CHROMATIN STRUCTURE AND THE EXPRESSION OF CARDIAC GENES

Actively transcribed genes are more susceptible to nuclease digestion, an observation suggested to reflect an altered state of chromatin org anization. It has been hypothesized that exposure or sequestration of chromatin domains is a higher order gene regulatory mechanism. In orde r to test whether tissue lineage is organized by mechanisms at the lev el or chromatin structure, three cardiac phenotype-conferring genes (a trial natriuretic factor, myosin light chain-1-ventricular and alpha-t ropomyosin) have been assessed for DNase 1 sensitivity in nuclei prepa red from tissues of the developing guinea pig. These data have been re lated to the level of tissue mRNA expression of these genes to ascerta in whether the exposed state of genes can occur when transcription is low or undetectable. Although this phenomenon was evident in some case s, the data were not consistent with mechanisms at the level of chroma tin structure directing tissue type.