Reduced expression and increased CpG dinucleotide methylation of the rat APOBEC-1 promoter in transgenic rabbits.

Editing of apolipoprotein (apo) B mRNA in liver limits the plasma LDL levels in horses, dogs, rats or mice. Species such as man or rabbit do not edit the hepatic apo B mRNA and are therefore susceptible to atherosclerosis and coronary artery disease due to elevated plasma LDL levels. The catalytic subunit APOBEC-1 is the only missing component of the apo B mRNA editing enzyme complex in the human or rabbit liver. Here we describe the generation of transgenic rabbits in which APOBEC-1 expression is mediated by the proximal promoter of the rat APOBEC-1 gene. These transgenic rabbits are healthy and fertile, and rat APOBEC-1 mRNA is expressed in liver, intestine, kidney, lung, brain and muscle. The transgenic APOBEC-1 expression is low and not sufficient to induce editing in rabbit liver. In rat, the proximal APOBEC-1 promoter demonstrates a progressive loss of CpG dinucleotide methylation towards the core promoter region that is entirely unmethylated. In the transgenic rabbits, this distinct pattern of CpG methylation is lost, and throughout the entire rat APOBEC-1 promoter, >90% of the CpGs are methylated. Thus, the weak proximal rat APOBEC-1 promoter appears to be down-regulated in the rabbit and may be species-specific.