Caloric restriction (CR) protects against aging and disease but the mechanisms by which this affects mammalian lifespan are unclear. We show in mice that deletion of the nutrient-responsive mTOR (mammalian target of rapamycin) signaling pathway component ribosomal S6 protein kinase 1 (S6K1) led to increased lifespan and resistance to age-related pathologies such as bone, immune and motor dysfunction and loss of insulin sensitivity. Deletion of S6K1 induced gene expression patterns similar to those seen in CR or with pharmacological activation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), a conserved regulator of the metabolic response to CR. Our results demonstrate that S6K1 influences healthy mammalian lifespan, and suggest therapeutic manipulation of S6K1 and AMPK might mimic CR and provide broad protection against diseases of aging. Genetic studies in S. cerevisiae, C. elegans and D. melanogaster implicate several mechanisms in the regulation of lifespan. These include the insulin and insulin-like growth factor 1 (IGF-1) signaling (IIS) and mammalian target of rapamycin (mTOR) pathways which both activate the downstream effector ribosomal protein S6 kinase 1 (S6K1) (1, 2). Although the role of these pathways in mammalian aging is less clear, there is mounting evidence that IIS regulates lifespan in mice (1). Global deletion of one allele of the IGF1 receptor (Igf1r), adipose-specific deletion of the insulin receptor (Insr), global deletion of insulin receptor substrate protein 1 (Irs1) or neuron-specific deletion of Irs2 all increase mouse lifespan (1). Lifespan-extending mutations in the somatotropic axis also appear to work through attenuated IIS (3). Igf1r has also been implicated as a modulator of human longevity (4). However, the action of downstream effectors of IIS or mTOR signaling in mammalian longevity is not fully understood.S6K1 transduces anabolic signals that indicate nutritional status to regulate cell size and growth and metabolism through various mechanisms (5). These include effects on the translational machinery and on cellular energy levels through the activity of adenosine monophosphate (AMP)-activated protein kinase (AMPK) (6, 7). Furthermore, S6K1 serine phosphorylates IRS1 and IRS2 thereby decreasing insulin signaling (5). Given the key role of S6K1 in IIS and mTOR signaling, and the regulation of aging in lower organisms by mTOR, S6K, and their downstream effectors (2) we used log rank testing to evaluate differences in lifespan of wild-type (WT) and S6K1 -/-littermate mice on a C57BL/6 background (8). Data for both sexes combined showed median lifespan in S6K1 -/-mice increased by 80 days (from 862 to 942 days) or 9% relative to that of WT mice (X 2 = 10.52, p < 0.001) ( Fig. 1A and Table 1). Maximum lifespan (mean lifespan of the oldest 10% within a cohort) was also increased (1077±16 and 1175±24 days, p < 0.01 for WT and S6K1 -/-mice, respectively). Analysis of each sex separately showed that median lifespan in female S6K1 -/-mice was increased, by 153 d...

Recent evidence suggests that alterations in insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) can increase mammalian life span. For example, in several mouse mutants, impairment of the growth hormone (GH)/IGF1 axis increases life span and also insulin sensitivity. However, the intracellular signaling route to altered mammalian aging remains unclear. We therefore measured the life span of mice lacking either insulin receptor substrate (IRS) 1 or 2, the major intracellular effectors of the IIS receptors. Our provisional results indicate that female Irs1-/- mice are long-lived. Furthermore, they displayed resistance to a range of age-sensitive markers of aging including skin, bone, immune, and motor dysfunction. These improvements in health were seen despite mild, lifelong insulin resistance. Thus, enhanced insulin sensitivity is not a prerequisite for IIS mutant longevity. Irs1-/- female mice also displayed normal anterior pituitary function, distinguishing them from long-lived somatotrophic axis mutants. In contrast, Irs2-/- mice were short-lived, whereas Irs1+/- and Irs2+/- mice of both sexes showed normal life spans. Our results therefore suggest that IRS1 signaling is an evolutionarily conserved pathway regulating mammalian life span and may be a point of intervention for therapies with the potential to delay age-related processes.

The transcription factor SOX2 is expressed most notably in the developing CNS and placodes, where it plays critical roles in embryogenesis. Heterozygous de novo mutations in SOX2 have previously been associated with bilateral anophthalmia/microphthalmia, developmental delay, short stature, and male genital tract abnormalities. Here we investigated the role of Sox2 in murine pituitary development. Mice heterozygous for a targeted disruption of Sox2 did not manifest eye defects, but showed abnormal anterior pituitary development with reduced levels of growth hormone, luteinizing hormone, and thyroid-stimulating hormone. Consequently, we identified 8 individuals (from a cohort of 235 patients) with heterozygous sequence variations in SOX2. Six of these were de novo mutations, predicted to result in truncated protein products, that exhibited partial or complete loss of function (DNA binding, nuclear translocation, or transactivation). Clinical evaluation revealed that, in addition to bilateral eye defects, SOX2 mutations were associated with anterior pituitary hypoplasia and hypogonadotropic hypogonadism, variable defects affecting the corpus callosum and mesial temporal structures, hypothalamic hamartoma, sensorineural hearing loss, and esophageal atresia. Our data show that SOX2 is necessary for the normal development and function of the hypothalamo-pituitary and reproductive axes in both humans and mice. Introduction SOX2 is a member of the sex-determining region of the Y chromosome-related (SRY-related) high-mobility group (HMG) box (SOX) family of transcription factors, encoded by 20 genes in humans and mice, each of which carries a 79-amino acid HMG box DNA-binding domain similar to that of SRY as well as domains implicated in transcriptional regulation (1, 2). Based on HMG box homology, they are grouped into different subfamilies. SOX1, SOX2, and SOX3 belong to the B1 subfamily and are expressed in various phases of embryonic development and cell differentiation, where they play critical roles in embryogenesis (3, 4). All 3 mark neuroepithelial progenitors and stem cells from the earliest stages of development, and there is a strong, but not absolute, tendency for them to be downregulated as cells differentiate.In the mouse, Sox2 RNA is first detected in cells at the morula stage (2.5 dpc) and then in the inner cell mass of the blastocyst (3.5 dpc).

The development of complex organs composed of different cell types frequently depends on reciprocal induction events occurring between distinct tissue layers that lie adjacent to one another in the embryo. The pituitary is a well studied case in point. It originates from two ectoderm-derived tissues, with the posterior lobe developing from an evagination of the ventral diencephalon, the infundibulum, and the intermediate and anterior lobes deriving from Rathke's pouch, an invaginating domain in the roof of the oral ectoderm 1 . In the mature gland, the posterior lobe contains axon terminal projections from two populations of hypothalamic neuroendocrine neurons. The anterior and intermediate lobes contain several different endocrine cell types whose proliferation, hormone synthesis and secretion are regulated by factors secreted from hypothalamic neuroendocrine neurons.During early development the infundibulum has an inductive role in the formation of the pituitary. For example, the genetic ablation of this domain in Titf1-null mice results in the complete absence of the pituitary gland 2 . The essential signaling molecules made by the infundibulum are thought to be FGF8 and BMP4, as both are necessary to induce early development of Rathke's pouch. FGF and BMP signals are also required to control the pattern of differentiation of cell types derived from Rathke's pouch 3,4 .Even subtle mutations that affect signaling pathways during early organogenesis can have profound effects on subsequent development and specification of mature cell types. These could arise in genes encoding the signaling molecules or their receptors, in transcription factors responsible for their expression or in genes required to specify the interacting tissues. In humans, SOX3, an HMG box protein (for review see ref. 5), is implicated in a syndrome of X-linked hypopituitarism and mental retardation 6 . In a single family whose males were deficient in growth hormone, a mutation in SOX3 was identified. The consequences of this mutation on the function of the protein are not known. X-chromosome deletions encompassing SOX3 are linked to several syndromes in humans, including mental retardation, but defects in pituitary function have not been reported 7,8 .SOX3 is a single-exon gene on the X chromosome in all mammals and is thought to be the gene from which SRY, the Y-linked testis determining gene, evolved 9,10 . Based on sequence homology, however, SOX3 is more closely related to SOX1 and SOX2 (refs. 5,11). Together they comprise the SOXB1 subfamily and are coexpressed throughout the developing CNS [11][12][13] . To study the role of Sox3, we targeted null mutations in the gene into XY embryonic stem (ES) cells, but injection of these cells into blastocysts resulted in early lethality of the chimeras due to a gastrulation defect (M. Parsons, C. Wise, S.B., M. CohenTannoudji, K.R., L. Pevny & R.L.-B., unpublished data).Therefore, to access later functions of SOX3, we initiated experiments using a conditional targeting strategy. In contrast to th...

OBJECTIVE-Somatostatin (SST) is secreted by islet ␦-cells and by extraislet neuroendocrine cells. SST receptors have been identified on ␣-and ␤-cells, and exogenous SST inhibits insulin and glucagon secretion, consistent with a role for SST in regulating ␣-and ␤-cell function. However, the specific intraislet function of ␦-cell SST remains uncertain. We have used Sst Ϫ/Ϫ mice to investigate the role of ␦-cell SST in the regulation of insulin and glucagon secretion in vitro and in vivo. RESEARCH DESIGN AND METHODS-Islet morphology wasassessed by histological analysis. Hormone levels were measured by radioimmunoassay in control and Sst Ϫ/Ϫ mice in vivo and from isolated islets in vitro. RESULTS-Islet size and organization did not differ between SstϪ/Ϫ and control islets, nor did islet glucagon or insulin content. Sst Ϫ/Ϫ mice showed enhanced insulin and glucagon secretory responses in vivo. In vitro stimulus-induced insulin and glucagon secretion was enhanced from perifused Sst Ϫ/Ϫ islets compared with control islets and was inhibited by exogenous SST in Sst Ϫ/Ϫ but not control islets. No difference in the switch-off rate of glucose-stimulated insulin secretion was observed between genotypes, but the cholinergic agonist carbamylcholine enhanced glucose-induced insulin secretion to a lesser extent in Sst Ϫ/Ϫ islets compared with controls. Glucose suppressed glucagon secretion from control but not Sst Ϫ/Ϫ islets.CONCLUSIONS-We suggest that ␦-cell SST exerts a tonic inhibitory influence on insulin and glucagon secretion, which may facilitate the islet response to cholinergic activation. In addition, ␦-cell SST is implicated in the nutrient-induced suppression of glucagon secretion. Diabetes 58:403-411, 2009