Changes in the Cell Surface Level of GP126 during Development of Dictyostelium discoideum

The developmental regulation of the vegetative cohesion molecule, gp 126, has been monitored in the cellular slime mould Dictyostelium discoideum. As judged by immunoprecipitation using an anti-vegetative cell, cohesion blocking antibody, gp126 persisted until at least the grex stage of development although a decline in the level of the molecule was observed thereafter. Further, after the grex stage, cells showed an increasing loss of ability to absorb the cohesion-blocking effect of an anti-vegetative cell Fab. Therefore, the decline of gp 126 could be ascribed to a loss from the cell surface. By radio-iodination of vegetative cells followed by liquid-scintillation counting of gp 126, developmental-regulation could be determined quantitatively.
At the grex stage of development, whole aggregates were embedded in wax. Longitudinal sections were then stained with a monospecific anti-gp 126 Fab, followed by a fluorescent sheep anti-rabbit IgG. Fluorescence was observed only at the tip (the prestalk) region, thereby showing that gp 126 is a prestalk marker.
To confirm the above result, grexes were dissociated and cells were separated into prespore and prestalk populations on a gradient of Percoll. Prestalk but not prespore cells were able to absorb the cohesion-blocking effect of an anti-vegetative cell Fab.
To examine the biosynthesis of gp 126, cells were pulsed with radioactive glucosamine, mannose or acetate. The pattern of incorporation of radioactivity suggested that the de novo synthesis of gp 126 ceases upon commencement of development.