Deficiency of Lin28b in the FL. (A) WT or Lin28b KO embryos were isolated at E14.5, and FL cells were stained with the indicated antibodies. (B) The number of myeloid progenitor populations is shown. *, P = 0.007 by Student’s t test. n = 7 WT and 6 Lin28-deficient embryos across three experiments. (C) FL cells of the indicated genotypes were isolated, and granulocyte populations were analyzed by flow cytometry. (D) Numbers of Gr-1⁺/Mac-1⁺ granulocytes per 100,000 FL mononuclear cells are shown. *, P = 0.03 by Student’s t test. n = 7 WT and 5 Lin28b-deficient embryos across three experiments. (E) Mature let-7 species were measured in FL CMP cells from E14.5 embryos of the indicated genotypes. *, P < 0.05 by Student’s t test. n = 3 replicates for each genotype from independent litters. Error bars represent SEM.