| Lyn, a member of the Src Family Kinases (SFKs), is known to modulate the development and function of B-cells, myeloid cells, megakaryocytes and mast cells. Among mice with germline ablation of SFK genes, Lyn -/- mice have been shown to develop age-dependent increase in splenic erythroid cells. Also recently cases have been outlined for Lyn's negative vs. positive erythropoietic actions.;In phenylhydrazine-treated Lyn-/- mice, extramedullary splenic erythropoiesis was hyper-activated. There was an increase in erythroid splenic progenitors and Ter119pos erythroblast subpopulations. This amplified erythroid response in the spleens of Lyn-/- mice, however, was not accompanied with accelerated recovery from anemia. To further investigate the intrinsic role for Lyn in erythroid cells, novel culture systems for expansion of murine bone marrow erythroid progenitor cells (EPCs) were established.;In these primary culture systems, analyses of bone marrow-derived Lyn-/- erythroblast development further indicated positive roles for Lyn at two stages. Late stage Lyn -/- erythroblasts exhibited deficit Ter119pos cell formation, and this was paralleled by decreased Bcl-xL expression, and increased apoptosis. Early stage Lyn-/- erythroblasts accumulated at a KitposCD71high stage, possessed decreased proliferative capacity, and were apparently defective in entering the G1/S cell cycle phase. Analyses of erythroblasts expressing a Kit allele with a mutated Y567F Src-family kinase binding site further revealed related defects in expansion, and survival.;This expansion system allowed isolation and further biochemical analyses on relatively purified sub-populations of erythroblasts based on Kit and transferrin receptor surface expression. Biochemical analyses revealed that Stat5 activation and Bcl-xL expression were significantly decreased together with decreased survival and developmental potentials in the late EPCs. In proposed compensatory responses, KitposCD71high Lyn -/- EPCs expressed increased levels of activated Akt, and decreased levels of DAPK2.;Lyn therefore is proposed to function via erythroid cell-intrinsic mechanisms to support late erythroblast formation, and erythroid progenitor expansion beyond a KitposCD71 high stage. |
