Golgi apparatus of epithelial principal cells of the epididymal initial segment of the rat: Structure, relationship with endoplasmic reticulum, and role in the formation of secretory vesicles
Authors: Hermo Louis , Green Harold , Clermont Yves 
Published: February 2005

The initial segment of the epididymis of rats, fixed with glutaral‐dehyde, was postfixed with reduced osmium, a technique that clearly delineates the membranes of cisternae of the endoplasmic reticulum (ER) and the various elements of the Golgi apparatus, or with tannic acid to enhance the coats of vesicles and ribosomes on ER cisternae. The material was also treated to demonstrate various phosphatase activities (NADPase, TPPase, CMPase, G‐6‐Pase) or impregnated with osmium tetroxide.

In osmium‐impregnated material, the Golgi apparatus of the epithelial principal cells of the initial segment appeared in the light microscope as a branching, anastomosing ribbon forming a large network in the supranuclear region. In the electron microscope, ER were of two types: the heavily granulated, flattened, rough ER seen in the infranuclear and juxtanuclear regions and the distended, tubular, sparsely granulated ER, showing only few ribosomes, seen interlaced with the Golgi ribbon in the supranuclear region and at the apical pole of the cell.

Of particular interest in this cell was the fact that the sparsely granulated ER approximated the Golgi stack on both its cis‐ and trans‐faces. On the cis‐face of the Golgi stack, the sparsely granulated ER cisternae showed the usual finger‐ or bud‐like protrusions directed toward the cis element of the Golgi stack and around which numerous small 80 nm vesicles or membranous tubules were clustered. The Golgi stack consisted of the following elements in a cis‐trans axis: the cis osmio‐philic element, a first saccule slightly dilated, saccules two to four (S2–S4), which were NADPase‐positive, and saccules five to seven and the eight Golgi element, which were TPPase‐positive. On the trans‐aspect of the Golgi stacks, several (up to four) CMPase‐positive trans‐Golgi networks were observed often in close apposition to the sparsely granulated ER cisternae. One of the trans‐Golgi networks showed a “peeling‐off” configuration, i.e. part of it was closely apposed to the overlying Golgi element of the stack, whereas the remaining part was separated from the stack by a space occupied by a cisterna of sparsely granulated ER. The other trans‐Golgi networks were completely separated from the stack and were often seen sandwiched between sparsely granulated ER cisternae. Thus, ER cisternae showed extensive areas of close apposition but no continuity with the trans‐Golgi networks. Although the saccules of the Golgi stacks showed NADPase and/or TPPase activity, the trans‐Golgi networks displayed CMPase activity, thus facilitating their identification from the closely associated unreactive sparsely granulated ER cisternae.

The trans‐Golgi networks were variable in appearance but often showed sporadic electron‐lucent dilations along their length that were comparable to uncoated vesicles of similar size (150–300 nm) and appearance found in the trans‐region of the Golgi apparatus and at the apical pole of the cells. Such vesicles appeared to arise from the trans‐Golgi networks that eventually undergo fragmentation. Their identification as possible secretory vesicles will be discussed.