Fucose in alpha(1-6)-linkage regulates proliferation and histogenesis in reaggregated retinal spheroids of the chick embryo

We have used the lectin from A leuria aurantia (AAL) which is highly specif ic for alpha(1-6)-linked fucose, to examine its effect on chicken retinogen esis in a reaggregation culture system, When dispersed cells of the embryon ic chick retina are reaggregated to form histotypic retinospheroids, AAL el icits strong inhibition of spheroid growth. The action of AAL is specific, since its effect is dose-dependent, saturable, and inhibited by an excess o f fucose. Fucosidase treatment entirely abolishes reaggregation. In contras t, Anguilla anguilla agglutinin (AAA) binding to fucose in alpha(1-2)-linka ge does not show any effects. Incubation with CAB4-a specific monoclonal an tibody for fucose in alpha(1-6)-linkage-reduces spheroid size and shape. AA L does not much affect primary aggregation, but rather subsequent processes of cell proliferation and histogenesis. In particular, AAL inhibits uptake of bromo-desoxyuridine (BrdU), most efficiently so during days in vitro 2 (div2) and div3. As a consequence, the histological differentiation is enti rely disturbed, as evidenced by vimentin immunostaining; particularly, rose ttes are not forming and the radial glia scaffold is disorganized. We concl ude that glycoproteins exhibiting fucose in alpha(1-6)-linkage may play maj or roles in early processes of retinal tissue formation.