Cyclin A1 and B-myb are localized in similar stages of spermatogenesis in meiotic male germ cells.

(A) Cyclin A1 expression was visualized as EGFP expression in the testes of mice that were transgenic for a cyclin A1 promoter-EGFP construct. The confocal laser microscopy image (top) shows EGFP expression in green and non-specific fluorescence in Leydig cells in red. The EGFP expression accurately reflects expression of cyclin A1 as determined previously by Western blotting of cells sorted by flow cytometry.23 To analyze B-myb expression in testis cells with and without cyclin A1 expression, EGFP-expressing testis cells were sorted and analyzed for B-myb expression using Western blot analysis (bottom). There was no B-myb expression found in cells not expressing EGFP, whereas expression could be found in cyclin A1 (EGFP)–expressing cells. (B) The 2 B-myb bands in Figure 7A were similar to the bands seen in human leukemic cells. To analyze whether the 2 bands represented differentially phosphorylated forms of B-myb, protein lysates from mouse testis were treated with Protein Phosphatase 1 before Western blotting. Phosphatase treatment led to an increase in the intensity of the faster migrating band, which is consistent with protein dephosphorylation.