Department of Molecular Physiology, National Cerebral and Cardiovascular Center Research Institute, Suita, Osaka, Japan.
Department of Cell Physiology, The Jikei University School of Medicine, Minato-ku, Tokyo, Japan.
Dev Growth Differ. 2021 Jan;63(1):82-92. doi: 10.1111/dgd.12707. Epub 2021 Jan 27.
A basic helix-loop-helix transcription factor Hey2 is expressed in the ventricular myocardium and endocardium of mouse embryos, and Hey2 null mice die perinatally showing ventricular septal defect, dysplastic tricuspid valve and hypoplastic right ventricle. In order to understand region-specific roles of Hey2 during cardiac morphogenesis, we generated Hey2 conditional knockout (cKO) mice using Mef2c-AHF-Cre, which was active in the anterior part of the second heart field and the right ventricle and outflow tract of the heart. Hey2 cKO neonates reproduced three anomalies commonly observed in Hey2 null mice. An earliest morphological defect was the lack of right ventricular extension along the apico-basal axis at midgestational stages. Underdevelopment of the right ventricle was present in all cKO neonates including those without apparent atresia of right-sided atrioventricular connection. RNA sequencing analysis of cKO embryos identified that the gene expression of a non-chamber T-box factor Tbx2 was ectopically induced in the chamber myocardium of the right ventricle. Consistently, mRNA expression of the Mycn transcription factor, which was a cell cycle regulator transcriptionally repressed by Tbx2, was down regulated, and the number of S-phase cells was significantly decreased in the right ventricle of cKO heart. These results suggest that Hey2 plays an important role in right ventricle development during cardiac morphogenesis, at least in part, through mitigating Tbx2-dependent inhibition of Mycn expression.
一个基本的螺旋-环-螺旋转录因子 Hey2 在鼠胚胎的心室心肌和心内膜中表达，Hey2 基因敲除小鼠在围产期死亡，表现为室间隔缺损、发育不良的三尖瓣和右心室发育不良。为了了解 Hey2 在心脏形态发生过程中的区域特异性作用，我们使用在第二心脏场的前部和右心室以及心脏的流出道中具有活性的 Mef2c-AHF-Cre 生成了 Hey2 条件性敲除（cKO）小鼠。Hey2 cKO 新生儿重现了在 Hey2 基因敲除小鼠中常见的三种异常。最早的形态缺陷是在中孕期时右心室沿心尖-基底轴的延伸缺乏。所有 cKO 新生儿的右心室发育不良，包括那些右侧房室连接无明显闭锁的新生儿。cKO 胚胎的 RNA 测序分析表明，非腔室 T 盒因子 Tbx2 的基因表达在右心室的腔室心肌中异位诱导。一致地，Mycn 转录因子的 mRNA 表达被 Tbx2 转录抑制，其作为细胞周期调节剂，在 cKO 心脏的右心室中下调，并且 S 期细胞的数量显著减少。这些结果表明，Hey2 在心脏形态发生过程中的右心室发育中发挥重要作用，至少部分是通过减轻 Tbx2 依赖性的 Mycn 表达抑制。
