Keiko Oga

A radiation hybrid map of the rat genome containing 5,255 markers

A whole-genome radiation hybrid (RH) panel was used to construct a high-resolution map of the rat genome based on microsatellite and gene markers. These include 3,019 new microsatellite markers described here for the first time and 1,714 microsatellite markers with known genetic locations, allowing comparison and integration of maps from different sources. A robust RH framework map containing 1,030 positions ordered with odds of at least 1,000:1 has been defined as a tool for mapping these markers, and for future RH mapping in the rat. More than 500 genes which have been mapped in mouse and/or human were localized with respect to the rat RH framework, allowing the construction of detailed rat-mouse and rat-human comparative maps and illustrating the power of the RH approach for comparative mapping.

MUTATED G-PROTEIN-COUPLED RECEPTOR GPR10 IS RESPONSIBLE FOR THE HYPERPHAGIA/DYSLIPIDAEMIA/OBESITY LOCUS OF Dmo1 IN THE OLETF RAT

1. We have confirmed the Diabetes Mellitus OLETF type I (Dmo1) effect on hyperphagia, dyslipidaemia and obesity in the Otsuka Long‐Evans Tokushima Fatty (OLETF) strain. The critical interval was narrowed down to 570 kb between D1Got258 to p162CA1 by segregation analyses using congenic lines.

Characterization of newly developed SSLP markers for the rat.

Abstract. We have isolated more than 12,000 clones containing microsatellite sequences, mainly consisting of (CA)n dinucleotide repeats, using genomic DNA from the BN strain of laboratory rat. Data trimming yielded 9636 non-redundant microsatellite sequences, and we designed oligonucleotide primer pairs to amplify 8189 of these. PCR amplification of genomic DNA from five different rat strains yielded clean amplification products for 7040 of these simple-sequence-length-polymorphism (SSLP) markers; 3019 markers had been mapped previously by radiation hybrid (RH) mapping methods (Nat Genet 22, 27–36, 1998). Here we report the characterization of these newly developed microsatellite markers as well as the release of previously unpublished microsatellite marker information. In addition, we have constructed a genome-wide linkage map of 515 markers, 204 of which are derived from our new collection, by genotyping 48 F2 progeny of (OLETFxBN)F2 crosses. This map spans 1830.9 cM, with an average spacing of 3.56 cM. Together with our ongoing project of preparing a whole-genome radiation hybrid map for the rat, this dense linkage map should provide a valuable resource for genetic studies in this model species.

Quantitative trait loci for lipid metabolism in the study of OLETF x (OLETF x Fischer 344) backcross rats.

1. The Otsuka Long‐Evans Tokushima Fatty (OLETF) rat is a model of type II diabetes with accompanying dyslipidaemia and obesity.

Effects of Dmo1 on obesity, dyslipidaemia and hyperglycaemia in the Otsuka Long Evans Tokushima Fatty strain

Whole-genome scans have identified Dmo1 as a major quantitative trait locus (QTL) for obesity and dyslipidaemia in the Otsuka Long Evans Tokushima Fatty (OLETF) rat. We have produced congenic rats for the Dmo1 locus, using marker-assisted speed congenic protocols, enforced by selective removal of other QTL regions (QTL-marker-assisted counterselection), to efficiently transfer chromosomal segments from non-diabetic Fischer 344 (F344) rats into the OLETF background. In the third generation of congenic animals, we observed a substantial therapeutic effect of the Dmo1 locus on lipid metabolism, obesity control and plasma glucose homeostasis. We conclude that single-allele correction of an impaired genetic pathway can generate a substantial therapeutic effect, despite the complex polygenic nature of type II diabetic syndromes.

A < 1.7 cM interval is responsible for Dmo1 obesity phenotypes in OLETF rats

1. Dmo1 (Diabetes Mellitus OLETF type I) is a major quantitative trait locus for dyslipidaemia, obesity and diabetes phenotypes of male Otsuka Long Evans Tokushima Fatty (OLETF) rats.

Genetic analysis of pancreatic duct hyperplasia in Otsuka Long-Evans Tokushima Fatty rats : Possible association with a region on rat chromosome 14 that includes the disrupted cholecystokinin-A receptor gene

An Otsuka Long–Evans Tokushima Fatty (OLETF) strain of rat spontaneously developed hyperglycemia, hyperinsulinemia, insulin resistance and mild obesity, which had been studied as animal model for type II diabetes mellitus (T2DM). Recently, we observed that this strain coincidentally developed atypical hyperplasia of the choledocho‐pancreatic ductal epithelium with a complete incidence. In an effort to locate genes responsible for this hyperplasia, we prepared 288 backcross progeny from a mating between OLETF rats and BN rats (which do not develop hyperplasia), and performed a genome‐wide scan using 207 polymorphic genetic markers. We observed a prominent association of hyperplasia with a region involving a marker locus D14Mit4 (P = 0.00020, Fishers exact test) and Cckar (the cholecystokinin‐A receptor gene; P = 0.00025, Fishers exact test) which is known to be disrupted in an OLETF strain. Our findings indicated that epithelial hyperplasia of the choledocho‐pancreatic duct is associated with a region on rat chromosome 14 around the Cckar gene in an additive fashion with another two susceptible loci, each on chromosome 9 and 7. This implied the possibility that Cckar deficiency could result in a predisposition towards pancreatic duct hyperplasia.