Kirchgessner T G, LeBoeuf R C, Langner C A, Zollman S, Chang C H, Taylor B A, Schotz M C, Gordon J I, Lusis A J
Department of Medicine, University of California, Los Angeles 90024.
J Biol Chem. 1989 Jan 25;264(3):1473-82.
We report here a study of the developmental and genetic control of tissue-specific expression of lipoprotein lipase, the enzyme responsible for hydrolysis of triglycerides in chylomicrons and very low density lipoproteins. Lipoprotein lipase (LPL) mRNA is present in a wide variety of adult rat and mouse tissues examined, albeit at very different levels. A remarkable increase in the levels of LPL mRNA occurs in heart over a period of several weeks following birth, closely paralleling developmental changes in lipase activity and myocardial beta-oxidation capacity. Large increases in LPL mRNA also occur during differentiation of 3T3L1 cells to adipocytes. As previously reported, at least two separate genetic loci control the tissue-specific expression of LPL activity in mice. One of the loci, controlling LPL activity in heart, is associated with an alteration in LPL mRNA size, while the other, controlling LPL activity in adipose tissue, appears to affect the translation or post-translational expression of LPL. To examine whether these genetic variations are due to mutations of the LPL structural locus, we mapped the LPL gene to a region of mouse chromosome 8 using restriction fragment-length polymorphisms and analysis of hamster-mouse somatic cell hybrids. This region is homologous to the region of human chromosome 8 which contains the human LPL gene as judged by the conservation of linked genetic markers. Genetic variations affecting LPL expression in heart cosegregated with the LPL gene, while variations affecting LPL expression in adipose tissue did not. Furthermore, Southern blotting analysis indicates that LPL is encoded by a single gene and, thus, the genetic differences are not a consequence of independent regulation of two separate genes in the two tissues. These results suggest the existence of cis-acting elements for LPL gene expression that operate in heart but not adipose tissue. Our results also indicate that two genetic mutations resulting in deficiencies of LPL in mice, the W mutation on chromosome 5 and the cld mutation on mouse chromosome 17, do not involve the LPL structural gene locus. Finally, we show that the gene for hepatic lipase, a member of a gene family with LPL, is unlinked to the gene for LPL. This indicates that combined deficiencies of LPL and hepatic lipase, observed in humans as well as in certain mutant strains of mice, do not result from focal disruptions of a cluster of lipase genes.
我们在此报告一项关于脂蛋白脂肪酶组织特异性表达的发育和遗传控制的研究，该酶负责乳糜微粒和极低密度脂蛋白中甘油三酯的水解。在所检测的多种成年大鼠和小鼠组织中均存在脂蛋白脂肪酶（LPL）mRNA，尽管其水平差异很大。出生后的几周内，心脏中LPL mRNA水平显著增加，这与脂肪酶活性和心肌β氧化能力的发育变化密切平行。在3T3L1细胞分化为脂肪细胞的过程中，LPL mRNA水平也大幅增加。如先前报道，至少有两个独立的基因位点控制小鼠中LPL活性的组织特异性表达。其中一个位点控制心脏中的LPL活性，与LPL mRNA大小的改变有关，而另一个位点控制脂肪组织中的LPL活性，似乎影响LPL的翻译或翻译后表达。为了研究这些遗传变异是否由于LPL结构基因座的突变引起，我们使用限制性片段长度多态性和仓鼠 - 小鼠体细胞杂种分析将LPL基因定位到小鼠染色体8的一个区域。根据连锁遗传标记的保守性判断，该区域与包含人类LPL基因的人类染色体8区域同源。影响心脏中LPL表达的遗传变异与LPL基因共分离，而影响脂肪组织中LPL表达的变异则不然。此外，Southern印迹分析表明LPL由单个基因编码，因此，遗传差异不是两个组织中两个独立基因独立调控的结果。这些结果表明存在在心脏而非脂肪组织中起作用的LPL基因表达的顺式作用元件。我们的结果还表明，导致小鼠LPL缺乏的两个基因突变，即5号染色体上的W突变和17号小鼠染色体上的cld突变，不涉及LPL结构基因座。最后，我们表明肝脂肪酶基因（与LPL属于一个基因家族）与LPL基因不连锁。这表明在人类以及某些小鼠突变品系中观察到的LPL和肝脂肪酶的联合缺乏并非由脂肪酶基因簇的局部破坏引起。
