Immunocytochemical evidence for intragranular processing of pro-opiomelanocortin in the melanotropic cells of the rabbit.
The immunogold technique, employing antisera with clear-cut specificities, was used to localise different processing stages of pro-opiomelanocortin (POMC) in rabbit melanotropic cells. While the antiserum against gamma 3-MSH labelled all the secretory granules including intrasaccular condensations in the Golgi apparatus, antisera against alpha-MSH only labelled extra-Golgi secretory vesicles (SV). All extra-Golgi SV were likewise labelled with the three antisera against alpha-MSH used, despite their different specificities for the deacetylated, N-acetylated or C-amidated forms of the peptide. The antibody against beta-endorphin also labelled the extra-Golgi SV, while only some SV were labelled with the antibody against gamma-endorphin. These results correlate with biochemical data in favour of mainly--if not exclusively--intragranular processing of POMC. Except for gamma 3-MSH, the cleavage of which could coincide with Golgi packaging of secretory material, other post-translational modifications of the precursor seem to occur when SV are discharged outside the Golgi area. The cleavage of gamma-endorphin appears to be a later step in POMC processing, occurring in some mature SV.
D000818:Animals; D000918:Antibody Specificity; D003429:Cross Reactions; D003594:Cytoplasmic Granules / Q000378:metabolism*; D004723:Endorphins / Q000032:analysis; D004797:Enzyme-Linked Immunosorbent Assay; D006046:Gold; D006651:Histocytochemistry; D007106:Immune Sera; D009074:Melanocyte-Stimulating Hormones / Q000031:analogs & derivatives / Q000276:immunology; D008854:Microscopy, Electron; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D011333:Pro-Opiomelanocortin / Q000276:immunology / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011817:Rabbits; D011863:Radioimmunoassay; D000521:alpha-MSH / Q000031:analogs & derivatives*
D004723:Endorphins; D007106:Immune Sera; C040237:N-acetyl-MSH; D000521:alpha-MSH; D011333:Pro-Opiomelanocortin; D006046:Gold; D009074:Melanocyte-Stimulating Hormones