Immunocytochemical localization of ras p21 product in thyroid follicular cells of normal rats using monoclonal antibody RAP-5.

The ultrastructural localization of ras p21 product was studied immunocytochemically in thyroid follicular cells of normal rats using pre-embedded peroxidase-labelled antibody techniques and a monoclonal antibody, RAP-5, which had been raised against a synthetic peptide corresponding to amino acid positions 10-17 of the ras p21 protein. The ras p21 product was detected in cisternae of rough endoplasmic reticulum, Golgi apparatus and the subapical portion of apical plasma membrane, in which it was most concentrated. This study indicated that the p21 product may be synthesized in the rough endoplasmic reticulum and finally localized at the subapical portion of the thyroid follicular cells, and also that the apical plasma membrane may be a major site for the reception of environmental stimuli.