Mazariegos M R, Leblond C P, van der Rest M
Am J Anat. 1987 May;179(1):79-93. doi: 10.1002/aja.1001790110.
The biogenesis of basement-membrane components was investigated in the endodermal cells of the rat parietal yolk sac in 12.5-day pregnant rats; 3H-proline was injected into conceptuses. After various time intervals, the parietal yolk sac, including endodermal cells and the associated Reichert's membrane, was removed and processed for electron-microscopic radioautography. Silver grains were counted over endodermal cell organelles and Reichert's membrane. At 2 and 5 min after 3H-proline injection, endodermal cells showed heavy labeling in rough endoplasmic reticulum (rER). Silver grain density over the rER decreased from 2 to 20 min and then remained at a plateau. Grain density was moderate over the Golgi apparatus initially but rose to a peak at 2 hr and decreased by 4 hr and later. Grain density was negligible over secretory granules at 2 and 5 min and increased moderately with time to reach a maximum at 8 hr. Thus, radioautographic peaks occurred sequentially in rER, Golgi apparatus, and secretory granules. By 4 hr and later, silver grains accumulated over Reichert's membrane. These results indicated that endodermal cells incorporated labeled proline into substances which were processed from the rER through the Golgi apparatus, transported from there to the cell surface by secretory granules, and released for export to Reichert's membrane. To clarify the nature of the exported substances, the amount of label present in proline and hydroxyproline residues after 3H-proline injection was measured in Reichert's membrane with or without the associated endodermal cells. Within the cells, 61.8% of the labeled proteins were classified as "sedentary" and 38.2% as "exportable." Of the label exported to Reichert's membrane, 66.3% consisted of type IV collagen and the rest of other basement-membrane components. The results obtained with this model suggest that basement-membrane proteins, including type IV collagen, are elaborated by the associated cells through the classical pathway: rER-Golgi apparatus-secretory granules.
在怀孕12.5天的大鼠中，研究了大鼠壁层卵黄囊内胚层细胞中基底膜成分的生物合成；将3H-脯氨酸注射到胚胎中。在不同的时间间隔后，取出包括内胚层细胞和相关的赖歇特膜的壁层卵黄囊，并进行电子显微镜放射自显影处理。对内胚层细胞器和赖歇特膜上的银颗粒进行计数。在注射3H-脯氨酸后2分钟和5分钟，内胚层细胞的粗面内质网（rER）显示出强烈的标记。rER上的银颗粒密度在2至20分钟内下降，然后保持在一个平台期。高尔基体上的颗粒密度最初适中，但在2小时时升至峰值，4小时及以后下降。在2分钟和5分钟时，分泌颗粒上的颗粒密度可忽略不计，随时间适度增加，在8小时时达到最大值。因此，放射自显影峰值依次出现在rER、高尔基体和分泌颗粒中。到4小时及以后，银颗粒在赖歇特膜上积累。这些结果表明，内胚层细胞将标记的脯氨酸掺入从rER经高尔基体加工、通过分泌颗粒从那里运输到细胞表面并释放以输出到赖歇特膜的物质中。为了阐明输出物质的性质，在有或没有相关内胚层细胞的情况下，测量了赖歇特膜中注射3H-脯氨酸后脯氨酸和羟脯氨酸残基中存在的标记量。在细胞内，61.8%的标记蛋白被归类为“固定”蛋白，38.2%为“可输出”蛋白。输出到赖歇特膜的标记物中，66.3%由IV型胶原组成，其余为其他基底膜成分。用该模型获得的结果表明，包括IV型胶原在内的基底膜蛋白是由相关细胞通过经典途径：rER-高尔基体-分泌颗粒合成的。
