Formation of fetal rat cardiac cell clones by retroviral transformation: retention of select myocyte characteristics.

Ventricular myocyte (cardiomyocyte) growth is exquisitely regulated such that embryonic and fetal development are the primary periods of active cellular division. This report describes formation of three separate cardiomyocyte cell clones obtained by replication-defective retroviral (v/myc and v-H-ras) transformation of primary cultures of day-16 fetal rat cardiomyocytes. The cell clones do not spontaneously contract, yet they express several cardiac-specific (cardiac troponin-C, alpha-cardiac actin) and associated genes (Connexin 43, Early growth response gene-1) with stable expression of several genes determined through the 28th passage. None of these cell clones express skeletal muscle actin or the skeletal muscle regulatory gene MyoD1; yet all display ultrastructural and biochemical evidence of their cardiac muscle lineage. Molecular and biochemical studies of cardiac-specific gene regulation can be anticipated from the cell clones as it pertains to nuclear transcription factors and transient CAT-based reporter gene constructs. The formation of these cell clones will enable further studies of growth and development of this unique muscle cell population of the cardiovascular system to be performed at the cellular and molecular level.