Heller F A, Xue C, Fisher A, Everett A D
Department of Pediatrics, University of Virginia, Charlottesville 22908, USA.
Pediatr Res. 1998 Jan;43(1):68-76. doi: 10.1203/00006450-199801000-00011.
Protein phosphatase 2A (PP2A) is a second messenger involved in cell cycle regulation, cell transformation, and cell fate determination. We previously identified a gene encoding the alpha catalytic subunit of PP2A in the embryonic rat heart, but its role in cardiac morphogenesis was unknown. In this study, we examined the developmental expression of PP2A alpha mRNA and protein in the heart using Northern and Western analysis, in situ hybridization, and immumohistochemical staining. We found two major PP2A alpha transcripts in the rat heart (1.8 and 2.4 kb), at all stages examined. By Western blotting, PP2A alpha protein levels were twice as high in the embryonic rat heart compared with the adult. In situ hybridization on embryonic d 12 showed that PP2A alpha mRNA was expressed in the heart, brain, tail, and limb buds. Cardiac PP2A alpha expression was regionally restricted to the atrium, ventricle, and truncus arteriosus. PP2A alpha expression did not extend into the more distal aortic sac or aortic arches. Cross-sectional hybridization revealed PP2A alpha mRNA in the epicardium, pericardium, and endothelium. Later in development, mRNA expression was also detected at high levels in mesenchymal cells populating the endocardial cushions and in myocardium. At term, PP2A alpha was highly expressed in endothelial cells, but not in the underlying myocardium. PP2A alpha protein had a similar distribution at all embryonic stages examined. These results show that there is transcriptional, translational, and cell-specific regulation of PP2A alpha during heart development. We speculate on the role of PP2A alpha-mediated dephosphorylation in cardiac morphogenesis and suggest a number of possible molecular targets.
蛋白磷酸酶2A（PP2A）是一种参与细胞周期调控、细胞转化和细胞命运决定的第二信使。我们之前在胚胎大鼠心脏中鉴定出一个编码PP2Aα催化亚基的基因，但其在心脏形态发生中的作用尚不清楚。在本研究中，我们使用Northern和Western分析、原位杂交和免疫组织化学染色，检测了心脏中PP2Aα mRNA和蛋白的发育表达。我们发现在所有检测阶段，大鼠心脏中存在两种主要的PP2Aα转录本（1.8和2.4 kb）。通过Western印迹分析，胚胎大鼠心脏中PP2Aα蛋白水平是成年大鼠的两倍。胚胎第12天的原位杂交显示，PP2Aα mRNA在心脏、脑、尾和肢芽中表达。心脏PP2Aα表达在区域上局限于心房、心室和动脉干。PP2Aα表达未延伸至更远端的主动脉囊或主动脉弓。横断面杂交显示，心外膜、心包膜和内皮中有PP2Aα mRNA。在发育后期，在心内膜垫的间充质细胞和心肌中也检测到高水平的mRNA表达。足月时，PP2Aα在内皮细胞中高表达，但在其下方的心肌中不表达。在所有检测的胚胎阶段，PP2Aα蛋白具有相似的分布。这些结果表明，在心脏发育过程中，PP2Aα存在转录、翻译和细胞特异性调控。我们推测了PP2Aα介导的去磷酸化在心脏形态发生中的作用，并提出了一些可能的分子靶点。
