Fig. 6. ZCs in bases of Mist1^-/- animals have substantial deficiencies in apical cytoplasmic development. (A) ZC from the base of a gastric unit in a Mist1^-/- mouse. Upper right inset: normal apical tight (upper arrow, JC), adherens (lower arrows) and desmosomal (arrowhead) complexes and scattered, abnormally small secretory granules (SV). The apical plasma membrane is abnormally tufted with occasional surface blebs or projections (bracketed and labeled Projection). rER is disorganized apical to the nucleus, and there is a band 500 nm thick of amorphous granular cytoplasm just beneath the apical plasma membrane. Bottom right inset: normal sized vesicles (SV) and abundant rER, indistinguishable from basolateral cytoplasm of wild-type ZCs. (B) Apical cytoplasm of another Mist1^-/- ZC from the base of a different gastric unit showing scattered, scant rough ER and region of amorphous apical cytoplasm (bracketed). (C) Higher magnification of apical cytoplasm of the control mature ZC in Fig. 1D for reference, where large secretory vesicles and complex rER can be seen extending to the apical plasma membrane. (D) Mean area of secretory vesicles at each developmental stage is plotted. Statistically significant decrease in secretory vesicle size occurs in Mist1^-/- mice relative to control only in basal ZCs (P-value by two-tailed Student's t-test).