Characterization of naturally occurring myosin heavy chain antisense mRNA in rat heart.

Analysis of mRNA by Northern blot and reverse transcription-polymerase chain reaction demonstrated the expression of sense and considerable amounts of naturally occurring antisense mRNA for beta-myosin heavy chain (MHC) and alpha-MHC in the neonatal rat heart: antisense MHC mRNA expression of alpha-MHC and beta-MHC was approximately half of the corresponding sense MHC mRNA expression. Using a computational approach, we could identify a reverse Pol II promoter in the beta-MHC gene. Both sense and antisense MHC mRNA demonstrated similar sizes of approximately 6,000 bp in the Northern blot. Alpha-MHC antisense mRNA consisted of approximately 3,700 bp of complementary exon sequences and beta-MHC consisted of approximately 2,700 bp, suggesting a higher probability of alpha-MHC mRNA dimerization. Hence, sense mRNA transcripts and protein of alpha-MHC should exist at different relative levels in the neonatal state. In fact, the relative proportion of alpha-MHC was 52.0 +/- 2.6% on the sense mRNA but only 36.3 +/- 1.8% on the protein level. Because of its high abundance in the heart, we suggest that in the neonatal heart naturally occurring antisense mRNA may play a role in the regulation of MHC expression and, therefore, in the control of the energetical and contractile behaviour of the heart.