ES cells can be described based on a characteristic morphology, the presence of
cell surface markers such as SSEA - 1 and Pecam1, or the expression of the key transcription factors such as Oct4, Sox2, Nanog, and a number of ES cell - specific transcripts (ECATs)[4]--[6].
Oct - 4 is most consistently expressed of the pluripotency genes that we have studied, and it is switched off only in populations that have lost other measurable features of pluripotency,
such as stem
cell surface marker expression and the capacity for self - renewal.