Proximal Portion Of Chromosome Research Articles

Through Regulation of TCR Expression Levels, anIdd7Region Gene(s) Interactively Contributes to the Impaired Thymic Deletion of Autoreactive Diabetogenic CD8+ T Cells in Nonobese Diabetic Mice

When expressed in NOD, but not C57BL/6 (B6) genetic background mice, the common class I variants encoded by the H2g7 MHC haplotype aberrantly lose the ability to mediate the thymic deletion of autoreactive CD8+ T cells contributing to type 1 diabetes (T1D). This indicated some subset of the T1D susceptibility (Idd) genes located outside the MHC of NOD mice interactively impair the negative selection of diabetogenic CD8+ T cells. In this study, using both linkage and congenic strain analyses, we demonstrate contributions from a polymorphic gene(s) in the previously described Idd7 locus on the proximal portion of Chromosome 7 predominantly, but not exclusively, determines the extent to which H2g7 class I molecules can mediate the thymic deletion of diabetogenic CD8+ T cells as illustrated using the AI4 TCR transgenic system. The polymorphic Idd7 region gene(s) appears to control events that respectively result in high vs low expression of the AI4 clonotypic TCR alpha-chain on developing thymocytes in B6.H2g7 and NOD background mice. This expression difference likely lowers levels of the clonotypic AI4 TCR in NOD, but not B6.H2g7 thymocytes, below the threshold presumably necessary to induce a signaling response sufficient to trigger negative selection upon Ag engagement. These findings provide further insight to how susceptibility genes, both within and outside the MHC, may interact to elicit autoreactive T cell responses mediating T1D development in both NOD mice and human patients.

ENU mutagenesis reveals a highly mutable locus on mouse Chromosome 4 that affects ear morphogenesis

Chemical mutagenesis followed by screening for abnormal phenotypes in the mouse holds much promise as a method for revealing gene function. This method is particularly well-suited for discovering genes involved in hearing or balance function, as these defects are relatively easy to screen for in the mouse. We report here the inner ear abnormalities and genetic localization of seven new dominant mutations created by ENU mutagenesis. All seven mutant stocks were identified because of circling and/or head-weaving behavior, which is an indication of balance dysfunction. Investigation of the inner ears of the seven mutant stocks revealed very similar lateral and posterior semicircular canal defects. Studies of the development of the canals in one mutant stock revealed that the affected canals showed reduced outgrowth and delayed canal fusion. Physiological studies performed in one mutant stock showed raised average compound-action-potential thresholds of approximately 10-20 dB sound pressure level (SPL) (depending on frequency), indicating a mild hearing impairment, although scanning electron microscopy performed in several of the mutant stocks revealed no obvious structural defects in the organ of Corti. All seven mutations mapped to the proximal portion of Chromosome (Chr) 4, near the centromere. On the basis of their similar phenotype and map location, we suggest that the seven mutant genes may be allelic and represent a highly mutable locus on Chr 4 that may be particularly susceptible to ENU-induced mutation on the BALB/c genetic background.

Genetic control of susceptibility to infection with Mycobacterium tuberculosis in mice.

Genetic factors play a key role in host response, disease severity, and ultimate outcome of infection with Mycobacterium tuberculosis in humans. In the mouse, the DBA/2J strain is very susceptible to M. tuberculosis H37Rv infection, while the C57Bl/6J strain is resistant. In DBA/2J, a heavier bacterial burden causes a unique phenotype, that includes very severe and rapidly fatal pulmonary disease with extensive exudation of neutrophils and tissue necrosis, as opposed to slower progressive pulmonary disease characterized by the accumulation of epithelioid macrophages with protective immune and inflammatory responses in C57Bl/6J. To identify the genes responsible for differences in host response to M. tuberculosis in these two strains, 95 animals of an informative (C57Bl/6J x DBA/2J) F2 cross were infected intravenously with M. tuberculosis (1 x 10(5) CFU) and duration of survival was used as a quantitative phenotypic measure of susceptibility in a whole genome scan. Quantitative trait locus analysis (QTL) showed that the genetically controlled susceptibility was multigenic. QTL analysis identified two significant linkages on the distal portion of chromosome 1 (Trl-1, LOD, 4.80) and on the proximal portion of chromosome 7 (Trl-3, LOD, 4.66) that each account for approximately 21% of the phenotypic variance. A third suggestive linkage was identified on the proximal portion of chromosome 3 (Trl-2, LOD, 3.93; additional 18% of the variance). At each locus, homozygosity for the parental C57Bl/6J alleles was associated with increased resistance to infection. These novel mouse loci provide the basis for evaluating a possible association of the corresponding syntenic chromosomal regions in humans with susceptibility to tuberculosis.

Mouse beta-defensin 3 is an inducible antimicrobial peptide expressed in the epithelia of multiple organs.

One component of host defense at mucosal surfaces is epithelium-derived peptides with antimicrobial activity called defensins. We describe in this report the isolation and characterization of a murine homologue of human beta-defensin 2 (hBD-2) called mouse beta-defensin 3 (mBD-3). The predicted amino acid sequence shows the hallmark features of other known epithelial defensins, including the ordered array of six cysteine residues. Analysis of a genomic clone of mBD-3 revealed two exons separated by a 1.7-kb intron. The mBD-3 gene is localized at the proximal portion of chromosome 8, the site where genes for mouse alpha- and beta-defensins are found. Under basal condition, mBD-3 transcripts were detected at low levels in epithelial cells of surface organs, such as the intestine and lung. After instillation of Pseudomonas aeruginosa PAO1 into mouse airways, mBD-3-specific mRNA was upregulated significantly not only in large airways but also in the small bowel and liver. Recombinant mBD-3 peptide, produced from a baculovirus expression system, showed antimicrobial activity against P. aeruginosa PAO1 (MIC of 8 micrograms/ml) and Escherichia coli D31 (MIC of 16 micrograms/ml) in a salt-dependent manner. This study demonstrates that a murine homologue of hBD-2 is present in the respiratory system and other mucosal surfaces. These similarities between murine and human host defense apparatus provide further impetus to evaluate the mouse as a model for studying the human innate host defense system.

Assignment of the Melatonin-Related Receptor to Human Chromosome X (GPR50) and Mouse Chromosome X (Gpr50)

Recent efforts to clone further members of the melatonin receptor family have led to the identification of a novel G-protein-coupled receptor in human pituitary. This receptor, referred to as H9, is clearly related to high-affinity melatonin receptors yet unable to bind this hormone. We now report the cloning and expression of the cDNA encoding the H9 receptor in mice. The mouse clone encodes a protein of 591 amino acids that shares 74% amino acid identity with the human receptor and is unable to bind 2-[125I]iodomelatonin when transiently expressed in COS-7 cells. We also determined the chromosome loci of the human and mouse H9 receptor genes. Both genes were found to be X-linked: radiation hybrid mapping revealed that the human H9 gene (GPR50) is localized to Xq28. The mouse gene (Gpr50) was determined to lie in the proximal portion of chromosome X by means of interspecific backcross analysis. These loci might be relevant to genetically based neuroendocrine disorders.

Mouse beta-defensin 1 is a salt-sensitive antimicrobial peptide present in epithelia of the lung and urogenital tract.

One component of host defense at mucosal surfaces appears to be epithelium-derived peptides with antimicrobial activity called defensins. Human beta-defensin 1 (hBD-1) represents the first member of the beta-defensin family isolated from humans and has been implicated in the pathogenesis of cystic fibrosis. We describe in this report the isolation and characterization of a murine homolog of hBD-1 called mouse beta-defensin 1 (mBD-1). The predicted amino acid sequence shows the hallmark features of other known epithelial beta-defensins, including the ordered array of six cysteine residues. Analysis of a genomic clone of mBD-1 revealed two exons separated by a 15-kb intron. By use of fluorescence in situ hybridization, the mBD-1 gene was localized at the proximal portion of chromosome 8, the site where mouse alpha-defensins are found. Lysates from cells transfected with the mBD-1 cDNA showed antibacterial activity against gram-positive and gram-negative bacteria. mBD-1 transcripts were found in kidney, liver, and female reproductive organ tissues. In the airways, mBD-1 is expressed diffusely throughout the epithelial cells of the large proximal airways with less expression in the small distal airways and no expression in alveolar cells. The present study demonstrates that a beta-defensin potentially homologous to human beta-defensin 1 is present in the respiratory system and other mucosal surfaces in mice.

The host resistance locus Bcg is tightly linked to a group of cytoskeleton-associated protein genes that include villin and desmin

In the mouse, innate resistance or susceptibility to infection with a group of unrelated intracellular parasites which includes, Mycobacteria, Salmonella, and Leishmania is determined by the expression of a single dominant autosomal gene designated Bcg located on the proximal portion of chromosome 1. The gene is expressed at the level of the mature tissue macrophage and influences its capacity to restrict intracellular proliferation of the parasites. We have used restriction fragment length polymorphism analysis in segregating populations of inter- and intraspecific backcross mice and in recombinant inbred strains to position four new marker genes, trasition protein 1 ( Tp-1), desmin ( Des), the α subunit of inhibin ( Inha), and retinal S-antigen ( Sag), in the vicinity of the host resistance locus, Bcg. The gene order for Tp-1, Des, Inha, and Sag was established in an eight-point testcross with respect to anchor loci previously assigned to that portion of mouse chromosome 1 and was found to be centromere- Fn-1-Tp-1-(Vil,Bcg)-Des-Inha-Akp-3-Acrg-Sag. Two of these new marker genes were found very tightly linked to Bcg: Des was located 0.3 ± 0.3 cM distal from ( Vil,Bcg) and 0.3 ± 0.3 cM proximal to Inha. Tp-1 mapped 0.8 ± 0.5 cM proximal and Sag 12.8 ± 1.7 cM distal to (Vil,Bcg). Tp-1, Des, Inha, and Sag all fall within a large mouse chromosome 1 segment homologous with the telomeric region of the long arm of human chromosome 2 (2q). Our findings indicate that the two closest markers to the host resistance locus, Bcg, encode cytoskeleton-associated proteins which are capable of interaction with actin filaments.