HSCs exhibit high Krt18 expression. (A-B) Expression levels of Krt18 in the hematopoietic system determined by the Gene Expression Commons (A; https://gexc.riken.jp/) and by the hematopoietic fingerprints (B; http://franklin.imgen.bcm.tmc.edu/loligag/). (C) Expression of Krt18 in the hematopoietic system determined by quantitative PCR. Expression levels of Krt18 were normalized with β-actin, and fold change in expression levels was normalized to the expression levels of whole bone marrow (WBM) (n = 3-4). Color codes of each population were taken from panel A. (D) Immunofluorescence staining of HSCs and the indicated cell populations for Krt18 protein. HSCs had significantly higher protein expression levels of Krt18 than any other population. Signal intensities of each cell were normalized to that of a negative control (secondary antibody only). All data represent mean ± standard deviation; ***P < .001 by 1-way ANOVA with post hoc Tukey’s multiple comparison test against all other groups. B, B cell; BLP, earliest B-lymphoid progenitor; DN, double-negative T cell; DP, double-positive T cell; FoB, folicular B cell; FrB-D, fraction B-D B cell; GMLP, granulocyte/macrophage/lymphoid progenitor; Gra Gr+, granulocyte; MkP, megakaryocyte progenitor; mono, monocyte; My, myeloid cell; MzB, marginal zone B cell; NK, natural killer cell; p-CFU-E, pre–colony forming unit-erythroid; pGMP, pre–granulocyte/macrophage progenitor; pMEP, pre–megakaryocyte/erythrocyte progenitor; sCMP, strict common myeloid progenitor; T, T cell.