miR-1/133a Clusters Cooperatively Specify the Cardiomyogenic Lineage by Adjustment of Myocardin Levels during Embryonic Heart Development

Abstract

miRNAs are small RNAs directing many developmental processes by posttranscriptional regulation of protein-coding genes. We uncovered a new role for miR-1-1/133a-2 and miR-1-2/133a-1 clusters in the specification of embryonic cardiomyocytes allowing transition from an immature state characterized by expression of smooth muscle (SM) genes to a more mature fetal phenotype. Concomitant knockout of miR-1-1/133a-2 and miR-1-2/133a-1 released suppression of the transcriptional co-activator myocardin, a major regulator of SM gene expression, but not of its binding partner SRF. Overexpression of myocardin in the embryonic heart essentially recapitulated the miR-1/133a mutant phenotype at the molecular level, arresting embryonic cardiomyocytes in an immature state. Interestingly, the majority of postulated miR-1/133a targets was not altered in double mutant mice, indicating that the ability of miR-1/133a to suppress target molecules strongly depends on the cellular context. Finally, we show that myocardin positively regulates expression of miR-1/133a, thus constituting a negative feedback loop that is essential for early cardiac development.

Genetic Networks Governing Heart Development

“…These phenotypes are remarkably mild compared with cardiac knockout phenotypes of kernel or hub genes, and are consistent with studies showing a more prominent role for miRNA networks in the development of cardiomyocyte maturity, growth, function, and physiology (Porrello 2013). Indeed, a number of knockouts in genes for individual miRNA or paralogous clusters have led to mild, partially penetrant, or no detectable phenotypes (Zhao et al 2007;Porrello 2013;Wystub et al 2013). Notwithstanding the intricate networks regulated by specific miRNA families in cardiac tissue (van Rooij et al 2009;Qian et al 2011), because they act predominantly at a level of the GRN below cis-regulatory architecture, their major function is likely to confer robustness to network output.…”

ROS-mediated bidirectional regulation of miRNA results in distinct pathologic heart conditions

“…However, a very recent study reported that miR-1 regulates myocardin expression, suggesting the mutual regulation of these two molecules [23]. Our data clearly demonstrated that myocardin is regulated by miR-1 during hypertrophy and apoptosis.…”

Disruption of spatiotemporal hypoxic signaling causes congenital heart disease in mice

“…), E8.0 (5 pairs of somites) and E9.0 (14 pairs of somites) embryos or individual embryonic hearts from E15.5 embryos were dissected and dissociated into single cells as described previously (55). ISL1 + or NKX2.5 + CPCs were isolated from embryoid bodies (EB) by treatment with 0.05% trypsin/EDTA for 3 minutes at 37°C.…”