FIG. 4.

Cell sorting is altered in the rbrA mutant. (A) Wild-type and rbrA⁻ cells were transformed with cell-type-specific GFP expression plasmids PsA-ubi-s65tGFP or 63-ubi-s65tGFP, which contained the GFP cDNA expressed by the prestalk-specific promoter from ecmAO (ecmAO-GFP) or the prespore-specific promoter from pspA (pspA-GFP), respectively. Cells were developed to the slug stage on filters and photographed by using light and fluorescence imaging. The slugs shown are representative of those seen in two independent experiments. (B) In chimeric slugs, rbrA⁻ cells preferentially sort to prespore region. Wild-type (WT) and rbrA⁻ cells were transformed with a plasmid carrying the GFP cDNA expressed under the control of the constitutively expressed actin-15 promoter (pTX-GFP). GFP-expressing cells of one strain were mixed with non-GFP-expressing cells of the other strain and developed on filters. Each mixture contained 10% wild-type cells. The chimeric slugs were photographed by using light and fluorescence imaging. Bar, 0.5 mm.