Transgenic mice expressing a human apolipoprotein[a] allele

Abstract

The most important determinant of plasma levels of Lp[a] are sequence differences at the highly polymorphic apolipoprotein[a] (apo[a]) locus. To define the sequences that mediate the regulation of apo[a] expression, we cloned a 370 kb DNA fragment that included a 130 kb apo[a] gene, and 40 kb 5′- and 200 kb 3′-flanking region from an individual with high plasma levels of Lp[a] using a YAC vector. This genomic clone was used to generate transgenic mice. In the YAC-apo[a] transgenic mouse, apo[a] was only expressed in the liver, as it is in humans. The mean serum level of apo[a] in 4-week-old YAC-apo[a] transgenic mice was 20 mg/dl. In the female mice the levels of apo[a] varied over a 1.5-fold range during the 4-day estrus cycle and the levels correlated directly with serum progesterone levels. The serum levels of apo[a] decreased to almost undetectable level in male mice after puberty and this decrease was reversed by castration. Ingestion of a high-fat diet resulted in a ∼100-fold fall in hepatic apo[a] mRNA levels and >60-fold decrease in serum apo[a] levels. To delimit the control elements that mediate tissue-specific and sex hormone-responsive apo[a] transcription, we derived a reporter YAC in which 40 kb of 5′ flanking sequences from the cloned apo[a] allele were linked to a luciferase reporter gene. Analysis of four independent transgenic lines revealed no hepatic luciferase expression, suggesting that important cis-acting elements located outside the apo[a] 5′-flanking region are necessary for in vivo expression of apo[a].—Acquati, F., R. Hammer, B. Ercoli, V. Mooser, R. Tao, V. Rönicke, A. Michalich, G. Chiesa, R. Taramelli, H. H. Hobbs, and H-J. Müller. Transgenic mice expressing a human apolipoprotein[a] allele. J. Lipid Res. 1999. 40: 994–1006.

Keywords

• yeast artificial chromosomes
• homologous recombination