Abstract 15172: Pou6f1 Regulates Bmp4 Expression to Orchestrate Atrioventricular Canal Development
Introduction: A critical step during cardiac morphogenesis involves partitioning of atrial and ventricular chamber myocardium from non-chamber myocardium of the atrioventricular canal (AVC). Identification of numerous congenital heart defects (CHD) resulting from malformation of AVC-derived structures (i.e. valves, septum, and AV node) underscores the importance of proper AVC patterning. Communication between myocardial and endocardial cells through sequential Notch-Wnt-BMP signaling directs AVC formation, culminating in Smad-dependent activation of Tbx2 expression to inhibit chamber-specific genes and reinforce AVC myocyte identity. Although the AVC developmental hierarchy has been extensively characterized, the precise mechanism by which BMP signaling is activated to pattern the AVC remains to be elucidated.
Hypothesis: We directly tested the hypothesis that pou6f1 impacts an early step during AVC formation.
Methods: To test our hypothesis, we carried out morpholino-based knockdown experiments in zebrafish, which possess a single highly-conserved POU6F1 ortholog.
Results: Pou6f1 morphant embryos display severe cardiovascular defects, including improper AVC morphogenesis, pericardial edema, bradycardia, and impaired contractility. Importantly, pou6f1 morpholino treatment can be partially rescued by morpholino-resistant pou6f1 mRNA. Furthermore, molecular phenotyping of pou6f1 morphant embryos revealed a reduction in the AVC myocardial markers bmp4 and versican, while notch1b, a marker of AVC endocardium, is not affected. Finally, markers of atrial (amhc) and ventricular (vmhc) specification are unchanged, while anf is ectopically expressed in the AV junction of pou6f1 morphant embryos.
Conclusions: Our results demonstrate that pou6f1 regulates an early step during AVC patterning by activating myocardial bmp4 expression. Consistent with this finding, pou6f1 impacts transcriptional events downstream of bmp4, including tbx2b-dependent inhibition of anf expression within the AVC. In conclusion, our experiments support an essential role for pou6f1 in AVC morphogenesis and identify POU6F1 as a potential candidate susceptibility gene for CHD patients with AVC defects of unknown genetic etiology.
- © 2013 by American Heart Association, Inc.