Sequence analysis of Tnf as a candidate for Idd16

Linkage analysis and congenic mapping have localized 18 loci (Iddl-18) that contribute to the development of autoimmune type I diabetes in the nonobese diabetic (NOD) mouse. By using a congenic NOD strain which possesses recombinant MHC from a closely related CTS strain, a susceptible region (Iddl6) was mapped to the segment adjacent to, but distinct from class 11 A and E genes (Iddl). The tumor necrosis factor alpha gene (Tnf), which is located within the Iddl6 region, has been suspected to be a candidate gene for type 1 diabetes in the NOD mouse. Although the protein-coding region in Tnf has been sequenced in the NOD mouse and its related strains, the complete upstream region (approximately 1400 bp, including the 5'-untranslated region) has not yet been studied. To study the possible contribution of the transcriptional regulation of Tnf to susceptibility to type I diabetes, we determined the complete nucleotide sequences of the NOD strain and its related strain, CTS, in comparison with the non-diabetic control strain, C57BL/6. The nucleotide sequence of the 5'-upstream region in the NOD mouse was identical to that in the C57BL/6 mouse, but different from that in the CTS mouse. In particular, a C to A substitution at position 3408 in the CTS mouse creates a new GATA family binding site, which may be responsible for the lower incidence of type I diabetes in the NOD, CTS-H-2 congenic strain despite the presence of the same class 11 MHC.