Schlange T, Andrée B, Arnold H H, Brand T
Department of Cell and Molecular Biology, Institute of Biochemistry and Biotechnology, Technical University of Braunschweig, Spielmannstrasse 7, 38106, Braunschweig, Germany.
Mech Dev. 2000 Mar 1;91(1-2):259-70. doi: 10.1016/s0925-4773(99)00311-1.
BMP2, like its Drosophila homologue dpp, is an important signaling molecule for specification of cardiogenic mesoderm in vertebrates. Here, we analyzed the time-course of BMP2-requirement for early heart formation in whole chick embryos and in explants of antero-lateral plate mesoderm. Addition of Noggin to explants isolated at stage 4 and cultured for 24 h resulted in loss of NKX2.5, GATA4, eHAND, Mef2A and vMHC expression. At stages 5-8 the individual genes showed differential sensitivity to Noggin addition. While expression of eHAND, NKX2.5 and Mef2A was clearly reduced by Noggin vMHC was only marginally affected. In contrast, GATA4 expression was enhanced after Noggin treatment. The developmental period during which cardiac mesoderm required the presence of BMP signaling in vivo was assessed by implantation of Noggin expressing cells into stage 4-8 embryos which were then cultured until stage 10-11. Complete loss of NKX2.5 and eHAND expression was observed in embryos implanted at stages 4-6, and expression was still suppressed in stages 7 and 8 implanted embryos. GATA4 expression was also blocked by Noggin at stage 4, however increased at stages 5, 6 and 7. Explants of central mesendoderm, that normally do not form heart tissue were employed to study the time-course of BMP2-induced cardiac gene expression. The induction of cardiac lineage markers in central mesendoderm of stage 5 embryos was distinct for different genes. While GATA4, -5, -6 and MEF2A were induced to maximal levels within 6 h after BMP2 addition, eHAND and dHAND required 12 h to reach maximum levels of expression. NKX2.5 was induced by 6 h and accumulated over 48 h. vMHC and titin were induced at significant levels only after 48 h of BMP2 addition. These results indicate that cardiac marker genes display distinct expression kinetics after BMP2 addition and differential response to Noggin treatment suggesting complex regulation of myocardial gene expression in the early tubular heart.
骨形态发生蛋白2（BMP2）与其果蝇同源物dpp一样，是脊椎动物中确定心脏中胚层的重要信号分子。在此，我们分析了全鸡胚和前外侧板中胚层外植体早期心脏形成过程中对BMP2需求的时间进程。向在第4阶段分离并培养24小时的外植体中添加Noggin会导致NKX2.5、GATA4、eHAND、Mef2A和vMHC表达缺失。在第5 - 8阶段，各个基因对添加Noggin表现出不同的敏感性。虽然Noggin明显降低了eHAND、NKX2.5和Mef2A的表达，但vMHC仅受到轻微影响。相反，Noggin处理后GATA4表达增强。通过将表达Noggin的细胞植入第4 - 8阶段的胚胎中，然后培养至第10 - 11阶段，评估了心脏中胚层在体内需要BMP信号存在的发育时期。在第4 - 6阶段植入的胚胎中观察到NKX2.5和eHAND表达完全缺失，并且在第7和8阶段植入的胚胎中表达仍受到抑制。GATA4表达在第4阶段也被Noggin阻断，但在第5、6和7阶段增加。利用通常不形成心脏组织的中央中胚层外植体来研究BMP2诱导心脏基因表达的时间进程。对于不同基因，第5阶段胚胎中央中胚层中心脏谱系标志物的诱导情况各不相同。添加BMP2后6小时内，GATA4、-5、-6和MEF2A被诱导至最高水平，而eHAND和dHAND需要12小时才能达到最大表达水平。NKX2.5在6小时被诱导并在48小时内积累。仅在添加BMP2 48小时后，vMHC和肌联蛋白才被诱导至显著水平。这些结果表明，添加BMP2后心脏标志物基因表现出不同的表达动力学以及对Noggin处理的不同反应，这表明早期管状心脏中心肌基因表达受到复杂调控。
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