Kanai M, Soji T, Sugawara E, Watari N, Oguchi H, Matsubara M, Herbert D C
Department of Anatomy, Nagoya City University Medical School, Japan.
Microsc Res Tech. 1996 Nov 1;35(4):340-8. doi: 10.1002/(SICI)1097-0029(19961101)35:4<340::AID-JEMT5>3.0.CO;2-Q.
We ultrastructually examined the chick yolk sac endodermal epithelium and evaluated our findings in combination with the biochemical analysis of serum and yolk lipoproteins. Twenty-five to 30 nm-sized particles were demonstrated to be a principal element of the extracellular yolk mass and these were determined to be yolk very low density lipoprotein (VLDL). The particles were shown to be taken up by the epithelial cells via coated pits and engulfed by plasma membrane invaginations together with yolk subdroplets, another element of the yolk mass. Through apical vacuoles, the two yolk elements were incorporated into yolk drops, which were identified to be one of the lysosomal structures by a cytochemical procedure using acid phosphatase (AcP)ase activity. During the last week of incubation, which is the final third of the incubation period, the digestion seemed to progress rapidly in the yolk drops, which came to resemble lipolysosomes; lipoprotein production became active as expressed by an enlarged Golgi apparatus. The newly produced lipoprotein particles were electron-lucent and irregular in size (50-120 nm). They were sequestered in secretory vacuoles and secreted from the vascular surface of the epithelial cells. Finally, the particles were thought to be taken into the vitelline circulation as plasma lipoproteins. The major component of lipoprotein in serum was determined to be low density lipoprotein (LDL) and high density lipoprotein (HDL), while cholesterol content was found to increase during incubation. We concluded that endodermal epithelial cells participate the synthesis of plasma LDL and HDL. For this synthesis the cells probably apply lipids and apo-protein generated from yolk VLDL degradation.
我们对鸡卵黄囊内胚层上皮进行了超微结构检查，并结合血清和卵黄脂蛋白的生化分析对结果进行了评估。25至30纳米大小的颗粒被证明是细胞外卵黄物质的主要成分，这些颗粒被确定为卵黄极低密度脂蛋白（VLDL）。这些颗粒通过有被小窝被上皮细胞摄取，并与卵黄物质的另一个成分——卵黄亚滴一起被质膜内陷吞噬。通过顶端液泡，这两种卵黄成分被整合到卵黄滴中，通过使用酸性磷酸酶（AcP）酶活性的细胞化学方法，卵黄滴被鉴定为溶酶体结构之一。在孵化的最后一周，即孵化期的最后三分之一时间里，卵黄滴中的消化似乎迅速进行，卵黄滴变得类似于脂溶酶体；高尔基体增大表明脂蛋白产生活跃。新产生的脂蛋白颗粒电子密度低且大小不规则（50 - 120纳米）。它们被隔离在分泌泡中，并从上皮细胞的血管表面分泌出来。最后，这些颗粒被认为作为血浆脂蛋白进入卵黄循环。血清中脂蛋白的主要成分被确定为低密度脂蛋白（LDL）和高密度脂蛋白（HDL），而胆固醇含量在孵化过程中增加。我们得出结论，内胚层上皮细胞参与血浆LDL和HDL的合成。对于这种合成，细胞可能利用卵黄VLDL降解产生的脂质和载脂蛋白。
