Essential but partially redundant roles for POU4F1/Brn-3a and POU4F2/Brn-3b transcription factors in the developing...

Area of Science:

• Developmental biology
• Molecular genetics
• Cardiovascular research

Background:

• Congenital heart defects (CHDs) are a leading cause of embryonic and neonatal mortality.
• The intricate molecular mechanisms governing cardiac development remain incompletely understood.
• Transcription factors play critical roles in orchestrating developmental processes.

Purpose of the Study:

• To investigate the roles of transcription factors Brn-3a (POU4F1) and Brn-3b (POU4F2) in cardiac development.
• To elucidate the molecular interactions between Brn-3a and Brn-3b during heart formation.
• To understand the contribution of these factors to CHDs.

Main Methods:

• Generation and analysis of Brn-3a knockout (KO) mouse models.
• Assessment of gene expression (mRNA levels) and protein targets (cyclin D1, Bax).
• Utilized zebrafish (ZF) models with morpholino-targeted knockdown of Brn-3a and Brn-3b to study conserved functions.

Main Results:

• Brn-3a represses Brn-3b promoter activity in cardiomyocytes.
• Brn-3a KO mutants exhibit increased Brn-3b mRNA, elevated cyclin D1, and hyperplastic growth.
• During late gestation, Brn-3b cooperates with p53 to induce apoptosis (Bax), leading to cardiac malformations and lethality.
• Double KO mutants (Brn-3a-/- : Brn-3b-/-) show early embryonic lethality, indicating essential redundant roles.
• Zebrafish double morphants display significant cardiac defects, including looping and valve abnormalities.

Conclusions:

• Brn-3a and Brn-3b are essential for normal mammalian and zebrafish cardiac development.
• Their antagonistic and cooperative interactions regulate cardiomyocyte proliferation and apoptosis.
• Dysregulation of Brn-3a/Brn-3b pathways contributes to congenital heart defects and embryonic lethality.
• These TFs represent potential targets for understanding and potentially treating CHDs.