Distinct mechanisms regulate ventricular and atrial chamber wall formation.

Area of Science:

• Cardiovascular biology
• Developmental biology
• Cellular morphogenesis

Background:

• The heart's internal muscle structures are crucial for efficient contraction.
• Ventricular wall formation (trabeculation) involves cardiomyocyte delamination.
• Mechanisms of atrial wall formation remain poorly understood.

Purpose of the Study:

• To investigate the cellular and molecular mechanisms underlying atrial wall formation in zebrafish.
• To compare atrial muscle network formation with known ventricular trabeculation processes.

Main Methods:

• Longitudinal in vivo imaging of zebrafish embryos.
• Analysis of cardiomyocyte shape changes and tissue thickening.
• Investigated roles of Nrg/ErbB, Notch, and Yap signaling pathways.

Main Results:

• Observed that approximately 25% of atrial cardiomyocytes elongate along the heart's long axis.
• Elongation leads to cell intercalation and convergent thickening, forming the atrial muscle network.
• Found no evidence for Nrg/ErbB or Notch signaling in atrial muscle formation.
• Identified Yap signaling as a potential regulator of atrial cardiomyocyte elongation.

Conclusions:

• Atrial and ventricular internal muscle structures are built by distinct cellular and molecular mechanisms.
• Atrial muscle network formation relies on cardiomyocyte elongation and intercalation, regulated by Yap.
• This study reveals novel insights into cardiac morphogenesis and highlights pathway divergence between heart chambers.