Conditional Targeting of Cholesterol Biosynthesis

Cholesterol is synthesized by almost every mammalian cell. Squalene synthase (SQS; Fdft1; farnesyl-pyrophosphate:farnesyl-pyrophosphate farnesyltransferase, EC2.5.1.21) catalyzes the condensation of two farnesyl-pyrophosphate molecules to squalene which is the first committed step to sterol biosynthesis. HMG-CoA reductase is the rate-limiting enzyme of this pathway. Inactivation of either enzyme is lethal during embryonic development (Tozawa et al., 1999; Ohashi et al., 2003), by severely affecting multiple organ systems. Therefore, conditional inactivation is necessary to study cholesterol biology in vivo.

We generated a conditional allele of the Fdft1 gene in the mouse (SQS-Flox mice) by introducing two loxP sites flanking exon 5 (Fig. 1). Exon 5 of Fdft1 encodes the active site of the enzyme and removal of exons 4 and 5 was shown to inactivate SQS function in a conventional Fdft1 null mutant (Tozawa et al., 1999).