Enhanced insulin secretion and cholesterol metabolism in congenic strains of the spontaneously diabetic (Type 2) Goto Kakizaki rat are controlled by independent genetic loci in rat chromosome 8

Abstract

Aims/hypothesis. Genetic investigations in the spontaneously diabetic (Type 2) Goto Kakizaki (GK) rat have identified quantitative trait loci (QTL) for diabetes-related phenotypes. The aims of this study were to refine the chromosomal mapping of a QTL (Nidd/gk5) identified in chromosome 8 of the GK rat and to define a pathophysiological profile of GK gene variants underlying the QTL effects in congenics. Methods. Genetic linkage analysis was carried out with chromosome 8 markers genotyped in a GKxBN F2 intercross previously used to map diabetes QTL. Two congenic strains were designed to contain GK haplotypes in the region of Nidd/gk5 transferred onto a Brown Norway (BN) genetic background, and a broad spectrum of diabetes phenotypes were characterised in the animals. Results. Results from QTL mapping suggest that variations in glucose-stimulated insulin secretion in vivo, and in body weight are controlled by different chromosome 8 loci (LOD3.53; p=0.0004 and LOD4.19; p=0.00007, respectively). Extensive physiological screening in male and female congenics at 12 and 24 weeks revealed the existence of GK variants at the locus Nidd/gk5, independently responsible for significantly enhanced insulin secretion and increased levels of plasma triglycerides, phospholipids and HDL, LDL and total cholesterol. Sequence polymorphisms detected between the BN and GK strains in genes encoding ApoAI, AIV, CIII and Lipc do not account for these effects. Conclusions/interpretation. We refined the localisation of the QTL Nidd/gk5 and its pathophysiological characteristics in congenic strains derived for the locus. These congenic strains provide novel models for testing the contribution of a subset of GK alleles on diabetes phenotypes and for identifying diabetes susceptibility genes.

Genetic control of plasma lipid levels in a cross derived from normoglycaemic Brown Norway and spontaneously diabetic Goto–Kakizaki rats

“…Resulting changes in the balance between GK and BN alleles in congenics may in turn unmask phenotypic effects of some gene variants at the targeted locus. This may explain the effect of GK alleles in chromosome 8 on plasma lipid up-regulation, which we detected in BN.GK congenic rats [38] but do not replicate here in the GK×BN F2 cross. We found no significant evidence of genetic interaction (epistasis) in the F2 cross between GK alleles on chromosome 8 and BN alleles in the genetic background that could explain the absence of QTL replication (data not shown).…”

“…Further studies in congenic strains containing regions of GK QTLs introgressed on to the genetic background of the BN strain [38] are required to validate the lipid QTLs reported here and carry out the identification of the underlying gene variant(s). Congenics allow the study of phenotypic consequences of selected GK alleles at a specific locus in a different genetic context than that of a hybrid GK×BN F2 population, because GK variants throughout the genetic background, including at GK diabetes QTLs, are eliminated.…”

A Novel Susceptibility Locus on Rat Chromosome 8 Affects Spontaneous but Not Experimentally Induced Type 1 Diabetes

“…Genetic analysis. Genotyping was performed as previously described (19,20). All microsatellite primers were purchased from Sigma-Genosys available at www.well.ox.ac.uk/rat_mapping_resources.…”

Quantitative trait locus dissection in congenic strains of the Goto-Kakizaki rat identifies a region conserved with diabetes loci in human chromosome 1q

“…Construction of the congenics was specifically designed to introgress GK alleles from RNO2 regions covering the QTL Nidd/gk2 and Niddm2 onto the genetic background of the BN strain (BN.GK congenics), using a genetic marker-assisted breeding strategy (24), as previously described (35). Although the production of reciprocal congenics (GK.BN) was also initiated, it proved to be problematic, because of a high perinatal mortality rate in (GKϫBN)ϫGK backcross progenies, which remained, however, similar to that observed in GK rats.…”

“…Linkage between marker genotypes and diabetes-related phenotypes in the GKϫBN F2 cross was initially evaluated by an ANOVA test followed by a permutation test as previously used (35). Interval mapping was performed with the MAPMAKER/QTL computer package (22).…”