Transcriptional environment and chromatin modifications interplay decides globin expression patterns.

Background: Developmental stage-specific globin expression is a complex phenomenon that involves both trans- and cis-acting elements. While functional analyses ensuing recent genome-wide association studies have highlighted the important roles of trans-factors in regulating hemoglobin expression, these factors can not exert their functions without permissive chromatin domains. By transferring thoroughly profiled beta globin locus of undifferentiated human embryonic stem cells (hESCs) or hESC-derived erythroid cells into an adult erythroid transcriptional environment, we studied the influences of histone modifications on the globin expression decision within a fixed transcriptional environment. Shortly after the locus transfer, embryonic epsilon globin was not expressed regardless of original chromatin states, whereas fetal gamma globin was either expressed or not activated depending on original chromatin configurations, and the originally silent adult beta globin either remained silent or became activated depending on the expression status of gamma globin. These data suggest the interplay between transcriptional environment and the chromatin modifications determine the outcome of globin expression. As the ultimate silencing of gamma globin from hESC-derived erythroid cells in the adult transcriptional environment occurred after months-long cell proliferation, our work also has implications on attempts to generate beta globin expressing erythroid cells from hESCs or induced pluripotent stem cells.

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Chang KH, Huang A, Han H, Jiang Y, Fang X, Song CZ, Padilla S, Wang H, Qu H, Stamatoyannopoulos J, Li Q, Papayannopoulou T