THE ROLE OF EXTRACELLULAR MATERIAL IN OPTIC CUP FORMATION

During chick optic cup formation, a cetylpyridinium chloride (CPC)-precipitate appeared at the edge of the retinal disc concomitant with the invagination of the optic vesicle. Further quantitative analysis of this CPC-precipitate from stage-12 to stage-15 was done under the Scanning Electron Microscope. The results showed that the precipitate appeared just before the invagination of the optic vesicle. The amount of the CPC-precipitate increased as the invagination of the optic vesicle proceeded. A lot of the precipitate still remained at the edge of the retinal disc of stage-14 and stage-14+ embryos even after high salt extraction.;The disappearance of these materials after diazo-oxo-norleucine (DON) or Tunicamycin (TM) treatment suggested that they are glycoconjugates. Optic cups did not form after DON or TM treatment, indicating the importance of these materials for optic cup formation. Incorporation studies showed that the lack of optic cup formation is not a result of decreased protein or collagen synthesis since the incorporation of ('14)C-proline or ('3)H-tryptophan were not affected by TM. The incorporation of ('35)S-sulfate into the TM samples was decreased after 6 hr of incubation but later increased from 6 hr to 21 hr of incubation. The incorporation of ('3)H-glucosamine stayed the same as the controls after 6 hr of incubation but decreased after that. This coincided with the fact that embryos are not able to reverse the effect of TM on optic cup formation after 6 hr of incubation. These results suggest that the lack of optic cup formation is caused by inhibition of the synthesis of glycoconjugates. Keratan sulfate is probably the major component of these CPC-precipitates. The increase of sulfate incorporation from 6 hr to 21 hr of incubation probably results from increased synthesis of other glycosaminoglycans since blocking keratan sulfate synthesis accumulated more precursors for other glycosaminoglycans. The disappearance of certain attachment sites between the overlying ectoderm and the optic vesicle after DON or TM treatment suggests that they are also important for optic cup formation.