Mouse embryos undergo genome-wide methylation reprogramming by demethylation in early preimplantation development, followed by remethylation thereafter. Here we show that genomewide reprogramming is conserved in several mammalian species and ask whether it also occurs in embryos cloned with the use of highly methylated somatic donor nuclei. Normal bovine, rat, and pig zygotes showed a demethylated paternal genome, suggesting active demethylation. In bovine embryos methylation was further reduced during cleavage up to the eight-cell stage, and this reduction in methylation was followed by de novo methylation by the 16-cell stage. In cloned one-cell embryos there was a reduction in methylation consistent with active demethylation, but no further demethylation occurred subsequently. Instead, de novo methylation and nuclear reorganization of methylation patterns resembling those of differentiated cells occurred precociously in many cloned embryos. Cloned, but not normal, morulae had highly methylated nuclei in all blastomeres that resembled those of the fibroblast donor cells. Our study shows that epigenetic reprogramming occurs aberrantly in most cloned embryos; incomplete reprogramming may contribute to the low efficiency of cloning.

More than one-third of the worldwide population is overweight or obese and therefore at risk of developing type 2 diabetes mellitus. In order to mitigate this pandemic, safer and more potent therapeutics are urgently required. This necessitates the continued use of animal models to discover, validate and optimize novel therapeutics for their safe use in humans. In order to improve the transition from bench to bedside, researchers must not only carefully select the appropriate model but also draw the right conclusions. In this Review, we consolidate the key information on the currently available animal models of obesity and diabetes and highlight the advantages, limitations and important caveats of each of these models.

It has been proposed that two amino acid substitutions in the transcription factor FOXP2 have been positively selected during human evolution due to effects on aspects of speech and language. Here, we introduce these substitutions into the endogenous Foxp2 gene of mice. Although these mice are generally healthy, they have qualitatively different ultrasonic vocalizations, decreased exploratory behavior and decreased dopamine concentrations in the brain suggesting that the humanized Foxp2 allele affects basal ganglia. In the striatum, a part of the basal ganglia affected in humans with a speech deficit due to a nonfunctional FOXP2 allele, we find that medium spiny neurons have increased dendrite lengths and increased synaptic plasticity. Since mice carrying one nonfunctional Foxp2 allele show opposite effects, this suggests that alterations in cortico-basal ganglia circuits might have been important for the evolution of speech and language in humans.

Aging is a major risk factor for a large number of disorders and functional impairments. Therapeutic targeting of the aging process may therefore represent an innovative strategy in the quest for novel and broadly effective treatments against age-related diseases. The recent report of lifespan extension in mice treated with the FDA-approved mTOR inhibitor rapamycin represented the first demonstration of pharmacological extension of maximal lifespan in mammals. Longevity effects of rapamycin may, however, be due to rapamycin's effects on specific life-limiting pathologies, such as cancers, and it remains unclear if this compound actually slows the rate of aging in mammals. Here, we present results from a comprehensive, large-scale assessment of a wide range of structural and functional aging phenotypes, which we performed to determine whether rapamycin slows the rate of aging in male C57BL/6J mice. While rapamycin did extend lifespan, it ameliorated few studied aging phenotypes. A subset of aging traits appeared to be rescued by rapamycin. Rapamycin, however, had similar effects on many of these traits in young animals, indicating that these effects were not due to a modulation of aging, but rather related to aging-independent drug effects. Therefore, our data largely dissociate rapamycin's longevity effects from effects on aging itself.

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During differentiation, somatic nuclei acquire highly specialized DNA and chromatin modifications, which are thought to result in cellular memory of the differentiated state. Upon somatic nuclear transfer into oocytes, the donor nucleus may have to undergo reprogramming of these epigenetic marks in order to achieve totipotency. This may involve changes in epigenetic features similar to those that occur in normal embryos during early development. However, there is accumulating evidence that epigenetic reprogramming is severely deficient in cloned embryos. Several reports reveal inefficient demethylation and inappropriate reestablishment of DNA methylation in quantitative and qualitative patterns on somatic nuclear transfer. Here we examine histone H3 lysine 9 (H3-K9) methylation and acetylation in normal embryos and in those created by somatic nuclear transfer. We find that H3-K9 methylation is reprogrammed in parallel with DNA methylation in normal embryos. However, the majority of cloned embryos exhibit H3-K9 hypermethylation associated with DNA hypermethylation, suggesting a genome-wide failure of reprogramming. Strikingly, the precise epigenotype in cloned embryos depends on the donor cell type, and the proportion of embryos with normal epigenotypes correlates closely with the proportion developing to the blastocyst stage. These results suggest a mechanistic link between DNA and histone methylation in the mammalian embryo and reveal an association between epigenetic marks and developmental potential of cloned embryos.

In the post-genome era, the mouse will have a major role as a model system for functional genome analysis. This requires a large number of mutants similar to the collections available from other model organisms such as Drosophila melanogaster and Caenorhabditis elegans. Here we report on a systematic, genome-wide, mutagenesis screen in mice. As part of the German Human Genome Project, we have undertaken a large-scale ENU-mutagenesis screen for dominant mutations and a limited screen for recessive mutations. In screening over 14,000 mice for a large number of clinically relevant parameters, we recovered 182 mouse mutants for a variety of phenotypes. In addition, 247 variant mouse mutants are currently in genetic confirmation testing and will result in additional new mutant lines. This mutagenesis screen, along with the screen described in the accompanying paper, leads to a significant increase in the number of mouse models available to the scientific community. Our mutant lines are freely accessible to non-commercial users (for information, see http://www.gsf.de/ieg/groups/enu-mouse.html).

It was the aim of this study to further explore the functional role of vitamin D in the endocrine pancreas. By gene targeting, we have recently generated mice in which a lacZ reporter gene is driven by the endogenous vitamin D receptor (VDR) promoter. These mice express a functionally inactive mutant VDR. Pancreatic islets but not exocrine pancreas cells showed strong lacZ reporter gene expression in mutant mice. To rule out possible influences of hypocalcemia on pancreatic endocrine function, a rescue diet enriched with calcium, phosphorus, and lactose was fed to wild-type (WT) and VDR mutant mice. The rescue diet normalized body weight and mineral homeostasis in VDR mutants. In glucose tolerance tests, baseline blood glucose levels were unchanged in fasting VDR mutants. However, blood glucose was elevated after oral or subcutaneous glucose loading, and maximum serum insulin levels were reduced by approximately 60% in VDR mutants vs. WT mice on either diet. In addition, insulin mRNA levels were decreased in VDR mutant mice on both diets, whereas pancreatic beta cell mass, islet architecture, and islet neogenesis were normal. These findings clearly establish a molecular role of the vitamin D-responsive elements in pancreatic insulin synthesis and secretion in vivo.