Sagittal section of adult brain from an En1Dre; RC:RLTG double heterozygote. tdTomato expression, indicating recombination of the rox-flanked stop cassette, is restricted to cells derived from embryonic midbrain and rhombomere 1 of the anterior hindbrain. Nuclear DAPI staining (false-colored gray) reveals tissue that does not express tdTomato (a, b). At higher magnification, recombination appears complete, with no unlabeled cells observed in superior colliculus (c) and cerebellum (d). Images show immunofluorescence. Scalebar: 2000 μm (a) or 97 μm (b–d).