C57BL/6J strain. These results suggest that 1) also in mice, maternal exposure to TCDD attenuates gonadotropin-regulated steroidogenesis and GH expression leading to the impairment of pup development and sexual immaturity; and 2) Ahr activation during the late fetal and early postnatal stages is required for these defects.

Luteinizing hormone and human chorionic gonadotropin: distinguishing unique physiologic roles

Luteinizing hormone (LH) and human chorionic gonadotropin (hCG) are integral components of the hypothalamic-pituitary-gonadal axis, which controls sexual maturation and functionality. In the absence of signaling through their shared receptor, fetal sexual differentiation and post-natal development cannot proceed normally. Although they share a high degree of homology, the physiologic roles of these hormones are unique, governed by differences in expression pattern, biopotency and regulation. Whereas LH is a key regulator of gonadal steroidogenesis and ovulation, hCG is predominantly active in pregnancy and fetal development. Emerging evidence has revealed endogenous functions not previously ascribed to hCG, including participation in ovulation and fertilization, implantation, placentation and other activities in support of successful pregnancy. Spontaneous and induced mutations in LH, hCG and their mutual receptor have contributed substantially to our understanding of reproductive development and function. The lack of naturally occurring, functionally significant mutations in the β-subunit of hCG reinforce its putative role in establishment of pregnancy. Rescue of reproductive abnormalities resulting from aberrant gonadotropin signaling is possible in certain clinical contexts, depending on the nature of the underlying defect. By understanding the physiologic roles of LH and hCG in normal and pathologic states, we may better harness their diagnostic, prognostic and therapeutic potential.

Cell-specific actions of a human LHX3 gene enhancer during pituitary and spinal cord development

The LIM class of homeodomain protein 3 (LHX3) transcription factor is essential for pituitary gland and nervous system development in mammals. In humans, mutations in the LHX3 gene underlie complex pediatric syndromes featuring deficits in anterior pituitary hormones and defects in the nervous system. The mechanisms that control temporal and spatial expression of the LHX3 gene are poorly understood. The proximal promoters of the human LHX3 gene are insufficient to guide expression in vivo and downstream elements including a conserved enhancer region appear to play a role in tissue-specific expression in the pituitary and nervous system. Here we characterized the activity of this downstream enhancer region in regulating gene expression at the cellular level during development. Human LHX3 enhancer-driven Cre reporter transgenic mice were generated to facilitate studies of enhancer actions. The downstream LHX3 enhancer primarily guides gene transcription in α-glycoprotein subunit -expressing cells secreting the TSHβ, LHβ, or FSHβ hormones and expressing the GATA2 and steroidogenic factor 1 transcription factors. In the developing nervous system, the enhancer serves as a targeting module active in V2a interneurons. These results demonstrate that the downstream LHX3 enhancer is important in specific endocrine and neural cell types but also indicate that additional regulatory elements are likely involved in LHX3 gene expression. Furthermore, these studies revealed significant gonadotrope cell heterogeneity during pituitary development, providing insights into the cellular physiology of this key reproductive regulatory cell. The human LHX3 enhancer-driven Cre reporter transgenic mice also provide a valuable tool for further developmental studies of cell determination and differentiation in the pituitary and nervous system.

An investigation into pituitary gonadotrophic hormone synthesis, secretion, subunit gene expression and cell structure in normal and mutant male mice

To investigate brain-pituitary-gonadal inter-relationships, we have compared the effects of mutations that perturb the hypothalamic-pituitary-gonadal axis in male mice. Specifically, serum and pituitary gonadotrophin concentrations, gonadotrophin gene expression, and gonadotroph structure and number were measured. Follicle-stimulating hormone (FSH)β knockout (FSHβKO), FSH receptor knockout (FSHRKO), luteinising hormone (LH) receptor knockout (LuRKO), hypogonadal (hpg), testicular feminised (tfm) and gonadectomised mice were compared with control wild-type mice or heterozygotes. Serum levels of LH were similar in FSHβKO, FSHRKO and heterozygote males despite decreased androgen production in KO males. As expected, there was no detectable FSH in the serum or pituitary and an absence of expression of the FSHβ subunit gene in FSHβKO mice. However, there was a significant increase in expression of the common α and LHβ subunit genes in FSHRKO males. The morphology of FSHβKO and FSHRKO gonadotrophs was not significantly different from controls, except that the subpopulation of granules consisting of an electron-dense core and electron-lucent 'halo' was not observed in FSHβKO gonadotrophs and the granules were smaller in diameter. In the gonadotrophin-releasing hormone deficient hpg mouse, gonadotrophin mRNA and hormone levels were significantly lower compared to control mice and gonadotrophs were correspondingly smaller, with less abundant endoplasmic reticulum and reduced secretory granules. In LuRKO, tfm and gonadectomised mice, hyperstimulation of LHβ and FSHβ mRNA and serum protein concentrations was reflected by subcellular changes in gonadotroph morphology, including more dilated rough endoplasmic reticulum and more secretory granules distributed adjacent to the plasma membrane. In summary, major differences in pituitary content and serum concentrations of the gonadotrophins LH and FSH have been found between normal and mutant male mice. These changes are associated with changes in transcriptional activity of the gonadotrophin subunit genes and are reflected by changes in the cellular structure and secretory granule architecture within the gonadotroph cells.

Novel insights on thyroid-stimulating hormone receptor signal transduction

The TSH receptor (TSHR) is a member of the glycoprotein hormone receptors, a subfamily of family A G protein-coupled receptors. The TSHR is of great importance for the growth and function of the thyroid gland. The TSHR and its endogenous ligand TSH are pivotal proteins with respect to a variety of physiological functions and malfunctions. The molecular events of TSHR regulation can be summarized as a process of signal transduction, including signal reception, conversion, and amplification. The steps during signal transduction from the extra- to the intracellular sites of the cell are not yet comprehensively understood. However, essential new insights have been achieved in recent years on the interrelated mechanisms at the extracellular region, the transmembrane domain, and intracellular components. This review contains a critical summary of available knowledge of the molecular mechanisms of signal transduction at the TSHR, for example, the key amino acids involved in hormone binding or in the structural conformational changes that lead to G protein activation or signaling regulation. Aspects of TSHR oligomerization, signaling promiscuity, signaling selectivity, phenotypes of genetic variations, and potential extrathyroidal receptor activity are also considered, because these are relevant to an understanding of the overall function of the TSHR, including physiological, pathophysiological, and pharmacological perspectives. Directions for future research are discussed.

Precocious puberty and Leydig cell hyperplasia in male mice with a gain of function mutation in the LH receptor gene

The LH receptor (LHR) is critical for steroidogenesis and gametogenesis. Its essential role is underscored by the developmental and reproductive abnormalities that occur due to genetic mutations identified in the human LHR. In males, activating mutations are associated with precocious puberty and Leydig cell hyperplasia. To generate a mouse model for the human disease, we have introduced an aspartic acid to glycine mutation in amino acid residue 582 (D582G) of the mouse LHR gene corresponding to the most common D578G mutation found in boys with familial male-limited precocious puberty (FMPP). In transfected cells, mouse D582G mLHR exhibited constitutive activity with a 23-fold increase in basal cAMP levels compared with the wild-type receptor. A temporal study of male mice from 7 days to 24 weeks indicated that the knock-in mice with the mutated receptor (KiLHR(D582G)) exhibited precocious puberty with elevated testosterone levels as early as 7 days of age and through adulthood. Leydig cell-specific genes encoding LHR and several steroidogenic enzymes were up-regulated in KiLHR(D582G) testis. Leydig cell hyperplasia was detected at all ages, whereas Sertoli and germ cell development appeared normal. A novel finding from our studies, not previously reported in the FMPP cases, is that extensive hyperplasia is commonly found around the periphery of the testis. We further demonstrate that the hyperplasia is due to premature proliferation and precocious differentiation of adult Leydig cells in the KiLHR(D582G) testis. The KiLHR(D582G) mice provide a mouse model for FMPP, and we suggest that it is a useful model for studying pathologies associated with altered LHR signaling.

Disruption of the Sec24d gene results in early embryonic lethality in the mouse

Transport of newly synthesized proteins from the endoplasmic reticulum (ER) to the Golgi is mediated by the coat protein complex COPII. The inner coat of COPII is assembled from heterodimers of SEC23 and SEC24. Though mice with mutations in one of the four Sec24 paralogs, Sec24b, exhibit a neural tube closure defect, deficiency in humans or mice has not yet been described for any of the other Sec24 paralogs. We now report characterization of mice with targeted disruption of Sec24d. Early embryonic lethality is observed in mice completely deficient in SEC24D, while a hypomorphic Sec24d allele permits survival to mid-embryogenesis. Mice haploinsufficient for Sec24d exhibit no phenotypic abnormality. A BAC transgene containing Sec24d rescues the embryonic lethality observed in Sec24d-null mice. These results demonstrate an absolute requirement for SEC24D expression in early mammalian development that is not compensated by the other three Sec24 paralogs. The early embryonic lethality resulting from loss of SEC24D in mice contrasts with the previously reported mild skeletal phenotype of SEC24D deficiency in zebrafish and restricted neural tube phenotype of SEC24B deficiency in mice. Taken together, these observations suggest that the multiple Sec24 paralogs have developed distinct functions over the course of vertebrate evolution.

Function of focal adhesion kinase scaffolding to mediate endophilin A2 phosphorylation promotes epithelial-mesenchymal transition and mammary cancer stem cell activities in vivo

Tyrosine kinases have been shown to play critical roles in cancer development and progression, and their inhibitors hold the potential as effective targeted therapies for breast and other cancers. However, some of these kinases like focal adhesion kinase (FAK) also possess scaffolding functions in intracellular signaling, but such kinase-independent functions of FAK or other kinases have not been examined in cancer directly in vivo. Here, we report that disruption of the function of FAK scaffolding through its Pro-878/881 motif suppressed mammary tumor growth and metastasis in a well characterized murine model of human breast cancer. P878A/P881A mutation in the endogenous FAK gene decreased the expression of markers for epithelial-mesenchymal transition (EMT) and mammary cancer stem cell (MaCSC) activities in tumors derived from mutant mice. This mutation disrupted the function of FAK scaffolding to mediate endophilin A2 phosphorylation at Tyr-315 by Src, leading to the decreased surface expression of MT1-MMP, as observed previously in transformed fibroblasts in vitro. Inhibition of the downstream components of this FAK scaffolding function by Y315F endophilin A2 mutant or MT1-MMP knockdown reduced markers for EMT and MaCSC activities. Conversely, bypass of the scaffolding function using the phosphorylation mimic mutant Y315E endophilin A2 or endophilin A2 knockdown rescued the decreased markers for EMT and MaCSCs as well as surface expression of MT1-MMP in tumor cells harboring the P878A/P881A mutation. Together, these results identify a novel role of FAK scaffolding function in breast cancer, which could serve as a new target in combination with kinase inhibition for more effective treatment strategies.

Let-7b/c enhance the stability of a tissue-specific mRNA during mammalian organogenesis as part of a feedback loop involving KSRP

Gene silencing mediated by either microRNAs (miRNAs) or Adenylate/uridylate-rich elements Mediated mRNA Degradation (AMD) is a powerful way to post-transcriptionally modulate gene expression. We and others have reported that the RNA-binding protein KSRP favors the biogenesis of select miRNAs (including let-7 family) and activates AMD promoting the decay of inherently labile mRNAs. Different layers of interplay between miRNA- and AMD-mediated gene silencing have been proposed in cultured cells, but the relationship between the two pathways in living organisms is still elusive. We conditionally deleted Dicer in mouse pituitary from embryonic day (E) 9.5 through Cre-mediated recombination. In situ hybridization, immunohistochemistry, and quantitative reverse transcriptase-PCR revealed that Dicer is essential for pituitary morphogenesis and correct expression of hormones. Strikingly, αGSU (alpha glycoprotein subunit, common to three pituitary hormones) was absent in Dicer-deleted pituitaries. αGSU mRNA is unstable and its half-life increases during pituitary development. A transcriptome-wide analysis of microdissected E12.5 pituitaries revealed a significant increment of KSRP expression in conditional Dicer-deleted mice. We found that KSRP directly binds to αGSU mRNA, promoting its rapid decay; and, during pituitary development, αGSU expression displays an inverse temporal relationship to KSRP. Further, let-7b/c downregulated KSRP expression, promoting the degradation of its mRNA by directly binding to the 3'UTR. Therefore, we propose a model in which let-7b/c and KSRP operate within a negative feedback loop. Starting from E12.5, KSRP induces the maturation of let-7b/c that, in turn, post-transcriptionally downregulates the expression of KSRP itself. This event leads to stabilization of αGSU mRNA, which ultimately enhances the steady-state expression levels. We have identified a post-transcriptional regulatory network active during mouse pituitary development in which the expression of the hormone αGSU is increased by let7b/c through downregulation of KSRP. Our study unveils a functional crosstalk between miRNA- and AMD-dependent gene regulation during mammalian organogenesis events.

Characterization of a novel human testis-specific gene: testis developmental related gene 1 (TDRG1)

Spermatogenesis is a highly coordinated physiological process that requires the correct expression and functions of thousands of developmentally regulated genes. The regulation of spermatogenesis is not well defined, since majority of the related genes have neither been identified nor fully characterized. Hence, it is meaningful to identify and characterize these genes to reveal the mechanism underlying spermatogenesis. In this study, using digital differential display, we identified a novel human testis-specific gene, testis developmental related gene 1 (TDRG1, GenBank DQ168992), via electronic subtraction of human testis UniGene databases from those of non-reproductive tissues. The transcript of the TDRG1 gene has an open-reading frame that encodes 100 amino acids. We next prepared the anti-TDRG1 monoclonal antibody 10B6 and confirmed that it specifically recognizes an 11-kDa protein in the tissue extracts from an adult human testicular sample (age 31 years) by Western blot analysis. RT-PCR coupled with immunohistochemistry of human tissues demonstrated that TDRG1 is exclusively expressed in the testis but not in any other non-reproductive tissues. TDRG1 is mainly located in spermatogenic cells in seminiferous tubules of adult testis. Furthermore, TDRG1 shows the highest expression level in human post-puberty testis, with the expression levels decreasing afterwards with aging. Importantly, TDRG1 mRNA is undetectable in the fetal testis, as judged by RT-PCR. In conclusion, TDRG1 is a developmentally regulated testicular-specific gene. We suggest that TDRG1, a newly identified testis-specific gene, may play important roles in human spermatogenesis.

PITX2 AND PITX1 regulate thyrotroph function and response to hypothyroidism

Pitx2 is a homeodomain transcription factor required in a dose-dependent manner for the development of multiple organs. Pitx2-null homozygotes (Pitx2(-/-)) have severe pituitary hypoplasia, whereas mice with reduced-function alleles (Pitx2(neo/neo)) exhibit modest hypoplasia and reduction in the developing gonadotroph and Pou1f1 lineages. PITX2 is expressed broadly in Rathke's pouch and the fetal pituitary gland. It predominates in adult thyrotrophs and gonadotrophs, although it is not necessary for gonadotroph function. To test the role of PITX2 in thyrotroph function, we developed thyrotroph-specific cre transgenic mice, Tg(Tshb-cre) with a recombineered Tshb bacterial artificial chromosome that ablates floxed genes in differentiated pituitary thyrotrophs. We used the best Tg(Tshb-Cre) strain to generate thyrotroph-specific Pitx2-deficient offspring, Pitx2(flox/-;)Tg(Tshb-cre). Double immunohistochemistry confirmed Pitx2 deletion. Pitx2(flox/-);Tg(Tshb-cre) mice have a modest weight decrease. The thyroid glands are smaller, although circulating T(4) and TSH levels are in the normal range. The pituitary levels of Pitx1 transcripts are significantly increased, suggesting a compensatory mechanism. Hypothyroidism induced by low-iodine diet and oral propylthiouracil revealed a blunted TSH response in Pitx2(flox/-);Tg(Tshb-cre) mice. Pitx1 transcripts increased significantly in control mice with induced hypothyroidism, but they remained unchanged in Pitx2(flox/-);Tg(Tshb-cre) mice, possibly because Pitx1 levels were already maximally elevated in untreated mutants. These results suggest that PITX2 and PITX1 have overlapping roles in thyrotroph function and response to hypothyroidism. The novel cre transgene that we report will be useful for studying the function of other genes in thyrotrophs.

A single nucleotide polymorphism in a miR-1302 binding site in CGA increases the risk of idiopathic male infertility

OBJECTIVE

To explore the possible association between single nucleotide polymorphisms (SNPs) in the miRNA-binding sites of spermatogenesis-related genes and idiopathic infertility in humans.

DESIGN

Prospective study.

SETTING

Research laboratory of a university hospital.

PATIENT(S)

A total of 494 patients with azoospermia or severe oligozoospermia and 357 fertile controls were included in our study.

INTERVENTION(S)

The 3' untranslated region sequences of 140 candidate genes for male infertility were analyzed using specialized algorithms including Pictar, miRanda, Targetscan, and RNAhybrid and 39 SNPs located at putative miRNA-binding sites were identified. The possible association of 6 putatively functional SNPs and male infertility was explored further with the use of case-control studies. The function of SNPs significantly associated with male infertility was analyzed by dual luciferase assay.

MAIN OUTCOME MEASURE(S)

Significantly associated SNPs and their influence on gene expression.

RESULT(S)

Two SNPs from two genes (rs6631 of CGA and rs2303846 of CPEB1) were found to be associated with idiopathic male infertility. Functionally, the substitution of A by T in rs6631 results in decreased binding affinity of miR-1302 and overexpression of CGA in vitro.

CONCLUSION(S)

Our results reveal for the first time that SNPs residing in miRNA-binding sites of CGA could influence expression of CGA and elevate the risk of spermatogenesis impairment.

Mendelian genetics of male infertility

Infertility is defined as the inability of a couple to conceive despite trying for a year, and it affects approximately 15% of the reproductive-age population. It is considered a genetically lethal factor, as the family lineage stops at that individual with no progeny produced. A genetic defect associated with an infertile individual cannot be transmitted to the offspring, ensuring the maintenance of reproductive fitness of the species. However, with the advent of assisted reproductive techniques (ART), we are now able to overcome sterility and bypass nature's protective mechanisms that developed through evolution to prevent fertilization by defective or deficient sperm.

Role of kinase-independent and -dependent functions of FAK in endothelial cell survival and barrier function during embryonic development

Focal adhesion kinase (FAK) is essential for vascular development as endothelial cell (EC)-specific knockout of FAK (conditional FAK knockout [CFKO] mice) leads to embryonic lethality. In this study, we report the differential kinase-independent and -dependent functions of FAK in vascular development by creating and analyzing an EC-specific FAK kinase-defective (KD) mutant knockin (conditional FAK knockin [CFKI]) mouse model. CFKI embryos showed apparently normal development through embryonic day (E) 13.5, whereas the majority of CFKO embryos died at the same stage. Expression of KD FAK reversed increased EC apoptosis observed with FAK deletion in embryos and in vitro through suppression of up-regulated p21. However, vessel dilation and defective angiogenesis of CFKO embryos were not rescued in CFKI embryos. ECs without FAK or expressing KD FAK showed increased permeability, abnormal distribution of vascular endothelial cadherin (VE-cadherin), and reduced VE-cadherin Y658 phosphorylation. Together, our data suggest that kinase-independent functions of FAK can support EC survival in vascular development through E13.5 but are insufficient for maintaining EC function to allow for completion of embryogenesis.

Disruption of the single copy gonadotropin-releasing hormone receptor in mice by gene trap: severe reduction of reproductive organs and functions in developing and adult mice

Mutations in the GnRH receptor gene (GNRHR) can result in hypogonadotropic hypogonadism in humans. Unlike most mammals, mice lack a second form of GnRH (GnRH2) and a type 2 GnRH receptor. To determine whether the GnRH receptor is critical at all stages of reproduction and whether this receptor has additional physiological functions in developing and adult mice, we have generated mice from an embryonic stem cell line containing a retroviral vector with multiple stop codons inserted into intron 1 of the Gnrhr gene. This gene trap insertion resulted in the disruption of exon 2 and exon 3 of the Gnrhr gene. The insertion also contained a lacZ gene that was used as a reporter for GnRH receptor expression in these mice. This model has a similar phenotype to the clinical syndrome of hypogonadotropic hypogonadism. Null Gnrhr mice had small sexual organs, low levels of FSH, LH, and steroid hormones, failure of sexual maturation, infertility, and inability to respond to exogenous GnRH. However, the defective GnRH receptor did not prevent morula/blastocyst development, implantation, masculinization of fetal male mice, or maintenance of early pregnancy. The phenotype of this null Gnrhr mouse was more severe than models in the literature, including the N-ethyl-N-nitrosourea-induced Gnrhr mutant, the kisspeptin (Kiss1) knockout, and the kisspeptin receptor (Gpr54) knockout. In terms of gonadal morphology, adult gene trap-Gnrhr null mice demonstrate a complete cessation of reproduction and serve as an important model for understanding GnRH/GnRHR physiology.

Spermatogenesis in fish

Spermatogenesis is a developmental process during which a small number of diploid spermatogonial stem cells produce a large number of highly differentiated spermatozoa carrying a haploid, recombined genome. We characterise morphologically the different germ cell stages with particular attention for the spermatogonial generations, including the stem cells and their specific capacity to colonise a recipient's testis after transplantation. We propose a nomenclature for fish germ cells to improve the comparability among different teleost fish but also to higher vertebrates. Survival and development of germ cells depends on their continuous and close contact to Sertoli cells, and we review their multiple roles in the cystic mode of spermatogenesis seen in fish. We then discuss gene expression patterns associated with testis maturation. The endocrine system of vertebrates has evolved as master control system over spermatogenesis. In fish, both pituitary gonadotropins LH and FSH stimulate gonadal sex steroid hormone production directly by activating Leydig cells. Information is reviewed on the effects of progestin, androgens, and estrogens on global testicular gene expression patterns (microarray analysis), and on the molecular mechanisms by which steroids regulate specific candidate genes (identified by subtractive hybridization approaches) during early stages of testis maturation. Moreover, progestin and androgen effects on spermiation and milt hydration are discussed. Sex steroids mainly act via receptors expressed by Sertoli cells. One type of response is that Sertoli cells change growth factor expression, which subsequently modulates germ cell proliferation/differentiation via mechanisms yet to be characterised. Finally, we review data on germ cell autonomous processes, mainly derived from loss-of-function mutant fish lines, before identifying a number of focus areas for future research activities.

Telomere protection by TPP1 is mediated by POT1a and POT1b

Mammalian telomeres are protected by the shelterin complex, which contains single-stranded telomeric DNA binding proteins (POT1a and POT1b in rodents, POT1 in other mammals). Mouse POT1a prevents the activation of the ATR kinase and contributes to the repression of the nonhomologous end-joining pathway (NHEJ) at newly replicated telomeres. POT1b represses unscheduled resection of the 5'-ended telomeric DNA strand, resulting in long 3' overhangs in POT1b KO cells. Both POT1 proteins bind TPP1, forming heterodimers that bind to other proteins in shelterin. Short hairpin RNA (shRNA)-mediated depletion had previously demonstrated that TPP1 contributes to the normal function of POT1a and POT1b. However, these experiments did not establish whether TPP1 has additional functions in shelterin. Here we report on the phenotypes of the conditional deletion of TPP1 from mouse embryo fibroblasts. TPP1 deletion resulted in the release of POT1a and POT1b from chromatin and loss of these proteins from telomeres, indicating that TPP1 is required for the telomere association of POT1a and POT1b but not for their stability. The telomere dysfunction phenotypes associated with deletion of TPP1 were identical to those of POT1a/POT1b DKO cells. No additional telomere dysfunction phenotypes were observed, establishing that the main role of TPP1 is to allow POT1a and POT1b to protect chromosome ends.

Seasonal differences of gene expression profiles in song sparrow (Melospiza melodia) hypothalamus in relation to territorial aggression

Background

Male song sparrows (Melospiza melodia) are territorial year-round; however, neuroendocrine responses to simulated territorial intrusion (STI) differ between breeding (spring) and non-breeding seasons (autumn). In spring, exposure to STI leads to increases in luteinizing hormone and testosterone, but not in autumn. These observations suggest that there are fundamental differences in the mechanisms driving neuroendocrine responses to STI between seasons. Microarrays, spotted with EST cDNA clones of zebra finch, were used to explore gene expression profiles in the hypothalamus after territorial aggression in two different seasons.

Methodology/Principal Findings

Free-living territorial male song sparrows were exposed to either conspecific or heterospecific (control) males in an STI in spring and autumn. Behavioral data were recorded, whole hypothalami were collected, and microarray hybridizations were performed. Quantitative PCR was performed for validation. Our results show 262 cDNAs were differentially expressed between spring and autumn in the control birds. There were 173 cDNAs significantly affected by STI in autumn; however, only 67 were significantly affected by STI in spring. There were 88 cDNAs that showed significant interactions in both season and STI.

Conclusions/Significance

Results suggest that STI drives differential genomic responses in the hypothalamus in the spring vs. autumn. The number of cDNAs differentially expressed in relation to season was greater than in relation to social interactions, suggesting major underlying seasonal effects in the hypothalamus which may determine the differential response upon social interaction. Functional pathway analyses implicated genes that regulate thyroid hormone action and neuroplasticity as targets of this neuroendocrine regulation.

Steroidogenesis in the fetal testis and its susceptibility to disruption by exogenous compounds

Masculinization depends on adequate production of testosterone by the fetal testis within a specific "masculinization programming window." Disorders resulting from subtle deficiencies in this process are common in humans, and environmental exposures/lifestyle could contribute causally because common therapeutic and environmental compounds can affect steroidogenesis. This evidence derives mainly from rodent studies, but because there are major species differences in regulation of steroidogenesis in the fetal testis, this may not always be a guide to potential effects in the human. In addition to direct study of the effects of compounds on steroidogenesis, information also derives from study of masculinization disorders that result from mutations in genes in pathways regulating steroidogenesis. This review addresses this issue by critically reviewing the comparative timing of production and regulation of steroidogenesis in the fetal testis of humans and of rodents and its susceptibility to disruption; where there is limited information for the fetus, evidence from effects on steroidogenesis in the adult testis is considered. There are a number of fundamental regulatory differences between the human and rodent fetal testis, most notably in the importance of paracrine vs. endocrine drives during masculinization such that inactivating LH receptor mutations block masculinization in humans but not in rodents. Other large differences involve the steroidogenic response to estrogens and GnRH analogs and possibly phthalates, whereas for other compounds there may be differences in sensitivity to disruption (ketoconazole). This comparison identifies steroidogenic targets that are either vulnerable (mitochondrial cholesterol transport, CYP11A, CYP17) or not (cholesterol uptake) to chemical interference.

A homolog of the vertebrate thyrostimulin glycoprotein hormone alpha subunit (GPA2) is expressed in Amphioxus neurons

The cystine-knot glycoprotein hormone alpha (GPA) family regulates gonadal and thyroid functions in vertebrates. Little is known concerning GPA family members in primitive chordates. A previous genomic analysis revealed the presence of two genes homologous to the thyrostimulin alpha subunit (GPA2) in an amphioxus (Branchiostoma florideae); however only one GPA2 homolog contained both the cystine-knot structure and N-glycosylation site characteristic of family members. Gene-specific PCR was used to obtain the cDNA and genomic sequences of the GPA2 homolog of the amphioxus Branchiostoma belcheri. Whole-mount in situ hybridization revealed GPA2 mRNA expression in the anterior part of the nerve cord and on the left side of the central canal. Because amphioxus possesses only one true GPA2 homolog, while vertebrates possess two glycoprotein hormone alpha subunits (thyrostimulin alpha, or GPA2, and the common alpha subunit of gonadal and thyroid glycoprotein hormones, GPA1), our results suggest that GPA1 was acquired later in the vertebrate lineage through gene duplication.