Figure 1. C1galt1-deficient human corneal keratinocytes display plasma membrane invaginations on the apical surface.

(A) Scheme for mucin-type O-glycan biosynthesis. The core 1 β,3-galactosyltransferase (C1galt1 or T-synthase) is a key branchpoint enzyme that directs the synthesis of core 1 (T-antigen), the precursor structure for many extended mucin-type O-glycans in a wide variety of glycoproteins. (B) Electron micrograph at low magnification of an ultrathin section (60 to 90-Å) of C1galt1 keratinocytes grown on Transwell® inserts demonstrating cell stratification and the presence of flattened epithelial cells on the apical layer (top) Scale bar, 10 µm. Membrane invaginations (arrowheads, inset) can be observed occasionally on the apical portion of the plasma membrane in apical cells of C1galt1 keratinocytes (middle), more frequently than in scramble control (bottom). Scale bar, 200 nm.