There is growing evidence that mitochondria, recognized as the energy powerhouse of eukaryotic cells, also fulfill other essential roles beyond supplying the cell with most of the ATP. Mitochondria play an active role in apoptosis, intracellular calcium homeostasis, regulation of innate immunity, amino acid metabolism and stem cell regulation, among others. The human and domestic mammalian mitochondrial genome (mtDNA) encodes 2 rRNAs (16S and 12S), 22 tRNAs and 13 polypeptides involved in oxidative phosphorylation. There is already ample evidence that the mitochondrial genome contains long non-coding RNAs and micrRNAs. However, the function of these ncRNAs and their mode of operation are just beginning to be discovered. Proteomic assessments have identified over 1500 proteins present in mitochondria. The majority of mitochondrial proteins are products of nuclear genes and are synthesized in the cytosol and then transported into the mitochondria. More and more studies have shown a bidirectional communication between mitochondria and the nucleus, coordinating multiple cellular functions. Nevertheless, this connection is not limited to the mitochondrial import of proteins encoded by the nucleus and the export of metabolites, but involves other processes, including non-coding RNAs involved in this inter-organism communication.

Since the identification of microRNAs in the mitochondrial compartment in 2009-2011, publications on this topic have greatly increased. Most of these studies provide new information on how these ncRNAs within mitochondria modify cellular function. For the first time, bringing together all the experts studying mitochondria-associated lncRNAs in a single issue will be extremely useful in educating the scientific community. Recent advances in RNA sequencing technology have prompted new investigators to begin studying mitochondrial lncRNAs. Therefore, there is a great need for basic information and standardized guidelines, such as standardization controls and mitochondrial isolation procedures, to conduct rigorous research in this area. By bringing together all the experts exploring mitochondrial ncRNAs, we believe we can produce a comprehensive report for the entire community, including areas that require further research and validation.

Communication between the nucleus and other cellular organelles, such as the mitochondrion, is critically mediated by a myriad of long and small non-coding RNAs, which are receiving increasing attention. Dissecting the multiple aspects of this process will shed light on the pathways involved in the mechanisms underlying the normal and pathological involvement of non-coding RNAs in communication between mitochondria and other organelles, particularly the nucleus. Further knowledge of these cellular events will lay the foundation for the development of potential therapeutic strategies for various human pathologies.

Contact:

• Eric Barrey (eric.barrey@inrae.fr)