Differential localization of
glycoconjugates was detected on microvilli and microridges of the intact cell surface of frog pronephric
tumor cells in tissue culture.
Alcian blue and
Alcian blue/PAS staining showed a heavy concentration of
dye limited to the unique short microvilli and extensive microridges of the
tumor cells as previously seen with SEM (Tweedell and Williams 1976). Staining was absent or greatly reduced on microvilli of the normal pronephric cell surface. Previous exposure of each kind of cells to
neuraminidase or extraction by mild hydrolysis removed the active staining sites but
Alcian blue uptake was unaffected by prior digestion with testicular
hyaluronidase.
Fluorescein isothiocyanate (
FITC) bound
wheat germ agglutinin (WGA) produced a similar pattern of fluorescence on the microvilli of the
tumor cells and a limited distribution on the normal cells. Digestion with
neuraminidase preferentially removed but did not completely eliminate the surface binding of WGA on both the normal and
tumor cells. Exposure of
tumor cell monolayers to
FITC bound
limulin, a
lectin specific for
sialic acid, also produced an intense surface fluorescence on the microvilli and ridges of
tumor cells. Prior treatment with
neuraminidase prevented the surface fluorescence but not internal binding. Normal pronephric cells gave sparse surface fluorescence but extensive internal binding. Each procedure indicates a preferential localization of complex
carbohydrates, including
sialic acid, on the unique microvilli of the
tumor cells. Concurrent assays for
sialic acid recovered from the
tumor cells indicated that
lectin bound surface
sialic acid was removable with
neuraminidase.