Generation of rat "supersonic" congenic/conplastic strains using superovulation and embryo transfer

High-Speed Mouse Backcrossing Through the Female Germ Line

Transferring mouse mutations into specific mouse strain backgrounds can be critical for appropriate analysis of phenotypic effects of targeted genomic alterations and quantitative trait loci. Speed congenic breeding strategies incorporating marker-assisted selection of progeny with the highest percentage target background as breeders for the next generation can produce congenic strains within approximately 5 generations. When mating selected donor males to target strain females, this may require more than 1 year, with each generation lasting 10 to 11 weeks including 3 weeks of gestation and 7 to 8 weeks until the males reach sexual maturity. Because ovulation can be induced in female mice as early as 3 weeks of age, superovulation-aided backcrossing of marker-selected females could accelerate the production of congenic animals by approximately 4 weeks per generation, reducing time and cost. Using this approach, we transferred a transgenic strain of undefined genetic background to >99% C57BL/6J within 10 months, with most generations lasting 7 weeks. This involved less than 60 mice in total, with 9 to 18 animals per generation. Our data demonstrate that high-speed backcrossing through the female germline is feasible and practical with small mouse numbers.

Effects of mtDNA in SHR-mtF344 versus SHR conplastic strains on reduced OXPHOS enzyme levels, insulin resistance, cardiac hypertrophy, and systolic dysfunction

Common inbred strains of the laboratory rat can be divided into four major mitochondrial DNA (mtDNA) haplotype groups represented by the BN, F344, LEW, and SHR strains. In the current study, we investigated the metabolic and hemodynamic effects of the SHR vs. F344 mtDNA by comparing the SHR vs. SHR-mt(F344) conplastic strains that are genetically identical except for their mitochondrial genomes. Altogether 13 amino acid substitutions in protein coding genes, seven single nucleotide polymorphisms in tRNA genes, and 12 single nucleotide changes in rRNA genes were detected in F344 mtDNA compared with SHR mtDNA. Analysis of oxidative phosphorylation system (OXPHOS) in heart left ventricles (LV), muscle, and liver revealed reduced activity and content of several respiratory chain complexes in SHR-mt(F344) conplastic rats compared with the SHR strain. Lower function of OXPHOS in LV of conplastic rats was associated with significantly increased relative ventricular mass and reduced fractional shortening that was independent of blood pressure. In addition, conplastic rats exhibited reduced sensitivity of skeletal muscles to insulin action and impaired glucose tolerance. These results provide evidence that inherited alterations in mitochondrial genome, in the absence of variation in the nuclear genome and other confounding factors, predispose to insulin resistance, cardiac hypertrophy and systolic dysfunction.

Nonsynonymous variants in mt-Nd2, mt-Nd4, and mt-Nd5 are linked to effects on oxidative phosphorylation and insulin sensitivity in rat conplastic strains

Common inbred strains of the laboratory rat can be divided into four different mitochondrial DNA haplotype groups represented by the SHR, BN, LEW, and F344 strains. In the current study, we investigated the metabolic and hemodynamic effects of the SHR vs. LEW mitochondrial genomes by comparing the SHR to a new SHR conplastic strain, SHR-mt(LEW); these strains are genetically identical except for their mitochondrial genomes. Complete mitochondrial DNA (mtDNA) sequence analysis comparing the SHR and LEW strains revealed gene variants encoding amino acid substitutions limited to a single mitochondrial enzyme complex, NADH dehydrogenase (complex I), affecting subunits 2, 4, and 5. Two of the variants in the mt-Nd4 subunit gene are located close to variants known to be associated with exercise intolerance and diabetes mellitus in humans. No variants were found in tRNA or rRNA genes. These variants in mt-Nd2, mt-Nd4, and mt-Nd5 in the SHR-mt(LEW) conplastic strain were linked to reductions in oxidative and nonoxidative glucose metabolism in skeletal muscle. In addition, SHR-mt(LEW) conplastic rats showed increased serum nonesterified fatty acid levels and resistance to insulin stimulated incorporation of glucose into adipose tissue lipids. These results provide evidence that inherited variation in mitochondrial genes encoding respiratory chain complex I subunits, in the absence of variation in the nuclear genome and other confounding factors, can influence glucose and lipid metabolism when expressed on the nuclear genetic background of the SHR strain.

Recent advances in genetics of the spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) is the most widely used animal model of essential hypertension and associated metabolic disturbances. Multiple quantitative trait loci associated with hemodynamic and metabolic parameters have been mapped in the SHR. Recently, it has become possible to identify some of the specific quantitative trait gene (QTG) variants that underlie quantitative trait loci linked to complex cardiovascular and metabolic traits in SHR related strains. Recombinant inbred strains derived from SHR and Brown Norway progenitors, together with SHR congenic and transgenic strains, have proven useful for establishing the identity of several QTGs in SHR models. It is anticipated that the combined use of linkage analyses and gene expression profiles, together with the recently available genome sequences of both the SHR and Brown Norway strains and new methods for manipulating the rat genome, will soon accelerate progress in identifying QTGs for complex traits in SHR-related strains.