Expression of genes involved in lipid metabolism correlate with peroxisome proliferator-activated receptor gamma expression in human skeletal muscle.

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) activation in adipose tissue is known to regulate genes involved in adipocyte differentiation and lipid metabolism. However, the role of PPAR-gamma in muscle remains unclear. To examine the potential regulation of genes by PPAR-gamma in human skeletal muscle, we used semiquantitative RT-PCR to determine the expression of PPAR-gamma, lipoprotein lipase (LPL), muscle carnitine palmitoyl transferase-1 (mCPT1), fatty acid-binding protein (FABP), carnitine acylcarnitine transferase (CACT), and glucose transporter-4 (GLUT4) in freeze-dried muscle samples from 14 male subjects. These samples were dissected free of adipose and other tissue contamination, as confirmed by minimal or absent adipsin expression. Between individuals, the messenger ribonucleic acid concentration of PPAR-gamma varied up to 3-fold, whereas LPL varied up to 6.5-fold, mCPT1 13-fold, FABP 4-fold, CACT 4-fold, and GLUT4 up to 3-fold. The expression of LPL (r2 = 0.54; P = 0.003), mCPT1 (r2 = 0.42; P = 0.012), and FABP (r2 = 0.324; P = 0.034) all correlated significantly with PPAR-gamma expression in the same samples. No significant correlation was observed between the expression of CACT and PPAR-gamma or between GLUT4 and PPAR-gamma. These findings demonstrate a relationship between PPAR-gamma expression and the expression of other genes of lipid metabolism in muscle and support the hypothesis that PPAR-gamma activators such as the antidiabetic thiazolidinediones may regulate fatty acid metabolism in skeletal muscle as well as in adipose tissue.

Localization of a human receptor tyrosine kinase (ETK1) to chromosome region 3p11.2.

We have recently described a human receptor tyrosine kinase (hek) that is expressed by some pre-B and thymic T cell lines, but is not detectable on normal adult human tissues. Gene cloning studies established that hek is a new member of the EPH family of receptor tyrosine kinases. The expression of hek may normally be developmentally regulated and inappropriate expression may contribute to oncogenesis. In the present study, we have used Southern blot analysis of somatic cell hybrids and fluorescence in situ hybridization to localize the hek gene to human chromosome region 3p11.2. Karyotype analysis of the cell lines that over-express hek showed no cytogenetically visible abnormality involving the hek locus.

Chromosomal location of the human transketolase gene.

The gene encoding the human transketolase enzyme (TKT) was localized by fluorescence in situ hybridization to normal and FRA3B human chromosomes. Southern blot analysis of a series of human x mouse and human x hamster hybrid cell lines confirmed this localisation. TKT maps to 3p14 and distal to FRA3B, localizing TKT to 3p14.3.

No evidence for linkage of a novel CA repeat polymorphism for apoptosis antigen 1 (APO-1 or fas) with type I diabetes in a Caucasian population.

A novel microsatellite marker was found within 48.5 kb of the Fas gene. The observed heterozygosity in 160 healthy unrelated controls was 0.78. There was no evidence of linkage to type I diabetes mellitus in 120 diabetic children using the transmission disequilibrium test.

High-resolution cytogenetic-based physical map of human chromosome 16.

A panel of 54 mouse/human somatic cell hybrids, each possessing various portions of chromosome 16, was constructed; 46 were constructed from naturally occurring rearrangements of this chromosome, which were ascertained in clinical cytogenetics laboratories, and a further 8 from rearrangements spontaneously arising during tissue culture. By mapping 235 DNA markers to this panel of hybrids, and in relation to four fragile sites and the centromere, a cytogenetic-based physical map of chromosome 16 with an average resolution of 1.6 Mb was generated. Included are 66 DNA markers that have been typed in the CEPH pedigrees, and these will allow the construction of a detailed correlation of the cytogenetic-based physical map and the genetic map of this chromosome. Cosmids from chromosome 16 that have been assembled into contigs by use of repetitive sequence fingerprinting have been mapped to the hybrid panel. Approximately 11% of the euchromatin is now both represented in such contigs and located on the cytogenetic-based physical map. This high-resolution cytogenetic-based physical map of chromosome 16 will provide the basis for the cloning of genetically mapped disease genes, genes disrupted in cytogenetic rearrangements that have produced abnormal phenotypes, and cancer breakpoints.

Relationship of a novel polymorphic marker near the human obese (OB) gene to fat mass in healthy women.

The cloning of the murine obese (ob) gene and its human homologue has recently been reported. Mutations in the mouse ob gene result in hereditary obesity; however, the role of variations of OB in the regulation of bodyweight in humans has yet to be determined. The contribution of putative genetic variations in the human OB gene to total and regional fat mass in a normal twin population has been analyzed through linkage and association with a novel polymorphic marker, located in proximity to this gene. The polymorphic dinucleotide repeat, isolated from a P1 clone containing the human OB gene, was physically localized by long-range restriction mapping to within 30 kilobases of the OB locus. The marker was genotyped in a population of 47 healthy female/female dizygotic (DZ) twin pairs for which direct measures of central abdominal and whole body fat had been obtained by dual X-ray absorbtiometry. Possible linkage between the microsatellite marker and whole-body (p = 0.008), but not central abdominal (p = 0.09), fat deposits was indicated. No association between fat depot phenotype and marker genotype was detected. These results suggest that genetic variation in or close to the human OB gene may play a role in the size of body fat stores in healthy women.