Abstract
A cDNA clone for mouse apolipoprotein E has been identified from a mouse liver cDNA library by a combination of differential colony hybridization and hybrid selection-translation. The identity of the clone was unambiguously established by partial sequencing and comparison with human apolipoprotein E nucleotide and amino acid sequences. In conjunction with an in vitro translation assay for apolipoprotein E, the clone has been used to examine the relative levels of apolipoprotein E mRNA in various tissues of the mouse and the regulation of apolipoprotein E synthesis in response to a diet rich in saturated fat and cholesterol. In the tissues examined, the clone was found to hybridize to a polyadenylated RNA species of approximately 1400 nucleotides. Of the tissues involved in lipoprotein synthesis, liver is very rich (about 1% of total) in apolipoprotein E mRNA while intestine contains only trace amounts. Appreciable levels of active apolipoprotein E mRNA (up to 10% of that in liver) are also detected in peripheral tissues not associated with lipoprotein synthesis, including lung, kidney, spleen, and heart. Thus, extrahepatic apolipoprotein E synthesis may contribute significantly to the levels present in plasma, and a possible function in "reverse cholesterol transport" is considered. When mice were placed on a high lipid diet there was no discernible change in the level of apolipoprotein E mRNA in liver or intestine, although the level of the circulating protein increased about 3-fold. We conclude that in mice the effect of diet on apolipoprotein E levels in blood does not result from induction of mRNA in these tissues.
Highlights
A cDNA clone for mouse apolipoprotein E has been identified from a mouse liver cDNA library by a combination of differential colony hybridization and hybrid selection-translation
Genetic studies in humans have defined 3 alleles for the apo-E structural gene and ithas been discovered that homozygosity for one of these alleles correlates with the occurrence of familial type I11 hyperlipoproteinemia, a disease associated with premature atherosclerosis [19,20,21,22,23], These observations, coupled with the fact that apo-E has been detected in all mammalian species examined [4, 22], indicate that apo-E may serve a crucial function in lipid transport and metabolism
It is clear that apo-E is expressed in appreciable levels in a variety of peripheral tissues not associated with lipoprotein production
Summary
A comprehensive characterization of the genetic control of plasma lipid transport hasbeen initiated in themouse (2931), and, due to accessibility and thesuperiority of the mouse for biochemical genetic studies, we have chosen to utilize the mouse as a model to study the regulation of apo-E synthesis Toward this end, we have developed a mRNA assay and isolated and characterized a clone for apo-E from a mouse liver cDNA library. In conjunction with the mRNA assay, the apo-E cDNA clone has been used to quantitate therelative levels of apo-E mRNA in several mouse tissues and to investigate possible differences in mRNA synthesis and activity in the liver and intestine of mice maintained on normal and high lipid diets. Mice were maintained on a standard diet of laboratory mouse chow(Purina 5001) which contains
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
