Yin Yang 1 (YY1) is a transcription factor that can activate or repress expression of a variety of genes and is involved in several developmental processes. While some transcription factors are known to modulate skeletal myogenesis, the regulation of fetal troponin I (ssTnI) expression by YY1 in cardiac development has not been studied. The present study shows that the fetal troponin I gene expression in neonatal myocardium was reduced by overexpression of YY1, while cardiac troponin I (cTnI) did not show any significant decrease. And a dose-response inhibition by YY1 was observed in fetal troponin I promoter induced transcriptional activities. Mutation of YY1-binding site can abolish the inhibitory effect and YY1 silencing in neonatal myocardium resulted in an increase of ssTnI protein expression. Our results indicate that YY1 is a novel regulator of fetal TnI transcription in the heart. (C) 2008 Elsevier Inc. All rights reserved.