Promiscuous gene expression of nonhematopoiesis-affiliated genes in HSCs.

(A). A list of nonhematopoiesis-affiliated genes predominantly expressed in HSCs. Note that the majority of genes that are predominantly expressed in HSCs show attenuated expression in the downstream progenitors. Genes listed in this figure have been confirmed by the hybridization result derived from CD45⁺ HSCs with expression levels of the majority of genes more than 200. A standardized (normalized) gene expression level is equal to (an expression level of a gene minus mean of the expression levels of this gene)/(the SD of the expression levels of this gene). All the gene expression levels are translated into these normalized values so that their means are all brought to 0 (allowing a comparison of gene expression on the same table). Therefore, the patterns of the genes are comparable on the basis of these normalized expression levels. In this image, the normalized expression levels of genes are presented according to a colored gradient scale from the highest (red) to the lowest (green; see colored scale). Importantly, the normalized expression level only reflects a relative score of the expression level of a gene, not the absolute expression levels of that gene. Therefore, “−1.5” may not indicate “no expression” but may only indicate a very low expression relative to the expressions of this gene under other conditions.