Fine mapping of the hyperglycemic and obesity QTL by congenic strains suggests multiple loci on rat chromosome 14

Linkage analysis previously identified a hyperglycemic quantitative trait locus (QTL), Nidd 2/of, on rat Chromosome 14 in crosses utilizing OLETF (Otsuka Long Evans Tokushima Fatty) rat, a model for type 2 diabetes. A separate QTL study mapped an obesity QTL, Obs5, to the same chromosomal region. A congenic strain placing ca. 38 cM OLETF-derived segments containing both Nidd2/of and Obs5 on the F344 background was shown to possess mild diabetic and obese phenotypes, suggesting the presence of mutations affecting the glucose metabolism and fat accumulation. In order to localize the loci more precisely, we generated a series of deletion-subcongenic strains in which OLETF-segments were shortened from either ends. We found that there are at least two hyperglycemic QTLs within the Nidd2/of locus. We predict that they are localized towards both ends of the Nidd2/of region. In contrast, Obs5 QTL was further narrowed down to a single region of ca. 10 cM fragment.