What have gonadotrophin overexpressing transgenic mice taught us about gonadal function?

Elevated chorionic gonadotropic hormone in transgenic mice induces parthenogenetic activation and ovarian teratomas

Both male and female reproductive functions are impacted by altered gonadotrophin secretion and action, which may also influence the development of endocrine tumours. To ascertain if chronic hypersecretion of human chorionic gonadotropin (hCG) contributes to the development of gonadal tumours, double transgenic (TG) mice that overexpress hCGα- and β-subunits were analysed. By the age of two months, ovarian tumours with characteristics of teratomas developed with 100% penetrance. Teratomas were also seen in wild-type ovaries orthotopically transplanted into TG mice, demonstrating an endocrine/paracrine mechanism for the hCG-induced ovarian tumorigenesis. Both in vitro and in vivo experiments showed oocyte parthenogenetic activation in TG females. In addition, ovaries showed reduced ovulatory gene expression, inhibited ERK1/2 phosphorylation, and impaired cumulus cell expansion. Hence, persistently high endocrine hCG activity causes parthenogenetic activation and development of ovarian teratomas, along with altered follicle development and impaired ERK1/2 signalling, offering a novel mechanism associated with the molecular pathogenesis of ovarian teratomas.

Persistently expressed human chorionic gonadotropin induces premature luteinization and progressive alterations on the reproductive axis in female mice

The hypothalamic-pituitary-gonadal axis plays a fundamental role in the endocrine regulation of the reproductive function in mammals. Any change in the function of the participating hormones or their receptors can lead to alterations in sexual differentiation, the onset of puberty, infertility, cancer development, and other dysfunctions. In this study, we analyzed the influence of persistently elevated levels of the human chorionic gonadotropin hormone (hCG), a powerful agonist of pituitary luteinizing hormone (LH), on the reproductive axis of female mice. As a consequence of chronic hCG hypersecretion through a global expression of the hCGbeta-subunit in transgenic (TG) female mice, a series of events perturbed the prepubertal to juvenile transition. The imbalance in gonadotropin action was first manifested by precocious puberty and alterations in gonadal hormone production, with the consequent ovarian function disruption and infertility in adulthood. The expansion of cumulus cells in vivo and in vitro, ovulatory capacity, and gene expression of ovulation-related marker genes after hormone stimulation were normal in 3-week-old TG females. However, the expression of genes related to steroidogenesis and luteinization such as Lhcgr, Prlr, and the steroidogenic enzymes Cyp11a1, Cyp17a1, and Cyp19a1 were significantly elevated in the TG females. This study demonstrates that the excessive secretion of hCG in concert with high prolactin, induced premature luteinization, and enhanced ovarian steroidogenesis, as was shown by the up-regulation of luteal cell markers and progesterone synthesis in the TG mice. Furthermore, progressively impaired reproductive function of the TG females occurred from the peripubertal stage to adulthood, thus culminating in infertility.

Estrogen Biosynthesis and Signal Transduction in Ovarian Disease

Estrogen mainly binds to estrogen receptors (ERs) to regulate menstrual cycles and reproduction. The expression of ERalpha (ERα), ERbeta (ERβ), and G-protein-coupled estrogen receptor (GPER) mRNA could be detected in ovary, suggesting that they play an important role in estrogen signal transduction in ovary. And many studies have revealed that abnormal expression of estrogen and its receptors is closely related to ovarian disease or malignant tumors. With the continuous development and research of animal models, tissue-specific roles of both ERα and ERβ have been demonstrated in animals, which enable people to have a deeper understanding of the potential role of ER in regulating female reproductive diseases. Nevertheless, our current understanding of ERs expression and function in ovarian disease is, however, incomplete. To elucidate the biological mechanism behind ERs in the ovary, this review will focus on the role of ERα and ERβ in polycystic ovary syndrome (PCOS), ovarian cancer and premature ovarian failure (POF) and discuss the major challenges of existing therapies to provide a reference for the treatment of estrogen target tissue ovarian diseases.

High Dosages of Equine Chorionic Gonadotropin Exert Adverse Effects on the Developmental Competence of IVF-Derived Mouse Embryos and Cause Oxidative Stress-Induced Aneuploidy

Gonadotropins play vital roles in the regulation of female reproductive ability and fertility. Our study aimed to determine the effects of superovulation induced by increasing doses of equine chorionic gonadotropin [eCG; also referred to as pregnant mare serum gonadotropin (PMSG)] on the developmental competence of mouse embryos and on aneuploidy formation during in vitro fertilization (IVF). eCG dose-dependently enhanced the oocyte yield from each mouse. Administration of 15 IU eCG significantly reduced the fertilization rate and the formation of four-cell embryos and blastocysts and increased the risk of chromosome aneuploidy. The IVF-derived blastocysts in the 15 IU eCG treatment group had the fewest total cells, inner cell mass (ICM) cells and trophectoderm (TE) cells. Moreover, more blastocysts and fewer apoptotic cells were observed in the 0, 5, and 10 IU eCG treatment groups than in the 15 IU eCG treatment group. We also investigated reactive oxygen species (ROS) levels and variations in several variables: mitochondrial membrane potential (MMP); active mitochondria; mitochondrial superoxide production; adenosine triphosphate (ATP) content; spindle structures; chromosome karyotypes; microfilament distribution; and the expression of Aurora B [an important component of the chromosomal passenger complex (CPC)], the spindle assembly checkpoint (SAC) protein mitotic arrest deficient 2 like 1 (MAD2L1), and the DNA damage response (DDR) protein γH2AX. Injection of 15 IU eCG increased ROS levels, rapidly reduced MMP, increased active mitochondria numbers and mitochondrial superoxide production, reduced ATP content, increased abnormal spindle formation rates, and induced abnormalities in chromosome number and microfilament distribution, suggesting that a high dose of eCG might alter developmental competence and exert negative effects on IVF-obtained mouse embryos. Additionally, the appearance of γH2AX and the significantly increased expression of Aurora B and MAD2L1 suggested that administration of relatively high doses of eCG caused Aurora B-mediated SAC activation triggered by ROS-induced DNA damage in early mouse IVF-derived embryos for self-correction of aneuploidy formation. These findings improve our understanding of the application of gonadotropins and provide a theoretical basis for gonadotropin treatment.

Follicle Depletion Provides a Permissive Environment for Ovarian Carcinogenesis

We modeled the etiology of postmenopausal biology on ovarian cancer risk using germ cell-deficient white-spotting variant (Wv) mice, incorporating oncogenic mutations. Ovarian cancer incidence is highest in peri- and postmenopausal women, and epidemiological studies have established the impact of reproductive factors on ovarian cancer risk. Menopause as a result of ovarian follicle depletion is thought to contribute to higher cancer risk. As a consequence of follicle depletion, female Wv mice develop ovarian tubular adenomas, a benign epithelial tumor corresponding to surface epithelial invaginations and papillomatosis frequently found in postmenopausal human ovaries. Lineage tracing using MISR2-Cre indicated that the tubular adenomas that developed in Wv mice were largely derived from the MISR2 lineage, which marked only a fraction of ovarian surface and oviduct epithelial cells in wild-type tissues. Deletion of p27, either heterozygous or homozygous, was able to convert the benign tubular adenomas into more proliferative tumors. Restricted deletion of p53 in Wv/Wv mice by either intrabursal injection of adenoviral Cre or inclusion of the MISR2-Cre transgene also resulted in augmented tumor growth. This finding suggests that follicle depletion provides a permissive ovarian environment for oncogenic transformation of epithelial cells, presenting a mechanism for the increased ovarian cancer risk in postmenopausal women.

BAC mediated transgenic Large White boars with FSHα/β genes from Chinese Erhualian pigs

Follicle-stimulating hormone (FSH) is a critical hormone regulating reproduction in mammals. Transgenic mice show that overexpression of FSH can improve female fecundity. Using a bacterial artificial chromosome (BAC) system and somatic cell nuclear transfer, we herein generated 67 Large White transgenic (TG) boars harboring FSHα/β genes from Chinese Erhualian pigs, the most prolific breed in the world. We selected two F0 TG boars for further breeding and conducted molecular characterization and biosafety assessment for F1 boars. We showed that 8-9 copies of exogenous FSHα and 5-6 copies of exogenous FSHβ were integrated into the genome of transgenic pigs. The inheritance of exogenous genes conforms to the Mendel's law of segregation. TG boars had higher levels of serum FSH, FSHα mRNA in multiple tissues, FSHβ protein in pituitary and more germ cells per seminiferous tubule compared with their wild-type half sibs without any reproductive defects. Analysis of growth curve, hematological and biochemical parameters and histopathology illustrated that TG boars grew healthily and normally. By applying 16S rRNA gene sequencing, we demonstrated that exogenous genes had no impact on the bacterial community structures of pig guts. Moreover, foreign gene drift did not occur as verified by horizontal gene transfer. Our findings indicate that overexpression of FSH could improve spermatogenesis ability of boars. This work provides insight into the effect of FSHα/β genes on male reproductive performance on pigs by a BAC-mediated transgenic approach.

Global deletion of Trp53 reverts ovarian tumor phenotype of the germ cell-deficient white spotting variant (Wv) mice

White spotting variant (Wv) mice are spontaneous mutants attributed to a point mutation in the c-Kit gene, which reduces the tyrosine kinase activity to around 1% and affects the development of melanocytes, mast cells, and germ cells. Homozygous mutant mice are sterile but can live nearly a normal life span. The female Wv mice have a greatly reduced ovarian germ cell and follicle reserve at birth, and the remaining follicles are largely depleted soon after the females reach reproductive stage at around 7 weeks of age. Consequently, ovarian epithelial tumors develop in 100% of Wv females by 3 to 4 months of age. These tumors, called tubular adenomas, are benign but can become invasive in older Wv mice.

We tested if additional genetic mutation(s) could convert the benign ovarian epithelial tumors to malignant tumors by crossing the Wv mutant into the Trp53 knockout background. Surprisingly, we found that global deletion of Trp53 suppressed the development of ovarian tubular adenomas in Wv mice. The ovaries of Wv/Wv; Trp53 (−/−) mice were covered by a single layer of surface epithelium and lacked excessive epithelial proliferation. Rather, the ovaries contained a small number of follicles. The presence of ovarian follicles and granulosa cells, as indicated by Pgc7 and inhibin-alpha expression, correlated with the absence of epithelial lesions. A reduction of Pten gene dosage, as in Wv/Wv; Pten (+/−) mice, produced a similar, though less dramatic, phenotype. We conclude that deletion of Trp53 prolongs the survival of ovarian follicles in Wv mice and consequently prevents the proliferation of ovarian epithelial cells and development of ovarian tubular adenomas. The results suggest that various cell types within the ovary communicate and mutually modulate, and an intact tissue environment is required to ensure homeostasis of ovarian surface epithelial cells. Especially, the current finding emphasizes the importance of ovarian follicles in suppressing the hyperplastic growth of ovarian epithelial cells, dominating over the loss of p53.

Effects of FSH extracted from in vitro cultured anterior pituitary cells of male buffalo calves on body and testes weight, serum FSH and total cholesterol and hematological variables in male rabbits

In this study, anterior pituitary glands were collected from 12 young male buffalo calves after slaughter, cultured with gonadotropin releasing hormone (GnRH) and estrogen stimulus and the extract obtained. Adult male rabbits (n = 15) were divided into three equal groups. Rabbits of Group A served as control; those of Groups B and C were given extract containing 4 and 8 mIU of follicle stimulating hormone (FSH), respectively twice daily for 3 weeks. Body weight of rabbits was recorded before and after treatment; blood samples were collected after treatment and analyzed for hemoglobin (Hb), red blood cell (RBC) count, white blood cell (WBC) count, packed cell volume (PCV), platelet counts, mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH), while serum samples were analyzed for FSH and total cholesterol. Then, all rabbits were slaughtered, and weight of paired testes was recorded. Results showed that the values for weight gain, RBC count, WBC count, PCV and MCH did not differ among rabbits of three groups. Blood Hb was greater (P < 0.05) in rabbits of Group B than Group C. Testis weight, serum FSH, total cholesterol and blood platelets count were greater in rabbits of Groups B and C, while MCV was less in rabbits of Group C, compared to the control (P < 0.05). In conclusion, in vitro cultured cells of adenohypophysis from male buffalo calves showed FSH activity. This FSH increased testes size, serum FSH, total cholesterol and blood platelets counts and decreased MCV in rabbits. However, it had no effect on weight gain, RBC counts, WBC counts, PCV and MCH.

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.

The ERK1/2 pathway regulates testosterone synthesis by coordinately regulating the expression of steroidogenic genes in Leydig cells

Adult mice with a Leydig cell specific deletion of MAPK kinase (MEK) 1 and 2 (Mek1(f)(/)(f);Mek2(-/-);Cre(+)) mice display Leydig cell hypoplasia and hypergonadotropic hypogonadism. We used radioimmunoassays and quantitative PCR to evaluate the function and expression of the Leydig cell genes involved in the conversion of cholesterol to testosterone (Star, Cyp11a1, Hsd3b6, Cyp17a1 and Hsd17b3), androgen metabolism (Srda1 and Dhrs9), and four transcription factors (Creb1, Nr5a1, Nr4a1 and Nr0b1) that regulate the expression of steroidogenic genes. We show that Star, Hsd3b6, Cyp17a1 and Hsd17b3 are downregulated in Ledyig cells of adult Mek1(f)(/)(f);Mek2(-/-);Cre(+) mice whereas Srda1 and Dhrs9 are upregulated and Creb1, Nr5a1, Nr4a1 and Nr0b1 are unchanged or upregulated. Functionally, all the downregulated genes but none of the upregulated genes contribute to the decrease in testosterone synthesis in Leydig cells of adult Mek1(f)(/)(f);Mek2(-/-);Cre(+) mice because they produce low testosterone and dihydrotestosterone when stimulated with hCG or when incubated with testosterone precursors such as progesterone or androstenedione.

Short-term pharmacological suppression of the hyperprolactinemia of infertile hCG-overproducing female mice persistently restores their fertility

Female infertility is often associated with deregulation of hormonal networks, and hyperprolactinemia is one of the most common endocrine disorders of the hypothalamic-pituitary axis affecting the reproductive functions. We have shown previously that transgenic female mice overexpressing human chorionic gonadotropin β-subunit (hCGβ+ mice), and producing elevated levels of bioactive LH/hCG, exhibit increased production of testosterone and progesterone, are overweight and infertile, and develop hyperprolactinemia associated with pituitary lactotrope adenomas in adult age. In the present study, we analyzed the influence of the hyperprolactinemia of hCGβ+ females on their reproductive phenotype by treating them with the dopamine agonists, bromocriptine and cabergoline. Long-term bromocriptine treatment of adult mice was effective in the control of obesity, pituitary growth, and disturbances in the hormone profile, demonstrating that hyperprolactinemia was the main cause of the hCGβ+ female phenotype. Interestingly, short-term treatment (1 wk) with cabergoline applied on 5-wk-old mice corrected hyperprolactinemia, hyperandrogenism, and hyperprogesteronemia, prevented pituitary overgrowth, normalized gonadal function, and recovered fertility of adult hCGβ+ females after hormone-induced and natural ovulation. The same cabergoline treatment in the short term applied on 3-month-old hCGβ+ females failed to recover their reproductive function. Hence, we demonstrated that the short-term cabergoline treatment applied at a critical early stage of the phenotype progression effectively prevented the hyperprolactinemia-associated reproductive dysfunction of hCG-overproducing females.

Pituitary-specific overexpression of porcine follicle-stimulating hormone leads to improvement of female fecundity in BAC transgenic mice

Follicle-stimulating hormone (FSH) is a pituitary glycoprotein that, together with luteinizing hormone, plays a crucial role in ovarian folliculogenesis and female fertility. We previously found that FSH beta is a major gene controlling high prolificacy of Chinese Erhualian pigs. To directly study the biological effects on reproductive function of porcine FSH (pFSH) for polyovulatory species, we generated a novel gain-of-function mouse model using a bacterial artificial chromosome (BAC) system to jointly introduce 92 kb and 165 kb genomic fragments comprising the pFSH α- and β-subunit genes. These directed the physiological expression of pFSH with the same temporal and spatial pattern as endogenous FSH in female transgenic (TG) mice. Serum levels of biologically active pFSH heterodimers in independent TG lines ranged from 6.36 to 19.83 IU/L. High basal pFSH activity led to a significant reduction of serum LH and testosterone levels in TG females compared to wild-type (WT) littermates, yet endogenous FSH and estradiol levels were significantly elevated. Interestingly, ovarian histology showed that the number of corpora lutea was significantly higher at 14 and 28 weeks of age in TG females and breeding curves revealed that mean litter sizes of TG females were obviously larger than for WT littermates before 52 weeks of age. These findings indicate that pituitary-specific overexpression of pFSH within physiological boundaries can increase ovulation rate and litter size, but it does not cause reproductive defects. Therefore, our TG mouse model provides exciting insights for investigating the actions of pFSH in vivo.

Gonadal and nongonadal FSHR and LHR dysfunction during lipopolysaccharide induced failure of blastocyst implantation in mouse

PURPOSE

The purpose of the present study was to investigate the impact of lipopolysaccharide (LPS) on follicle-stimulating hormone (FSH), luteinizing hormone (LH) and their receptors during preimplantation days of pregnancy.

METHOD

The PBS or lipopolysaccharide (LPS) was injected intraperitoneally in the pregnant females on day 0.5 of pregnancy and serum, embryos, ovaries and uterine horns were collected on days 1.5, 2.5, 3.5, 4.0, 4.125, 4.33 and 4.42 of pregnancy.

RESULT(S)

In the LPS-treated pregnant females, the secretion of FSH and LH is disturbed with respect to normal pregnancy. Furthermore, the expression of FSHR mRNA in embryos and ovaries, LHR mRNA in embryos and uterus get modulated in response to LPS during preimplantation days of pregnancy.

CONCLUSION(S)

The disturbance in the serum level of FSH and LH in response to LPS leads implantation failure in mouse which suggests that these gonadotropins plays an integral role in the process of the successful implantation. This study also suggests a possible nongonadal role of FSHR and LHR in LPS-induced implantation failure in the mouse.

Animal models for aberrations of gonadotropin action

During the last two decades a large number of genetically modified mouse lines with altered gonadotropin action have been generated. These mouse lines fall into three categories: the lack-of-function mice, gain-of-function mice, and the mice generated by breeding the abovementioned lines with other disease model lines. The mouse strains lacking gonadotropin action have elucidated the necessity of the pituitary hormones in pubertal development and function of gonads, and revealed the processes from the original genetic defect to the pathological phenotype such as hypo- or hypergonadotropic hypogonadism. Conversely, the strains of the second group depict consequences of chronic gonadotropin action. The lines vary from those expressing constitutively active receptors and those secreting follicle-stimulating hormone (FSH) with slowly increasing amounts to those producing human choriogonadotropin (hCG), amount of which corresponds to 2000-fold luteinizing hormone (LH)/hCG biological activity. Accordingly, the phenotypes diverge from mild anomalies and enhanced fertility to disrupted gametogenesis, but eventually chronic, enhanced and non-pulsatile action of both FSH and LH leads to female and male infertility and/or hyper- and neoplasias in most of the gonadotropin gain-of-function mice. Elevated gonadotropin levels also alter the function of several extra-gonadal tissues either directly or indirectly via increased sex steroid production. These effects include promotion of tumorigenesis in tissues such as the pituitary, mammary and adrenal glands. Finally, the crossbreedings of the current mouse strains with other disease models are likely to uncover the contribution of gonadotropins in novel biological systems, as exemplified by the recent crossbreed of LHCG receptor deficient mice with Alzheimer disease mice.

Thoc1 deficiency compromises gene expression necessary for normal testis development in the mouse

Accumulating evidence suggests that regulation of RNA processing through an RNP-driven mechanism is important for coordinated gene expression. This hypothesis predicts that defects in RNP biogenesis will adversely affect the elaboration of specific gene expression programs. To explore the role of RNP biogenesis on mammalian development, we have characterized the phenotype of mice hypomorphic for Thoc1. Thoc1 encodes an essential component of the evolutionarily conserved TREX complex. TREX accompanies the elongating RNA polymerase II and facilitates RNP assembly and recruitment of RNA processing factors. Hypomorphic Thoc1 mice are viable despite significantly reduced Thoc1 expression in the tissues examined. While most tissues of Thoc1-deficient mice appear to develop and function normally, gametogenesis is severely compromised. Male infertility is associated with a loss in spermatocyte viability and abnormal endocrine signaling. We suggest that loss of spermatocyte viability is a consequence of defects in the expression of genes required for normal differentiation of cell types within the testes. A number of the genes affected appear to be direct targets for regulation by Thoc1. These findings support the notion that Thoc1-mediated RNP assembly contributes to the coordinated expression of genes necessary for normal differentiation and development in vivo.

Coexpression of human chorionic gonadotropin beta subunit and its receptor in nontrophoblastic gynecological cancer

A considerable number of biochemical and physiologic studies evaluate the roles of gonadotropins in carcinogenesis. Latest reports show that human chorionic gonadotropin (hCG), and especially its beta subunit, are secreted by a variety of malignant tumors of different origin. However, the mechanism of hCG action and its role in tumor development is not known yet. This study, with the help of reverse transcription-polymerase chain reaction and immunohistochemistry, is an attempt to document the molecular presence of the hCGβ and luteinizing hormone/hCG receptor (LH/hCGR) in the ovarian, endometrial, and uterine cervix cancer tissues. The LH/hCGR, coexpressed with hCGβ, may act as a potential mediator of hCG action in nontrophoblastic gynecological cancers

An estrogen receptor-alpha knock-in mutation provides evidence of ligand-independent signaling and allows modulation of ligand-induced pathways in vivo

Estrogen-nonresponsive estrogen receptor-alpha (ERalpha) knock-in (ENERKI) mice were generated to distinguish between ligand-induced and ligand-independent ER-alpha actions in vivo. These mice have a mutation [glycine 525 to leucine (G525L)] in the ligand-binding domain of ERalpha, which significantly reduces ERalpha interaction with and response to endogenous estrogens, whereas not affecting growth factor activation of ligand-independent pathways. ENERKI mice had hypoplastic uterine tissues and rudimentary mammary gland ductal trees. Females were infertile due to anovulation, and their ovaries contained hemorrhagic cystic follicles because of chronically elevated levels of LH. The ENERKI phenotype confirmed that ligand-induced activation of ERalpha is crucial in the female reproductive tract and mammary gland development. Growth factor treatments induced uterine epithelial proliferation in ovariectomized ENERKI females, directly demonstrating that ERalpha ligand-independent pathways were active. In addition, the synthetic ERalpha selective agonist propyl pyrazole triol (PPT) and ER agonist diethylstilbestrol (DES) were still able to activate ligand-induced G525L ERalpha pathways in vitro. PPT treatments initiated at puberty stimulated ENERKI uterine development, whereas neonatal treatments were needed to restore mammary gland ductal elongation, indicating that neonatal ligand-induced ERalpha activation may prime mammary ducts to become more responsive to estrogens in adult tissues. This is a useful model for in vivo evaluation of ligand-induced ERalpha pathways and temporal patterns of response. DES did not stimulate an ENERKI uterotrophic response. Because ERbeta may modulate ERalpha activation and have an antiproliferative function in the uterus, we hypothesize that ENERKI animals were particularly sensitive to DES-induced inhibition of ERalpha due to up-regulated uterine ERbeta levels.

Opportunities and challenges in applying genomics to the study of oogenesis and folliculogenesis in farm animals

Ovarian oogenesis and folliculogenesis are complex and coordinated biological processes which require a series of events that induce morphological and functional changes within the follicle, leading to cell differentiation and oocyte development. In this context, the challenge of the researchers is to describe the dynamics of gene expression in the different compartments and their interactions during the follicular programme. In recent years, high-throughput arrays have become a powerful tool with which to compare the whole population of transcripts in a single experiment. Here, we review the challenges of applying genomics to this model in farm animal species. The first limitation lies in limited the availability of biological material, which makes the study of the follicle compartments (oocyte, granulosa cells and thecal cells) or early embryo much more difficult. The concept of observing all transcripts at once is very attractive but despite progress in sequencing, the genome annotation remains very incomplete in non-model species. Particularly, oogenesis and early embryo development relate to the high proportion of unknown expressed sequence tags. Then, it is important to consider post-transcriptional and translational regulation to understand the role of these genes. Ultimately, these new inferred insights will still have to be validated by functional approaches. In addition toin vitroorex vivofunctional approaches, both ‘natural mutant’ ewe models and RNA interference represent, at the moment, the best hope for functional genomics. Advances in our understanding of reproductive physiology should be facilitated by gene expression data exchange and translation into a better understanding of the underlying biological phenomena.

Age-related changes in trabecular architecture differ in female and male C57BL/6J mice

We used microCT and histomorphometry to assess age-related changes in bone architecture in male and female C57BL/6J mice. Deterioration in vertebral and femoral trabecular microarchitecture begins early, continues throughout life, is more pronounced at the femoral metaphysis than in the vertebrae, and is greater in females than males.

INTRODUCTION

Despite widespread use of mice in the study of musculoskeletal disease, the age-related changes in murine bone structure and the relationship to whole body BMD changes are not well characterized. Thus, we assessed age-related changes in body composition, whole body BMD, and trabecular and cortical microarchitecture at axial and appendicular sites in mice.

MATERIALS AND METHODS

Peripheral DXA was used to assess body composition and whole body BMD in vivo, and microCT and histomorphometry were used to measure trabecular and cortical architecture in excised femora, tibia, and vertebrae in male and female C57BL/6J mice at eight time-points between 1 and 20 mo of age (n = 6-9/group).

RESULTS

Body weight and total body BMD increased with age in male and female, with a marked increase in body fat between 6 and 12 mo of age. In contrast, trabecular bone volume (BV/TV) was greatest at 6-8 wk of age and declined steadily thereafter, particularly in the metaphyseal region of long bones. Age-related declines in BV/TV were greater in female than male. Trabecular bone loss was characterized by a rapid decrease in trabecular number between 2 and 6 mo of age, and a more gradual decline thereafter, whereas trabecular thickness increased slowly over life. Cortical thickness increased markedly from 1 to 3 mo of age and was maintained or slightly decreased thereafter.

CONCLUSIONS

In C57BL/6J mice, despite increasing body weight and total body BMD, age-related declines in vertebral and distal femoral trabecular bone volume occur early and continue throughout life and are more pronounced in females than males. Awareness of these age-related changed in bone morphology are critical for interpreting the skeletal response to pharmacologic interventions or genetic manipulation in mice.

Lutropin/choriogonadotropin stimulate the proliferation of primary cultures of rat Leydig cells through a pathway that involves activation of the extracellularly regulated kinase 1/2 cascade

Primary cultures of progenitor and immature rat Leydig cells were established from the testes of 21- and 35-d-old rats, respectively. The cell population remained homogeneous after 4-6 d in culture as judged by staining for 3beta-hydroxysteroid dehydrogenase, but the cells were unable to bind 125I-human chorionic gonadotropin (hCG) or to respond to hCG with classical LH receptor (LHR)-mediated responses, including cAMP and inositol phosphate accumulation, steroid biosynthesis, or the phosphorylation of ERK1/2. Infection of primary cultures with recombinant adenovirus coding for beta-galactosidase showed that approximately 65% of the cells are infected. Infection with adenovirus coding for the human LHR (hLHR) allowed for expression of the hLHR at a density of approximately 25,000 receptors per cell and allowed the cells to respond to hCG with increases in cAMP and inositol phosphate accumulation, steroid biosynthesis, and the phosphorylation of ERK1/2. Although progenitor and immature cells were able to respond to hCG with an increase in progesterone, only the immature cells responded with an increase in testosterone. In addition to these classical LHR-mediated responses, the primary cultures of progenitor or immature rat Leydig cells expressing the recombinant hLHR proliferated robustly when incubated with hCG, and this proliferative response was sensitive to an inhibitor of ERK1/2 phosphorylation. These studies establish a novel experimental paradigm that can be used to study the proliferative response of Leydig cells to LH/CG. We conclude that activation of the LHR-provoked Leydig cell proliferation requires activation of the ERK1/2 cascade.

Gonadotrophin-releasing hormone (GnRH) release in marmosets II: pulsatile release of GnRH and pituitary gonadotrophin in adult females

Unlike other mammals, including rodents, Old World primates and humans, common marmosets and probably all other New World primates synthesise and release chorionic gonadotrophin (CG), and not luteinising hormone (LH) from pituitary gonadotrophs. However, little is known about the physiological dynamics of gonadotrophin-releasing hormone (GnRH)-regulated CG release from gonadotrophs and whether such CG release has pulsatile release characteristics similar to those of LH in other mammalian species. Consequently, we performed a series of in vivo and in vitro studies in ovariectomised laboratory rats and female marmosets to compare GnRH-induced pituitary LH and CG release characteristics, respectively. Exogenous GnRH stimulated a slower onset of release of marmoset pituitary CG, both in vivo and in vitro, and induced an approximately 400% greater increase in the duration of marmoset pituitary CG release compared to that for rat LH. Not surprisingly, hypothalamic pulsatile release of GnRH in vivo was not obviously concordant with endogenous episodic changes in circulating levels of CG in marmosets, in contrast to the clear concordance observed between in vivo GnRH and LH release previously demonstrated in rats and other mammals. Pituitary CG release in marmosets thus demonstrates considerable divergence from the timely hypothalamic GnRH-regulated LH release in other female mammals, implying potentially different physiological dynamics in gonadotrophin regulation of marmoset ovarian function.

Activation of the lutropin/choriogonadotropin receptor in MA-10 cells stimulates tyrosine kinase cascades that activate ras and the extracellular signal regulated kinases (ERK1/2)

We show that activation of the recombinant lutropin/choriogonadotropin receptor (LHR) in mouse Leydig tumor cells (MA-10 cells) leads to the tyrosine phosphorylation of Shc (Src homology and collagen homology) and the formation of complexes containing Shc and Sos (Son of sevenless), a guanine nucleotide exchange factor for Ras. Because a dominant-negative mutant of Shc inhibits the LHR-mediated activation of Ras and the phosphorylation of ERK1/2, we conclude that the LHR-mediated phosphorylation of ERK1/2 is mediated, at least partially, by the classical pathway used by growth factor receptors. We also show that the endogenous epidermal growth factor receptor (EGFR) present in MA-10 cells is phosphorylated upon activation of the LHR. The LHR-mediated phosphorylation of the EGFR and Shc, the activation of Ras, and the phosphorylation of ERK1/2 are inhibited by expression of a dominant-negative mutant of Fyn, a member of the Src family kinases (SFKs) expressed in MA-10 cells and by PP2, a pharmacological inhibitor of the SFKs. These are also inhibited, but to a lesser extent, by AG1478, an inhibitor of the EGFR kinase. We conclude that the SFKs are responsible for the LHR-mediated phosphorylation of the EGFR and Shc, the formation of complexes containing Shc and Sos, the activation of Ras, and the phosphorylation of ERK1/2.

Atm-deficient mice: an osteoporosis model with defective osteoblast differentiation and increased osteoclastogenesis

Atm is a Ser/Thr kinase involved in DNA damage response and is required for genome integrity and stem cell renewal. Here, we report an additional role for Atm in bone remodeling. Atm-/- mice showed reduced bone mass, especially at the trabecular bones, accompanied by a decrease in bone formation rate and defective differentiation of osteoblasts, but normal numbers of osteoprogenitor cells and osteoblasts. Atm might affect osteoblast differentiation by modulating the expression of osterix, a lineage-specific transcription factor essential for osteoblast maturation, likely via the bone morphogenetic proteins pathway. Atm-/- mice also displayed a marked increase in osteoclastogenesis and bone resorption, although Atm had no cell-autonomous effect on osteoclast differentiation and resorption. Increased osteoclastogenesis could be caused by a substantial reduction in testosterone and estradiol levels in male and female mice, respectively. The steroid hormone deficiency is a result of gonad developmental defects, which led to an increase in serum gonadotrophic hormone, FSH via a feedback regulation. Overall, these results indicate that Atm deficiency leads to osteoporosis mainly as a result of hypogonadism-induced bone resorption together with compromised osteoblast differentiation, and that Atm plays a positive role in regulating expression of osteoblast-specific transcription factor, osterix.