Features of the polarity of the Golgi apparatus of frog photoreceptors: studies with lectins and with Brefeldin A.
The cis-trans polarity of the Golgi apparatus is important in Golgi functioning in glycosylation, sorting and other processes. The present work extends our prior studies on the polarity of the Golgi apparatus of frog (Rana) rod photoreceptors. We demonstrate that Golgi structures with the morphology and distribution of cis elements show the heaviest deposition of osmium. Elements with morphology and cytochemical reactivities resembling trans Golgi structures remain discernible as discrete arrays after exposure of the cells to Brefeldin A. These properties strengthen our identification of cis and trans elements since they are shared with corresponding Golgi structures in other cell types. We have also investigated the binding of lectins to sections prepared by cryoultramicrotomy. We find that Concanavalin A, with probable chief affinity for core mannoses in oligosaccharides, localizes to cis, medial and trans elements of the photoreceptor's Golgi apparatus. Wheat germ agglutinin, with likely affinity at least partly for terminal N-acetylglucosamines, localizes to trans and medial elements. A trans localization is seen with Ricinus communis agglutinin (RCA 120), but this lectin binds extensively only after neuraminidase treatments suggesting that its chief affinity is for galactose residues that are penultimate to sialic acids (neuraminic acids) in the native oligosaccharides. Overall, the pattern of lectin binding to Golgi structures that we observe resembles that seen in a variety of other cell types. The distribution of glycosylated molecules we detect in the photoreceptor's Golgi apparatus may bear upon such matters as the unusual features of the glycosylation of mature opsin.
St Jules
R
R
Department of Biological Sciences, Columbia University, NY 10027.
Santa-Hernandez
M
M
Ungar
F
F
Holtzman
E
E
D000818:Animals; D020126:Brefeldin A; D003517:Cyclopentanes / Q000494:pharmacology*; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D037102:Lectins / Q000378:metabolism*; D008854:Microscopy, Electron; D010786:Photoreceptor Cells / Q000378:metabolism / Q000648:ultrastructure*; D011894:Rana pipiens
D003517:Cyclopentanes; D037102:Lectins; D020126:Brefeldin A