In vivo effects of Δ5TpoR and TpoRW515A where cytosolic tyrosine residues were substituted to phenylalanine. (A) Peripheral blood counts of mice that received a transplant of bone marrow cells expressing the indicated Δ5TpoR (left) or TpoRW515 (right) mutants at day 30 after reconstitution. All mice present more than 95% GFP-positive cells at 3 weeks after reconstitution. (B) The Y112F mutation abrogates spleen myelofibrosis induced by Δ5TpoR or TpoRW515A at day 60 after reconstitution. Silver staining of spleen sections shows the presence of reticulin fibers in spleens from mice reconstituted with Δ5TpoR or TpoRW515A, but not in spleens from mice reconstituted with Δ5TpoR-Y112F, TpoRW515A-Y112F, or TpoRwt.