Cell surface localization of 5′AMP nucleotidase in prestalk cells of Dictyostelium discoideum

Abstract

5′AMP nucleotidase activity was localized by electron microscopy in Dictyostelium discoideum during cell differentiation. In addition, the activity was assayed by micro enzymic methods in sections dissected from specific cellular regions of lyophilized individuals. The results of the 2 procedures were in agreement, demonstrating that at the culmination stage of development the activity is strikingly localized in the prestalk cells adjacent to the prespore region. The cytochemically stained reaction product appeared only along the plasma membrane of the cells. As prestalk cells migrate into the stalk sheath and undergo differentiation, the activity is rapidly lost. Examination of stained cells at high magnification revealed the product accumulation to be primarily at the cell surface, suggesting that the enzyme functions extracellularly. Occasionally, cells having the morphological appearance of prestalk cells were found within the prespore region. These cells demonstrated 5′AMP nucleotidase activity at their plasma membrane in sharp contrast with neighbouring prespore cells. The strategic localization of 5′AMP nucleotidase may reflect a mechanism for establishing and maintaining regulatory levels of extracellular 5′AMP and/or adenosine during pattern formation in this model system.