Distribution of N-acetyl-Î±-D-galactosamine (GalNAc) in normal and malignant oral epithelium
In this project, the N-acetyl-ex-D-galactosamine (GalNAc) binding lectin from the green
marine alga Codium fragile ssp. tomentosoides (C. fragile) was purified and techniques
developed to label the lectin for visualisation by light and electron microscopy and
electrophoresis. This represents the first time a histochemical reagent has been developed
from a marine alga.
The new reagent was initially assessed for transmission electron microscopy using human
blood group A1 erythrocytes. A novel method gave a topographical view, and showed the
distribution of gold particles on the surface of erythrocytes.
The pattern of C. fragile lectin binding to pig normal oral epithelium was studied in the
environmental scanning electron microscope to avoid charging artefact, using paraffin
wax sections of pig normal epithelium stained with C. fragile lectin-gold conjugate
enhanced with silver. X-ray micro analysis demonstrated lectin binding on the plasma
membrane surface of epithelial cells at cells to cell contacts suggesting binding to cellular
Biotinylated lectins binding GalNAc were used to investigate, identify and compare the
binding of lectins in pig normal oral epithelium and altered glycoconjugates in cultured
malignant cells from human oral tumours, using lectin histochemistry in the light
microscope. Lectin from C. fragile was compared with Dolichos biflorus, a lectin from plants,
and Helix pomatia (HP A) from snails. Although each lectin binds GalNAc it was shown
that their binding pattern to pig normal oral epithelium was different, demonstrating that
these lectins could be used to identify altered cellular glycosylation in the normal cellular
Cultured human oral tumour cells from different grades of malignancy were investigated
using this panel of lectins. Binding of GalNAc specific lectins to cultured tumour cells
changed in relation to their level of differentiation. This discriminating capability of
GalNAc specific lectins offers exciting potential as indicators of tumour prognosis in
human oral epithelial tumours.
The lectins from C. fragile and HP A gave very similar staining results using histochemistry.
Binding of these lectins to cell membrane glycoproteins was investigated using
electrophoresis to show that C. fragile lectin binds to more and different cell membrane
glycoproteins than lectin from HP A, but did not bind to purified CD44, excluding this
adhesion molecule as a candidate for binding these lectins.