KRAB-ZFP expression in B cells. (A) Heat map of KRAB-ZFP (and control genes) that were significantly more expressed in B cells than in other hematopoietic lineages as assessed by NanoString nCounter direct RNA quantification. For the staining strategy used to sort the different populations, see supplemental Methods. HPC indicates hematopoietic progenitor cells; red, erythrocyte lineage; and Myelo/Mega, myeloid/megakaryocyte. For a description of the B-cell population, see Figure 1 legend. Arrowheads indicate KRAB-ZFP analyzed in panel B. (B) Q-PCR analysis performed on cDNA from thymus and B-enriched splenocytes (spleen B), using primers specific for the indicated KRAB-ZFP (indicated by arrowheads in panel A and supplemental Figure 6A). P = .0046; b, P = .0022; c, P = .0022; and d, P = .041 by Mann-Whitney test. Averages plus SEM are shown (n = 6). (C) Phylogenetic trees of the depicted KRAB-ZFP based on ZF exon sequence alignment. Each protein is defined by the genome: mouse, mmus; human, hsap; macaque, mmul; marmoset, cjac; cow, btau; dog, cfam; horse, ecab; rat, rnor; guinea pig; cpor; rabbit, ocun; elephant, lafr; and opossum, mdom. Query protein is depicted as index, in green in the left and middle panels and in red in the right panel. Green indicates mouse paralogs present in the list of differentially expressed ZFP in B cells (supplemental Figure 4); blue, 1:1 orthologs; aqua, closest rodent paralogs; and mustard, closest human genome matches. In the right panel, only rodents and human hits are shown (rodents + human). Also see supplemental Figure 6.