Regional Differences in Synthesis, Intracellular Transport, and Secretion of Protein in the Mouse Epididymis

Abstract

The synthesis, intracellular transport, and secretion of proteins were studied in different parts of the mouse epididymis. Adult mice were administered [³H]leucine, and at subsequent intervals between 10 min and 12 h two animals were killed. Samples of initial, middle, and terminal segments were prepared for light and electron microscope radioautography. In the initial and middle segments, the proportion of silver grains showed successive peaks over endoplasmic reticulum, Golgi apparatus, coated vesicles, and the apical cell surface. Labeling of luminal contents increased at the end of this sequence, at 1-2 h after injection of precursor. These events, however, occurred earlier in the middle segment than in the initial segment. Similar structures were labeled in the terminal segment, but radioactivity of the rough endoplasmic reticulum remained relatively high, peaks in labeling of other organelles were not sharp, and luminal labeling did not rise as much as in the more proximal segments. The results suggest that the synthesis and transport of proteins was more rapid in the middle than in the initial segment. At least in the middle segment, the sparsely granulated reticulum appeared to participate in protein synthesis along with the rough endoplasmic reticulum. In both initial and middle segments, coated vesicles may have been involved in transport from the Golgi apparatus to the cell surface and lumen. Relatively little protein secretion occurred in the terminal segment, where much newly synthesized protein appeared to be retained within the epithelial cells. The findings are related to the function of sperm maturation in initial and middle segments and of sperm storage in the terminal segment.