cudA: a Dictyostelium gene with pleiotropic effects on cellular differentiation and slug behaviour.

The Dictyostelium cudA gene encodes a nucleoplasmic protein that is essential for normal culmination. There are no functionally characterised homologues in other organisms but there is a related gene of unknown function in Entamoeba histolytica. The cudA gene is expressed by the prestalk cells that constitute the slug tip (the pstA cells), it is not detectably expressed in the band of prestalk cells that lies behind the tip (the pstO cells) but it is expressed in the prespore cells. This unusual pattern of expression suggests a role on both the stalk and spore pathways of differentiation and cudA- mutant cells are indeed defective in both stalk and spore formation. Furthermore, the slugs formed by cudA- cells continue to migrate under environmental conditions where normal slugs culminate immediately. This aspect of their behaviour can be reversed when the cudA gene is selectively expressed in the pstA cells. This shows that processes occurring in the pstA cells regulate entry into culmination.