FIGURE 1.

Different levels of regulation of gene expression in erythropoiesis. Cell-specific transcription factors control which genes are expressed. Transcript levels per gene differ because of transcription rate, but also due to mRNA stability. Transcript levels poorly predict protein expression. Translation factors and mRNA structure control protein synthesis efficiency. Transcript and protein expression is partly cell intrinsically regulated as a cascade of subsequent gene expression regulation (left hand arrows). In addition, signal transduction (Epo and SCF in erythroid progenitors) can modify signaling molecules to activate transcription and translation. For instance, phosphorylation of STAT5 causes dimerization and activates the transcription activity, ERK phosphorylation cause nuclear location and phosphorylation of transcription factors. PI3K activates mTOR, a critical factor in protein synthesis.