Fig. 7. Morphological characteristics of dying enteric ganglion cells. (A) Longitudinal section of enteric ganglia in a segment of the colon from E16.5 control and cKO mouse embryos 1 day after inactivation of GFR1. Many nuclei exhibited constricted and irregularly shaped morphologies in cKO embryos (top right). (Bottom) Schematic figures depicting the location of the myenteric ganglia (circled by dotted lines) and the positions of the nuclei in myenteric ganglion cells (indicated by N). Multiple nuclear profiles observed in a single cell plane are marked by pink and green. (B) A parallel section series of a single cell in cKO colon, revealing abnormal lobulation of the nucleus, but not fragmentation. (C) High-magnification view of perinuclear regions of control and cKO cells. Note that electron-dense structures in the nucleus (N) are more prominent in cKO than in control cells (right, arrows). No significant changes were observed in mitochondrial morphology (arrowheads). (D) Clearance of dying cells by large vacuoles (arrowheads) in cKO enteric ganglia. Conditional KO colon 27 hours after inactivation of GFR1 shown as an example (upper panel). A phagocytotic vacuole containing cell debris of high electron density, possibly representing a condensed nucleus of the engulfed cell (lower panel). (E) Left: a typical degenerating cell with severely depleted cytoplasm in the cKO distal colon 27 hours after inactivation of GFR1. Middle: representative image of a single-membraned vacuole containing cellular components (arrowhead) in a degenerating ganglion cell. Right: a degenerating cell with high electron-dense cytoplasm throughout the entire cell body. Note that the cell also contains multivesicles (arrowhead). Broken lines depict cell margins. Scale bar: 5 µm in A; 1 µm in B,D,E; 0.5 µm in C. Cm, circular muscle; Ga, enteric ganglia; Lm, longitudinal muscle; N, nucleus.