Variation and immunocyochemical localization of processing enzymes in proopiomelanocortin cells during ontoneny

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PC1/PC3 and PC2 are endoproteases involved in prohormone cleavage at pairs of basic amino acids. To determine the cellular and subcellular distribution of PC1/PC3 and PC2 in the pituitary glands, we generated their polyclonal antisera in rabbits, using two synthetic peptide antigens corresponding to amino acids 442-459 (ST-28) of PC1/PC3 and 613-629 (ST-29) of PC2 and two bacterially expressed antigens covering amino acids 145-414 (KN-1) of PC1/PC3 and 385-637 (KN-2) of PC2. Western blot analysis revealed the presence of PC1/PC3 87 and 68 kDa) and PC2 (70 kDa) in the rat pancreatic islets, indicating that each of the antisera was specific for the corresponding antigen. In the present immunocyochemical studies, many neuroendcrine cells displayd positive reaction to these antibodies. In almost all the animals as far as examined, PC1/PC3 and PC2 showed differential immunoreactivity in proopiomelanocortin (POMC) cells. In the anterior lobe, antiserum against PC1/PC3 exclusively immunostained corticotrophs in the intermediate lobe. Immunoelectron microscopy, using double-labeling with gold particles of different sizes revealed that almost all of immunolabeled ACTH- or alpha-MSH-secretory granules were also positive to PC1/PC3 and PC2 antibody. This differential localization of PC1/PC3 and PC2 provides a novel argument for the subtrate-specificity of the PC1/PC3 and PC2 enzymes in the processing of pituitary POMC cells. To elucidate factors that regulate changes in the processing patterns of POMC in the pituitary corticotrophs during postnatal development, in near further, the presence of PC1/PC3 and PC2 will be examined immunocytochemically.