Fig. 6. Electronmicrographs of adrenal medullae of wild-type (A,C) and Mash1^–/– mice (B,D) at E14.5 (A,B) and E16.5 (C,D). Most adrenal medullary cells in Mash1^–/– mice lack chromaffin granules and ultrastructurally resemble immature neuroblasts. Note the similarity of adrenal medullary cells of E16.5 Mash1^–/– to cells in the sympathetic suprarenal ganglion of E16.5 wild-type mice (E). Scale bars: 2 µm. (F) Semi-quantitative analysis of percentages of adrenal medullary cells that lack chromaffin granules, cells with predominantly small granules (core diameter <50 nm) and cells with typical large chromaffin granules (core diameter 100 nm) in Mash1^–/– mice and wild-type littermates at E16.5. At least 100 cells per group were analyzed in random sections through different levels of the adrenal gland.