Cell type-dependent variations in the subcellular distribution of alpha-mannosidase I and II

Abstract

Abstract. a-mannosidases I and II (Man I and 11) are resident enzymes of the Golgi complex involved in oligosaccharide processing during N-linked glycoprotein biosynthesis that are widely considered to be markers of the cis-and medial-Golgi compartments, respectively. We have investigated the distribution of these enzymes in several cell types by immunofluorescence and immunoelectron microscopy. Man 1I was most commonly found in medial-and/or trans-cisternae but showed cell type-dependent variations in intra-Golgi distribution. It was variously localized to either medial (NRK and CHO ceils), both medial and trans (pancreatic acinar cells, enterocytes), or trans-(goblet ceils) cisternae, or distributed across the entire Golgi stack (hepatocytes and some enterocytes). The distribution of Man I largely coincided with that of Man II in that it was detected primarily in medialand trans-cisternae. It also showed cell type dependent variations in its intra-Golgi distribution. Man I and Man II were also detected within secretory granules and at the cell surface of some cell types (enterocytes, pancreatic acinar cells, goblet cells). In the case of Man II, cell surface staining was shown not to be due to antibody cross-reactivity with oligosaccharide epitopes. These results indicate that the distribution of Man I and Man II within the Golgi stack of a given cell type overlaps considerably, and their distribution from one cell type to another is more variable and less compartmentalized than previously assumed.

Accumulation of Mutant Huntingtin Fragments in Aggresome-like Inclusion Bodies as a Result of Insufficient Protein Degradation

“…Comparison of the fluorescence of HDQ83 protein aggregates with the immunostaining of ␥-tubulin, a known marker for the centrosome (Dictenberg et al, 1998), revealed that both structures colocalize at least partially (Figure 2d). On the other hand, the fluorescence of the HD exon 1 protein aggregates did not overlap with the immunostaining of ␣-mannosidase II, a marker for the Golgi apparatus (Figure 2e), indicating that the Golgi apparatus, which is also located in the perinuclear region (Velasco et al, 1993), is distinct from the HDQ83 protein aggregates. Accumulation of mutant HDQ83 protein in 293 Tet-Off cells also appeared to cause the reorganization of the intermediate filament vimentin.…”

High-resolution calcium mapping of the endoplasmic reticulum-Golgi-exocytic membrane system. Electron energy loss imaging analysis of quick frozen-freeze dried PC12 cells.

“…Although not resolved as clearly as in chemically fixed specimens, the organelles retained part of their dense appearance and were therefore easily recognized. The polyclonal antibodies used were addressed to components of two of the investigated organelles, the Ca2+ binding protein calreticulin (CRT), specific of the ER lumen (Villa et al, 1993;Nash et al, 1994), and mannosidase II (MA-NII), a GC membrane enzyme (Velasco et al, 1993). With the first, the immunogold labeling was strong, uniformly and strictly confined to the lumen of ER cisternae ( Figure 2A) including the nuclear envelope ; short and often slightly swollen ER cisternae, most often covered with discrete, dense polysomes; a clearly visible GC and various dense granules (arrows).…”

Heterogeneous Distribution of the Unusual Phospholipid Semilysobisphosphatidic Acid through the Golgi Complex

“…The underlying organization of these subcompartments is not fully known, but it must be maintained in the face of continuous bidirectional traffic. Although it is clear that resident proteins are localized to discrete compartments in the organelle (Dunphy and Rothman, 1985), their distribution may substantially overlap (Nilsson et al, 1993;Velasco et al, 1993). Also, the subcompartment localization of some Golgi-associated proteins varies with cell type (Brown and Farquhar, 1987;Colley, 1997).…”