A lens fibre differentiation factor from calf neural retina

During growth of the eye lens, epithelial cells differentiate into fibre cells under the influence of neural retina. The fibre differentiation factor (FDF) was partially characterized from calf retina-conditioned medium, using lens epithelial explants from young rats, to provide a bioassay for differentiation. FDF was associated with large-protein aggregates, the smallest of which eluted at approximately 500-600 kD on Sephacryl S-300 columns and migrated as a single protein band near 600 kD on gradient gels. This protein resolved into nine major peptides on SDS-polyacrylamide gels, ranging between 23 and 27 kD. Eight of these peptides were present oa four doublets, but did not appear to contain specific carbohydrate residues. The approximately 500-600 kD complex could be slightly disrupted by trypsin or heat treatment to release a less stable 90 kD component. Fractionation of FDF invariably led to loss of activity, possibly due to gradual dissociation into less active and/or less stable components. A working hypothesis suggested by these findings is that FDF is associated with a small group of peptides, each contributing an essential function to the process of fibre differentiation.