EXPRESSION OF RETINOIC ACID NUCLEAR RECEPTORS IN THE MOUSE EMBRYONAL CARCINOMA CELL-LINE PCC7-MZ1

Mouse embryonal carcinoma cell line PCC7-Mz1 can serve as a model of mammalian neural development [1989, J. Cell. Biol. 109, 2481-2493]. Upon exposure to all-trans retinoic acid (RA), Mz1 cells differentiate into a stable pattern of neurons, astroglia and fibroblasts whereas variants of the parental cell line either are restricted in their patterns of derivatives or do not respond at all to RA. Using gene probes specific for the alpha1, alpha2 and beta2 isoforms of the retinoic acid nuclear receptor, we have studied by Northern blot analysis the expression of these transcription factors in uninduced and induced cells of clone Mz1 and in variants with different developmental potential. Alpha1-RAR is expressed constitutively in all variants independent of whether RA is present or not. Soon after addition of 10(-7) M RA, alpha2-RAR is induced in RA-responsive cells reaching within a few hours a plateau level that remains unchanged throughout the developmental process. In contrast, the beta2 isoform is expressed only transiently after RA-induction despite the continuous presence of RA. Other RAR isoforms are expressed only in trace amounts