Studies on the Fibrogenesis of Collagen 

 Sylvia Fitton Jackson 



Medical Research Council Biophysics Research Unit, 

 Wheat sioiie Laboratory, King's College, London, W.C.2 



Collagen protein is widely distributed in the 

 various phyla of the animal kingdom (3; Rudall, 

 1955). Recognition of its presence may be based in 

 the characteristic fibre diagrams obtained from va- 

 rious materials by means of high angle x-ray ditlYac- 

 tion. Though different sources of collagen give fibre 

 diagrams indicating substantial differences of orien- 

 tation and crystallinity. they are all recognizably 

 belonging to the same class of protein. On the other 

 hand, there are variations, for instance, in the amino- 

 acid composition and in the structure of the con- 

 stituent fibrils as seen by means of electron micros- 

 copy. 



It is of interest, therefore, that though a typical 

 fibre diagram for collagen is obtained from the 

 cuticle of annelids (I), the characteristic axial perio- 

 dicity of about 640 A of the fibrils is apparently 

 lacking (4). It was thought that an investigation of 

 the fine structure of the cuticle of the annelid, 

 Liimbricus sp., by the use of thin sections in the 

 electron microscope might help to elucidate the 



Fig. 1. Section through the ctiticlc of Liiinhriciis sp. whicli 

 shows the layers of fibrils which lie adjacent to the epidermal 

 cells. Cytoplasmic processes stretch between the cell surface 

 and the outer membrane of the worm, and form a basket- 

 weave pattern with the fibrils. The microvilli on the outer 

 surface of the worm are seen at the top of the micrograph. 

 Magnification 23,000. 



method whereby the protein molecules became orien- 

 tated into the distinctive layered structure which has 

 been shown to be a feature of this material. 



This work is still in a preliminary stage, but it has 

 been found that the cuticle is composed of five 

 regions. The region adjacent to the main body of 

 the epidermal cells, which lie immediately beneath 

 the cuticle, contains many evenly spaced folds of 

 cytoplasm; these folds appear to taper into fine 

 cytoplasmic processes which penetrate through the 

 cuticle and are connected to the exterior membrane 

 of the worm (fig. 1). In sections cut parallel to the 

 surface of the worm, these processes are seen to be 

 arranged in rows; they are usually about 700-1000 A 

 in diameter and about 2000 A apart. Each row 

 appears to be embedded in a ribbon of less dense 

 material about 2500 A wide. It is possible that the 

 processes correspond to the granular layer recorded 

 by Read and Rudall (4) in replicas of the earthworm 

 cuticle. 



Region 2, immediately above this lowest layer, con- 

 tains fibrils about 200 A in diameter; there are about 

 4 layers of fibrils in this region. Region 3, which 

 is about 5 // thick, is composed of about 18 layers 

 of apparently unhanded fibrils. Transverse sections 

 show that the fibrils are irregular in outline, in fact 

 some are nearly square, and measure up to about 

 2000 A across (fig. 2). Longitudinal sections demon- 

 strate that the fibrils are in layers, which confirms 

 previous observations. Measurements have shown 

 that the layers of fibrils are orientated from 74' 

 to 106' to each other; these measurements vary 

 depending on whether the worm was contracted or 

 extended on fixation, and suggest that the layers 



Fig. 2. Transverse sections of the fibrils of the cuticle, which 

 shows they are irregular in outline. Magnification 30,000. 



Fig. 3. The fibrous honeycomb of amorphous material which 

 surrounds each fibril. Magnification 23,000. 



