Ectopic expression of JAK2^V617F attenuates TNFα-mediated suppression of myeloid colony formation. JAK2^V617F or empty MIG vector was retrovirally expressed in hematopoietic progenitors (lineage^neg c-kit⁺ Sca-1⁻) from the bone marrow of (A) wild-type and (B) Fancc^−/− C57B/6J mice. Transduced (GFP⁺) cells were plated in methycellulose supplemented with 50 ng/mL mSCF, 10 ng/mL mIL-3 and 3 U/mL hEPO, either with or without TNFα (20 ng/mL for wild-type 10 ng/mL for Fancc^−/−). Colony number was enumerated at day 12, with colony formation in conditions without TNFα set to 100%.