Intracellular and Intranuclear Localization of Discoidin I in Aggregating Cells of Dictyostelium Discoideum

ABSTRACT

The endogenous lectin of Dictyostelium discoideum, discoidin I, is primarily intracellular and its appearance coincides with the acquisition of mutual cohesiveness by the cells. Subcellular localization of the lectin in intact cells by immunocytochemistry has been hampered by the fact that fixation with glutaraldehyde renders it antigenically inactive. A fixation protocol has been developed that both preserves morphology adequately and maintains antigenicity. Thin sections of aggregating cells were indirectly immunolabelled using the protein A-colloidal gold method. The lectin is distributed throughout the cytosol and is not specifically located inside any endomembrane compartment except the nuclei and some mitochondria. Gold particles were counted over nuclei and cytoplasm and areas determined for each. Discoidin I is concentrated in nuclei about twice that found in the cytoplasm.

Key Words:

• lectin
• immunocytochemistry
• slime mold
• nucleus