Expression patterns of cell-type-specific genes in Dictyostelium

Cell-type specific genes were recognized by interrogating microarrays carry ing Dictyostelium gene fragments with probes prepared from fractions enrich ed in prestalk and prespore cells. Cell-type specific accumulation of mRNA from 17 newly identified genes was confirmed by Northern analyses. DNA n-de roarrays carrying 690 targets were used to determine expression profiles du ring development. The profiles were fit to a biologically based kinetic equ ation to extract the times of transcription onset and cessation. Although t he majority of the genes that were cell-type enriched at the slug stage wer e first expressed as the prespore and prestalk cells sorted out in aggregat es, some were found to be expressed earlier before the cells had even aggre gated. These early genes may have been initially expressed in all cells and then preferentially turned over in one or the other cell type. Alternative ly, cell type divergence may start soon after the initiation of development .