Messenger RNA content and complexity in normal and overloaded rat heart: a preliminary report

Cardiac overload is associated with two different changes in gene expression: an increase in overall protein synthesis leading to hypertrophy, and at least two isoenzymic redistributions affecting myosin and creatine kinase. This preliminary report was an attempt to study the cardiac genome in this model. Total RNA (ribonucleic acid) was prepared by a combination of the guanidine-ethanol and phenol procedures. A DNA (deoxyribonucleic acid)-, t(transfer)-RNA-free preparation containing non-degraded 28 and 18 S rRNA and 3% poly A+-m (messenger) RNA was obtained. The poly A+mRNA isolated on an oligo (dT) cellulose column had an average nucleotide length of 1300 to 1800 and its c (complementary) DNA was 600 to 1400 base pairs. The first analysis of the kinetics of hybridation revealed a complex pattern which could be described by division into three components. Northern blot and dot blot using a recombinant cDNA plasmid complementary to myosin heavy chain or to actin mRNA (a gift from A. Weydert and M. Buckingham) indicated the presence of these two mRNA, with the former being frequently degraded. After aortic stenosis, both the content and the concentration of total RNA and poly A+mRNA increased in parallel and peaked by the 4th day at +35%. This is the first suggestion that the control of gene expression is transcriptional in this model.