Sietse Mosselman

ERβ: Identification and characterization of a novel human estrogen receptor

A novel estrogen receptor (hereinafter referred to as ERβ) was cloned using degenerate PCR primers. A comparison of the amino acid sequence of ERβ with the ‘classical’ ER (ERα) shows a high degree of conservation of the DNA‐binding domain (96%), and of the ligand‐binding domain (58%). In contrast, the A/B domain, the hinge region and the F‐domain are not conserved. Northern blot analysis revealed that ERβ is expressed in human thymus, spleen, ovary and testis. Transient transfections of an ERβ expression construct together with an ERE‐based reporter construct in CHO cells clearly demonstrated transactivation of ERβ by 17β‐estradiol. In addition, the ERα antagonist ICI‐164384 is a potent antagonist for ERβ as well. Interestingly, the level of transactivation by 17β‐estradiol is higher for ERα than for ERβ, which may reflect suboptimal conditions for ERβ at the level of the ligand, responsive element or cellular context.

Impaired Nipple Development and Parturition in LGR7 Knockout Mice

ABSTRACT LGR7 is a G-protein coupled receptor with structural homology to the gonadotrophin and thyrotrophin receptors. Recently, LGR7 was deorphanized, and it was shown that relaxin is the ligand for LGR7. To further study the function of this receptor, mice deficient for LGR7 were generated by replacing part of the transmembrane-encoding region with a LacZ reporter cassette. Here we show that LGR7 is expressed in various tissues, including the uterus, heart, brain, and testis. Fertility studies using female LGR7−/− mice showed normal fertility and litter size. However, some females were incapable of delivering their pups, and several pups were found dead. Moreover, all offspring died within 24 to 48 h after delivery because female LGR7−/− mice were unable to feed their offspring due to impaired nipple development. In some male LGR7−/− mice, spermatogenesis was impaired, leading to azoospermia and a reduction in fertility. Interestingly, these phenomena were absent in mutant mice at older ages or in later generations. Taken together, results from LGR7 knockout mice indicate an essential role for the LGR7 receptor in nipple development during pregnancy. Moreover, a defect in parturition was observed, suggesting a role for LGR7 in the process of cervical ripening.

Estrogen Receptors alpha and beeta Two Receptors of a Kind

Ever since the discovery of estradiol and the elucidation of its chemical structure, there has been a great deal of interest in its mechanism of action and its potential therapeutic value. It is now well established that estrogens have many different functions in many different cell-types. With respect to the potential use of estrogens as therapeutics, there is an interest in controlling reproductive function, bone metabolism, cardiovascular disease, as well as in the prevention of hot flushes, mood changes and Alzheimer s disease. For over a decade, it was believed that estrogens signal through a a single estrogen receptor, now referred to as ERalpha, which belongs to a family of ligand-activated transcription factors. More recently, however, a second estrogen receptor ERbeta was identified. The current review describes similarities as well as differences between these two distinct estrogen receptors. Both ERalpha and ERbeta bind 17beta-estradiol with high affinity and they bind to classical estrogen response elements in a similar if not identical fashion. However, there are also major differences between ERalpha and ERbeta for instance with respect to their tissue distribution, the phenotype of the corresponding knock-out mice and their transcriptional activities. It is anticipated that a better understanding of these two receptors will eventually lead to more selective ways of modulating physiological processes which are influenced by estrogens. For this purpose, the development of ERalpha and ERbeta specific ligands, both agonists as well as antagonists, will be of great importance.

Linkage Analysis of Extremely Discordant and Concordant Sibling Pairs Identifies Quantitative Trait Loci Influencing Variation in Human Menopausal Age

Age at natural menopause may be used as parameter for evaluating the rate of ovarian aging. Environmental factors determine only a small part of the large variation in menopausal age. Studies have shown that genetic factors are likely to be involved in variation in menopausal age. To identify quantitative-trait loci for this trait, we performed a genomewide linkage study with age at natural menopause as a continuous quantitative phenotype in Dutch sister pairs, through use of a selective sampling scheme. A total of 165 families were ascertained using extreme selected sampling and were genotyped for 417 markers. Data were analyzed by Haseman-Elston regression and by an adjusted variance-components analysis. Subgroup analyses for early and late menopausal age were conducted by Haseman-Elston regression. In the adjusted variance-components analysis, 12 chromosomes had a LOD score of > or =1.0. Two chromosomal regions showed suggestive linkage: 9q21.3 (LOD score 2.6) and Xp21.3 (LOD score 3.1). Haseman-Elston regression showed rather similar locations of the peaks but yielded lower LOD scores. A permutation test to obtain empirical P values resulted in a significant peak on the X chromosome. To our knowledge, this is the first study to attempt to identify loci responsible for variability in menopausal age and in which several chromosomal regions were identified with suggestive and significant linkage. Although the finding of the region on the X chromosome comes as no surprise, because of its widespread involvement in premature ovarian failure, the definition of which particular gene is involved is of great interest. The region on chromosome 9 deserves further consideration. Both findings require independent confirmation.

Localization of LGR7 Gene Expression in Adult Mouse Brain Using LGR7 Knock-out/LacZ Knock-in Mice: Correlation with LGR7 mRNA Distribution

Abstract: Knowledge of the distribution of the relaxin receptor, LGR7, in the brain provides a basis for studies of the physiologic actions of relaxin. LGR7 knock‐out (KO) mice were produced by the in‐frame replacement of LGR7 exon 10 and 11 with a LacZ‐reporter cassette (knock‐in [KI]), and in this study we used LGR7‐KO/LacZ‐KI mice to determine the regional/cellular distribution of LGR7 gene expression in adult mouse brain by assessing β‐galactosidase activity in perfusion‐fixed sections. High densities of β‐galactosidase‐positive neurons were detected in anterior olfactory and claustrum/endopiriform nuclei, deep layers of cortex (particularly somatosensory), and the subiculum. Low to moderate densities were detected in olfactory bulb (periglomerular layer), cingulate cortex, subfornical organ, hippocampal CA2/dentate hilus, amygdala, hypothalamus, and thalamus. This LGR7/LacZ expression appears to recapitulate that of native LGR7 in wild‐type mice and provides a model to further investigate the phenotype of LGR7‐responsive neurons in the brain and to help reveal functions associated with central relaxin signaling.