Terasawa Y, Cases S J, Wong J S, Jamil H, Jothi S, Traber M G, Packer L, Gordon D A, Hamilton R L, Farese R V
Gladstone Institute of Cardiovascular Disease, University of California, San Francisco, CA 94110, USA.
J Lipid Res. 1999 Nov;40(11):1967-77.
In mice, the yolk sac appears to play a crucial role in nourishing the developing embryo, especially during embryonic days (E) 7;-10. Lipoprotein synthesis and secretion may be essential for this function: embryos lacking apolipoprotein (apo) B or microsomal triglyceride transfer protein (MTP), both of which participate in the assembly of triglyceride-rich lipoproteins, are apparently defective in their ability to export lipoproteins from yolk sac endoderm cells and die during mid-gestation. We therefore analyzed the embryonic expression of apoB, MTP, and alpha-tocopherol transfer protein (alpha-TTP), which have been associated with the assembly and secretion of apoB-containing lipoproteins in the adult liver, at different developmental time points. MTP expression or activity was found in the yolk sac and fetal liver, and low levels of activity were detected in E18.5 placentas. alpha-TTP mRNA and protein were detectable in the fetal liver, but not in the yolk sac or placenta. Ultrastructural analysis of yolk sac visceral endoderm cells demonstrated nascent VLDL within the luminal spaces of the rough endoplasmic reticulum and Golgi apparatus at E7.5 and E8.5. The particles were reduced in diameter at E13.5 and reduced in number at E18.5;-19. The data support the hypothesis that the yolk sac plays a vital role in providing lipids and lipid-soluble nutrients to embryos during the early phases (E7;-10) of mouse development. secretion in mouse yolk sac during embryonic development.
在小鼠中，卵黄囊似乎在滋养发育中的胚胎方面发挥着关键作用，尤其是在胚胎期（E）7至10天期间。脂蛋白的合成和分泌对于该功能可能至关重要：缺乏载脂蛋白（apo）B或微粒体甘油三酯转移蛋白（MTP）的胚胎，这两者都参与富含甘油三酯脂蛋白的组装，其从卵黄囊内胚层细胞输出脂蛋白的能力显然存在缺陷，并在妊娠中期死亡。因此，我们分析了apoB、MTP和α-生育酚转移蛋白（α-TTP）在不同发育时间点的胚胎表达情况，这些蛋白在成年肝脏中与含apoB脂蛋白的组装和分泌有关。在卵黄囊和胎儿肝脏中发现了MTP的表达或活性，在E18.5胎盘检测到低水平的活性。在胎儿肝脏中可检测到α-TTP mRNA和蛋白，但在卵黄囊或胎盘中未检测到。对卵黄囊脏层内胚层细胞的超微结构分析表明，在E7.5和E8.5时，粗面内质网和高尔基体的管腔内有新生的极低密度脂蛋白（VLDL）。在E13.5时颗粒直径减小，在E18.5至19时数量减少。这些数据支持了这样的假设，即在小鼠发育的早期阶段（E7至10），卵黄囊在为胚胎提供脂质和脂溶性营养方面起着至关重要的作用。胚胎发育期间小鼠卵黄囊中的分泌情况。
