Molecular Analysis of the Growth-Differentiation-Transitition in Dictyostelium

Zeng, Changjiang

kassel university press, ISBN: 978-3-933146-08-3, 1998, 144 Pages

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Content: This dissertation deals with the genetic/biochemical pathways which trigger the transition from growth to development in the soil amoeba Dictyostelium discoideum. Dictyostelium is unique in its properties to build up a multicellular organism from originally independent, solitary cells. This process is initiated by environmental signals (depletion of the food bacterial source) and by cell to cell signalling.

The thesis describes the generation of mutants which are specifically impaired in the growth differentiation transition. Mutants have been found which do not enter development while others do so prematurely. One of the affected genes (gdt1) was further analyzed and found to apparently be a cellsurface receptor which inhibits the onset of development. The signal stimulating the receptor may be metabolites of food bacteria or the bacteria themselves. A positive pathway which initiates development has previously been described. Experiments with mutant strains impaired in both pathways demonstrate that there is obviously crosstalk: the cAMP dependent protein kinase A (PKA) seems to be a positive regulator of the inducing pathway but at the same time downregulates the negative pathway. In-vitro experiments provide evidence that the gdt1 protein itself may be a target for inhibitory phosphorylation by PKA.

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