Gene expression analysis of WT and Dot1L KO progenitor cells in yolk sac. (A-B) mRNA was extracted from c-kit⁺ yolk sac progenitor cells sorted by fluorescence-activated cell sorting. Reverse transcription was performed, and genes known to be important in erythropoiesis were assessed by quantitative reverse transcription–PCR. mRNA was obtained from c-kit⁺, sorted cells from 3 to 10 individual yolk sacs. (*P < .01, t test).