c-Kit signaling depends on Jak2 and is modulated by Stat5. (A) WT and Jak2^−/− fetal liver cells transduced with GFP or cS5 were subjected to colony assays supplemented with SCF (50 ng/mL). Colonies were scored at day 8. (B) Photographs of colonies from (A). Representative pictures of 4 for each condition are shown. (C) E12.5 WT and Jak2^−/− fetal livers analyzed for HSC content (lin⁻c-Kit⁺Sca-1⁺ cells) by flow cytometry. The percentage of HSCs is depicted (n = 4).