A mouse model of chylomicron deficiency was recently developed ; these mice express a human apolipoprotein (apo) B transgene in the liver but do not synthesize any apoB in the intestine. Despite severe intestinal fat malabsorption, the mice maintain normal concentrations of plasma lipids and liverderived apoB 100-containing lipoproteins. We investigated the metabolic mechanisms by which plasma lipid levels are kept normal. De no o lipogenesis (DNL) and cholesterogenesis were measured by mass isotopomer distribution analysis (MIDA). Plasma non-esterified fatty acid (NEFA) fluxes and hepatic reesterification of labelled plasma NEFA were also measured. Hepatic and plasma triacylglycerol (TG) concentrations and plasma NEFA fluxes were not different between chylomicrondeficient mice and controls. The contribution from DNL to the hepatic TG pool was only modestly higher in chylomicrondeficient mice [12p2n1 % (n l 7) compared with 3n7p1n0 % (n l 9) ; meanspS.E.M.], whereas cholesterogenesis was markedly elevated. The fractional contribution from plasma NEFA to hepatic TG was greatly elevated in the chylomicron-
A highly efficient and reproducible transformation system for rice ( Oryza sativa L. cv. Taipei 309) was developed using microprojectile bombardment of highly regenerative, green tissues. These tissues were induced from mature seeds on NB-based medium containing 2,4-dichlorophenoxyacetic acid (2,4-D), 6-benzylaminopurine (BAP) and high concentrations of cupric sulfate under dim light conditions; germinating shoots and roots were completely removed. Highly regenerative, green tissues were proliferated on the same medium and used as transformation targets. From 431 explants bombarded with transgenes [i.e. a hygromycin phosphotransferase ( hpt) gene plus one of a wheat thioredoxin h ( wtrxh), a barley NADP-thioredoxin reductase ( bntr), a maize Mutator transposable element ( mudrB) or beta-glucuronidase ( uidA; gus) gene], 28 independent transgenic events were obtained after an 8- to 12-week selection period, giving a 6.5% transformation frequency. Of the 28 independent events, 17 (61%) were regenerable. Co-transformation of the second introduced transgene was detected in 81% of the transgenic lines tested. Stable integration and expression of the foreign genes in T(0) plants and T(1) progeny were confirmed by DNA hybridization, western blot analyses and germination tests.
A mouse model of chylomicron deficiency was recently developed; these mice express a human apolipoprotein (apo) B transgene in the liver but do not synthesize any apoB in the intestine. Despite severe intestinal fat malabsorption, the mice maintain normal concentrations of plasma lipids and liver-derived apoB 100-containing lipoproteins. We investigated the metabolic mechanisms by which plasma lipid levels are kept normal. De novo lipogenesis (DNL) and cholesterogenesis were measured by mass isotopomer distribution analysis (MIDA). Plasma non-esterified fatty acid (NEFA) fluxes and hepatic re-esterification of labelled plasma NEFA were also measured. Hepatic and plasma triacylglycerol (TG) concentrations and plasma NEFA fluxes were not different between chylomicron-deficient mice and controls. The contribution from DNL to the hepatic TG pool was only modestly higher in chylomicron-deficient mice [12+/-2.1% (n=7) compared with 3.7+/-1.0% (n=9); means+/-S.E.M.], whereas cholesterogenesis was markedly elevated. The fractional contribution from plasma NEFA to hepatic TG was greatly elevated in the chylomicron-deficient animals (62% compared with 23%). Accordingly, 73% of hepatic TG was neither from DNL nor from plasma NEFA in controls, presumably reflecting prior contribution from chylomicron remnants, compared with only 26% in the chylomicron-deficient group. The long-term contribution from DNL to adipose fat stores reached approximately the same steady-state values (approximately 30%) in the two groups. Body fat accumulation was much lower in chylomicron-deficient animals; thus, whole-body absolute DNL was significantly lower. We conclude that plasma and hepatic TG pools and hepatic secretion of apoB-containing particles are maintained at normal levels in chylomicron-deficient mice, not by de novo fatty acid synthesis, but by more avid re-esterification of plasma NEFA, replacing the normally predominant contribution from chylomicrons, and that some dietary fat can be absorbed by apoB-independent mechanisms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.