Intracellular localization of fibronectin using immunoperoxidase cytochemistry in light and electron microscopy

An immunocytochemical staining method for light and electron microscopy was developed to permit adequate penetration of staining conjugates with high specificity, while preserving acceptable ultrastructure. For this purpose an indirect immunoperoxidase method with Staphylococcal protein A-peroxidase conjugates was used in the presence of saponin on aldehyde-saponin-fixed cells. As the first application, fibronectin was localized intracellularly in human embryonic skin fibroblasts. Fibronectin was detected in large amounts in the cisternae of rough endoplasmic reticulum and in 200 nm (secretory?) vesicles. Little fibronectin was present in the Golgi complex; the stacked Golgi cisternae were conspicuously devoid of this protein. The 200 nm vesicles were mostly distributed on the mature side of the Golgi apparatus. These results indicate that fibronectin is exclusively localized to intracellular structures involved in secretory function and suggest that fibronectin may not be processed in significant amounts within the cisternal stacks of the Golgi complex.