Eisenberg Leonard M, Eisenberg Carol A
Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston, SC 29425, USA.
Stem Cells Dev. 2004 Dec;13(6):614-24. doi: 10.1089/scd.2004.13.614.
Explants from gastrula-stage avian embryos have provided an important culture model for examining the formation of the vertebrate heart. Explants harvested from anterior regions containing the precardiac mesoderm faithfully recapitulate cardiogenesis and generate contractile tissue in culture. Posterior regions of the early embryo do not supply cellular material to the developing heart in situ, and thus have been commonly employed as negative control tissues for studying cardiogenic induction. To begin to understand the cellular mechanisms that account for the distinct cell fates of precardiac and posterior tissue within the embryo, we undertook a comprehensive investigation on the myocardial potential of presumptive noncardiac tissue. Myocardial differentiation was assayed by expression of the myocardium-associated transcription factor gene Nkx2.5 and positive immunostaining for sarcomeric myosin, muscle alpha-actinin, and smooth muscle alpha-actin. Our results demonstrate that regions of the early embryo that do not provide a cellular contribution to the myocardium in situ are capable of generating myocardial tissue when removed from their normal embryonic environment and placed in culture under nontreated conditions. Although treatment with the presumptive cardiac inducer Dickkopf-1 increased the frequency that cardiac tissue appeared within cultures of posterior tissue, no difference was observed in either the size or morphology of the myocardium-positive areas among treated and nontreated explants. These findings suggest that progenitor cells within the early embryo possess an innate phenotypic plasticity and that presumptive cardiac inducing signals do not induce cardiac differentiation but instead augment a pre-existing cardiac potential of embryonic tissue.
原肠胚期禽胚的外植体为研究脊椎动物心脏的形成提供了一个重要的培养模型。从前部含有心脏前中胚层的区域采集的外植体能够如实地重现心脏发生过程,并在培养中产生收缩性组织。早期胚胎的后部区域在原位并不为发育中的心脏提供细胞物质,因此通常被用作研究心脏诱导的阴性对照组织。为了开始理解解释胚胎中心脏前和后部组织不同细胞命运的细胞机制,我们对假定的非心脏组织的心肌潜能进行了全面研究。通过心肌相关转录因子基因Nkx2.5的表达以及对肌节肌球蛋白、肌肉α-肌动蛋白和平滑肌α-肌动蛋白的阳性免疫染色来检测心肌分化。我们的结果表明,早期胚胎中那些在原位不为心肌提供细胞贡献的区域,当从其正常胚胎环境中取出并置于未处理条件下培养时,能够产生心肌组织。尽管用假定的心脏诱导因子Dickkopf-1处理增加了后部组织培养物中心脏组织出现的频率,但在处理和未处理的外植体之间,心肌阳性区域的大小或形态均未观察到差异。这些发现表明,早期胚胎中的祖细胞具有内在的表型可塑性,并且假定的心脏诱导信号不会诱导心脏分化,而是增强胚胎组织预先存在的心脏潜能。