The regulation of sexual development in Dictyostelium discoideum: cannibalistic behaviour of the giant cell

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Abstract
Sexual development leading to macrocyst formation in Dictyostelium discoideum involves the development of zygote giant cells which subsequently chemoattract and cannibalize local unfused amoebae of the same genotypes from which they formed. A system for assessing this process was developed wherein purified giant cells were fed amoebae under various conditions with the production of endocytes being assessed after neutral red staining of living cells. The phagocytic rate was linear during the 3-h assay period, was directly related to the concentration of amoebae, and demonstrated limited pH and temperature optima. Light which inhibits macrocyst development had no effect on sexual endocytosis. Cell-free conditioned medium from sexual cultures actively involved in phagocytosis enhanced giant cell endocytosis in the assay system. Drug studies revealed that microfilaments and microtubules are involved in the endocytic process and energy for it is supplied by both aerobic and anaerobic metabolic pathways. The data are discussed in terms of phagocytosis in D. discoideum and other organisms.