Estrogen prevents osteoporotic bone loss by attenuating bone resorption; however, the molecular basis for this is unknown. Here, we report a critical role for the osteoclastic estrogen receptor alpha (ERalpha) in mediating estrogen-dependent bone maintenance in female mice. We selectively ablated ERalpha in differentiated osteoclasts (ERalpha(DeltaOc/DeltaOc)) and found that ERalpha(DeltaOc/DeltaOc) females, but not males, exhibited trabecular bone loss, similar to the osteoporotic bone phenotype in postmenopausal women. Further, we show that estrogen induced apoptosis and upregulation of Fas ligand (FasL) expression in osteoclasts of the trabecular bones of WT but not ERalpha(DeltaOc/DeltaOc) mice. The expression of ERalpha was also required for the induction of apoptosis by tamoxifen and estrogen in cultured osteoclasts. Our results support a model in which estrogen regulates the life span of mature osteoclasts via the induction of the Fas/FasL system, thereby providing an explanation for the osteoprotective function of estrogen as well as SERMs.

MicroRNAs (miRNAs) control cell proliferation, differentiation and fate through modulation of gene expression by partially base-pairing with target mRNA sequences. Drosha is an RNase III enzyme that is the catalytic subunit of a large complex that cleaves pri-miRNAs with distinct structures into pre-miRNAs. Here, we show that both the p68 and p72 DEAD-box RNA helicase subunits in the mouse Drosha complex are indispensable for survival in mice, and both are required for primary miRNA and rRNA processing. Gene disruption of either p68 or p72 in mice resulted in early lethality, and in both p68(-/-) and p72(-/-) embryos, expression levels of a set of, but not all, miRNAs and 5.8S rRNA were significantly lowered. In p72(-/-) MEF cells, expression of p72, but not a mutant lacking ATPase activity, restored the impaired expression of miRNAs and 5.8S rRNA. Furthermore, we purified the large complex of mouse Drosha and showed it could generate pre-miRNA and 5.8S rRNA in vitro. Thus, we suggest that DEAD-box RNA helicase subunits are required for recognition of a subset of primary miRNAs in mDrosha-mediated processing.

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As locally converted estrogen from testicular testosterone contributes to apparent androgen activity, the physiological significance of androgen receptor (AR) function in the beneficial effects of androgens on skeletal tissues has remained unclear. We show here that inactivation of AR in mice using a Cre-loxP system-mediated gene-targeting technique caused bone loss in males but not in females. Histomorphometric analyses of 8-week-old male AR knockout (ARKO) mice showed high bone turnover with increased bone resorption that resulted in reduced trabecular and cortical bone mass without affecting bone shape. Bone loss in orchidectomized male ARKO mice was only partially prevented by treatment with aromatizable testosterone. Analysis of primary osteoblasts and osteoclasts from ARKO mice revealed that AR function was required for the suppressive effects of androgens on osteoclastogenesis supporting activity of osteoblasts but not on osteoclasts. Furthermore, expression of the receptor activator of NF-B ligand (RANKL) gene, which encodes a major osteoclastogenesis inducer, was found to be up-regulated in osteoblasts from ARdeficient mice. Our results indicate that AR function is indispensable for male-type bone formation and remodeling.

Testicular testosterone produced during a critical perinatal period is thought to masculinize and defeminize the male brain from the inherent feminization program and induce male-typical behaviors in the adult. These actions of testosterone appear to be exerted not through its androgenic activity, but rather through its conversion by brain aromatase into estrogen, with the consequent activation of estrogen receptor (ER)-mediated signaling. Thus, the role of androgen receptor (AR) in perinatal brain masculinization underlying the expression of male-typical behaviors remains unclear because of the conversion of testosterone into estrogen in the brain. Here, we report a null AR mutation in mice generated by the Cre-loxP system. The AR-null mutation in males (AR L؊/Y ) resulted in the ablation of male-typical sexual and aggressive behaviors, whereas female AR-null homozygote (AR L؊/L؊ ) mice exhibited normal female sexual behaviors. Treatment with nonaromatizable androgen (5␣-dihydrotestosterone, DHT) was ineffective in restoring the impaired male sexual behaviors, but it partially rescued impaired male aggressive behaviors in AR L؊/Y mice. Impaired maletypical behaviors in ER␣ ؊/؊ mice were restored on DHT treatment. The role of AR function in brain masculinization at a limited perinatal stage was studied in AR L؊/L؊ mice. Perinatal DHT treatment of females led to adult females sensitive to both 17␤-estradiol and DHT in the induction of male-typical behaviors. However, this female brain masculinization was abolished by AR inactivation. Our results suggested that perinatal brain masculinization requires AR function and that expression of male-typical behaviors in adults is mediated by both AR-dependent and -independent androgen signaling.