Demmer L A, Levin M S, Elovson J, Reuben M A, Lusis A J, Gordon J I
Proc Natl Acad Sci U S A. 1986 Nov;83(21):8102-6. doi: 10.1073/pnas.83.21.8102.
Expression of the apolipoprotein B (apoB) gene was examined in a variety of fetal, neonatal, and adult rat tissues by probing RNA blots with a cloned rat apoB cDNA. Among 10 adult male tissues surveyed, small intestine had the highest concentration of apoB mRNA. Its abundance in liver and adrenal gland was 40% and 0.5%, respectively, of that in small bowel, while none was detected in colon, kidney, testes, spleen, lung, heart, or brain. ApoB mRNA is as abundant in 18-day fetal liver as at any subsequent period of hepatic development. In contrast, the concentration of apoB mRNA remains low in fetal intestine until the last (21st) day of gestation, when it increases sharply to levels that are several-fold higher than in the liver. ApoB mRNA levels in fetal membranes harvested during this late gestational period were 10 times greater than in fetal liver. Since the major lipoprotein species in 19-day fetal plasma is low density lipoprotein, these observations suggest that fetal liver, and particularly its functional homologue, the yolk sac, are the principal sites of fetal lipoprotein synthesis at this stage of development. A 20-fold increase in placental apoB mRNA concentrations during the last 48 hr of pregnancy (to a level that is 50% of that encountered in fetal membrane RNA) suggests a specific role for this organ in maternal-fetal lipid transport immediately prior to parturition. Pulse-labeling experiments using 21-day fetal tissue slices showed that the liver synthesizes both apoB-100 (B-PI) and apoB-48 (B-PIII) albeit in somewhat different ratios than the adult organ. Fetal intestine produces almost exclusively the smaller apoB species, while fetal membranes and placenta synthesize only the larger peptide. The postnatal pattern of apoB mRNA accumulation is similar in liver and intestine. Profound decreases were observed during the late suckling and weaning periods, followed by an increase to adult levels. These final concentrations were similar to those encountered at birth. Analysis of these developmental changes offers an opportunity to generate testable hypotheses about the factors that modulate apoB synthesis.
利用克隆的大鼠载脂蛋白B（apoB）cDNA对RNA印迹进行杂交，研究了apoB基因在各种胎鼠、新生鼠和成年大鼠组织中的表达情况。在所检测的10种成年雄性组织中，小肠中apoB mRNA的浓度最高。其在肝脏和肾上腺中的丰度分别为小肠中的40%和0.5%，而在结肠、肾脏、睾丸、脾脏、肺、心脏或大脑中未检测到。apoB mRNA在18天胎肝中的丰度与肝脏发育的任何后续阶段一样高。相比之下，apoB mRNA在胎肠中的浓度在妊娠最后（第21）天之前一直较低，之后会急剧增加到比肝脏中高出几倍的水平。在妊娠后期采集的胎膜中，apoB mRNA水平比胎肝中的高10倍。由于19天胎鼠血浆中的主要脂蛋白种类是低密度脂蛋白，这些观察结果表明，在发育的这个阶段，胎肝，尤其是其功能同源物卵黄囊，是胎儿脂蛋白合成的主要部位。妊娠最后48小时胎盘apoB mRNA浓度增加20倍（达到胎膜RNA中浓度的50%），表明该器官在分娩前母婴脂质转运中具有特定作用。使用21天胎鼠组织切片进行的脉冲标记实验表明，肝脏能合成apoB-100（B-PI）和apoB-48（B-PIII），尽管其比例与成年器官略有不同。胎肠几乎只产生较小的apoB种类，而胎膜和胎盘只合成较大的肽。apoB mRNA在肝脏和小肠中的产后积累模式相似。在哺乳后期和断奶期观察到显著下降，随后增加到成年水平。这些最终浓度与出生时的浓度相似。对这些发育变化的分析为提出有关调节apoB合成的因素的可检验假设提供了机会。
