Genetic dissection reveals diabetes loci proximal to the gimap5 lymphopenia gene

Abstract

Congenic DRF. f/f rats are protected from type 1 diabetes (T1D) by 34 Mb of F344 DNA introgressed proximal to the gimap5 lymphopenia gene. To dissect the genetic factor(s) that confer protection from T1D in the DRF. f/f rat line, DRF. f/f rats were crossed to inbred BBDR or DR. lyp/lyp rats to generate congenic sublines that were genotyped and monitored for T1D, and positional candidate genes were sequenced. All (100%) DR. lyp/lyp rats developed T1D by 83 days of age. Reduction of the DRF. f/f F344 DNA fragment by 26 Mb (42.52–68.51 Mb) retained complete T1D protection. Further dissection revealed that a 2 Mb interval of F344 DNA (67.41–70.17 Mb) ( region 1) resulted in 47% protection and significantly delayed onset ( P < 0.001 compared with DR. lyp/lyp). Retaining <1 Mb of F344 DNA at the distal end (76.49–76.83 Mb) ( region 2) resulted in 28% protection and also delayed onset ( P < 0.001 compared with DR. lyp/lyp). Comparative analysis of diabetes frequency in the DRF. f/f congenic sublines further refined the RNO4 region 1 interval to ∼670 kb and region 2 to the 340 kb proximal to gimap5. All congenic DRF. f/f sublines were prone to low-grade pancreatic mononuclear cell infiltration around ducts and vessels, but <20% of islets in nondiabetic rats showed islet infiltration. Coding sequence analysis revealed TCR Vβ 8E, 12, and 13 as candidate genes in region 1 and znf467 and atp6v0e2 as candidate genes in region 2. Our results show that spontaneous T1D is controlled by at least two genetic loci 7 Mb apart on rat chromosome 4.