TRANS-GOLGI NETWORK (TGN) OF DIFFERENT CELL-TYPES - 3-DIMENSIONAL STRUCTURAL CHARACTERISTICS AND VARIABILITY

Background: The trans-Golgi network (TGN) is generally considered as a distinct and permanent structural compartment of the Golgi apparatus of various cell types. To verify this postulate we examined and compar ed the three-dimensional characteristics of the TGNs of 14 different m ammalian cell types as presented in our various publications since 197 9 when we initially described the trans-tubular network of Sertoli cel ls. Methods: In all these studies we used low and high voltage electro n microscopes on thin or thick sections of tissues fixed with glutaral dehyde and postfixed with reduced osmium. The sections were stained wi th uranyl acetate and lead citrate. Stereopairs, prepared from photogr aphs of tilted specimens, permitted a direct observation of the three- dimensional structure of the various elements of the Golgi apparatus. Results: The TGNs are multilayered and extensive in cells which do not form large typical secretory granules (Sertoli cells, nonciliated cel ls of ductuli efferentes, spinal ganglion cells) but have an extensive lysosomal system. The TGN is absent in cells forming very large secre tory granules (secretory cells of seminal vesicles and lactating mamma ry glands). The TGNs are small in cells producing small to medium-size secretory granules and/or appear as residual fragments on the trans a spect of the Golgi stacks (e.g., mucous cells of Brunner's gland, panc reatic acinar cells, etc.). In cells with multiple and extensive TGNs, a continuity of these tubular networks with the two or three transmos t saccules of the stack is observed but there are seemingly no connect ions between the TGNs. Whenever the TGNs are present, they do not form a continuous structure along the Golgi ribbon. However, they do prese nt, in all cases, configurations suggestive of desquamation and renewa l. Conclusions: The structure of the TGN varies considerably from one cell type to another, being extensive in cells not showing typical sec retory granules but having an extensive lysosomal system, while in sec retory cells showing small or large secretory granules the TGN is eith er small or even entirely absent. (C) 1995 Wiley-Liss, Inc.