Department of Cell and Molecular Biology, Tulane University, New Orleans, Louisiana 70118, USA.
J Biol Chem. 2011 May 13;286(19):17029-38. doi: 10.1074/jbc.M111.234252. Epub 2011 Mar 28.
The homeodomain transcription factor Shox2 plays a crucial regulatory role in the development of sinoatrial node (SAN) by repressing the expression of Nkx2.5, as demonstrated by failed differentiation of SAN in Shox2 null mice. The SHOX (short stature homeobox) gene family consists of two closely related members, SHOX and SHOX2 in humans, but a SHOX ortholog does not exist in the mouse genome. These two genes exhibit overlapping and distinct expression patterns in many developing organs but whether they share functional redundancy is not known. In this study, we set to investigate possible functional redundancy between SHOX and SHOX2 in vitro and in vivo. We first showed that human SHOX and SHOX2 and mouse Shox2 possess similar transcriptional repressive activities in cell cultures, particularly the repressive effects on the Nkx2.5 promoter activity. We further created an SHOX/Shox2 knock-in mouse line (replacement of Shox2 with SHOX, referred as Shox2(KI/KI)). Mice carrying the hypomorphic Shox2(KI+Neo/KI+Neo) allele exhibit bradycardia and arrhythmia and die a few days after birth. However, mice carrying the Shox2(KI/KI) allele grow to adulthood. Physiological, histological, and molecular analyses demonstrate a fully developed SAN and normal pacemaking function in Shox2(KI/KI) mice. Our results demonstrate a functional redundancy between human SHOX and mouse Shox2 in the regulation of SAN formation and pacemaking function in addition to several other organs. The SHOX/Shox2 dose appears to be critical for normal pacemaking function.
同源盒转录因子 Shox2 通过抑制 Nkx2.5 的表达，在窦房结（SAN）的发育中发挥关键的调节作用，这一点在 Shox2 基因敲除小鼠中表现为 SAN 分化失败。SHOX（短体节同源盒）基因家族由两个密切相关的成员组成，人类中的 SHOX 和 SHOX2，但在小鼠基因组中不存在 SHOX 同源物。这两个基因在许多发育器官中表现出重叠和独特的表达模式，但它们是否具有功能冗余尚不清楚。在这项研究中，我们旨在研究 SHOX 和 SHOX2 在体外和体内可能存在的功能冗余。我们首先表明，人 SHOX 和 SHOX2 以及鼠 Shox2 在细胞培养中具有相似的转录抑制活性，特别是对 Nkx2.5 启动子活性的抑制作用。我们进一步创建了一个 SHOX/Shox2 基因敲入小鼠系（用 SHOX 替换 Shox2，称为 Shox2(KI/KI)）。携带 Shox2(KI+Neo/KI+Neo) 杂合子的小鼠表现出心动过缓和心律失常，并在出生后几天内死亡。然而，携带 Shox2(KI/KI) 等位基因的小鼠可以生长到成年。生理、组织学和分子分析表明，Shox2(KI/KI) 小鼠的 SAN 完全发育并具有正常的起搏功能。我们的结果表明，在 SAN 形成和起搏功能的调节中，人 SHOX 和鼠 Shox2 之间存在功能冗余，此外还有其他几个器官。SHOX/Shox2 的剂量似乎对正常起搏功能至关重要。
