The fate of the Golgi apparatus and the endoplasmic reticulum during lens fiber cell differentiation

Purpose. To establish the fate of the Golgi apparatus and the endoplasmic reticulum (ER) during lens fiber differentiation. Methods. Organelles were visualized by confocal or electron microscopy. For fluorescence microscopy, organelles were labeled with fluorescent probes or antibodies raised against organelle-resident proteins. The cytoplasmic volume was reconstructed from optical sections using volume rendering techniques. Results. The Golgi apparatus was located apically in epithelial cells. In the annular pad, Golgi elements were transformed into ribbon-like structures running parallel to the long axes of the cells. Toward the lens equator, the Golgi apparatus fragmented. In the lens fibers, the Golgi apparatus was detected only in the superficial cells. The ER was present as vesicular or tubular elements in both epithelial and cortical fiber cells, and ER probes co-labeled the nuclear membrane and revealed that the ER and nuclei disappeared coincidentally in the deep cortex. Using a lipophilic dye and volume rendering, the relationships between organelles could be evaluated in three dimensions. Conclusions. The Golgi apparatus was not a prominent organelle in differentiating lens fibers. In contrast, the ER was more abundant and extended to the edge of the organelle-free region, where it was degraded along with the nuclei and mitochondria.