SummaryA diet deficient in the amino acid methionine has previously been shown to extend lifespan in several stocks of inbred rats. We report here that a methionine-deficient (Meth-R) diet also increases maximal lifespan in (BALB/ cJ × × × × C57BL/6 J)F1 mice. Compared with controls, Meth-R mice have significantly lower levels of serum IGF-I, insulin, glucose and thyroid hormone. Meth-R mice also have higher levels of liver mRNA for MIF (macrophage migration inhibition factor), known to be higher in several other mouse models of extended longevity. Meth-R mice are significantly slower to develop lens turbidity and to show age-related changes in T-cell subsets. They are also dramatically more resistant to oxidative liver cell injury induced by injection of toxic doses of acetaminophen. The spectrum of terminal illnesses in the Meth-R group is similar to that seen in control mice. Studies of the cellular and molecular biology of methionine-deprived mice may, in parallel to studies of calorie-restricted mice, provide insights into the way in which nutritional factors modulate longevity and late-life illnesses.

Mutations in the Wnt co-receptor LRP5 alter bone mass in humans, but the mechanisms responsible for Wnts actions in bone are unclear. To investigate the role of the classical Wnt signaling pathway in osteogenesis, we generated mice lacking the ␤-catenin or adenomatous polyposis coli (Apc) genes in osteoblasts. Loss of ␤-catenin produced severe osteopenia with striking increases in osteoclasts, whereas constitutive activation of ␤-catenin in the conditional Apc mutants resulted in dramatically increased bone deposition and a disappearance of osteoclasts. In vitro, osteoblasts lacking the ␤-catenin gene exhibited impaired maturation and mineralization with elevated expression of the osteoclast differentiation factor, receptor activated by nuclear factor-B ligand (RANKL), and diminished expression of the RANKL decoy receptor, osteoprotegerin. By contrast, Apc-deficient osteoblasts matured normally but demonstrated decreased expression of RANKL and increased osteoprotegerin. These findings suggest that Wnt/␤-catenin signaling in osteoblasts coordinates postnatal bone acquisition by controlling the differentiation and activity of both osteoblasts and osteoclasts.

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Understanding the signaling pathways that drive aggressive breast cancers is critical to the development of effective therapeutics. The oncogene MET is associated with decreased survival in breast cancer, yet the role that MET plays in the various breast cancer subtypes is unclear. We describe a knockin mouse with mutationally activated Met (Met mut ) that develops a high incidence of diverse mammary tumors with basal characteristics, including metaplasia, absence of progesterone receptor and ERBB2 expression, and expression of cytokeratin 5. With gene expression and tissue microarray analysis, we show that high MET expression in human breast cancers significantly correlated with estrogen receptor negative/ERBB2 negative tumors and with basal breast cancers. Few treatment options exist for breast cancers of the basal or trastuzumab-resistant ERBB2 subtypes. We conclude from these studies that MET may play a critical role in the development of the most aggressive breast cancers and may be a rational therapeutic target.ErbB2 ͉ mouse model