polr2i is Required for Zebrafish Early Cardiac Development

Area of Science:

• Genetics
• Developmental Biology
• Cardiovascular Research

Background:

• Congenital heart disease (CHD) is a common birth defect with significant genetic contributions.
• The RNA polymerase II subunit I (POLR2I) protein was previously identified as a potential genetic factor in CHD.
• The precise functional role of POLR2I in CHD pathogenesis remained largely uncharacterized.

Purpose of the Study:

• To investigate the functional role of the RNA polymerase II subunit I (POLR2I) gene in congenital heart disease (CHD).
• To elucidate the impact of POLR2I on cardiac development, function, and organ asymmetry in a zebrafish model.

Main Methods:

• Bioinformatic analysis of POLR2I evolutionary conservation across vertebrates.
• Quantitative real-time PCR (qRT-PCR) to assess polr2i gene expression patterns.
• Morpholino oligonucleotide (MO)-mediated knockdown of polr2i in zebrafish embryos.
• Rescue experiments using co-injected mRNA to confirm gene specificity.
• Analysis of cardiac and vascular development, mitochondrial quality, and organ asymmetry using transgenic zebrafish and histological staining.

Main Results:

• POLR2I knockdown resulted in severe developmental defects, including reduced body size, axial curvature, and increased mortality.
• Zebrafish embryos with reduced POLR2I exhibited cardiac malformations such as elongated heart tubes, pericardial edema, and impaired cardiac function (reduced stroke volume and cardiac output).
• Disruption of POLR2I led to defects in angiogenesis, myocardial mitochondrial quality, and left-right asymmetry in multiple organs (heart, liver, pancreas).

Conclusions:

• The RNA polymerase II subunit I (POLR2I) gene plays a critical role in maintaining cardiac structure and function during embryonic development.
• POLR2I is essential for establishing normal left-right asymmetry in multiple organs.
• These findings highlight POLR2I as a significant contributor to CHD pathogenesis and a potential therapeutic target.