An inhibitor of cell cohesion from Dictyostelium discoideum

Abstract

The cohesive properties of slime mould cells during azenic growth and during development on solid supports have been studied. Axenically-grown log phase cells are cohesive, but lose this property as they approach the onset of stationary phase. A low molecular weight substance which inhibits cell cohesion has been found to accumulate in the medium of a stationary phase culture. This inhibitor which has a molecular weight of approximately 500, has been partially characterised by biochemical methods. Its effects are not mimicked by simple sugars or by cyclic nucleotides. A certain concentration has been found to completely inhibit the cohesion of vegetative (feeding and dividing) cells of axenically-grown and bacterially cultured Dictyostelium discoideum cells. It also inhibits the cohesion of vegetative cells of D.mucoroides, D.purnureum and Polysnhondylium violaceum. The cohesion of cells at aggregation-competence and later stages of development is only partially blocked. Evidence is presented which suggests that the cohesion inhibitor binds to the cell surface. It is not homologous with the transcription and division inhibitors also known to accumulate in the medium in stationary phase. The importance of the cohesion inhibitor as a means of evaluating the necessity for cell-contact in development is proposed as an alternative to existing methods. The effects of this inhibitor are discussed in relation to the known aspects of cell cohesion in the slime moulds. A mode of action is suggested based on the results of this investigation.

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