3D TOPOGRAPHY OF NONCOMPACT ZONE GOLGI TUBULES IN RAT SPERMATIDS - A COMPUTER-ASSISTED SERIAL SECTION RECONSTRUCTION STUDY

Background: In the Gels apparatus, the 3D topography of saccules in th e compact zones (CZs) is better understood than that of tubules in the noncompact zones (NCZs), The positioning of NCZ tubules relative to e ach other and to CZ saccules was studied in rat spermatids by computer -assisted serial section microscopy. Methods: Twenty-four (semi) seria ls (3-6 consecutive sections each) in total were collected from untrea ted tissues and from tissues treated for glucose-6-phosphatase (G6P) c ytochemistry as an alignment tool, The serials proceeded along either the cis-trans or the medial-lateral axes of the Golgi and collectively sampled all portions of this organelle, Selected serials were compute r reconstructed and the final models displayed in red-green/red-blue s tereo. Results: In single thin sections, NCZ tubules typically appeare d randomly oriented; however, in serial sections a high degree of orga nization was evident. Most tubules were traceable to the type of tubul ar networks (TNs) that interconnect equivalent CZ saccules (see review Rambourg and Clermont, 1990) Such TNs were present at consecutive sac cular levels through each NCZ, were stacked like the saccules from whi ch they originate, and in many regions were aligned from cis-trans, Th e cis-most of the TNs projected above the cis-pole of the stacked sacc ules and were penetrated by coated and uncoated ER buds. Conclusions: The function of the extensive NCZ tubular domain, consisting of the st acked and aligned TNs, will have to be addressed in future studies. Ho wever, the specific topography of the cis-most TNs make them candidate s to serve as acceptor membranes in ER-Golgi transport. (C) 1998 Wiley -Liss, Inc.