The v-erbA Oncogene: Assessing Its Differentiation-Blocking Ability Using Normal Chicken Erythrocytic Progenitor Cells

The v-erbA oncogene is the most clear-cut case of an oncogene that acts by blocking a differentiation sequence (for a review, see ref. 1 ). It has been discovered as one of the two oncogenes carried by the avian erythroblastosis virus (AEV), a leukemia-inducing retrovirus. It is derived from the c-erbA protooncogene, which encodes the α form of the nuclear receptor for the thyroid hormone triiodothyronine (T3Rα) (2 ,3 ); for a detailed description of the structural differences between v-erbA and T3Rα, see ref. 4 ). Thyroid hormone receptors belong to the large superfamily of structurally and functionally related receptors that includes the receptors for thyroid hormone (T3R), retinoic acid (either all-trans or 9-cis isoforms, RARs and RXRs) and vitamin D3 (VD3R), which are all lipophilic ligand-regulated transcription factors (5 ).