Fig. 4. dimB^- exhibits gene expression and cell-autonomous defects. (A) Expression pattern of representative prestalk and prespore markers at the slug stage of development. The prestalk marker ecmAO/lacZ shows a reduced zone of expression compared with wild type. The prespore marker cotB/lacZ shows an expanded zone of expression, although expression is weaker in the expanded region than in the prespore zone proper. (B) The dimB^- mutant exhibits cell-autonomous defects when mixed with wild-type cells. A minority (2%) of wild-type or dimB^- mutant cells were labelled by constitutive expression of lacZ and mixed with unlabelled cells. Wild-type and dimB^- mutant cells are evenly distributed in homotypic control chimaeras (a and d). dimB^- mutant cells preferentially localize to the rear of the prespore zone when mixed with an excess of wild-type cells (b). Wild-type cells localize to the pstO and prespore zone when mixed with dimB^- mutant cells (c).