Sclerosteosis is a progressive sclerosing bone dysplasia with an autosomal recessive mode of inheritance. Radiologically, it is characterized by a generalized hyperostosis and sclerosis leading to a markedly thickened and sclerotic skull, with mandible, ribs, clavicles and all long bones also being affected. Due to narrowing of the foramina of the cranial nerves, facial nerve palsy, hearing loss and atrophy of the optic nerves can occur. Sclerosteosis is clinically and radiologically very similar to van Buchem disease, mainly differentiated by hand malformations and a large stature in sclerosteosis patients. By linkage analysis in one extended van Buchem family and two consanguineous sclerosteosis families we previously mapped both disease genes to the same chromosomal 17q12-q21 region, supporting the hypothesis that both conditions are caused by mutations in the same gene. After reducing the disease critical region to approximately 1 Mb, we used the positional cloning strategy to identify the SOST gene, which is mutated in sclerosteosis patients. This new gene encodes a protein with a signal peptide for secretion and a cysteine-knot motif. Two nonsense mutations and one splice site mutation were identified in sclerosteosis patients, but no mutations were found in a fourth sclerosteosis patient nor in the patients from the van Buchem family. As the three disease-causing mutations lead to loss of function of the SOST protein resulting in the formation of massive amounts of normal bone throughout life, the physiological role of SOST is most likely the suppression of bone formation. Therefore, this gene might become an important tool in the development of therapeutic strategies for osteoporosis.

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Both activin and GnRH can independently stimulate expression of the FSHbeta subunit gene. In this study, we used the gonadotrope-derived LbetaT2 cell line to investigate the potential interaction between activin and GnRH in regulating the transcriptional activity of the rat FSHbeta gene promoter. Activin A and GnRH synergistically enhanced rat FSHbeta transcriptional activity. Overexpression of SMAD3 (mediator of decapentaplegic-related protein 3), but not of SMAD2, increased transcriptional activation of the rat (r) FSHbeta gene promoter, which was further enhanced by the combined overexpression of SMAD3 and 4 (3+4). The stimulatory effects of SMAD3 overexpression were localized to -472/-256 of the rFSHbeta gene promoter, and activin- and GnRH-responsive proteins were shown to bind to region -284/-252. Sequence analysis identified a consensus palindromic SMAD-binding site at -266/-259 of the rFSHbeta gene promoter. Mutation of two bases located in the center of this palindrome effectively abrogated SMAD4 binding, markedly reduced SMAD3 and 3+4 stimulation of the rFSHbeta gene promoter, and significantly decreased the synergistic enhancement of promoter activity by both activin A and GnRH, and SMAD3 and GnRH. Blockade of the MAPK-signaling pathway did not significantly affect the response to combined stimulation with activin and GnRH. In contrast, interference with SMAD3 signaling caused a significant reduction in activin and GnRH synergy. The results indicate that SMAD3 plays an important role in the synergistic effects of activin and GnRH and demonstrate that this synergy is mediated by a palindromic cis-element located at -266/-259 of the rFSHbeta gene promoter.

Oscillatory synthesis and secretion of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), under the control of pulsatile hypothalamic gonadotropin-releasing hormone (GnRH), is essential for normal reproductive development and fertility. The molecular mechanisms by which various patterns of pulsatile GnRH regulate gonadotrope responsiveness remain poorly understood. In contrast to the ␣ and LH␤ subunit genes, FSH␤ subunit transcription is preferentially stimulated at low rather than high frequencies of pulsatile GnRH. In this study, mutation of a cyclic AMP response element (CRE) within the FSH␤ promoter resulted in the loss of preferential GnRH stimulation at low pulse frequencies. We hypothesized that high GnRH pulse frequencies might stimulate a transcriptional repressor(s) to attenuate the action of CRE binding protein (CREB) and show that inducible cAMP early repressor (ICER) fulfills such a role. ICER was not detected under basal conditions, but pulsatile GnRH stimulated ICER to a greater extent at high than at low pulse frequencies. ICER binds to the FSH␤ CRE site to reduce CREB occupation and abrogates both maximal GnRH stimulation and GnRH pulse frequency-dependent effects on FSH␤ transcription. These data suggest that ICER production antagonizes the stimulatory action of CREB to attenuate FSH␤ transcription at high GnRH pulse frequencies, thereby playing a critical role in regulating cyclic reproductive function.The maintenance of normal reproductive function in all vertebrate species is dependent on the regulation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) synthesis and release by pituitary gonadotropes. These hormones are released in a pulsatile manner to regulate gametogenesis and gonadal hormone synthesis (2,11,17). The intermittent synthesis and secretion of LH and FSH by pituitary gonadotropes are tightly regulated, as evidenced by predictable and reproducible changes in circulating levels throughout the menstrual or estrous cycle. Although the synthesis and release of pituitary gonadotropins are affected by a number of endocrine, paracrine, and autocrine factors, the most important influence appears to be that of the hypothalamic decapeptide, gonadotropin-releasing hormone (GnRH). The tight inter-relationship between GnRH release and gonadotropin production is evidenced in patients with Kallmann's syndrome, in which GnRH deficiency results in low gonadotropin levels, absence of pubertal maturation, and infertility (42). Thus, GnRH is an essential coordinator of reproductive function.Regulation of gonadotropin biosynthesis and secretion by GnRH is critically dependent on GnRH delivery to the anterior pituitary. Pulsatile GnRH results in the stimulation of gonadotropin subunit mRNA levels and of LH and FSH secretion, whereas continuous exposure to GnRH downregulates mRNA levels and secretion (2, 45). Furthermore, the frequency and amplitude of GnRH pulses varies temporally and developmentally, for example, during different phases of the menst...