RNA-Binding Protein Trim71 Controls Epicardial Cell Migration

The epicardium is an embryonic tissue layer essential for heart morphogenesis, providing progenitor cells and regulatory signals that support myocardial growth and coronary vessel formation. Epicardial cells arise from the proepicardium (PE) and spread over the myocardium to form the embryonic epicardium (EE), a transition that requires tight coordination between proliferation, migration, and lineage priming. However, the molecular mechanisms controlling this developmental timing remain incompletely understood. Here, we identify Trim71 as a key regulator of epicardial cell behaviour during the PE-to-EE transition. Trim71 is enriched in the PE and subsequently downregulated as cells acquire migratory competence. Functional analyses show that loss of Trim71 function decreases proliferation while promoting migration, as well as inducing the expression of epicardial commitment markers, suggesting that Trim71 is a controller of a progenitor-like state. We further demonstrate that Trim71 is necessary for these processes through a reciprocal feedback loop with the microRNAs let-7c and miR-30c. Our findings establish Trim71 as a temporal gatekeeper that coordinates the balance between progenitor maintenance and migration during early epicardial development. This Trim71-miRNAs axis constitutes a novel post-transcriptional layer of regulation that ensures the correct timing of epicardium development during cardiogenesis.