Riad N H, Bruns M E, Fares N H, Bruns D E, Herr J C
Department of Anatomy, University of Virginia Medical Center, Charlottesville 22908.
Anat Rec. 1988 Nov;222(3):252-9. doi: 10.1002/ar.1092220306.
The calcium-binding protein (CaBP) calbindin has been implicated in the molecular mechanism of placental calcium transfer. Previous light microscopic studies have identified CaBP in visceral (but not parietal) endodermal cells of the yolk sac with the most intense immunocytochemical signal observed in the intraplacental yolk sac. In the present studies, electron microscopy was used to study the localization of CaBP in placenta. Placentas of 17-day pregnant mice were fixed by perfusion in 0.5% glutaraldehyde, embedded in low-temperature Lowicryl K4M, and examined in thin section for specific labeling with a polyclonal antiserum. Antibody to CaBP was localized by using protein A-gold particles which were quantified for subcellular compartmentation by using a Videoplan computer system. A high signal for CaBP was found in the visceral endodermal cells of the intraplacental yolk sac. In these cells, gold particles indicating the location of CaBP were observed over 1) the cytoplasmic matrix where the average number of gold particles per micron 2 was 33; 2) the microvilli (17/micron 2); 3) the mitochondria (17/micron 2); and 4) the nucleus (43/micron 2). Sections from antigen-absorbed controls, by contrast, showed few gold particles: cytosol, 2/micron 2; microvilli, 5/micron 2; mitochondria, 5/micron 2; and nucleus, 4/micron 2. Electron-lucent profiles of the Golgi and endoplasmic reticulum contained no particles in the controls and a low particle count (4/micron 2) in the stained sections. Parietal endodermal cells of the intraplacental yolk sac showed a relatively low signal for CaBP compared with the visceral endodermal cells (5 particles/micron 2 vs. 39).(ABSTRACT TRUNCATED AT 250 WORDS)
钙结合蛋白（CaBP）钙结合蛋白与胎盘钙转运的分子机制有关。先前的光学显微镜研究已在卵黄囊的脏层（而非壁层）内胚层细胞中鉴定出CaBP，在胎盘内卵黄囊中观察到最强的免疫细胞化学信号。在本研究中，使用电子显微镜研究CaBP在胎盘中的定位。对17天妊娠小鼠的胎盘进行灌注固定，置于0.5%戊二醛中，包埋于低温Lowicryl K4M中，制成薄切片，用多克隆抗血清进行特异性标记检查。使用蛋白A-金颗粒定位CaBP抗体，并使用Videoplan计算机系统对亚细胞区室进行定量。在胎盘内卵黄囊的脏层内胚层细胞中发现CaBP的高信号。在这些细胞中，指示CaBP位置的金颗粒出现在：1）细胞质基质，每平方微米平均金颗粒数为33；2）微绒毛（每平方微米17个）；3）线粒体（每平方微米17个）；4）细胞核（每平方微米43个）。相比之下，抗原吸收对照切片显示金颗粒很少：胞质溶胶，每平方微米2个；微绒毛，每平方微米5个；线粒体，每平方微米5个；细胞核，每平方微米4个。高尔基体和内质网的电子透明轮廓在对照中无颗粒，在染色切片中颗粒计数较低（每平方微米4个）。胎盘内卵黄囊的壁层内胚层细胞与脏层内胚层细胞相比，CaBP信号相对较低（每平方微米5个颗粒对39个）。（摘要截断于250字）
