EE-T-Y343 and EE-T-Y343F chimeras and expression in transgenic mice.

(A) Diagrammed are the wild-type mEPO receptor (mEpo-R) and the derived carboxyl-terminal deletion constructs EE-T-Y343 and EE-T-Y343F. In each chimera, the extracellular dimerization domain is that of the hEGF receptor (hEGF-R), and the EPO receptor cytoplasmic Box1 domain for Jak2 binding is retained (pm, plasma membrane). In EE-T-Y343, a Y343 site for STAT5 binding is retained, whereas in EE-T-Y343F this residue is mutated to phenylalanine. (B) Levels of EE-T-Y343 and EE-T-Y343F receptor expression in transgenic mice were assayed by flow cytometry of marrow cells after their culture for 72 hours in the presence of mSCF and EPO plus dexamethasone, β-estradiol, and insulinlike growth factor-1 under conditions shown by Panzenbock et al31 to selectively promote CFUe proliferation. As a control, marrow cells from nontransgenic mice were also analyzed. PE indicates phycoerythrin.