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Knockout of the mouse apolipoprotein B gene results in embryonic lethality in homozygotes and protection against diet-induced hypercholesterolemia in heterozygotes
- Farese, R.V. Jr., Ruland, S.L., Flynn, L.M., Stokowski, R.P., Young, S.G.
- Proceedings of the National Academy of Sciences of the United States of America 1995 v.92 no.5 pp. 1774-1778
- blood lipids, insertional mutagenesis, high fat diet, structural genes, hypercholesterolemia, blood proteins, apolipoproteins, heterozygosity, mice, cholesterol, animal models, mutants, gene targeting, embryonic stem cells, homozygosity, embryogenesis, lethal genes
- Apolipoprotein B is synthesized by the intestine and the liver in mammals, where it serves as the main structural component in the formation of chylomicrons and very low density lipoproteins, respectively. Apolipoprotein B is also expressed in mammalian fetal membranes. To examine the consequences of apolipoprotein B deficiency in mice, we used gene targeting in mouse embryonic stem cells to generate mice containing an insertional disruption of the 5' region of the apolipoprotein B gene. Mice that were heterozygous for the disrupted apolipoprotein B allele had an approximately 20% reduction in plasma cholesterol levels, markedly reduced plasma concentrations of the pre-beta and beta-migrating lipoproteins, and an approximately 70% reduction in plasma apolipoprotein B levels. When fed a diet rich in fat and cholesterol, heterozygous mice were protected from diet-induced hypercholesterolemia; these mice, which constitute an animal model for hypobetalipoproteinemia, should be useful for studying the effects of decreased apolipoprotein B expression on atherogenesis. The breeding of heterozygous mice yielded no viable homozygous apolipoprotein B knockout mice. Most homozygous embryos were resorbed by midgestation (before gestational day 11.5); several embryos that survived until later in gestation exhibited exencephalus. The embryonic lethal phenotype was rescued by complementation with a human apolipoprotein B transgene--i.e., human apolipoprotein B transgenic mice that were homozygous for the murine apolipoprotein B knockout mutation were viable. Our findings indicate that apolipoprotein B plays an essential role in mouse embryonic development.