Cardiac troponin I sense-antisense RNA duplexes in the myocardium

Natural antisense RNA is now thought to regulate, at least in part, a growing number of eukaryotic genes. It is becoming increasingly apparent that such endogenous antisense RNA molecules may modulate gene expression in a manner analogous to synthetic oligomers. Here, we report the detection of antisense-orientated RNA transcripts of cardiac specific troponin I in rat and human myocardium. Interestingly, the different sizes of the rat and human antisense cTNI transcripts suggest species-specific reverse transcription initiation sites. Moreover, for the first time in cardiomyocytes, we could demonstrate in vivo duplex formation between sense and antisense transcripts. The existence of antisense-sense duplexes represents compelling evidence and a potential mechanism for endogenous antisense transcript-mediated modulation of mRNA translation. The potential effect of attenuating translation was illustrated by in vitro and in vivo model systems. Testing several oligonucleotides based on the natural antisense sequences, the optimal region for inhibition of translation was identified as being close to the translational start codon.