Intracellular processing of procollagen induced by the action of colchicine

Corium fragments incubated in vitro with colchicine or obtained from chick embryos 11 days old after in vivo injection of this alkaloid were studied with the electron microscope. The well known effect of colchicine in producing an accumulation of procollagen was demonstrated by electrophoretic separation of the collagenous products in polyacrylamide gels after incubation of corium fragments in vitro with labelled amino acids. Electron microscopical studies showed various types of cytoplasmic vacuoles containing collagenous fibrillar structures. Some of these vacuoles contained non-striated filaments, fibres with the periodicity of native collagen, and segment long spacing (SLS) crystallites, embedded in an electrondense substance. The central aspect of this communication is the finding of intracellular SLS in cytoplasmic vacuoles. These crystallites were morphologically intact, and had no additional bands at the NH2 or COOH ends, suggesting that they were formed by the aggregation of tropocollagen molecules. Since the presence of intact SLS in cytoplasmic vacuoles suggests that these are secretory, we believe that inhibition of the transcellular transport system by colchicine permitted the visualization of vacuoles containing the products of tropocollagen interconversions. We interpret these findings as an example of autophagocytosis, with intracellular processing of procollagen, occurring in chick embryo fibroblasts when the secretion of procollagen is inhibited by colchicine.