The key information processing units within gene regulatory networks are enhancers. Enhancer activity is
associated with the production of tissue-specific non coding RNAs, yet the existence of such transcripts during
cardiac development has not been established. Using an integrated genomic approach, we demonstrate that
fetal cardiac enhancers generate long noncoding RNAs (lncRNAs) during cardiac differentiation and morphogenesis.
Enhancer expression correlates with the emergence of active enhancer chromatin states, the initiation
of RNA polymerase II at enhancer loci and expression of target genes. Orthologous human sequences are also
transcribed in fetal human hearts and cardiac progenitor cells. Through a systematic bioinformatic analysis,
we identified and characterized, for the first time, a catalog of lncRNAs that are expressed during embryonic
stem cell differentiation into cardiomyocytes and associated with active cardiac enhancer sequences.
RNA sequencing demonstrates that many of these transcripts are polyadenylated, multiexonic long noncoding
RNAs. Moreover, knockdown of two enhancer-associated lncRNAs resulted in the specific downregulation of
their predicted target genes. Interestingly, the reactivation of the fetal gene program, a hallmark of the stress
response in the adult heart, is accompanied by increased expression of fetal cardiac enhancer transcripts. Altogether,
these findings demonstrate that the activity of cardiac enhancers and expression of their target genes
are associated with the production of enhancer derived lncRNAs.