In another study, the subsetting of human ES cells on the basis of the GCTM-2 and CD9 antigens also appeared to dissect the early stages of human ES differentiation, revealing the co-expression of pluripotency associated and lineage specific transcription factors. Cells that express both sets of transcription factors may represent undifferentiated cells, lineage primed cells or transitional cell states in which the pluripotency markers have yet to be fully repressed. In the absence of functional analysis from single cell assays the nature of such cells remains elusive. These reports are consistent with the existence of discrete interconvertible subsets of cells existing within the stem cell compartment, and that some of these subsets are closer to exiting the stem cell compartment than others. If this is the case, it might also be that different subsets are poised/primed to enter different pathways of differentiation when exposed to appropriate cues that promote differentiation. Such ����prepatterned���� substates within the stem cell compartment could be indicated by the observations of Laslette et al in human ES cells, while previously Hu et al observed expression of lineage specific transcripts in single hematopoietic stem cells, which they suggested represents ��lineage priming��. Thus an apparently homogeneous population of stem cells may actually comprise cells biased with respect to their differentiation potential, which are capable of generating a non-uniform differentiated population even when exposed to a uniform environment. We have Phellodendrine-chloride tested this Lycopene hypothesis using the pluripotent human EC stem cell line, NTERA2, the differentiation of which can be easily controlled by exposure to retinoic acid. Under standard culture conditions these stem cells can be maintained with minimal spontaneous differentiation, but exposure to all-trans-retinoic acid for 1�C2 days is sufficient to cause almost all the cells to commit to differentiate irreversibly, after which they generate a mixed culture of neurons and other cell types. However, although prominent, the neurons only appear after 12�C14 days and constitute about 125% of the differentiated population.