Disruption of glycogen phosphorylase gene expression in Dictyostelium: Evidence for altered glycogen metabolism and developmental coregulation of the gene products

Glycogen phosphorylase 1 and 2, the isozymes responsible for glycogen degradation, are encoded by separate genes in Dictyostelium. The two gene products display different transcriptional and translational expression and distinct post-translational regulation. Using DNA-mediated transformation, Dictyostelium clones which lacked either glycogen phosphorylase 1 or 2 (gp 1 or gp 2) expression were obtained. The loss of either enzyme did not change axenic growth patterns, developmental progression, or gross organismic morphology. In gp 1 − strains, glycogen accumulated to a 17- to 28-fold higher level during late stationary phase without any obvious detrimental effects. This implies that no alternative pathway for glycogen degradation is present in amoebae, and that glycogen metabolism is not critical for vegetative cell growth. Developmental glycogen concentrations were not altered significantly in any of the transformants, but in gp 2 − cells the posttranslational regulation of the intact gp 1 enzyme was apparently modulated to compensate for the loss of gp 2. Western blots of microdissected, lyophilized Dictyostelium slugs and early culminates showed that gp 2 was found in both prestalk and prespore cells, with a slight enrichment in prespore cells. The gp 1 protein was highly enriched in prestalk cells in the parental strain. In gp 2 − transformants, however, gp 1 was detected in equal amounts in both cell types. The loss of gp 2 led to a shift in the cell-type-specific expression pattern of gp 1, presumably due to developmental co- ordinate regulation of gp 1 and gp 2 at the translational and/or transcriptional level.