Estrogen-related receptor ␣ (ERR␣) is an orphan member of the superfamily of nuclear hormone receptors. ERR␣ was initially isolated based on its sequence homology to the estrogen receptor but is not activated by classic estrogens. To identify possible physiologic functions for this orphan receptor, we cloned the mouse ERR␣ cDNA and used it to characterize the expression of ERR␣ transcripts and to identify potential ERR␣ target genes. RNA in situ hybridization studies detect ERR␣ transcripts in an organ-specific manner through mid-to late embryonic development, with persistent high-level expression in brown adipose tissue and intestinal mucosa. In the adult mouse, ERR␣ is most highly expressed in kidney, heart, and brown adipocytes, tissues which preferentially metabolize fatty acids. Binding site selection experiments show that ERR␣ preferentially binds to an ERR␣ response element ( The orphan nuclear receptor estrogen-related receptor ␣ (ERR␣) was initially cloned by low-stringency screening of a human kidney library with an estrogen receptor DNA binding domain probe (12). Subsequently, protein micropurification and microsequencing techniques identified ERR␣ as a repressor of the simian virus 40 major late promoter and implicated the receptor as a key regulator of the early-to-late switch of simian virus 40 gene expression (35). ERR␣ has also been shown to accentuate estrogen-dependent induction of the complex lactoferrin estrogen response element (ERE), possibly by forming heterodimers with the estrogen receptor (39). While ERR␣ displays significant homology to the estrogen receptor, it does not bind estrogens in vitro, nor is its transcriptional activity modulated by estrogens (12, 39). Like many other members of the nuclear receptor superfamily, ERR␣ has no known ligand and is therefore considered an orphan receptor. In the absence of an associated ligand, one approach to uncovering potential physiologic roles for ERR␣ is to identify possible target genes.

The estrogen-related receptor ␣ (ERR␣) is an orphan member of the superfamily of nuclear hormone receptors expressed in tissues that preferentially metabolize fatty acids. Despite the molecular characterization of ERR␣ and identification of target genes, determination of its physiological function has been hampered by the lack of a natural ligand. To further understand the in vivo function of ERR␣, we generated and analyzed Estrra-null (ERR␣ ؊/؊ ) mutant mice. Here we show that ERR␣ ؊/؊ mice are viable, fertile and display no gross anatomical alterations, with the exception of reduced body weight and peripheral fat deposits. No significant changes in food consumption and energy expenditure or serum biochemistry parameters were observed in the mutant animals. However, the mutant animals are resistant to a high-fat diet-induced obesity. Importantly, DNA microarray analysis of gene expression in adipose tissue demonstrates altered regulation of several enzymes involved in lipid, eicosanoid, and steroid synthesis, suggesting that the loss of ERR␣ might interfere with other nuclear receptor signaling pathways. In addition, the microarray study shows alteration in the expression of genes regulating adipogenesis as well as energy metabolism. In agreement with these findings, metabolic studies showed reduced lipogenesis in adipose tissues. This study suggests that ERR␣ functions as a metabolic regulator and that the ERR␣ ؊/؊ mice provide a novel model for the investigation of metabolic regulation by nuclear receptors.Nuclear receptors are ligand-regulated transcription factors that control key pathways required for normal development and maintenance of homeostasis throughout life (37). Nuclear receptors now comprise a family of 48 genes in mice and humans that encode structurally and functionally related proteins. However, the existence of fewer than 10 receptors had been predicted by classic physiological and biochemical studies (10). Since the discovery of many nuclear receptors had not been anticipated and thus is not linked to recognized natural ligands, these new gene products were referred to as orphan nuclear receptors. During the last decade, extensive study of this gene family revealed that orphan nuclear receptors control essential developmental and metabolic functions in response to natural ligands as diverse as steroid hormones, retinoic acids, leukotrienes, bile acids, cholesterol metabolites, and long-chain fatty acids (reviewed in references 5, 26, and 48). In addition, orphan nuclear receptors have been shown to react to the presence of exogenous ligands such as pesticides (15, 70), phenobarbital (53, 61), and a wide variety of xenobiotic agents and drugs (2,24,39,55,66,68,69). Gene deletion analyses in mice have been particularly useful to uncover biological functions of orphan nuclear receptors. Nuclear orphan receptors have been shown to participate in the development and/or maintenance of the placenta, somitogenesis, brain, heart, hypothalamus-pituitary axis, immune system, and pathways controlling s...

Classical endocrine studies have shown that steroid hormones are required for the maintenance of pregnancy and placental viability. The oestrogen-receptor-related receptor beta (ERR-beta) is an orphan member of the superfamily of nuclear hormone receptors. Although ERR-beta is homologous to the oestrogen receptor and binds the oestrogen response element, it is not activated by oestrogens. Expression of ERR-beta during embryogenesis defines a subset of extra-embryonic ectoderm that subsequently forms the dome of the chorion, suggesting that ERR-beta may be involved in early placental development. Homozygous mutant embryos generated by targeted disruption of the Estrrb gene have severely impaired placental formation, and die at 10.5 days post-coitum. The mutants display abnormal chorion development associated with an overabundance of trophoblast giant cells and a severe deficiency of diploid trophoblast. The phenotype can be rescued by aggregation of Estrrb mutant embryos with tetraploid wild-type cells, which contribute exclusively to extra-embryonic tissues. Our results indicate that ERR-beta has an important role in early placentation, and suggest that an inductive signal originating from or modified by the chorion is required for normal trophoblast proliferation and differentiation.

The orphan nuclear receptor ERR␤ is expressed in undifferentiated trophoblast stem cell lines and extraembryonic ectoderm, and genetic ablation of ERR␤ results in abnormal trophoblast proliferation and precocious differentiation toward the giant cell lineage. Here, we show that the synthetic estrogen diethylstilbestrol (DES) promotes coactivator release from ERR␤ and inhibits its transcriptional activity. Strikingly, treatment of trophoblast stem cells with DES led to their differentiation toward the polyploid giant cell lineage. In addition, DEStreated pregnant mice exhibited abnormal early placenta development associated with an overabundance of trophoblast giant cells and an absence of diploid trophoblast. These results define a novel pathway for DES action and provide evidence for steroidlike control of trophoblast development. Received December 12, 2000; revised version accepted February 7, 2001. Nuclear receptors constitute a large family of transcription factors that mediate responses to small lipophilic hormones and play essential roles in embryonic development and maintenance of homeostasis in adult animals (Mangelsdorf et al. 1995). Orphan nuclear receptors are members of the nuclear receptor family that lack identified ligands (Giguère 1999). Recent studies have identified several natural and synthetic ligands for a number of orphan nuclear receptors, which led to the discovery of new hormone-response systems implicated in the control of cell fate, organogenesis, and basic metabolic functions Kliewer et al. 1999). While the estrogen-receptor-related receptor (ERR) ␣ (NR3B1) and ERR␤ (NR3B2) were the first orphan nuclear receptors identified more than a decade ago (Giguère et al. 1988), the identification of natural and synthetic ERR ligands has remained elusive. Despite being closely related to the estrogen receptors, ERRs are not activated by natural estrogens (Giguère et al. 1988). In contrast, members of the ERR family, now known to contain a third member referred to as ERR␥ (NR3B3) (Eudy et al. 1998), display various levels of constitutive activity and can interact with coactivators in the absence of ligand Vanacker et al. 1999;Xie et al. 1999).Molecular and genetic studies have shown that ERR␤ plays an important role in early placentation. ERR␤ is expressed in undifferentiated trophoblast stem cell lines (Tanaka et al. 1998) and in a subset of cells in extraembryonic ectoderm destined to make up the chorion (Pettersson et al. 1996;Luo et al. 1997). Genetic ablation of ERR␤ in the mouse results in abnormal chorion formation followed by failure of diploid trophoblast self-renewal and an increase in trophoblast giant cells (Luo et al. 1997). Thus, ERR␤ is essential for normal placental formation, and pharmacological modulation of its activity could influence reproductive function.Diethylstilbestrol (DES) is a potent synthetic estrogen that was used clinically for the prevention of spontaneous abortions from the 1940s to 1971 (Smith 1948). The mechanism of action and factual effectiveness of DES ...