[Immunohistochemical study of fibronectin localization during the formation of the vascular coat under the influence of the pigment epithelium in chick embryos].

The role of fibronectin (FN) in cell interactions of retinal pigment epithelium (RPE) and mesenchyme surrounding the optic cup during choroid formation in chick embryos was studied by indirect immunofluorescence using antibodies against FN. Experimental coloboma of retina and choroid was used as a model. During the initial stages of coloboma the regions structured like retina rudiment appear in the outer layer of the optic cup. Such regions were formed in microphthalmic eyes obtained by excision of lens from the eyes of 3.5 day old chick embryos (stage 21). At stage 21 bright FN-specific immunofluorescence was observed in basal membrane located along the external surface of the normally differentiated RPE. Later on, FN-specific immunofluorescence appeared in mesenchyme condensing along the RPE. The most intensive FN-specific immunofluorescence was observed in chorio-capillary layer of choroid after 5-7 days of incubation. In microphthalmic eyes retina-like regions of RPE and adjacent mesenchyme showed negative reaction, and the choroid was not formed from the adjacent mesenchyme in such zones. The data obtained suggest that the presence of normally differentiated RPE producing FN-containing basal membrane is necessary for the formation of chorio-capillary layer of the choroid in chick embryos.