bZIP transcription factor interactions regulate DIF responses in Dictyostelium

The signalling molecule DIF-1 is required for normal cell fate choice and patterning in Dictyostelium. To understand how these developmental processes are regulated will require knowledge of how cells receive and respond to the DIF-1 signal. Previously, we have described a bZIP transcription factor, DimA, which is required for cells to respond to DIF-1. However, it was unknown whether DimA activity is required to activate the DIF response pathway in certain cells or is a component of the response pathway itself. In this study, we describe the identification of a DimA-related bZIP transcription factor, DimB. Rapid changes in the subcellular localisation of both DimA and DimB in response to DIF-1 suggest that they are directly downstream of the DIF-1 signal. Genetic and biochemical interactions between DimA and DimB provides evidence that their ability to regulate diverse targets in response to DIF-1 is partly due to their ability to form homo- and heterodimeric complexes. DimA and DimB are therefore direct regulators of cellular responses to DIF-1.