Integrative method for three-dimensional imaging of the entire Golgi apparatus by combining thiamine pyrophosphatase cytochemistry and array tomography using backscattered electron-mode scanning electron microscopy.

Thiamine pyrophosphatase (TPPase) cytochemistry is an established method for specific labeling of the trans-Golgi cisterns in tissue sections. Herein, we combined this enzyme cytochemical method with array tomography using scanning electron microscopy (SEM), a new imaging technique based on collection of backscattered electron (BSE) images of consecutive resin-embedded sections on glass slides, to detect the entire three-dimensional (3D) organization of the Golgi apparatus with sufficient spatial resolution. As the signal intensity of BSE depends on the atomic number of the materials, lead precipitates confined to the trans-Golgi cisterns after TPPase cytochemistry were clearly observed by BSE-mode SEM. The mild fixative used for TPPase cytochemistry also enabled accurate identification of target gonadotropes in the composite pituitary tissue by immunocytochemical staining. By 3D reconstruction of the entire trans-Golgi cisterns based on serial ultrathin section images of tissues after TPPase cytochemistry, we detected ultrastructural differences in the 3D configuration of the Golgi apparatus between cerebellar Purkinje cells and pituitary gonadotropes. The appropriate combination of enzyme cytochemistry and/or immunostaining with array tomography will further clarify the relationship between the organization and functional states of the Golgi apparatus.