Fig. 4.

Protruding and recessed fibripositors contain newly synthesized collagen fibrils. Pulse–chase analysis of embryonic tendon demonstrated that procollagen processing and secretion was prevented by DMOG and reduced the numbers of fibripositors and fibricarriers. (A) Proteins were sequentially extracted in neutral salt buffer (S1) and buffer containing Nonidet P-40 (N), and the ¹⁴C-labeled proteins were analyzed by SDS/PAGE and autoradiography. The identity of polypeptide chains of procollagen, pC-collagen, and collagen are indicated. (B) Visualization of the cell-matrix interface by SBF-SEM before and after treatment with DMOG for 48 h. Fewer fibrils occurred in fibricarriers (purple), protruding (green), and recessed (blue) fibripositors. (Scale bar: 2 µm.) (C) Quantitation of the frequency of fibril-containing compartments before and after inhibition of procollagen secretion by DMOG. *P ≤ 0.05.