Detection of variable levels of RARα and RARγ proteins in pluripotent and differentiating mouse embryonal carcinoma and mouse embryonic stem cells.

Pluripotent mouse embryonal carcinoma (mEC) and mouse embryonic stem (mES) cells differentiate into several cell lineages upon retinoic acid (RA) addition. Differentiation is facilitated, in part, by RA activation of nuclear RA receptors (RARs) that bind to DNA response elements located in the promoters of target genes. The purpose of the studies reported here was to immunolocalize RARα and RARγ protein in mEC and mES cells and in their RA-induced differentiated progeny. Fixed cells were reacted with three different RARα antibodies and one RARγ antibody. Pluripotent and differentiated mEC and mES cells showed positive nuclear immunoreactivity with all antibodies tested. Two RARα antibodies also showed positive reactivity in the cytoplasm. Surprisingly, our results revealed variability in immunofluorescence intensity and in RARα and RARγ distribution from one cell to the other, suggesting that RARα and RARγ protein levels were not synchronous throughout the cell population. The results indicate that RARα and RARγ are present in pluripotent and differentiating mEC and mES cells and suggest that the expression of these proteins is dynamic.