text_1: Human embryonic stem cells give rise to cell types from the outer embryonic germ layer, but not the other two layers.
text_2: Objective To explore the in vitro maintenance and characterization of human embryonic stem cells(hESCs).Methods hESCs were cultured on feeder layer with ES culture medium,which consists of 20% Knockout Serum Replacement,Knockout DMEM and 10 ng/mL bFGF.Undifferentiated status of hESCs was identified by cell morphology,and the expressions of cell surface marker SSEA-1,SSEA-3 and TRA-1-60.G banding technique was employed for cell karyotype analysis.