RESUMEN
Embryonic stem cells are pluripotent and their differentiation in vitro can serve as an experimental model to explore the molecular mechanisms of early embryonic development. To investigate the effect of stromal cell conditioned medium combined with cytokines (sccm + cys) on the differentiation from human embryonic stem cells to hematopoietic cells and endothelial cells, the mouse fibroblast feeder cells to make human embryonic stem cells grown into embryonic bodies (EBs) were initially deleted. After culture for 3 days, EB cells were trypsinized into single cells and induced for 8 days by sccm + cys. Then, the differentiated cells were cultured in the semisolid medium containing 0.9% methylcellulose and cytokines to study the colony forming and self-renewal ability of cells. Immunocytochemical staining was used to check the surface markers of the colony cells. During the induction, mRNA expression of flk-1, BMI-1, scl, and Zeta-globin genes was tested by RT-PCR. Surface markers, such as flk-1, CD34 were tested by the flow cytometry. The results demonstrated that: (1) cell clusters containing 20-30 cells were formed after culture for 8 - 14 days in the semisolid medium, replanting these cells resulted in similar cell cluster forming. In addition, CD45 positive in big cell colonies were also found in the semisolid medium; (2) attached cell colonies appeared after culture for 8 days in the semisolid medium and VIII factor, UEA and KDR could be detected as negative by immunocytochemical staining; (3) on the 4(th) day of induction, mRNAs of flk-1, BMI-1, scl and Zeta-globin were all expressed. On the 8(th) day of induction, all of the above genes except Zeta-globin were expressed, while ES cell and EB cells which served as controls did not express scl and Zeta-globin genes; (4) on the 8(th) day of induction, the proportions of flk-1(+) cells and CD34(+) cells among all the inducing population were 9.8% and 16.8%, respectively, while the corresponding positive populations were 0.36% and 1.16% in spontaneously differentiated 11(th) day's EB, and 0.04% and 0.16%, respectively, in ES cells. If is concluded that embryonic stem cells can differentiate into hematopoietic cells and endothelial cells in combinant culture system of this study.