Function of Vitamin A in Cell Differentiation and Morphogenesis

类维生素a一直被认为是一种必需营养素，但其功能的分子机制尚未完全了解。类维生素a是控制细胞分化的有效药物。例如，视黄酸（RA）局部应用于鸡肢芽，模拟了极化区的功能。然而，缺乏适当的实验系统，阻碍了在分子水平上进一步分析。在许多胚胎癌细胞系中，F9是特殊的，因为它的分化只有在RA治疗后才会被触发。当暴露于二丁基cAMP时，ra引发的F9细胞分化为壁内胚层样细胞，当允许聚集时，分化为内脏内胚层样细胞。本研究以F9细胞为模型系统，分析类视网膜细胞在细胞分化中的功能。我们之前的研究表明，依赖于二丁基cAMP的存在，ra引发的细胞向顶壁内胚层样细胞的分化是可逆的。从不同处理的F9细胞中提取的RNA与从细胞库中筛选的6个cDNA克隆进行北杂交，进一步证实了这种可逆性。这些克隆中包括一个编码层粘连蛋白b mRNA的克隆。F9细胞的分化，通过基底膜蛋白的分泌来监测，是双相的，这取决于使用的RA剂量。层粘连蛋白a的分泌在10 nM处达到平台，超过100 nM时再次增加。这种双相分化模式在很长一段时间内是稳定的，但加入1mm二丁基cAMP后，它就变成了单相分化。在sppiner瓶中培养1-50个ra诱导的F9细胞，在parcoll密度梯度上分离F9聚集体，发现只有直径大于0.18 mm的聚集体发育成胚状体并分泌a-胎蛋白（AFP）。这种大小与卵筒的大小相当，当它们第一次发育产生afp的内胚层时。这表明当核心细胞群的大小超过临界阈值时，内脏内胚层成熟被触发。少

Retinoids have long been recognized as an essential nutrient, but the molecular mechanism of their functions has not been fully understood. Retinoids are potent agents controlling cellular differentiation. The local application of retinoic acid (RA) to chick limb bud, for example, mimics the function of polarizing region. Lack of appropriate experimental system, however, had hindered further analysis at molecular level. Of many embryonal carcinoma cell lines, F9 is special since its differentiation is triggered only after treating with RA. RA-primed F9 cells differentiate into parietal endoderm-like cells when exposed to dibutyryl cAMP, and into visceral endoderm-like cells when allowed to aggregate. In this study, functions of retioids in cell differentiation were analyzed with F9 cells as a model system.We previously showed that the differentiation of RA-primed cells into parietal endoderm-like cells is reversible dependind on the presence of dibutyryl cAMP. The reversibility was fur … More ther confimed by northern hybridizarion of RNA exracted from variously treated F9 cells with 6 cDNA clones screened from libraly of parietal endoderm-like F9 cells. Among these clones, a clone coding laminin b mRNA was included. The differntiation of F9 cells, as monitored by the secretion of basement membrane proteins, was biphasic depending on the dose of RA used. Secretion of laminin a reached a plateau at 10 nM and increased again at more than 100 nM RA. This biphasic pattern of differentiation was stable for a long period of time but the addition of 1 mM dibutyryl cAMP changed it to monophasic. Fractionation of F9 aggregates, grown by culturing clumps of 1-50 RA-primed F9 cells in a sppiner bottle , on parcoll density gradients revealed that only aggregates with diameter larger than 0.18 mm developed embryoid dodies and secreted a-fetoprotein(AFP). This size is comparable to that of egg cylinders when they first develop AFP-producing vieceral endoderm. This suggests that visceral endoderm maturation is triggered when the size of core cell mass exceeds a critical threshold. Less