Spry1 is selectively up-modulated in developing (pro)erythroblasts and is subject to Gata1 modulation. (A) Selective representation of Spry1 in developing murine bone marrow–derived erythroid progenitors. After short-term expansion in SP34ex medium, CFUe-like Kit⁺CD71^highTer119⁻ cells (stage E1), Kit⁻CD71^highTer119⁻ proerythroblasts (stage E2), and Kit⁻CD71^highTer119⁺ erythroblasts (stage E3) were purified. Via gene profiling and RT-PCR analyses, Spry1 to Spry4 expression levels at each stage were then determined (mean ± SE; n = 3). Bottom panels: Giemsa-May-Grunwald–stained cytospins for isolated stage E1, E2, and E3 cells. (B) In erythromegakaryocytic splenocytes from Gata1-knockdown mice, Spry1 levels are decreased to approximately 25% of wild-type controls (GEO accession no. GSE2527).³⁰  (C) In human CD34⁺-derived developing erythroid progenitors, Spry1 is also selectively elevated at a maturing erythroblast stage. Here, values are relative expression intensities (mean ± SE) derived from Keller et al³¹  (and GEO accession no. GDS2431).