Fig. 6. Stimulation of Fn assembly by surface tTG is separate from its effects on cell spreading. Vector and tTG[2] transfectants were plated on vitronectin or laminin-coated surfaces in serum-free medium. Three hours later the cells were supplemented with 20 µg/ml of unlabeled (A,C) or ¹²⁵I-labeled (B) Fn in Fn-depleted 10% BCS and incubated for the following 6 hours. (A) tTG-mediated stimulation of Fn fibril formation on the dorsal cell surfaces. Cells were fixed and stained with anti-Fn antibody. Bar, 50 µm. (B) Quantitation of [¹²⁵I]Fn incorporation into the deoxycholate-insoluble pool. The results are representative of three independent experiments (mean±s.e.m.). (C) Quantitation of the extent of cell spreading. The average areas on the substrates was determined for 120 sparsely plated cells in each population (mean±s.e.m.).