OUTER SEGMENT DISC MEMBRANE ASSEMBLY IN THE ABSENCE OF THE PIGMENT-EPITHELIUM - THE EFFECT OF EXOGENOUS SUGARS

When retinal rudiments of Xenopus laevis embryos are allowed to differ entiate in vitro, membrane precursors destined for the outer segment d o not form well-ordered stacks of membrane leaflets if the pigment epi thelium is removed from the outer retinal surface. However, addition o f certain saccharides permits the organization of outer segment membra nes into stacked membranous saccules, much like that demonstrated duri ng in vivo or in vitro development in the presence of an investing pig ment epithelium. Sugars that support the formation of well-organized p hotoreceptor outer segments include lactose, galactose and their deriv atives, while numerous other carbohydrates failed to support outer seg ment organization.