Tissue-specific expression, developmental regulation, and chromosomal mapping of the lecithin: cholesterol acyltransferase gene. Evidence for expression in brain and testes as well as liver

Lecithin:cholesterol acyltransferase (LCAT) catalyzes the esterification of cholesterol in high density lipoproteins, thereby facilitating transport of excess cholesterol from peripheral tissues to liver. We report here studies of the developmental, dietary, and genetic control of LCAT gene expression. In adult male Sprague-Dawley rats fed a standard chow diet LCAT mRNA was most abundant in liver, a major source of the plasma enzyme, but appreciable levels were also present in brain and testes. Since both brain and testes are isolated from blood by tight cellular barriers, undoubtedly greatly reducing the level of plasma-derived LCAT in cerebrospinal fluid and testes, the production of LCAT in these tissues may be important for removal of excess cholesterol. Noteworthy changes in the expression of LCAT mRNA were observed during development of both rodents and humans. On the other hand, LCAT mRNA levels were relatively resistant to dietary challenge or to drugs affecting cholesterol metabolism. Since human epidemiological studies have suggested an association between LCAT levels and variations of high density lipoprotein cholesterol, we examined LCAT gene polymorphisms in a mouse animal model. Mapping of the LCAT gene (Lcat) to mouse Chromosome 8 within 2 centimorgans of the Es-2 locus indicates that it does not correspond to any previously mapped loci affecting high density lipoprotein phenotypes in the mouse.     

Quantitative trait locus analysis of susceptibility to diet-induced atherosclerosis in recombinant inbred mice

Quantitative trait locus (QTL) analysis is a statistical method that can be applied to identify loci making a significant impact on a phenotype. For the phenotype of susceptibility to diet-induced atherosclerosis in the mouse, we have studied four quantitative traits: area of aortic fatty streaks and serum concentrations of high-density lipoprotein-bound cholesterol (HDL-cholesterol), apolipoprotein A-I, and apolipoprotein A-II (apo A-II). QTL analysis revealed a significant locus on chromosome 1 distal impacting serum apo A-II concentration on a high-fat diet and serum HDL-cholesterol concentration on a chow diet. This locus is presumablyApoa-2, the structural gene for apo A-II. QTL analysis of aortic fatty streaks failed to reveal a significant locus.     

Mapping of the Glycoprotein 330 (Gp330) Gene to Mouse Chromosome 2

Glycoprotein 330 (Gp330) is a member of the low-density lipoprotein receptor gene family that is expressed in the kidney. We have mapped the Gp330 gene to mouse chromosome 2, 4.5 cM proximal to Acra, in an interspecific backcross of (C57BL/6J × Mus spretus) F1 × C57BL/6J.     

Regulation of phosphatidylcholine biosynthesis by mitogenic growth factors

Phosphatidylcholine (PC) biosynthesis in cultured 3T3 fibroblasts was increased in varying degrees by these mitogenic growth factors: fetal bovine serum, insulin, 12-O-tetradecanoylphorbol-13-acetate, epidermal growth factor, vasopressin, fibroblast growth factor and insulin-like growth factors I and II. PC synthesis was increased 2-4-fold by 10% serum, up to 4-fold by growth factors alone, and up to 8-fold by combinations of two or more growth factors. Single growth factors had no effect on the incorporation of [3H]choline into the acid-soluble precursors of PC, while serum or combinations of two or more mitogens could increase the incorporation of [3H]choline into acid-soluble material by up to 2-fold. Serum was shown to increase choline phosphorylation, choline kinase activity and the size of the phosphocholine pool. These data were utilized to calculate the radioactive specific activity of phosphocholine. Serum did not increase phosphocholine specific activity above control values; thus the increased incorporation of labelled choline into PC after serum stimulation resulted from increased PC synthesis and not from a simple change in specific activity of precursor phosphocholine.     

Electron transport in the cni-1 mutant of Neurospora crassa.

1. Mitochondria from the nuclear mutant cni-1 have no optically detectable cytochrome aa3 in early log phase growth. These mitochondria have a high level of respiration that is not inhibited by cyanide but is inhibited by salicylhydroxamic acid. They also show a substantial amount of cyanide-sensitive respiration. 2. As cultures of mutant cni-1 age, flux through the hydroxamate-sensitive pathway decreases markedly while flux through the cytochrome chain remains constant. 3. Growth studies with mutant cni-1 indicate that the cytochrome chain in this mutant is more important in supporting growth than the hydroxamate-sensitive pathway. 4. Measurements of the steady-state level of reduction of cytochrome c in mutant cni-1 indicate that the rate-limiting step in the cytochrome chain is at the position occupied by cytochrome oxidase. 5. Electron spin resonance studies with cni-1 mitochondria show normal cytochrome oxidase signals in the g approximately 6 region although there is little or no optically detectable cytochrome aa3.     

A flash photolysis ESR study of photosystem II signal IIvf, the physiological donor to P-680+.

In flash-illuminated, oxygen-evolving spinach chloroplasts and green algae, a free radical transient has been observed with spectral parameters similar to those of Signal II (g approximately 2.0045, deltaHpp approximately 19G). However, in contrast with ESR Signal II, the transient radical does not readily saturate even at microwave power levels of 200 mW. This species is formed most efficiently with "red" illumination (lambda less than 680 nm) and occurs stoichiometrically in a 1:1 ratio with P-700+. The Photosystem II transient is formed in less than 100 mus and decays via first-order kinetics with a halftime of 400-900 mus. Additionally, the t1/2 for radical decay is temperature independent between 20 and 4 degrees C; however, below 4 degrees C the transient signal exhibits Arrhenius behavior with an activation energy of approx. 10 kcal-mol-1. Inhibition of electron transport through Photosystem II by o-phenanthroline, 3-(3,4-dichlorophenyl)-1,1-dimethylurea or reduced 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone suppresses the formation of the light-induced transient. At low concentrations (0.2 mM), 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone partially inhibits the free radical formation, however, the decay kinetics are unaltered. High concentrations of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (1-5 mM) restore both the transient signal and electron flow through Photosystem II. These findings suggest that this "quinoidal" type ESR transient functions as the physiological donor to the oxidized reaction center chlorophyll, P-680+.