Fig. 2. A complex pattern of PU.1 expression in the mouse testis. (A) Immunodetection of the PU.1 protein in the adult (9-month-old) testis, in a fraction of spermatogonia (arrows) and in meiotic spermatocytes (asterisks). (B) A blocking peptide against PU.1 antibody was used to confirm the specifity of staining. (C-E) Expression of PU.1 in meiotic cells during the first synchroneous wave of germinal differentiation (3-week-old testis). (F) RT-PCR assay of PU.1 RNA in fractions enriched by elutriation (90%) in pachytene spermatocytes (lane 1) and elongated and round spermatids (lanes 2 and 3, respectively). (G-I) Expression in single (G), paired (H) and aligned (I) cells (arrows) in the peripheral compartment of the seminiferous tubule (A_single, A_paired and A_aligned spermatogonia). Scale bars: 50 µm in A-E; 25 µm in G-I.