Generation of floxed Sirtuin 1 Exon5-Exon6 for the construction of conditional knockout mice.

Sirtuin 1 (Sirt1), a homolog of yeast Sir 2, is an NAD-dependent histone and protein deacetylase. It has a wide range of biological functions, ranging from DNA damage repair to effects on glucose metabolism. Sirt1 null mice die before birth due to chromosomal aberrations and impaired DNA damage repair. Sirt1 is thought to affect energy metabolism, but the mechanism remains poorly understood. In order to study tissue-specific metabolic effects of Sirt1, floxed Sirt1 was constructed so that exons 5 and 6 would be deleted using the Cre-Lox strategy. In contrast to a previously reported deletion of Sirt1 exon4, no truncated (and potentially active) Sirt1 forms were detected when exons 5 and 6 were deleted.

Hepatic exon 5-6 null Sirt1 mice were generated when Floxed Sirt1 exon 5 and 6 mice were mated with mice that expressed the Cre-recombinase in liver. The hepatic exon 5-6 null Sirt1 mice developed fatty liver under normal feeding conditions. This was accompanied by increased expression of the carbohydrate responsive element binding protein, which is a major regulator of lipid synthesis. Sirt1-deficient liver also has an impaired insulin response, primarily due to reduced phosphorylation of the serine-threonine kinase Akt in the presence of insulin.