Analysis of the distribution of glycoconjugates in the digestive gland of the bivalve mollusc Mytilus galloprovincialis by conventional and lectin histochemistry

Abstract

We examined the distribution and pattern of reactivity of a panel of 16 lectins in the digestive gland of the bivalve mollusc Mytilus galloprovincialis at the light-microscopic level. Various chemical treatments were applied in combination with lectins to differentiate between N- and O-linked oligosaccharides. Several control reactions were carried out, including replacement of lectins by buffer and incubation with their specific competitive inhibitors. Some lectins reacted selectively with particular cell types, thus revealing a cell-specific glycoconjugate distribution pattern which is possibly related to the metabolic role of each cell type in the digestive gland. Glycoconjugates containing glucosamine, mannose, and sulfated galactose were associated with the endolysosomal system of digestive cells. These glycoconjugates were also found in small vesicles randomly distributed in the cytoplasm of adipogranular cells in the connective tissue. However galactosamine residues appeared to be associated mainly with basophilic cells. Fucose residues did not exhibit a cell-specific distribution and appeared in small amounts homogeneously distributed throughout the digestive gland tissue. Conventional histochemical reactions for carbohydrate detection revealed moderate amounts of periodic-acid-Schiff-positive, neutral carbohydrates widely distributed in digestive and connective tissues. Among the acid carbohydrates, most cell types contained complex sulfated carbohydrates, but not carboxylated ones; this agreed well with the complete lack of sialic acid residues in all cell types studied, as observed by lectin histochemistry.

Proteins and Saccharides of the Sea Urchin Organic Matrix of Mineralization: Characterization and Localization in the Spine Skeleton

“…If terminal GalNAc residues are present in some O-glycoproteins, they are not attached directly to the serine residue, as evidenced by the absence of VVL binding (Tollefsen and Kornfeld, 1983). Concerning the fucose (Fuc) residues, the UEA I binding could indicate the presence of terminal Fuc residues outside of the inner core of N-glycoproteins (Baldus et al, 1996;Robledo et al, 1997). On the other hand, AAL binding could indicate the presence in some N-glycoproteins of a terminal Fuc with an ␣1,6 link to the GlcNAc involved in the N-glycosylamine linkage (Debray and Montreuil, 1989).…”

“…The PHA-E and PHA-L bindings to the IOM demonstrate, in the matrix, the presence of bisected bi-or tri-antennary complex chains and of tri-or tetra-antennary complex chains, respectively (Cummings and Kornfeld, 1982;Hammarström et al, 1982;Liener et al, 1986). Con A binding to the IOM could indicate the presence of high-mannose-type N-glycoproteins or of biantennary complex N-glycoproteins (Lampreave et al, 1995) although it was also recently shown to react with O-glycoproteins (Robledo et al, 1997).…”

Glycosylation and sorting pathways of lysosomal enzymes in mussel digestive cells

“…In addition, a second control series was made for AcPase activity by adding a specific inhibitor (10 mM NaFl) to the complete incubation solution. Based on a previous study of mussel digestive gland tissue at the light-microscope level, in which 16 lectins (including chemical and enzymatic treatments, such as desulphation, β-elimination, treatment with endo-F enzyme and their combination) were employed (Robledo et al 1997), seven lectins that bound to digestive cells were selected for the present investigation (Table 1). The concentrations used in each case depended on the technical approach used (preembedding and post-embedding) and appear detailed in Tables 3 and 4.…”

“…Based on these results, seven lectins (see Table 1) have been selected for the present study in order to examine the five saccharide residues found in mussel digestive cells: fucose, galactose, mannose, Nacetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc). According to Robledo et al (1997), the binding of lectins to sialic acid is absent or weak in the mussel digestive gland, even after desulphation and chemical or enzymatic digestion; therefore, lectins able to recognize sialic acid residues have been omitted from the present investigation. Likewise, several other agglutinin types, e.g.…”

“…The histochemistry of GCs and acid hydrolases has previously been investigated by light microscopy (Robledo et al 1997). Based on these results, seven lectins (see Table 1) have been selected for the present study in order to examine the five saccharide residues found in mussel digestive cells: fucose, galactose, mannose, Nacetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc).…”