Quantitative dynamic models describing erythropoetin signaling used as examples.

The hormone erythropoietin (Epo) is the key regulator of erythropoiesis, the production of red blood cells. (a) Epo receptor model [2]. The model describes the interaction and the trafficking of the hormone and of its membrane receptor (EpoR). The active complex Epo_EpoR can be internalized (Epo_EpoR) and is either recycled back to the cell membrane or is degraded (dEpo, dEpo). (b) Model of Epo induced JAK2/STAT5 signaling [7]. In erythroid progenitor cells (CFU-E), the hormone Epo induces activation of the tyrosine kinase Janus kinase 2 (JAK2). Subsequently, the signal transducer and activator of transcription 5 protein (STAT5) is activated and shuttles to the nucleus where it induces target gene expression. Two of the target genes encode for the negative feedback regulators suppressor of cytokine signaling 3 (SOCS3) and cytokine-inducible SH2-containing protein (CIS).