The elucidation of the roles of transcription factor in heart diseases

小鼠心脏同源结构域基因CSX/NKX-2.5在心脏发育中起重要作用。为了研究CSX在VIVA中的功能，我们建立了在CMV增强子/鸡β-肌动蛋白启动子控制下过度表达CSX的转基因小鼠。转基因在心脏中大量表达，在骨骼肌中适度表达。过量表达CSX的转基因小鼠是存活和可育的，没有生长迟缓和心力衰竭的迹象。在转基因小鼠和野生型小鼠之间，左心室重量/体重比和动脉收缩压没有显著差异。超声心动图显示心功能和室壁厚度无明显差异。Northern印迹分析表明，与野生型小鼠相比，转基因小鼠脑室组织中ANP、BNP和CARP基因的表达水平更高。转基因小鼠心脏内源性CSX基因表达水平也有上调，提示在CSX基因转录过程中存在正自我调节环。电镜分析显示，转基因小鼠左室心肌内有大量分泌颗粒，而野生型小鼠左室心肌内无分泌颗粒。据报道，心钠素在脑室是结构性分泌的，而在心房是调节分泌的。因此，值得注意的是，在CSX转基因小鼠的脑室中可能诱导了调节分泌机制。分泌颗粒的形成有两种可能。首先，CSX诱导ANP的大量表达，从而诱导颗粒形成蛋白的产生。第二种可能性是CSX直接诱导颗粒形成蛋白的表达。有必要进行进一步的研究来阐明这些可能性。

A murine cardiac homeodomain gene Csx/Nkx-2.5 plays an essential role in the heart development. To examine the function of CSX in in viva context, we generated transgenic mice overexpressing CSX, a human homolog of Csx under the control of CMV enhancer/chicken beta-actin promoter. The transgene was expressed abundantly in the heart and moderately in the skeletal muscle. The transgenic mice overexpressing CSX were viable and fertile without growth retardation nor signs of heart failure. There was no significant difference in left ventricular weight to body weight ratio or systolic arterial blood pressure between the transgenic mice and the wild type litter mates. Ultrasonic echocardiography showed no significant difference in cardiac function and wall thickness. Northern blot analysis revealed that mRNA levels of ANP, BNP and CARP genes were more abundant in the ventricle of transgenic mice than that of wild type mice. Endogenous murine Csx mRNA levels were also up-regulated in the heart of transgenic mice, suggesting the existence of positive auto-regulatory loop in transcription of Csx gene. Electromicroscopic analysis showed that there are many secretory granules in the left ventricular myocardium of the transgenic mice, but not of wild type mice. It has been reported that ANP is secreted constitutively in the ventricle, while in the atrium, regulated secretion is operated. Therefore, it is noteworthy that regulated secretion mechanism may be induced in the ventricle of the CSX transgenic mice. There are two possibilities in the formation of secretory granules. First, CSX induces abundant expression of ANP, resulting in induction of granule-forming proteins. Second possibility is that CSX directly induces expression of granule-forming proteins. Further investigation is necessary to elucidate these possibilities.