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Comparative genomic analyses of the human NPHP1 locus reveal complex genomic architecture and its regional evolution in primates

ABSTRACT: Many loci in the human genome harbor complex genomic structures that can result in susceptibility to genomic rearrangements leading to various genomic disorders. Nephronophthisis 1 (NPHP1, MIM# 256100) is an autosomal recessive disorder that can be caused by defects of NPHP1; the gene maps within the human 2q13 region where low copy repeats (LCRs) are abundant. Loss of function of NPHP1 is responsible for approximately 85% of the NPHP1 cases - about 80% of such individuals carry a large recurrent homozygous NPHP1 deletion that occurs via non-allelic homologous recombination (NAHR) between two flanking directly oriented ~45 kb LCRs. Published data revealed a non-pathogenic inversion polymorphism involving the NPHP1 gene flanked by two inverted ~358 kb LCRs. Using optical mapping and array-comparative genomic hybridization, we identified three potential novel structural variant (SV) haplotypes at the NPHP1 locus that may protect a haploid genome from genomic instability and NPHP1 deletion. Inter-species comparative genomic analyses among primate genomes revealed massive genomic changes during evolution. The aggregated data suggest that dynamic genomic rearrangements occurred historically within the NPHP1 locus and generated SV haplotypes observed in the human population today, which may have differential susceptibility to the NPHP1 deletion within a personal genome. Our study documents diverse SV haplotypes at a complex LCR-laden human genomic region. Comparative analyses provide a model for how this complex region arose during primate evolution, and studies among humans reflect the possibility that intra-species polymorphism may potentially modulate an individual’s susceptibility to acquiring disease-associated alleles.

ORGANISM(S): Gorilla gorilla Pan troglodytes Pongo abelii Homo sapiens Papio anubis Macaca mulatta

PROVIDER: GSE73962 | GEO | 2015/11/30

SECONDARY ACCESSION(S): PRJNA298584

REPOSITORIES: GEO

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Project description:Genome-wide association studies in multiple sclerosis (MS) identified a polymorphism (rs6897932) located in the coding region of the alpha chain of the cytokine receptor interleukin 7 receptor (IL7R) as a component that increases susceptibility to develop the disease. This single nucleotide polymorphism (SNP) affects the splicing of the primary transcript leading to genotype-defined transcript ratios encoding either a full length membrane spanning form or a soluble receptor chain. Genotyping at the IL7R locus reveals that the region can be described by four haplotypes. Interestingly, only one out of three haplotypes harbouring the associated SNP is positively associated with MS whereas the other two do not show association. The minor allele containing haplotype shows a reduced susceptibility to develop MS. We hypothesized that additional functional or phenotypic differences exist between individuals homozygous for haplotypes shown to have either positive, negative, or neutral effect, on susceptibility to develop MS. Gene expression profiles of CD4+ T cells from MS individuals before and after stimulation with IL7 were recorded. Haplotype-specific gene signatures were found indicating small alterations in IL7/IL7R signal processing/sensitivity through JAK/STAT and p38/MAPK14. We can not exclude that the obtained signatures result from differences within the CD4+ T cell compartment that, in fact, should be seen as a consequence of systemic haplotype-specific processing of homeostatic and proliferation signals transmitted through IL7/IL7R. Samples of CD4+ cells were obtained from 7 MS patients (homozygous for Hap1 (3), Hap2 (2), Hap3 (2)). CD4+ cells were collected from peripheral blood, frozen and stored in liquid nitrogen. All samples were thawed and CD4+ cells were purified by magnetic bead separation. Purity and viability of cells was analyzed by Fluorescence Activated Cell Sorter (FACS). Total cellular RNA were extracted with TRIzol reagent and analyzed with the Human Gene 1.0 ST Array (affymetrix). IL7R haplotypes and susceptibility to develop MS: Hap1 homozygous <-> Risk <-> positive effect on MS susceptibility Hap2 homozygous <-> Hap2 <-> neutral effect on MS susceptibility Hap3 homozygous <-> Prot <-> neutral effect on MS susceptibility [Note: Haplotype nomenclature subject to revision.]

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Comparative genomic analyses of the human NPHP1 locus reveal complex genomic architecture and its regional evolution in primates

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