Molecular biological studies on differentiation of slime mold cells

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1. Aggregation of homogenous slime mold cells leads to differentiation of two types of cells (prespore and prestalk) which become spares and stalk cells respectively of the fruiting body. To isolate genes which are specifically expressed during differentiation of the presumptive cells, clones of DNA complementary to mRNAs enriched in prespore and prestalk cells were isolated, from which several genomic DNA clones were obtained. Some of these genes were selctively transcribed in either type of cells, while the others were expressed from the earlier stages and transcribed in both cell types. The fact that the latter mRNAs become enriched in one cell type was resulted from their destabilization in the other cell type. When slime mold cells were transformed by DNA fragments containing the 5' upstream regions of two prespore specific genes, they were specifically expressed at certain developmental stages and in a perticular cell type. The sequences of DNA responsible for requlation of trans … More cription of the genes are being identified and nuclear proteins binding to such sequences being isolated. The entire sequence of a plasmid contained in Dictyostelium sp. was disclosed. when D. discoideum cells were transformed by the plasmid, its expression began at the aggregation stage and was induced by exogenous cAMP.2. The conditions under which cells as isolated differentiate without forming a tissue were found, where differentiation of cells into spores and stalk cell was controlled by extracellular pH. We succeded in determining cytosolic Ca^<++> concentration and found that upon addition of cAMP it increased 4 times in aggregating cells. This suggests the involvement of Ca^<++> in signal transduction of chemotactic response of the cells. A part of the sugar chains of the cell adhesion molecule GP80 was likely to be responsible for cell adhesion. During the process of sexual reproduction (macrocyst formation), cells synthesize different kind of proteins from those made during asexual reproduction (fruiting body formation) and two glycoproteins, GP138 and 70, present on the surface both mating type cells were identified as the candidates of molecules involved in the sexual cell fusion. Less