Myocardin regulates BMP10 expression and is required for heart development.

Area of Science:

• Cardiovascular Biology
• Developmental Biology
• Molecular Genetics

Background:

• Myocardin is a key transcriptional coactivator essential for smooth muscle cell differentiation.
• Extracellular signals are transduced by myocardin to the nucleus, influencing cell fate.
• The role of myocardin in cardiac development and its interaction with signaling pathways remained largely unexplored.

Purpose of the Study:

• To investigate the role of myocardin in embryonic cardiac development.
• To identify novel signaling pathways involving myocardin in heart formation.
• To elucidate the molecular mechanisms by which myocardin regulates cardiomyocyte proliferation and survival.

Main Methods:

• Generation and analysis of Myocardin-null (Myocd) mouse embryos.
• Analysis of embryos with cardiomyocyte-restricted Myocd mutations.
• Ex vivo culture of embryonic hearts in BMP10-conditioned medium.
• Gene expression analysis of cardiac transcription factors and cell cycle regulators.

Main Results:

• Myocardin deficiency leads to embryonic lethality due to myocardial hypoplasia and defective chamber maturation.
• Myocardin-null hearts exhibit reduced cardiomyocyte proliferation and increased apoptosis.
• A novel myocardin/BMP10 signaling pathway was identified, where myocardin directly transactivates the Bmp10 gene.
• BMP10 signaling blockade in Myocd-/- hearts results in repressed cardiogenic transcription factors and induced p57kip2.
• Ex vivo BMP10 treatment rescued cardiomyocyte proliferation defects in Myocd-/- hearts.

Conclusions:

• Myocardin is essential for embryonic cardiac growth, chamber maturation, and survival through the novel BMP10 signaling pathway.
• This pathway regulates cardiomyocyte proliferation and apoptosis, critical for heart development.
• Myocardin acts by transactivating Bmp10, influencing downstream targets like NKX2.5, MEF2c, and p57kip2.