Nucleolus-like bodies in embryonal carcinoma cells of the embryoid bodies isolated from mouse teratocarcinoma.

Undifferentiated embryonal carcinoma cells (EC cells) in the embryoid bodies isolated from mouse teratocarcinoma contained nucleolus-like bodies (NLBs) of smaller sizes in their cytoplasm (their sectional area averaged about 0.036 micrometers2). At the onset of EC cell differentiation, the average sectional area of NLBs significantly increased (about 0.107 micrometers2). When EC cells had differentiated into mesenchymal cells and endothelial cells of primitive blood vessels, NLBs decreased dramatically both in size and number. The possible role of NLBs in the differentiation process of EC cells is discussed.