| Abstract: | When aggregates of HM-1 embryonal carcinoma (EC) cells were exposed to 10(-6) M retinoic acid for 2 days and cultured in medium lacking retinoic acid, they differentiated to nerve cells, endoderm cells, and myoblasts. Cells 2 days after initial exposure to retinoic acid were not significantly different from the parental EC cells, as judged by cell-surface architecture and by reactivity to lectins. On the fourth day, the surface of the aggregates was covered with two kinds of cells distinguishable from the parental cells. The round cells with short villi seemed to be precursors to endoderm cells. Receptors for Dolichos biflorus agglutinin (DBA) newly appeared and receptors for peanut agglutinin (PNA) were still expressed on their surfaces. The other cells, which were round cells with a few processes, might be precursors to nerve cells. PNA receptors had disappeared from their surfaces, and DBA receptors were not expressed. On the sixth day of differentiation, possible precursors to myoblasts were detected; they were flat cells with smooth surfaces. These cells lacked cell-surface receptors for the two lectins, while the precursor cells and the myoblasts excreted intercellular fibers reacting with PNA. HM-1 cells synthesized much embryoglycan, the structure of which was similar to that of the glycan isolated from quasinullipotent F9 cells. The only difference was that the glycan from HM-1 cells lacked DBA binding sites. Synthesis of fucosylated embryoglycan mainly decreased between the second and fourth day of differentiation. As above, cell-surface changes occurred mainly between the second and fourth day. The period seems to be important in determining the fate of the cells, since endoderm cells were scarcely seen among differentiated cells which had been continuously exposed to 10(-6) M retinoic acid during the period. |
