Molecular cloning of mouse hepatic triacylglycerol lipase: gene expression in combined lipase-deficient (cld/cld) mice

Abstract

cDNA clones coding for mouse hepatic triacylglycerol lipase (HL) were isolated from a mouse liver cDNA library with a human HL cDNA as a probe. The cloned HL cDNA of 1652 nucleotides predicts a mature protein of 488 amino acids preceded by a signal peptide of 22 amino acids. Two potential sites for N-glycosylation are identified, which are both conserved in rat and human HL. Combined lipase deficiency (cld) is a recessive mutation in mice, which causes the functional deficiency of HL and lipoprotein lipase, the isolated cDNA was used to study the expression of HL gene in cld/cld mice. Northern blot analysis of total cellular RNA from livers of cld/cld and normal mice showed that there are two mRNA species for HL with the sizes of 1.8 and 1.9 kilobases in both groups. However, the mRNA for HL was more abundant in cld/cld than in normal mice. RNase A protection assay of HL mRNA suggested that the multiple mRNA species for HL in cld/cld and normal mice are generated by differential utilization of polyadenylation signals and that there is no mutation in the structural gene for HL in cld/cld mice. The present study supports our hypothesis that the defect of HL activity in cld/cld mice is caused by abnormal post translational modification or processing of the lipase.