CELL DIFFERENTIATION AND PATTERN FORMATION IN DICTYOSTELIUM

Abstract

Taking advantage of the facts that differentiation of the prespore cell is characterized by synthesis of the specific antigen and that culminating cell masses are separated into the dissociable and the undissociable cell fractions, the proportions and the distributions of prespore and prestalk cells, spores and stalk cells were studied during the normal and abnormal courses of development of Dictyostelium discoideum NC-4. Prespore cells first appeared in the central mound of a young aggregate which was about to form a papilla. The proportion of prespore to total cells then rapidly increased up to the stationary level (70–80%) before completion of slug formation and thereafter remained constant until the time of culmination. During culmination, prestalk cells present in a slug quantitatively differentiated into stalk and basal disc cells in a fruiting body. A portion of prespore cells lost the antigen at early culmination, and these remained amoeboid even after complete formation of fruiting bodies. The proportion of prespore cells markedly decreased during prolonged migration, owing to the loss of the antigen from cells adjacent to the agar surface. Both the proportions and the distributions of prespore cells were quickly recovered to normal upon the initiation of culmination. The proportion of prespore cells remained constant regardless of the size of slugs. The size-independent proportionality was maintained, even after the proportion was decreased due to long migration. Cells in spheroidal agglutinates formed in a roller-tube culture of vegetative amoebae differentiated into spores and stalk cells with a distinct spatial pattern, despite the fact that the agglutinates were devoid of any polar structure (such as the tip) and of any polar morphogenetic movement. Appearance of prespore cells in developing cell masses were in no case random but mostly limited to certain regions from the beginning. These results were discussed in relation to formation of spatial pattern of differentiation in this organism.