https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/159777/1/j.cell.2006.07.024.pdf

Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors.

The epidemic of type 2 diabetes and impaired glucose tolerance is one of the main causes of morbidity and mortality worldwide. In both disorders, tissues such as muscle, fat and liver become less responsive or resistant to insulin. This state is also linked to other common health problems, such as obesity, polycystic ovarian disease, hyperlipidaemia, hypertension and atherosclerosis. The pathophysiology of insulin resistance involves a complex network of signalling pathways, activated by the insulin receptor, which regulates intermediary metabolism and its organization in cells. But recent studies have shown that numerous other hormones and signalling events attenuate insulin action, and are important in type 2 diabetes.

/pdf/insulin-signalling-and-the-regulation-of-glucose-and-lipid-6bdhstccqq.pdf

Insulin signalling and the regulation of glucose and lipid metabolism

PRL is an anterior pituitary hormone that, along with GH and PLs, forms a family of hormones that probably resulted from the duplication of an ancestral gene. The PRLR is also a member of a larger family, known as the cytokine class-1 receptor superfamily, which currently has more than 20 different members. PRLRs or binding sites are widely distributed throughout the body. In fact, it is difficult to find a tissue that does not express any PRLR mRNA or protein. In agreement with this wide distribution of receptors is the fact that now more than 300 separate actions of PRL have been reported in various vertebrates, including effects on water and salt balance, growth and development, endocrinology and metabolism, brain and behavior, reproduction, and immune regulation and protection. Clearly, a large proportion of these actions are directly or indirectly associated with the process of reproduction, including many behavioral effects. PRL is also becoming well known as an important regulator of immune function. A number of disease states, including the growth of different forms of cancer as well as various autoimmune diseases, appear to be related to an overproduction of PRL, which may act in an endocrine, autocrine, or paracrine manner, or via an increased sensitivity to the hormone. The first step in the mechanism of action of PRL is the binding to a cell surface receptor. The ligand binds in a two-step process in which site 1 on PRL binds to one receptor molecule, after which a second receptor molecule binds to site 2 on the hormone, forming a homodimer consisting of one molecule of PRL and two molecules of receptor. The PRLR contains no intrinsic tyrosine kinase cytoplasmic domain but associates with a cytoplasmic tyrosine kinase, JAK2. Dimerization of the receptor induces tyrosine phosphorylation and activation of the JAK kinase followed by phosphorylation of the receptor. Other receptor-associated kinases of the Src family have also been shown to be activated by PRL. One major pathway of signaling involves phosphorylation of cytoplasmic State proteins, which themselves dimerize and translocate to nucleus and bind to specific promoter elements on PRL-responsive genes. In addition, the Ras/Raf/MAP kinase pathway is also activated by PRL and may be involved in the proliferative effects of the hormone. Finally, a number of other potential mediators have been identified, including IRS-1, PI-3 kinase, SHP-2, PLC gamma, PKC, and intracellular Ca2+. The technique of gene targeting in mice has been used to develop the first experimental model in which the effect of the complete absence of any lactogen or PRL-mediated effects can be studied. Heterozygous (+/-) females show almost complete failure to lactate after the first, but not subsequent, pregnancies. Homozygous (-/-) females are infertile due to multiple reproductive abnormalities, including ovulation of premeiotic oocytes, reduced fertilization of oocytes, reduced preimplantation oocyte development, lack of embryo implantation, and the absence of pseudopregnancy. Twenty per cent of the homozygous males showed delayed fertility. Other phenotypes, including effects on the immune system and bone, are currently being examined. It is clear that there are multiple actions associated with PRL. It will be important to correlate known effects with local production of PRL to differentiate classic endocrine from autocrine/paracrine effects. The fact that extrapituitary PRL can, under some circumstances, compensate for pituitary PRL raises the interesting possibility that there may be effects of PRL other than those originally observed in hypophysectomized rats. The PRLR knockout mouse model should be an interesting system by which to look for effects activated only by PRL or other lactogenic hormones. On the other hand, many of the effects reported in this review may be shared with other hormones, cytokines, or growth factors and thus will be more difficult to study. (ABSTRACT TRUNCATED)

Prolactin (PRL) and Its Receptor: Actions, Signal Transduction Pathways and Phenotypes Observed in PRL Receptor Knockout Mice

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

/pdf/the-human-obesity-gene-map-the-2005-update-3zvtci1u6f.pdf

The human obesity gene map: the 2005 update.

The GLUT4 Glucose Transporter

THE insulin-sensitive glucose transporter, GLUT4, is the most abundant facilitative glucose transporter in muscle and adipose tissue, the major sites for postprandial glucose disposal. To assess the role of GLUT4 in glucose homeostasis, we have disrupted the murine GLUT4 gene. Because GLUT4 has been shown to be dysregulated in pathological states such as diabetes and obesity, it was expected that genetic ablation of GLUT4 would result in abnormal glucose homeostasis. The mice deficient in GLUT4 (GLUT4-null) are growth-retarded and exhibit decreased longevity associated with cardiac hypertrophy and severely reduced adipose tissue deposits. Blood glucose levels in female GLUT4-null mice are not significantly elevated in either the fasting or fed state; in contrast, male GLUT4-null mice have moderately reduced glycaemias in the fasted state and increased glycaemias in the fed state. However, both female and male GLUT4-null mice exhibit postprandial hyperinsulinaemia, indicating possible insulin resistance. Increased expression of other glucose transporters is observed in the liver (GLUT2) and heart (GLUT1) but not skeletal muscle. Oral glucose tolerance tests show that both female and male GLUT4-null mice clear glucose as efficiently as controls, but insulin tolerance tests indicate that these mice are less sensitive to insulin action. The GLUT4-null mice demonstrate that functional GLUT4 protein is not required for maintaining nearly normal glycaemia but that GLLJT4 is absolutely essential for sustained growth, normal cellular glucose and fat metabolism, and expected longevity.

Cardiac and adipose tissue abnormalities but not diabetes in mice deficient in GLUT4.

The Myb gene family currently consists of three members, named A-, B- and c-myb1,2. These genes encode nuclear proteins that bind DNA in a sequence-specific manner and function as regulators of transcription. In adult male mice, A-myb is expressed predominantly in male germ cells2,3. In female mice, A-myb is expressed in breast ductal epithelium, mainly during pregnancy-induced ductal branching and alveolar development. We report here that mice homozygous for a germline mutation in A-myb develop to term but show defects in growth after birth and male infertility due to a block in spermatogenesis. Morphological examination of the testes of A-myb−/− males revealed that the germ cells enter meiotic prophase and arrest at pachytene. In adult homozygous null A-myb female mice, the breast epithelial compartment showed underdevelopment of breast tissue following pregnancy and the female mice were unable to nurse their newborn pups. These results demonstrate that A-myb plays a critical role in spermatogenesis and mammary gland development.

Arrest of spermatogenesis and defective breast development in mice lacking A-myb.

Previous studies indicated that members of the myc gene family may be essential for preimplantation development. Other studies revealed that preimplantation embryos lacking c-myc, N-myc, or L-myc are viable, indicating that these genes are either not essential for preimplantation development or can be substituted for functionally by other myc gene family members. To investigate the possible role of these genes during preimplantation development, we determined the temporal patterns of expression of four members of the myc gene family, genes encoding myc-associated proteins, and four putative MYC target genes. We observed a sequential pattern of myc gene expression, with the L-myc mRNA expressed as a maternal transcript, the c-myc mRNA expressed during the 4-cell through morula stages, and the B-myc mRNA expressed highly at the morula and blastocysts stages. B-myc was the predominant family member expressed during preimplantation development. The mxi mRNA was not detectable and the mad mRNA was detectable only as a maternal transcript. The max mRNA, however, was expressed both as a maternal mRNA and as an embryonic message throughout most of preimplantation development. Three putative MYC target genes (Odc, cyclin E, and prothymosin-alpha) were transcriptionally induced during the 2-cell stage, and their mRNAs increased sharply in abundance during development to the morula and blastocyst stages. Another putative MYC target gene, cyclin A, was expressed both as a maternal mRNA and as an embryonic transcript. These data support the view that the expression of myc target genes may be supported initially through the expression of maternally inherited MYC proteins and corresponding mRNAs and that subsequent stage-specific changes in expression of myc genes, myc-associated genes, and myc target genes may control early differentiative events around the time of implantation.

Kimi S. Hatton

Papers

Cardiac and adipose tissue abnormalities but not diabetes in mice deficient in GLUT4.

Arrest of spermatogenesis and defective breast development in mice lacking A-myb.

Expression of myc-family, myc-interacting, and myc-target Genes During Preimplantation Mouse Development