The "spindle-shaped" body in fibroblasts: intracellular collagen fibrils.

The "spindle-shaped" or "fusiform" bodies of fibroblasts are membrane-bound collagen fibrils. These cellular organelles, also described in the literature as rods or cigars, can be induced massively in chick embryo fibroblasts by treatment with colchicine in vinblastine. These alkaloids also induce massively the presence of non-striated fibrils, segment long-spacing (SLS) and fibrous long-spacing (FLS) crystallites in cytoplasmic vacuoles. The intracellular fibrillar structures described within the cytoplasmic vacuoles suggest the occurrence of tropocollagen interconversions, indication that under the experimental conditions used in this work some procollagen is processed intracellularly. Our findings may represent the first step of autophagocytosis of collagenous products when the secretory process is blocked. It is possible that these agents, by blocking secretion, magnify a normal process, and that under normal conditions a population of procollagen molecules may be processed intracellularly, thus contributing to the process of fibrillogenesis.