Fig. 1. Mouse PU.I (Sfpi1) expression in the huCD4-positive SSC fraction. (A) Germ cell markers in the purified spermatogonial stem cell fraction. RT-PCR assays performed on RNA of huCD4⁺ cells and of the bulk of differentiated germ cells (huCD4^- fraction). Stra8 is expressed in both differentiated and stem spermatogonia (Oulad-Abelghani et al., 1996). Kit is expressed in differentiated spermatogonia, but absent from stem cells (Shinohara et al., 2000). The synaptonemal complex protein 1 gene (Sycp1) is expressed in pachytene spermatocytes (Meuwaissen et al., 1992). Prm1 (protamine 1) is expressed in haploid germ cells (Peschon et al., 1987). Gapdh served as a control. (B) Immunodetection of the PU.1 protein in huCD4⁺ cells (a) and DAPI staining (b). Note that after immunomagnetic sorting, the cells are still attached to the beads. (C) Quantitative RT-PCR assay of PU.1 RNA in the bulk of differentiated germ cells (huCD4^- cells) and in huCD4⁺ cells. Normalization was performed relative to Gapdh RNA.