The non-coding side of cardiac differentiation and regeneration.

Large scale projects such as FANTOM and ENCODE, led to a revolution in our comprehension of the mammalian transcriptomes by revealing that ~53% of the produced RNAs do not encode for proteins. These transcripts, defined as noncoding RNAs (ncRNAs), constitute a heterogeneous group of molecules which can be categorized in two main classes, namely small and long, according to their length. In animals, the first class includes Piwi-interacting RNAs (piRNAs), small interfering RNAs (siRNAs) and microRNAs (miRNAs). Among them, the best characterized subgroup is represented by miRNAs, which are known to regulate gene expression largely at the post-transcriptional level. In contrast, long noncoding RNAs (lncRNAs) represent a more heterogeneous group of > 200 nucleotides long transcripts, that act through a variety of mechanisms at both transcriptional and post-transcriptional level. Here we discuss how miRNAs and lncRNAs are emerging as pivotal regulators of cardiac muscle development and how the alteration of ncRNA expression was seen to disturb the physiology of all the different cell types forming the cardiac tissue. Particular emphasis is given to those species that are expressed and are known to regulate the capacity of cardiac progenitor cells (CPCs), currently used in regenerative medicine protocols, to proliferate and differentiate. Understanding how the ncRNA-mediated circuitries regulate heart homeostasis is one of the research areas expected to have a high impact, improving the therapeutic efficacy of stem/progenitor-cells treatments for translation into clinical applications.