3D topography of noncompact zone Golgi tubules in rat spermatids: A computer-assisted serial section reconstruction study

Abstract

Background: In the Golgi apparatus, the 3D topography of saccules in the compact zones (CZs) is better understood than that of tubules in the noncompact zones (NCZs). The positioning of NCZ tubules relative to each other and to CZ saccules was studied in rat spermatids by computer-assisted serial section microscopy. Methods: Twenty-four (semi) serials (3-6 consecutive sections each) in total were collected from untreated tissues and from tissues treated for glucose-6-phosphatase (G6P) cytochemistry 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 computer reconstructed and the final models displayed in red-green/red-blue stereo. Results: In single thin sections, NCZ tubules typically appeared randomly oriented; however, in serial sections a high degree of organization was evident. Most tubules were traceable to the type of tubular networks (TNs) that interconnect equivalent CZ saccules (see review Rambourg and Clermont, 1990) Such TNs were present at consecutive saccular levels through each NCZ, were stacked like the saccules from which they originate, and in many regions were aligned from cis-trans. The cis-most of the TNs projected above the cis-pole of the stacked saccules and were penetrated by coated and uncoated ER buds. Conclusions: The function of the extensive NCZ tubular domain, consisting of the stacked and aligned TNs, will have to be addressed in future studies. However, the specific topography of the cis-most TNs make them candidates to serve as acceptor membranes in ER-Golgi transport. Anat.

A New Look at the Functional Organization of the Golgi Ribbon

“…This relatively simple model places the focus on the cisternal stacks as the basic structural and functional units of the ribbon, but does not adequately take into account the extensive tubular networks that – as mentioned earlier – represent an additional key feature of this organelle (Mollenhauer and Morré, 1998; Kepes et al, 2005). Moreover, several studies indicate that the ultrastructural organization of the non-compact zones within the ribbon is more complex than presented by the prevailing “tubular bridge model” (Thorne-Tjomsland et al, 1998; Ladinsky et al, 1999; Martínez-Martínez et al, 2017).…”