Gladstone Institute of Cardiovascular Disease, University of California San Francisco, 1650 Owens Street, San Francisco, CA 94158, USA.
Dev Biol. 2011 Mar 1;351(1):62-9. doi: 10.1016/j.ydbio.2010.12.023. Epub 2010 Dec 23.
Cardiogenesis involves the contributions of multiple progenitor pools, including mesoderm-derived cardiac progenitors known as the first and second heart fields. Disruption of genetic pathways regulating individual subsets of cardiac progenitors likely underlies many forms of human cardiac malformations. Hand2 is a member of the basic helix loop helix (bHLH) family of transcription factors and is expressed in numerous cell lineages that contribute to the developing heart. However, the early embryonic lethality of Hand2-null mice has precluded lineage-specific study of its function in myocardial progenitors. Here, we generated and used a floxed allele of Hand2 to ablate its expression in specific cardiac cell populations at defined developmental points. We found that Hand2 expression within the mesoderm-derived second heart field progenitors was required for their survival and deletion in this domain recapitulated the complete Hand2-null phenotype. Loss of Hand2 at later stages of development and in restricted domains of the second heart field revealed a spectrum of cardiac anomalies resembling forms of human congenital heart disease. Molecular analyses of Hand2 mutant cells revealed several genes by which Hand2 may influence expansion of the cardiac progenitors. These findings demonstrate that Hand2 is essential for survival of second heart field progenitors and that the graded loss of Hand2 function in this cardiac progenitor pool can cause a spectrum of congenital heart malformation.
心脏发生涉及多个祖细胞池的贡献，包括中胚层来源的心脏祖细胞，称为第一和第二心脏场。调节单个心脏祖细胞亚群的遗传途径的破坏可能是许多人类心脏畸形的基础。Hand2 是基本螺旋环螺旋（bHLH）转录因子家族的成员，在许多有助于心脏发育的细胞谱系中表达。然而，Hand2 基因敲除小鼠的早期胚胎致死性排除了其在心肌祖细胞中的功能的谱系特异性研究。在这里，我们生成并使用了 Hand2 的 floxed 等位基因，以在特定的发育时间点在特定的心脏细胞群体中消除其表达。我们发现，中胚层来源的第二心脏场祖细胞中的 Hand2 表达对于其存活是必需的，并且该区域中的 Hand2 缺失重现了完整的 Hand2 基因敲除表型。在发育的后期阶段以及在第二心脏场的受限区域中丧失 Hand2 揭示了类似于人类先天性心脏病的多种心脏异常。Hand2 突变细胞的分子分析揭示了 Hand2 可能影响心脏祖细胞扩增的几个基因。这些发现表明 Hand2 对于第二心脏场祖细胞的存活是必需的，并且在该心脏祖细胞池中的 Hand2 功能的逐渐丧失可导致一系列先天性心脏畸形。
