Abstract
The molecular mechanisms governing self-renewal, differentiation, and lineage specification remain unknown. Transcriptional profiling is likely to provide insight into these processes but, as yet, has been confined to "static" molecular profiles of stem and progenitors cells. We now provide a comprehensive, statistically robust, and "dynamic" analysis of multipotent hemopoietic progenitor cells undergoing self-renewal in response to interleukin-3 (IL-3) and multilineage differentiation in response to lineage-affiliated cytokines. Cells undergoing IL-3-dependent proliferative self-renewal displayed striking complexity, including expression of genes associated with different lineage programs, suggesting a highly responsive compartment poised to rapidly execute intrinsically or extrinsically initiated cell fate decisions. A remarkable general feature of early differentiation was a resolution of complexity through the downregulation of gene expression. Although effector genes characteristic of mature cells were upregulated late, coincident with morphological changes, lineage-specific changes in gene expression were observed prior to this, identifying genes which may provide early harbingers of unilineage commitment. Of particular interest were genes that displayed differential behavior irrespective of the lineage elaborated, many of which were rapidly downregulated within 4 to 8 h after exposure to a differentiation cue. These are likely to include genes important in self-renewal, the maintenance of multipotentiality, or the negative regulation of differentiation per se.