Fig. 4. Apoptosis within groups of TH-positive (red) adrenal medullary cells of Mash1^–/– (B,D) and Mash1^+/+ (A,C) mice monitored by TUNEL staining (green). There were no TUNEL-positive nuclei in wild-type adrenal glands at E14.5 (A), and only few at E16.5 (C, arrowhead). MASH1 deficient adrenal glands displayed only very few apoptotic nuclei at E14.5 (B, arrowhead), but there were numerous TUNEL-positive nuclei at E16.5 (D, arrowheads). Scale bar: 50 µm.