No negative impact of reduced leptin secretion on bone metabolism in male decathletes.

This study investigated the effect of intense physical activities that generate high mechanical constraints on bone metabolism and serum leptin concentrations and the potential relationships among bone mineral density (BMD), bone biochemical markers and leptin variation. Thirteen male decathletes (mean age 22.4 +/- 2.9 years), nationally or internationally ranked (15.5 h/week of training), were compared with 13 healthy sedentary subjects (mean age 25.9 +/- 3.3 years). BMD was measured by DEXA and bone turnover was evaluated by specific markers. Leptin and calciotropic hormones levels were analysed in parallel. BMDs were higher in athletes than in controls at total body (13.9%), lumbar spine (17%), femoral neck (25%) and radius (9%), but not at the head. Athletes presented higher concentrations of osteocalcin (59.8%), cross-linked C-telopeptide of type-I collagen (41.1%) and 1,25-dihydroxyvitamin-D (37.1%). Basal leptin concentration was lower in athletes (0.94 +/- 0.54 vs. 5.07 +/- 1.1 ng ml(-1)), and this difference persisted when leptin levels were adjusted for whole body fat mass (WBFM). No difference was observed for bone-specific alkaline phosphatase or intact parathyroid hormone. Serum leptin levels were negatively correlated with various BMD values only when both the groups were pooled (n = 26). This relationship did not persist when leptin levels were adjusted for WBFM. Male athletes, who practise sports generating high mechanical constraints on the body, present a specific bone metabolism that includes high BMD, as well as high bone turnover. The blunted leptin secretion did not seem to have deleterious effect on the process of bone adaptation to high mechanical constraints.

KIT is required for hepatic function during mouse post-natal development.

BACKGROUND: The Kit gene encodes a receptor tyrosine kinase involved in various biological processes including melanogenesis, hematopoiesis and gametogenesis in mice and human. A large number of Kit mutants has been described so far showing the pleiotropic phenotypes associated with partial loss-of-function of the gene. Hypomorphic mutations can induce a light coat color phenotype while complete lack of KIT function interferes with embryogenesis. Interestingly several intermediate hypomorphic mutations induced in addition growth retardation and post-natal mortality. RESULTS: In this report we investigated the post-natal role of Kit by using a panel of chemically-induced hypomorphic mutations recently isolated in the mouse. We found that, in addition to the classical phenotypes, mutations of Kit induced juvenile steatosis, associated with the downregulation of the three genes, VldlR, Lpin1 and Lpl, controlling lipid metabolism in the post-natal liver. Hence, Kit loss-of-functions mimicked the inactivation of genes controlling the hepatic metabolism of triglycerides, the major source of energy from maternal milk, leading to growth and viability defects during neonatal development. CONCLUSION: This is a first report involving KIT in the control of lipid metabolism in neonates and opening new perspectives for understanding juvenile steatosis. Moreover, it reinforces the role of Kit during development of the liver and underscores the caution that should be exerted in using KIT inhibitors during anti-cancer treatment.

Behavior of mice with mutations in the conserved region deleted in velocardiofacial/DiGeorge syndrome.

Velocardiofacial/DiGeorge syndrome (VCFS/DGS) is a developmental disorder caused by a 1.5 to 3-Mb hemizygous 22q11.2 deletion. VCFS/DGS patients display malformations in multiple systems, as well as an increased frequency of neuropsychiatric defects including schizophrenia. Haploinsufficiency of TBX1 appears to be responsible for these physical malformations in humans and mice, but the genes responsible for the neuropsychiatric defects are unknown. In this study, two mouse models of VCFS/DGS, a deletion mouse model (Lgdel/+) and a single gene model (Tbx1 +/-), as well as a third mouse mutant (Gscl -/-) for a gene within the Lgdel deletion, were tested in a large behavioral battery designed to assess gross physical features, sensorimotor reflexes, motor activity nociception, acoustic startle, sensorimotor gating, and learning and memory. Lgdel/+ mice contain a 1.5-Mb hemizygous deletion of 27 genes in the orthologous region on MMU 16 and present with impairment in sensorimotor gating, grip strength, and nociception. Tbx1 +/- mice were impaired in grip strength similar to Lgdel/+ mice and movement initiation. Gscl -/- mice were not impaired in any of the administered tests, suggesting that redundant function of other Gsc family members may compensate for the loss of Gscl. Thus, although deletion of the genes in the Lgdel region in mice may recapitulate some of the behavioral phenotypes seen in humans with VCFS/DGS, these phenotypes are not found in mice with complete loss of Gscl or in mice with heterozygous loss of Tbx1, suggesting that the neuropsychiatric and physical malformations of VCFS/DGS may act by different genetic mechanisms.

Variation in IL-1beta gene expression is a major determinant of genetic differences in arthritis aggressivity in mice.

In humans and in animal models, susceptibility to arthritis is under complex genetic control, reflecting influences on the immunological processes that initiate autoimmunity and on subsequent inflammatory mechanisms in the joints. The effector phases are conveniently modeled by the K/BxN serum transfer system, a robust model well suited for genetic analysis where arthritis is initiated by pathogenic Ig. Here, we mapped the genetic loci distinguishing the high-responder BALB/c vs. low-responder SJL strains. After computational modeling of potential breeding schemes, we adapted a stepwise selective breeding strategy, with a whole-genome scan performed on a limited number of animals. Several genomic regions proved significantly associated with high sensitivity to arthritis. One of these regions, on distal chr2, was centered on the interleukin 1 gene family. Quantitation of transcripts of the Il1a and Il1b candidate genes revealed a 10-fold greater induction of Il1b mRNA in BALB/c than in SJL splenocytes after injection of LPS, whereas Il1a showed much less difference. The differential activity of the Il1b gene was associated with a particular sequence haplotype of noncoding polymorphisms. The BALB/c haplotype was found in 75% of wild-derived strains but was rare among conventional inbred strains (4/33 tested, one of which is DBA/1, the prototype arthritis-susceptible strain) and was associated with vigorous Il1b responses in a panel of inbred strains. Inbred strains carrying this allele were far more responsive to serum-transferred arthritis, confirming its broad importance in controlling arthritis severity.

Training and aging modulate the loss-of-balance phenotype observed in a new ENU-induced allele of Otopetrin1.

BACKGROUND INFORMATION: The sensing of head movement in mammals depends upon the vestibular endorgan of the inner ear, a complex structure made up of the semicircular canals and otoliths. Due to the similarity between the human and mouse vestibular apparatus, the analysis of mutant mouse is a valuable strategy aiming to identify genes involved in the control of balance and movement. RESULTS: In the course of a genome-wide chemical-mutagenesis programme, we isolated a recessive mutation, named ied (inner ear defect), which induced a severe loss-of-balance. A detailed phenotypic analysis of the mutant mice demonstrates that the balance impairment does not affect the motor activity and can be rescued, in part, by training, despite a complete agenesis of otoconia in the utricule and the saccule of the inner ear. Molecular characterization of the ied mutation revealed a transversion that affects the splicing of the second exon of the Otopetrin1 gene located on mouse chromosome 5. The consequence of such a mutation leads to a disruption of the transcription of the gene. CONCLUSIONS: The identification of the ied knock-down allele strengthens the role of the Otopetrin1 in the sensing of balance. Moreover, the rescue of the ied mutant phenotype in specific behavioural tasks confirmed that other sensory inputs or neural plasticity can compensate, to some extent, for the loss-of-balance. In the future, the ied mutant mice might be helpful to study the genetic control of the compensation strategies developed by organisms to counteract balance defects.

In silico genetics: identification of a functional element regulating H2-Ealpha gene expression.

Computational tools can markedly accelerate the rate at which murine genetic models can be analyzed. We developed a computational method for mapping phenotypic traits that vary among inbred strains onto haplotypic blocks. This method correctly predicted the genetic basis for strain-specific differences in several biologically important traits. It was also used to identify an allele-specific functional genomic element regulating H2-Ealpha gene expression. This functional element, which contained the binding sites for YY1 and a second transcription factor that is probably serum response factor, is located within the first intron of the H2-Ealpha gene. This computational method will greatly improve our ability to identify the genetic basis for a variety of phenotypic traits, ranging from qualitative trait information to quantitative gene expression data, which vary among inbred mouse strains.

Circulating leptin concentrations can be used as a surrogate marker of fat mass in acute spinal cord injury patients.

To determine the acute effect of neurological lesion on body composition, plasma leptin level, and the lipid profile, 7 male patients with acute and complete spinal cord injury (SCI) and 9 able-bodied (AB) males were investigated. At 16, 24, 36, and 48 weeks after injury, plasma leptin level and the lipid profile were analyzed, while whole body (WB) and regional fat mass (FM) and fat-free soft tissue (FFST) were measured by dual-energy x-ray absorptiometry (DXA). At all stages, despite no difference being found between both groups for body mass index (BMI), SCI patients had higher FM at WB (P < .01), lower (P < .01), and upper limbs (P < .05), while FFST was lower at WB (P < .05) and lower limbs (P < .01). The leptin level increased gradually from week 24 and was higher at weeks 16, 36, and 48 in SCI patients than in AB patients (7.0 +/- 3.9; 9.7 +/- 5.1; 10.6 +/- 5.3, respectively, v 3.5 +/- 2.5 ng. mL(-1)). SCI patients had lower high-density lipoprotein-cholesterol (HDL-C) (P < .05) and apolipoprotein (apo) A1 (P < .01), while no difference was found for total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C), or ApoB levels. At all stages, leptin was strongly and positively correlated with WB and regional FM % (r > 0.75; P < .05) and with TC, LDL-C, and ApoB levels (r > 0.65; P < .05). Leptin was negatively correlated with FFST and the ApoA1/ApoB ratio (r > -0.75; P < .05). In conclusion, neurological lesion induced an early and acute alteration in body composition and lipid profile. The strong relationship between serum leptin and FM suggests that this hormone can be used as a surrogate marker of FM in acute SCI patients and thus would serve as a good indicator for cardiovascular disease risk.

Genetics of dark skin in mice.

Chemical mutagenesis in the mouse is a powerful approach for phenotype-driven genetics, but questions remain about the efficiency with which new mutations ascertained by their phenotype can be localized and identified, and that knowledge applied to a specific biological problem. During a global screen for dominant phenotypes in about 30,000 animals, a novel class of pigmentation mutants were identified by dark skin (Dsk). We determined the genetic map location, homozygous phenotype, and histology of 10 new Dsk and 2 new dark coat (Dcc) mutations, and identified mutations in Agouti (Met1Leu, Dcc4), Sox18 (Leu220ter, Dcc1), Keratin 2e (Thr500Pro, Dsk2), and Egfr (Leu863Gln, Dsk5). Cutaneous effects of most Dsk mutations are limited to melanocytes, except for the Keratin 2e and Egfr mutations, in which hyperkeratosis and epidermal thickening precede epidermal melanocytosis by 3-6 wk. The Dsk2 mutation is likely to impair intermediate filament assembly, leading to cytolysis of suprabasal keratinocytes and secondary hyperkeratosis and melanocytosis. The Dsk5 mutation causes increased tyrosine kinase activity and a decrease in steady-state receptor levels in vivo. The Dsk mutations represent genes or map locations not implicated previously in pigmentation, and delineate a developmental pathway in which mutations can be classified on the basis of body region, microscopic site, and timing of pigment accumulation.

Genetic and physiological data implicating the new human gene G72 and the gene for D-amino acid oxidase in schizophrenia.

A map of 191 single-nucleotide polymorphism (SNPs) was built across a 5-Mb segment from chromosome 13q34 that has been genetically linked to schizophrenia. DNA from 213 schizophrenic patients and 241 normal individuals from Canada were genotyped with this marker set. Two 1,400- and 65-kb regions contained markers associated with the disease. Two markers from the 65-kb region were also found to be associated to schizophrenia in a Russian sample. Two overlapping genes G72 and G30 transcribed in brain were experimentally annotated in this 65-kb region. Transfection experiments point to the existence of a 153-aa protein coded by the G72 gene. This protein is rapidly evolving in primates, is localized to endoplasmic reticulum/Golgi in transfected cells, is able to form multimers and specifically binds to carbohydrates. Yeast two-hybrid experiments with the G72 protein identified the enzyme d-amino acid oxidase (DAAO) as an interacting partner. DAAO is expressed in human brain where it oxidizes d-serine, a potent activator of N-methyl-D-aspartate type glutamate receptor. The interaction between G72 and DAAO was confirmed in vitro and resulted in activation of DAAO. Four SNP markers from DAAO were found to be associated with schizophrenia in the Canadian samples. Logistic regression revealed genetic interaction between associated SNPs in vicinity of two genes. The association of both DAAO and a new gene G72 from 13q34 with schizophrenia together with activation of DAAO activity by a G72 protein product points to the involvement of this N-methyl-d-aspartate receptor regulation pathway in schizophrenia.