The expression profile of miRNAs in various tissues and cell lines.

(A) A heat map of hierarchical clustering of miRNAs detected in small RNA-seq data used in this study. (B) A heat map of 20 miRNAs highly expressed in PGCs. Relative miRNA expression is described according to the color scale. Red and green indicate high and low expression, respectively. Mouse embryonic fibroblasts (MEFs), embryonic stem (ES) cells, primordial germ cells (PGCs), spermatogonia (SPG), spermatozoa (SPZ). (C) The locus of XmiR genes on the X chromosome. (D) The expression of XmiRs in testes, ES cells, and MEFs determined by quantitative RT-PCR. Each expression level was normalized to the expression of U6 snRNA. The expression in ES cells was set as 1.0. Error bars show standard errors of three biological replicates. **P < 0.01.