Abstract
We have generated a polygenic mouse model for congenital hypothyroidism (CH) with thyroid dysgenesis (TD), caused by the combination of partial deficiencies in the Titf1 and Pax8 genes (DHTP). Since the phenotype is not observed in the 129/Sv strain (DHTP/Sv) but is manifested in the B strain (DHTP/B); additional loci, different between the two strains, must be involved in the establishment of CH. We have identified such loci by positional cloning using a large cohort of DHTP backcross mice (DHTP/bc) generated from a (DHTP/B x 129/Sv) x B. 143 DHTP/bc mice were genotyped using 235 Single Nucleotide Polymorphisms (SNPs). SNPs were detected by pyrosequencing. Analysis of genotyping data reveals two chromosomal regions associated to CH: one on Chr 2 (with a LOD score of 11.2) and another on Chr 5 (with a LOD score of 2.5). 800 genes have been mapped on region of Chr 2 associated to the CH phenotype; about 400 of these are expressed in the thyroid as detected by transcriptome analysis. Using dbSNPs database 150 out of 400 genes containing SNPs. Though no gene is responsible for nonsense mutation in the coding sequence, we have analyzed those genes containing SNPs causing nonsynonymous mutation in the their gene product. Using this approach, we have identified two candidate genes: calpain 3 and Dnajc17 and have focused our attention on DNAJc17.DNAJc17 presents a phenylalanine residue instead of tyrosine only in the B strain. We have generated a knock-out mouse for this gene to confirm the role of DNAJc17 in CH. We are also testing in vitro, the cooperation of DNAJc17 and Titf1 and Pax8 in the activation of thyroid genes