RESUMO
Very little is known about the genes involved in the pathogenesis of IDDM. One component is known to be linked to the major histocompatibility complex, but the other components are unknown. We know from the major animals models of IDDM, both the NOD mouse and the BB rat, that the disease is under multigenic control. However, due to the size and complexity of the mammalian genome as well as to the lack of useful clues, the location and identity of the other genes remains a mystery. This is compounded by the fact that well-characterized genetic markers are not available for all regions of the mammalian genome, and it is likely that at least some of the genes of interest are located in these regions. The testing of pedigrees for the linkage of RFLP with the genetic factors involved in IDDM promises to be the most effective means of mapping, and ultimately identifying, these genes. However, the number of genes which are theoretically necessary to test for linkage makes even this approach impractical. Here, we have described here how the amount of work and time can be significantly reduced by utilizing repetitive DNA sequences as probes for the linkage of random RFLPs to diabetes. With each screening, one can simultaneously test multiple unlinked loci in the genome. Preliminary results which show promising linkage to two of the genetic components have been presented, thereby supporting the usefulness of this approach.
Assuntos
Diabetes Mellitus Tipo 1/genética , Animais , Mapeamento Cromossômico , Humanos , Camundongos , Ratos , Ratos Endogâmicos BBAssuntos
Aberrações Cromossômicas/genética , Doenças em Gêmeos/genética , Regulação da Expressão Gênica/genética , Predisposição Genética para Doença , Gêmeos Monozigóticos/genética , Gêmeos/genética , Animais , Transtornos Cromossômicos , Fragilidade Cromossômica , Elementos de DNA Transponíveis , Herança Extracromossômica , Rearranjo Gênico , HumanosRESUMO
Class I major histocompatibility antigens are composed of a heavy chain that is noncovalently associated with beta 2-microglobulin (beta 2m). Most class I molecules are membrane bound, but mouse and rat cDNA clones and genes without a functional code for the transmembrane amino acids have been identified. The membrane-associated class I molecules are important in the control of cell-mediated cytotoxicity, while the function of the soluble molecules remains unclear. Previous studies have shown that beta 2m circulates in rat serum in three different molecular weight classes. The first is free beta 2m (Mr, 12,000), the second is about Mr 70,000, and the third is roughly Mr 200,000. In an inbred subline of immunodeficient, diabetes-prone BioBreeding rats (BioBreeding/Hagedorn), previous work detected two restriction fragment polymorphisms in class I major histocompatibility complex genes, one of them a gene deletion on a 7-kilobase BamHI fragment and the other on a 2-kilobase BamHI fragment. In these rats we have found that the third serum beta 2m-binding size class is absent. Analysis of F1 and F2 individuals following cross-breeding between BioBreeding/Hagedorn rats and genetically related (nondiabetic) control BioBreeding w-subline rats demonstrated that the large-size serum peak of beta 2m was associated with the presence of the class I restriction fragments.
Assuntos
Antígenos de Histocompatibilidade/genética , Complexo Principal de Histocompatibilidade , Ratos Mutantes/genética , Microglobulina beta-2/sangue , Animais , Deleção Cromossômica , Mapeamento Cromossômico , Enzimas de Restrição do DNA , Técnicas Imunológicas , Peso Molecular , Ratos , Ratos Mutantes/imunologia , Solubilidade , Microglobulina beta-2/imunologiaRESUMO
Fragments of cloned rat class I transplantation antigen genes were used to define the polymorphism detected between two lines of closely related BB rats. One line, BB-Hagedorn (BB/H), is prone to diabetes, and the other (BB control) is resistant. A cDNA probe representing part of the second extracellular domain of a class I antigen detected several DNA fragments and revealed a 2kb fragment present in resistant, but absent in diabetes-prone, BB/H rat DNA following digestion with BamH1. A 40 bp cDNA probe from the same domain showed a further simplified pattern in the DNA hybridization analysis. Only two fragments, 15 kb and 7 kb, were present in the resistant rats; the diabetes-prone BB/H rats lacked the 7 kb fragment. Several lines of evidence suggest that the gene contained in this 7 kb fragment may be deleted. Analysis of other diabetic BB rats and in the F2 generation of intercross offspring of F1 hybrid parents following crossbreeding between the resistant (BB-control) and diabetes-prone (BB/H) line demonstrate that the class I polymorphism was not linked directly to diabetes. Examination of various other BB lines and sublines indicate that these polymorphisms can be traced back to at least one other subline (Worcester) in the parent colony.
Assuntos
Complexo Principal de Histocompatibilidade , Ratos Mutantes/genética , Animais , Cruzamentos Genéticos , DNA/análise , Feminino , Masculino , Polimorfismo Genético , Ratos , Especificidade da EspécieRESUMO
DNA isolated from diabetic BB (BB/Hagedorn) rats was examined for restriction fragment length differences within the major histocompatibility complex (MHC) as compared with nondiabetic (W-subline) BB rats. Polymorphisms were detected using a mouse class I MHC gene as probe. Specifically, a 2-kb BamHI fragment was present in all the nondiabetic rats examined, but absent in the diabetic rats. Similar polymorphisms were observed with various other restriction enzymes, particularly XbaI, HindII, and SacI. There were no polymorphisms detected using either a human DR-alpha (class II antigen heavy chain) or a human DC-beta (class II antigen light chain) gene as probes. These results indicate that the BB rat diabetic syndrome may be linked to differences in class I MHC genes.
