Hematopoietic differentiation in Klf6^-/- yolk sacs is impaired. (A) Total RNAs were extracted from E 9.5 yolk sacs and corresponding cDNAs were analyzed by real-time PCR. The expression of indicated genes is shown. Each data point represents the average of 3 independent embryos. Error bars represent SE. (B-D) The cells from E 9.5 yolk sacs were subjected to a hematopoietic colony formation assay. Numbers of (B) Ery^D, (C) Mac, and (D) Mix colonies were counted, and each data point represents the average number of colonies per yolk sac. The hemoglobinized colonies were confirmed to be those of definitive erythrocytes but not primitive erythrocytes, based on lack of expression of the BH1 gene (not shown). Each data point represents the average colony number derived from at least 3 experiments (Klf6^+/+, n = 6; Klf6^+/-, n = 9; Klf6^-/-, n = 3). Error bars represent SE. ^*P < .05 (Student t test).