Chromatin Remodeling Complex Dosage Modulates Transcription Factor Function in Heart Development

Dominant mutations in cardiac transcription factor genes cause human inherited congenital heart defects (CHDs), but their molecular basis is not understood. Transcription factors and Brg1/Brm-associated factor (BAF) chromatin remodeling complex interactions suggest potential mechanisms, but the role of BAF complexes in cardiogenesis is not known. Here we show that dosage of Brg1 is critical for mouse and zebrafish cardiogenesis. Disrupting the balance between Brg1 and disease-causing cardiac transcription factors, including Tbx5, Tbx20, and Nkx2-5, causes severe cardiac anomalies, revealing an essential allelic balance between Brg1 and these cardiac transcription factor genes. This suggests that relative levels of transcription factors and BAF complexes are important for heart development, which is supported by reduced occupancy of Brg1 at cardiac genes in Tbx5 haploinsufficient hearts. Our results reveal complex dosage-sensitive interdependence between transcription factors and BAF complexes, providing a potential mechanism underlying transcription factor haploinsufficiency, with implications for multigenic inheritance of CHDs. We performed transcriptional profiling of E11.5 hearts from mice heterozygous for deletions of Brg1, Tbx5, or Nkx2-5, and mice that were compound heterozygotes for Brg1 and each transcription factor gene (Tbx5 and Nkx2-5).心脏转录因子基因的显性突变可导致人类遗传性先天性心脏缺陷（congenital heart defects, CHDs），但其分子机制尚未明确。转录因子与Brg1/Brm相关因子（BAF）染色质重塑复合物的相互作用提示了潜在致病机制，但BAF复合物在心脏发生中的作用仍未阐明。本研究证实，Brg1的剂量水平对小鼠和斑马鱼的心脏发生至关重要。破坏Brg1与致病心脏转录因子（包括Tbx5、Tbx20及Nkx2-5）之间的剂量平衡，会引发严重的心脏畸形，这揭示了Brg1与这些心脏转录因子基因之间存在必需的等位基因平衡关系。该结果表明，转录因子与BAF复合物的相对丰度对心脏发育具有关键作用，这一结论得到了Tbx5单倍体不足（haploinsufficient）小鼠心脏中，Brg1在心脏相关基因上的结合占有率降低现象的支持。我们的研究结果揭示了转录因子与BAF复合物之间存在复杂的剂量敏感型相互依赖关系，为转录因子单倍体不足的潜在分子机制提供了新的解释，并对先天性心脏缺陷的多基因遗传模式具有重要启示意义。本研究对Brg1、Tbx5或Nkx2-5缺失杂合子小鼠，以及Brg1与各转录因子基因（Tbx5和Nkx2-5）复合杂合子小鼠的胚胎发育第11.5天（E11.5）的心脏组织进行了转录谱分析。