Muscle-specific gene expression in differentiated embryonal carcinoma cells.

A chimeric gene consisting of the human cardiac actin promoter linked to the lac Z reporter gene encoding $\beta$-galactosidase ($\beta$-gal), was permanently transfected into P19 cells. Differentiation of these cultures into cardiac muscle resulted in high levels of $\beta$-gal activity, while differentiation along the neuroectodermal lineage did not lead to any increase in the expression of the actin-lacZ chimeric gene. The transcription of various muscle-specific genes can be activated in different nonmuscle cell lines by the expression of MyoD, a regulatory factor of skeletal myo-genesis. MyoD activates muscle-specific genes in cooperation with other factors which interact directly or indirectly at the various cis-acting regulatory sequences of the target gene. The role of MyoD in muscle differentiation was investigated in permanent transfections of P19 cells with the MyoD expression vector. MyoD transcripts were absent during the de novo differentiation of P19 cells into cardiac muscle. The myogenic differentiation program seems to be controlled by complex interactions among multiple upstream regulatory elements and myogenic factors that are functional only in the appropriate cellular context. (Abstract shortened by UMI.