Expression of KDR-LacZ in late embryonic and postnatal mouse testes (T). In E17 mice (a), intense KDR-LacZ staining was still present in the interstitium (i) surrounding the seminiferous cords, but the amount of staining within the mesonephros (M) had diminished. Staining was also localized to Sertoli cells and early stage germ cells within the seminiferous cords (c). In P0 testes (b), KDR expression continued to be strongly present within interstitial cells. At P20 (c), KDR-LacZ expression was present in round spermatids, and KDR-LacZ was located in round spermatids, elongating spermatids, and Sertoli cell cytoplasm within the seminiferous tubules (t) in P60 testes (d). Insets Higher-power views. Bars 100 μm (b), 50 μm (a, c-d)