Crystalloid smooth endoplasmic reticulum in the quail uropygial gland.

The occurrence, localization and organization of crystalloid smooth endoplasmic reticulum (SER) membrane aggregates in the male quail uropygial gland was investigated by electron microscopy. The lattice-like structures exhibiting a hexagonal honeycomb pattern are regularly found in the perinuclear region of the fully developed intermediate cell (type II) which is most effective in lipid biosynthesis and constitutes the middle layers of the stratified glandular epithelium undergoing sebaceous transformation. The crystalloids frequently exhibit a rectangular shape and tend to cluster, the latter exceeding 5 microns in length. They are composed of sets of highly ordered and densely packed tubular SER profiles. Diaminobenzidine (DAB) stained peroxisomes exhibit a close spatial relationship to the borders of crystalloids, but the organelles do not participate in the formation of these grid-like structures. The functional significance of the conformational change of the SER organization is not known. Local accumulation of specific lipogenic enzymes within this functional SER domain is discussed.