Humans and mice lacking Lrp5 have low BMD. To evaluate whether Lrp5 and Lrp6 interact genetically to control bone or skeletal development, we created mice carrying mutations in both Lrp5 and the related gene Lrp6. We found that compound mutants had dose-dependent deficits in BMD and limb formation, suggesting functional redundancy between these two genes in bone and limb development.Introduction: Lrp5 and Lrp6 are closely related members of the low density lipoprotein receptor family and are co-receptors for Wnt ligands. While Lrp5 mutations are associated with low BMD in humans and mice, the role of Lrp6 in bone formation has not been analyzed. Materials and Methods:To address whether Lrp5 and Lrp6 play complimentary roles in bone and skeletal development, we created mice with mutations in both genes. We inspected limbs of mice from the different genotypic classes of compound mutants to identify abnormalities. DXA and CT were used to evaluate the effect of mutations in Lrp5 and Lrp6 on BMD and microarchitecture. Results: Mice heterozygous for mutations in Lrp6 and either heterozygous or homozygous for a mutation in Lrp5 (Lrp6 ϩ/Ϫ ;Lrp5 ϩ/Ϫ or Lrp6 ϩ/Ϫ ;Lrp5

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Alterations of the Wnt/B-catenin signaling pathway are positively associated with the development and progression of human cancer, including carcinoma of the prostate. To determine the role of activated Wnt/B-catenin signaling in mouse prostate carcinogenesis, we created a mouse prostate tumor model using probasin-Cre-mediated deletion of Apc. Prostate tumors induced by the deletion of Apc have elevated levels of B-catenin protein and are highly proliferative. Tumor formation is fully penetrant and follows a consistent pattern of progression. Hyperplasia is observed as early as 4.5 weeks of age, and adenocarcinoma is observed by 7 months. Continued tumor growth usually necessitated sacrifice between 12 and 15 months of age. Despite the high proliferation rate, we have not observed metastasis of these tumors to the lymph nodes or other organs. Surgical castration of 6-week-old mice inhibited tumor formation, and castration of mice with more advanced tumors resulted in the partial regression of specific prostate glands. However, significant areas of carcinoma remained 2 months postcastration, suggesting that tumors induced by Apc loss of function are capable of growth under conditions of androgen depletion. We conclude that the prostate-specific deletion of Apc and the increased expression of B-catenin associated with prostate carcinoma suggests a role for B-catenin in prostate cancer and offers an appropriate animal model to investigate the interaction of Wnt signaling with other genetic and epigenetic signals in prostate carcinogenesis.

Cytogenetic abnormalities and high-frequency allele losses involving the short arm of human chromosome 3 have been identified in a variety of histologically different neoplasms. These fmdings suggest that a tumorsuppressor gene or genes may be located in the region of 3pl4-p25, although there has been no definitive functional proof for the involvement of a particular region of 3p. We report a rapid genetic assay system that has allowed functional analysis of defined regions of 3p in the suppression of tumorigenicity in vivo. Interspecific microcell hybrids containing fragments of chromosome 3p were constructed and screened for tumorigenicity in athymic nude mice. Hybrid clones were obtained that showed a dramatic tumor suppression and contained a 2-megabase fragment ofhuman chromosomal material encompassing the region 3p2l near the interface with 3p22. With these hybrid clones, we have defined a genetic locus at 3p2l-p22 intimately involved in tumor suppression.

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