Mef2c- and Nkx2-5-Divergent Transcriptional Regulation of Chick WT1_76127 and Mouse Gm14014 lncRNAs and Their Implication in Epicardial Cell Migration.

Cardiac development is a complex developmental process. The early cardiac straight tube is composed of an external myocardial layer and an internal endocardial lining. Soon after rightward looping, the embryonic heart becomes externally covered by a new epithelial lining, the embryonic epicardium. A subset of these embryonic epicardial cells migrate and colonize the embryonic myocardium, contributing to the formation of distinct cell types. In recent years, our understanding of the molecular mechanisms that govern proepicardium and embryonic epicardium formation has greatly increased. We have recently witnessed the discovery of a novel layer of complexity governing gene regulation with the discovery of non-coding RNAs. Our laboratory recently identified three distinct lncRNAs, adjacent to the , and chicken gene loci, with enhanced expression in the proepicardium that are distinctly regulated by Bmp, Fgf and thymosin β4, providing support for their plausible implication in epicardial formation. The expression of lncRNAs was analyzed in different chicken and mouse tissues as well as their subcellular distribution in chicken proepicardial, epicardial, ventricle explants and in different murine cardiac cell types. lncRNA transcriptional regulation was analyzed by using siRNAs and expression vectors of different transcription factors in chicken and mouse models, whereas antisense oligonucleotides were used to inhibit expression. Furthermore, RT-qPCR, immunocytochemistry, RNA pulldown, Western blot, viability and cell migration assays were conducted to investigate the biological functions of and . We demonstrated that in chicken and its putative conserved homologue in mice are widely distributed in different embryonic and adult tissues and distinctly regulated by cardiac-enriched transcription factors, particularly and . Furthermore, silencing assays demonstrated that mouse , but not chicken , is essential for epicardial, but not endocardial or myocardial, cell migration. Such processes are governed by partnering with Myl9, promoting cytoskeletal remodeling. Our data show that plays a pivotal role in epicardial cell migration essential for heart regeneration under these experimental conditions.