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Fig. 1. Transcription-factor-based and chromatin-based models for differentiation. Hypothetical models showing two views of how cells respond differently to similar signals (black arrows) received during differentiation. In model A, three different cells, each with permissive chromatin structure around the target gene (represented by green beads and loose nucleosomal packing), are discriminated by expression of different transcription factors. Only the first cell contains the correct complement of factors necessary to activate transcription and is therefore able to respond to the signal. In model B, all three cell types contain the correct factors for transcription, but a permissive chromatin environment is unique to the first cell. In each of the other cell types, repressive modifications (represented by red triangles or ovals and compacted nucleosomes) prevent transcription.
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