RESUMEN
Although central to many studies of phenotypic variation and disease susceptibility, characterizing the genetic architecture of complex traits has been unexpectedly difficult. For example, most of the susceptibility genes that contribute to highly heritable conditions such as obesity and type 2 diabetes (T2D) remain to be identified despite intensive study. We took advantage of mouse models of diet-induced metabolic disease in chromosome substitution strains (CSSs) both to characterize the genetic architecture of diet-induced obesity and glucose homeostasis and to test the feasibility of gene discovery. Beginning with a survey of CSSs, followed with genetic and phenotypic analysis of congenic, subcongenic, and subsubcongenic strains, we identified a remarkable number of closely linked, phenotypically heterogeneous quantitative trait loci (QTLs) on mouse chromosome 6 that have unexpectedly large phenotypic effects. Although fine-mapping reduced the genomic intervals and gene content of these QTLs over 3000-fold, the average phenotypic effect on body weight was reduced less than threefold, highlighting the "fractal" nature of genetic architecture in mice. Despite this genetic complexity, we found evidence for 14 QTLs in only 32 recombination events in less than 3000 mice, and with an average of four genes located within the three body weight QTLs in the subsubcongenic strains. For Obrq2a1, genetic and functional studies collectively identified the solute receptor Slc35b4 as a regulator of obesity, insulin resistance, and gluconeogenesis. This work demonstrated the unique power of CSSs as a platform for studying complex genetic traits and identifying QTLs.
Asunto(s)
Glucosa/metabolismo , Secuenciación de Nucleótidos de Alto Rendimiento/métodos , Homeostasis/genética , Proteínas de Transporte de Nucleótidos/genética , Obesidad/genética , Sitios de Carácter Cuantitativo , Animales , Peso Corporal/genética , Mapeo Cromosómico , Cromosomas de los Mamíferos/genética , Diabetes Mellitus Tipo 2/genética , Dieta , Regulación de la Expresión Génica , Gluconeogénesis/genética , Células Hep G2 , Humanos , Resistencia a la Insulina/genética , Masculino , Ratones , Ratones Congénicos , Modelos Animales , Proteínas de Transporte de Nucleótidos/metabolismo , Fenotipo , Análisis de Secuencia de ADNRESUMEN
Metabolic diseases such as obesity and atherosclerosis result from complex interactions between environmental factors and genetic variants. A panel of chromosome substitution strains (CSSs) was developed to characterize genetic and dietary factors contributing to metabolic diseases and other biological traits and biomedical conditions. Our goal here was to identify quantitative trait loci (QTLs) contributing to obesity, energy expenditure, and atherosclerosis. Parental strains C57BL/6 and A/J together with a panel of 21 CSSs derived from these progenitors were subjected to chronic feeding of rodent chow and atherosclerotic (females) or diabetogenic (males) test diets, and evaluated for a variety of metabolic phenotypes including several traits unique to this report, namely fat pad weights, energy balance, and atherosclerosis. A total of 297 QTLs across 35 traits were discovered, two of which provided significant protection from atherosclerosis, and several dozen QTLs modulated body weight, body composition, and circulating lipid levels in females and males. While several QTLs confirmed previous reports, most QTLs were novel. Finally, we applied the CSS quantitative genetic approach to energy balance, and identified three novel QTLs controlling energy expenditure and one QTL modulating food intake. Overall, we identified many new QTLs and phenotyped several novel traits in this mouse model of diet-induced metabolic diseases.
Asunto(s)
Aterosclerosis/genética , Metabolismo Energético/genética , Obesidad/genética , Animales , Composición Corporal , Peso Corporal , Cromosomas de los Mamíferos/genética , Dieta Alta en Grasa/efectos adversos , Femenino , Estudios de Asociación Genética , Predisposición Genética a la Enfermedad , Masculino , Ratones Endogámicos C57BL , Fenotipo , Sitios de Carácter CuantitativoRESUMEN
Current treatments have largely failed to slow the rapidly increasing world-wide prevalence of obesity and its co-morbidities. Despite a strong genetic contribution to obesity (40-70%), only a small percentage of heritability is explained with current knowledge of monogenic abnormalities, common sequence variants and conventional modes of inheritance. Epigenetic effects are rarely tested in humans because of difficulties arranging studies that distinguish conventional and transgenerational inheritance while simultaneously controlling environmental factors and learned behaviors. However, growing evidence from model organisms implicates genetic and environmental factors in one generation that affect phenotypes in subsequent generations. In this report, we provide the first evidence for paternal transgenerational genetic effects on body weight and food intake. This test focused on the obesity-resistant 6C2d congenic strain, which carries the Obrq2a(A/J) allele on an otherwise C57BL/6J background. Various crosses between 6C2d and the control C57BL/6J strain showed that the Obrq2a(A/J) allele in the paternal or grandpaternal generation was sufficient to inhibit diet-induced obesity and reduce food intake in the normally obesity-susceptible, high food intake C57BL/6J strain. These obesity-resistant and reduced food intake phenotypes were transmitted through the paternal lineage but not the maternal lineage with equal strength for at least two generations. Eliminating social interaction between the father and both his offspring and the pregnant dam did not significantly affect food intake levels, demonstrating that the phenotype is transmitted through the male germline rather than through social interactions. Persistence of these phenotypes across multiple generations raises the possibility that transgenerational genetic effects contribute to current metabolic conditions.
Asunto(s)
Peso Corporal/genética , Ingestión de Energía/genética , Animales , Epigénesis Genética , Femenino , Impresión Genómica , Genotipo , Células Germinativas , Tamaño de la Camada , Masculino , Ratones , Ratones Endogámicos C57BL , Obesidad/genética , Polimorfismo Genético , EmbarazoRESUMEN
Despite considerable effort, the identification of genes that regulate complex multigenic traits such as obesity has proven difficult with conventional methodologies. The use of a chromosome substitution strain-based mapping strategy based on deep congenic analysis overcame many of the difficulties associated with gene discovery and led to the finding that the juxtaparanodal proteins CNTNAP2 and TAG1 regulate diet-induced obesity. The effects of a mild Cntnap2 mutation on body weight were highly dependent on genetic background, as both obesity-promoting and obesity-resistant effects of Cntnap2 were observed on different genetic backgrounds. The more severe effect of complete TAG1 deficiency, by decreasing food intake, completely prevented the weight gain normally associated with high-fat-diet feeding. Together, these studies implicate two novel proteins in the regulation of diet-induced obesity. Moreover, as juxtaparanodal proteins have previously been implicated in various neurological disorders, our results suggest a potential genetic and molecular link between obesity and diseases such as autism and epilepsy.
Asunto(s)
Contactina 2/fisiología , Dieta Alta en Grasa/efectos adversos , Proteínas de la Membrana/fisiología , Proteínas del Tejido Nervioso/fisiología , Obesidad/genética , Adiposidad/genética , Alelos , Secuencia de Aminoácidos , Sustitución de Aminoácidos , Animales , Peso Corporal , Cromosomas de los Mamíferos , Contactina 2/deficiencia , Contactina 2/genética , Resistencia a la Enfermedad/genética , Ingestión de Energía/genética , Metabolismo Energético , Epistasis Genética , Femenino , Estudios de Asociación Genética , Genotipo , Canal de Potasio Kv.1.1/metabolismo , Masculino , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Ratones , Ratones de la Cepa 129 , Ratones Congénicos , Ratones Endogámicos C57BL , Ratones Noqueados , Datos de Secuencia Molecular , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Obesidad/etiología , Obesidad/metabolismo , Transporte de ProteínasRESUMEN
BACKGROUND: The genetic architecture of complex traits strongly influences the consequences of inherited mutations, genetic engineering, environmental and genetic perturbations, and natural and artificial selection. But because most studies are under-powered, the picture of complex traits is often incomplete. Chromosome substitution strains (CSSs) are a unique paradigm for these genome surveys because they enable statistically independent, powerful tests for the phenotypic effects of each chromosome on a uniform inbred genetic background. A previous CSS survey in mice and rats revealed many complex trait genes (QTLs), large phenotypic effects, extensive epistasis, as well as systems properties such as strongly directional phenotypic changes and genetically-determined limits on the range of phenotypic variation. However, the unusually close genetic relation between the CSS progenitor strains in that study raised questions about the impact of genetic divergence: would greater divergence between progenitor strains, with the corresponding changes in gene regulation and protein function, lead to significantly more distinctive phenotypic features, or alternatively would epistasis and systems constraints, which are pervasive in CSSs, limit the range of phenotypic variation regardless of the extent of DNA sequence variation? RESULTS: We analyzed results for an extensive survey of traits in two new panels of CSSs where the donor strains were derived from inbred strains with more distant origins and discovered a strong similarity in genetic and systems properties among the three CSS panels, regardless of divergence time. CONCLUSION: Our results argue that DNA sequence differences between host and donor strains did not substantially affect the architecture of complex traits, and suggest instead that strong epistasis buffered the phenotypic effects of genetic divergence, thereby constraining the range of phenotypic variation.
Asunto(s)
Cromosomas de los Mamíferos , Patrón de Herencia , Sitios de Carácter Cuantitativo , Animales , Cruzamientos Genéticos , Ratones , Ratones Endogámicos C57BL , FenotipoRESUMEN
AIMS: Recent evidence suggests that transgenerational genetic effects contribute to phenotypic variation in complex traits. To test for the general occurrence of these effects and to estimate their strength, we took advantage of chromosome substitution strains (CSSs) of mice where the Y chromosome of the host strain has been replaced with the Y chromosome of the donor strain. Daughters of these CSS-Y males and host strain females are genetically identical and should be phenotypically indistinguishable in the absence of transgenerational genetic effects of the fathers' Y chromosome on daughters' phenotypes. MATERIALS & METHODS: Assay results for a broad panel of physiological traits and behaviors were compared for genetically identical daughters of CSS-Y males and host strain females from the B6-Chr(A/J) and B6-Chr(PWD) panels of CSSs. In addition, behavioral traits including specific tests for anxiety-related behaviors were tested in daughters of B6-Chr(129) and 129-Chr(B6) CSS-Y males. RESULTS: Across a panel of 41 multigenic traits assayed in the B6-Chr(A/J) panel of CSSs females and 21 multigenic traits in the B6-Chr(PWD) panel females, the frequency and strength for transgenerational genetic effects were remarkably similar to those for conventional inheritance of substituted chromosomes. In addition, we found strong evidence that the Y chromosome from the 129 inbred strain significantly reduced anxiety levels among daughters of B6-Chr(129) CSS-Y males. CONCLUSION: We found that transgenerational genetic effects rival conventional genetic effects in frequency and strength, we suggest that some phenotypic variation found in conventional studies of complex traits are attributable in part to the action of genetic variants in previous generations, and we propose that transgenerational genetic effects contribute to 'missing heritability'.
Asunto(s)
Ansiedad/genética , Patrón de Herencia/genética , Fenotipo , Cromosoma Y/genética , Animales , Ansiedad/fisiopatología , Cruzamientos Genéticos , Femenino , Masculino , Aprendizaje por Laberinto , Ratones , Ratones Endogámicos C57BLRESUMEN
BACKGROUND: Development of viral-induced chronic myocarditis is thought to involve both environmental and genetic factors. However, to date, no susceptibility genes have been identified. METHODS AND RESULTS: We sought to identify loci that confer susceptibility to viral-induced chronic myocarditis with the use of chromosome substitution strain mice that are composed of 1 chromosome from the disease susceptible A/J strain on an otherwise resistant C57BL/6 background. By this method, we identified chromosome 17 to confer susceptibility. To further isolate the region of susceptibility, 8 strains of mice congenic for different portions of chromosome 17 were generated. Characterization of these strains identified at least 4 susceptibility loci on the chromosome. Three of these loci are located in the proximal 22.8 cM, whereas the fourth locus is located in the portion of the chromosome distal to 34.3 cM. CONCLUSIONS: We have identified 4 loci that confer susceptibility of viral-induced chronic myocarditis. Of these loci, 3 were distinct from the major histocompatibility complex locus and thus represent novel susceptibility loci. The close proximately of the 2 novel loci with susceptibility loci for other autoimmune diseases such as type 1 diabetes and chronic experimental autoimmune thyroiditis suggests the presence of global autoimmune susceptibility genes.