Identification of three loci affecting HDL-cholesterol levels in a screen for chemically induced recessive mutations in mice

Abstract

We conducted a genome-wide screen using the mutagen N-ethyl-N-nitrosourea to identify recessive mutations in genes that lead to altered lipid traits in mice. We screened 7,546 G3 mice that were of mixed C57BL/6J (B6)3C3.SW-H2 b /SnJ (C3) genomes and identified three pedigrees with differences in plasma HDL-cholesterol. Genome scan analyses mapped three distinct loci to chromosomes 3, 4, and 7. An S1748L missense mutation was identified in ABCA1 in one pedigree with undetectable levels of HDL-cholesterol and resulted in reduced protein levels. This phenotype was completely penetrant, semidominant, and cosegregated with high plasma triglycerides. Mice in a second pedigree had very high levels of plasma total cholesterol and HDL-cholesterol (up to 800 mg/dl total cholesterol). Despite a high degree of phenotype lability and reduced penetrance, an I68N missense mutation was identified in the transcription factor CCAAT/enhancer binding protein a (C/EBPa). Finally, a second high HDL-cholesterol pedigree of mice, again with a highly labile phenotype and reduced penetrance, was mapped to a 7 Mb locus on chromosome 3. These results illustrate the use of a hybrid background for simultaneous screening and mapping of mutagenized pedigrees of mice and identification of three novel alleles of HDL-cholesterol phenotypes.-Juan, T

A mutation in Ampd2 is associated with nephrotic syndrome and hypercholesterolemia in mice

“…Lipid parameters were analyzed on Ampd2 +/+ , Ampd2 +/m and Ampd2 m/m mice at 9 weeks of age (Figure 2 ). This time point was chosen after the observation was made that these phenotypes were transient in subsequent mouse plasma collections at 9, 11 and 13 weeks [ 11 ] and confirmed the previously reported elevated total cholesterol levels in Ampd2 m/m animals (Figure 2 A). Additionally Ampd2 m/m mice exhibited reduced penetrance, as evidenced by the appearance of some Ampd2 m/m mice with normal total cholesterol levels (Figure 2 A).…”

“…We previously reported [ 11 ] the mapping of the mutation for the hypercholesterolemic mice to a 7 Mb region on chromosome 3, with 131 possible candidate genes identified. Forty five were selected for further mutation analysis based on functional relevance.…”

“…Founder mice were identified at McLaughlin Research Institute [ 11 ] and subsequent generations were maintained at Charles River Laboratories to generate mixed C57BL/6 J (B6) C3.SW- H2 b /SnJ (C3) animals. The Ampd2 line was backcrossed to B6 via MAX-BAX® technology, and 2 of the 100% B6 congenic animals were obtained for further heterozygous × heterozygous mating.…”

“…ENU screens can also generate an allelic series of mutations that display a range of effects from complete or partial loss of function to exaggerated function, and reveal gene functions in an unbiased manner [ 10 ]. We previously performed an ENU screen to identify lines of mice with altered lipid profiles [ 11 ]. One line of mice presented undetectable levels of HDL-C, caused by a missense mutation in the ATP binding cassette transporter A1 ( Abca1 ) gene.…”

“…We now complete the physical mapping and define the remaining causative mutation in our hypercholesterolemia mice [ 11 ]. We further characterize the Ampd2 mutant mice as having a transient hypercholesterolemia phenotype that also present with transient nephrotic syndrome (NS).…”