S-adenosyl-L-homocysteine extends lifespan through methionine restriction effects.

Methionine restriction (MetR) can extend lifespan and delay the onset of aging-associated pathologies in most model organisms. Previously, we showed that supplementation with the metabolite S-adenosyl-L-homocysteine (SAH) extends lifespan and activates the energy sensor AMP-activated protein kinase (AMPK) in the budding yeast Saccharomyces cerevisiae. However, the mechanism involved and whether SAH can extend metazoan lifespan have remained unknown. Here, we show that SAH supplementation reduces Met levels and recapitulates many physiological and molecular effects of MetR. In yeast, SAH supplementation leads to inhibition of the target of rapamycin complex 1 (TORC1) and activation of autophagy. Furthermore, in Caenorhabditis elegans SAH treatment extends lifespan by activating AMPK and providing benefits of MetR. Therefore, we propose that SAH can be used as an intervention to lower intracellular Met and confer benefits of MetR.

Effect of Bcl11b genotypes and gamma-radiation on the development of mouse thymic lymphomas.

Bcl11b is a haploinsufficient tumor suppressor gene and expressed in many tissues such as thymus, brain and skin. Irradiated Bcl11b+/- heterozygous mice mostly develop thymic lymphomas, but the preference of Bcl11b inactivation for thymic lymphomas remains to be addressed. We produced Bcl11b+/- heterozygous and Bcl11b wild-type mice of p53+/- background and compared their incidence of gamma-ray induced thymic lymphomas. Majority of the tumors in p53+/- mice were skin tumors, and only 5 (36%) of the 14 tumors were thymic lymphomas. In contrast, Bcl11b+/-p53+/- doubly heterozygous mice developed thymic lymphomas at the frequency of 27 (79%) of the 34 tumors developed (P=0.008). This indicates the preference of Bcl11b impairment for thymic lymphoma development. We also analyzed loss of the wild-type alleles in the 27 lymphomas, a predicted consequence given by gamma-irradiation. However, the loss frequency was low, only six (22%) for Bcl11b and five (19%) for p53. The frequencies did not differ from those of spontaneously developed thymic lymphomas in the doubly heterozygous mice, though the latency of lymphoma development markedly differed between them. This suggests that the main contribution of irradiation at least in those mice is not for the tumor initiation by inducing allelic losses but probably for the promotion of thymic lymphoma development.

Mtf-1 lymphoma-susceptibility locus affects retention of large thymocytes with high ROS levels in mice after gamma-irradiation.

Mouse strains exhibit different susceptibilities to gamma-ray-induced thymic lymphomas. Our previous study identified Mtf-1 (metal responsive transcription factor-1) as a candidate susceptibility gene, which is involved in the radiation-induced signaling pathway that regulates the cellular reactive oxygen species (ROS). To reveal the mechanism for the increased susceptibility conferred by Mtf-1 locus, we examined early effects of gamma-ray on ROS levels in vivo and its difference between Mtf-1 susceptible and resistant congenic mice. Here, we show the detection of clonally growing thymocytes at 4 weeks after irradiation, indicating the start of clonal expansion at a very early stage. We also show that large thymocytes with higher ROS levels and a proliferation capacity were more numerous in the Mtf-1 susceptible mice than the resistant mice when examined at 7 days after irradiation, although such tendency was not found in mice lacking one allele of Bcl11b tumor suppressor gene. This high retention of the large thymocytes, at a high risk for ROS-induced mutation, is a compensatory proliferation and regeneration response to depletion of the thymocytes after irradiation and the response is likely to augment the development of prelymphoma cells leading to thymic lymphomas.

Update of mouse microsatellite database of Japan (MMDBJ).

We updated a database of microsatellite marker polymorphisms found in inbred strains of the mouse, most of which were derived from the wild stocks of four Mus musculus subspecies, M. m. domesticus, M. m. musculus, M. m.castaneus and M. m. molossinus. The major aim of constructing this database was to establish the genetic status of these inbred strains as resources for linkage analysis and positional cloning. The inbred strains incorporated in our database are A/J, C57BL/6J, CBA/J, DBA/2J, SM/J, SWR/J, 129Sv/J, MSM/Ms, JF1/Ms, CAST/Ei, NC/Nga, BLG2/Ms, NJL/Ms, PGN2/Ms, SK/CamEi and SWN/Ms, which have not or have only been poorly incorporated in the Whitehead Institute/MIT (WI/MIT) microsatellite database. The number of polymorphic microsatellite loci incorporated in our database is over 1,000 in all strains, and the URL site for our database is located at http:// www.shigen.nig.ac.jp /mouse/mmdbj/mouse.html.

Mutations in a new scaffold protein Sans cause deafness in Jackson shaker mice.

The Jackson shaker (js) mouse carries a recessive mutation causing phenotypes such as deafness, abnormal behavior (circling and/or head-tossing) and degeneration of inner ear neuroepithelia. Two alleles have been identified so far, the original js and js(seal). A contig of three BAC clones was isolated by positional cloning. Two of the clones rescue the js phenotype by BAC transgenesis. Analysis of transcripts in an overlapping region of the two clones revealed a gene encoding a new scaffold-like protein, Sans, that showed mutations in the two js mutants. One was a guanine nucleotide insertion in the original js allele and the other a 7-base insertion in the js(seal) allele. Both insertions are predicted to inactivate the Sans protein by frameshift mutations resulting in a truncated protein lacking the C-terminal SAM domain. Cochlear hair cells in the js mutants show disorganized stereocilia bundles, and Sans were highly expressed in inner and outer hair cells of cochlea. The existence of major motifs, ankyrin repeats and a SAM domain suggests that Sans may have an important role in the development and maintenance of the stereocilia bundles through protein-protein interaction.