MIXED CULTURES OF AVIAN BLASTODERM CELLS AND THE QUAIL MESODERM CELL-LINE QCE-6 PROVIDE EVIDENCE FOR THE PLURIPOTENTIALITY OF EARLY MESODERM

During the early stages of embryogenesis, the mesoderm gives rise to c ells of the cardiovascular system which include cardiac myocytes and v ascular endothelial and red blood cells. We have investigated the deve lopment of these cell phenotypes using aggregate cultures of avian bla stoderm cells, which replicated mesodermal cell diversification. The c ell phenotypes expressed by the blastoderm cells were dependent upon t he age of the blastoderm cells, with Hamburger-Hamilton stage 3 or 4 c ells giving rise to endothelial and red blood cell and stage 5 cells p roducing endothelial and myocardial cells. To begin to understand the stage dependency of the cellular diversification of these aggregate cu ltures, we treated the cultures with various signaling factors that ha ve been shown to be present in the early avian embryo. These experimen ts showed that stem cell factor and TGF alpha altered cell phenotypes by stimulating red blood cell and myocardial differentiation, respecti vely. The ability of these growth factors to shift the differentiation profile of aggregate cultures demonstrated the plasticity of early em bryonic cells. To explore the diversification of individual mesodermal cells, labeled QCE-6 cells were incorporated within these blastoderm aggregate cultures. Previous studies have shown that this quail mesode rmal cell line possesses characteristics of early nondifferentiated me sodermal cells and can be induced to express either myocardial or endo thelial cell phenotypes (C. A. Eisenberg and D. M. Bader, 1996, Circ. Res. 78, 205-216). In the present study, we show that when these cells were cultured as a component of blastoderm cell aggregates, they diff erentiated into fully contractile cardiomyocytes or endothelial or red blood cells. Moreover, QCE-6 cell differentiation was in accordance p ith that displayed by the blastoderm cells. Specifically, QCE-6 cells differentiated into red blood cells when cultured within stage 3 or st age 4, but not stage 5, blastoderm cell aggregates. Accordingly, the d ifferentiation of QCE-6 cells into beating cardiomyocytes only occurre d when these cells were incorporated into stage 5 blastoderm cell aggr egates. The identical sorting and differentiation patterns that were e xhibited by QCE-6 and blastoderm cells suggest that expression of diff erentiated cell types within the early mesoderm is directed by the sur rounding environment without immediate cellular commitment. In additio n, these results provide further evidence that QCE-6 cells are represe ntative of a multipotential mesodermal stem cell and that they possess the potential to exhibit fully differentiated cell phenotypes. (C) 19 97 Academic Press.