Whitman M M, Shen Y M, Soprano D, Soprano K J
Department of Microbiology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.
Cancer Res. 1990 Jun 1;50(11):3193-8.
Mouse F9 teratocarcinoma cell lines can be induced to differentiate into either parietal endoderm or embryoid bodies which contain visceral endoderm-like cells. The nature of the early molecular events involved in these two differentiation pathways has not yet been fully elucidated. Moreover, since the process of differentiation is often accompanied by changes in cell growth, it is often difficult to determine which of the events that do occur during the early stages of differentiation are a direct result of the process of differentiation and which events are indirect results that occur as a consequence of altered cell growth. In the experiments reported here we have attempted to distinguish between these two possibilities by examining the patterns of expression of a representative group of growth-associated genes (i.e., c-myc, p53, and histone H3) when F9 cell aggregates are induced to differentiate into embryoid bodies containing visceral endoderm. By analysis of the patterns of growth-associated gene expression in both retinoic acid treated and nontreated F9 cell aggregates, we were able to classify early events as differentiation-specific events (events which occurred only following retinoic acid treatment of aggregates) or nondifferentiation-specific events caused by reduction in cell growth (events which occurred even when aggregates were not treated with retinoic acid). Our results show that F9 cells differentiated into embryoid bodies containing visceral endoderm-like cell exhibit an early reduction in both growth and c-myc mRNAs which is neither retinoic acid-specific nor differentiation-specific. However, following this initial response to aggregation, constant levels of c-myc mRNA are maintained despite continued reduction in growth. Thus, it appears that alteration in c-myc expression is a differentiation-specific event along the pathway to formation of visceral endoderm. Interestingly, however, the nature and time course of this alteration in c-myc expression in F9 cells' differentiation into visceral endoderm is different from that observed in F9 cells differentiated into parietal endoderm.
小鼠F9畸胎瘤细胞系可被诱导分化为壁内胚层或含有内脏内胚层样细胞的胚状体。这两种分化途径中早期分子事件的本质尚未完全阐明。此外，由于分化过程常伴随着细胞生长的变化，因此通常很难确定在分化早期发生的哪些事件是分化过程的直接结果，哪些事件是细胞生长改变导致的间接结果。在本文报道的实验中，我们试图通过检测一组代表性的生长相关基因（即c-myc、p53和组蛋白H3）在F9细胞聚集体被诱导分化为含有内脏内胚层的胚状体时的表达模式，来区分这两种可能性。通过分析视黄酸处理和未处理的F9细胞聚集体中生长相关基因的表达模式，我们能够将早期事件分类为分化特异性事件（仅在视黄酸处理聚集体后发生的事件）或由细胞生长减少引起的非分化特异性事件（即使聚集体未用视黄酸处理也会发生的事件）。我们的结果表明，分化为含有内脏内胚层样细胞的胚状体的F9细胞，其生长和c-myc mRNA均早期降低，这既不是视黄酸特异性的，也不是分化特异性的。然而，在对聚集的初始反应之后，尽管生长持续减少，但c-myc mRNA仍维持恒定水平。因此，似乎c-myc表达的改变是内脏内胚层形成途径中的一个分化特异性事件。然而，有趣的是，F9细胞分化为内脏内胚层时c-myc表达改变的性质和时间进程与F9细胞分化为壁内胚层时观察到的不同。
