Fig. 13. Effect of paxillin on celltype differentiation. To assess the effect of paxillin loss on celltype-specific gene expression we measured the kinetics of prespore cell formation by using a prespore vesicle-specific polyclonal antibody as function of time. As can be seen for a typical experiment the number prespore cells starts to increase very dramatically at the mound stage. The time of the appearance of prespore cells is the same in the wild type and in the paxB^– strain but levels do not exceed 50% in the paxB^– knockout strain after which they start to decline, suggesting that many of the cells may differentiate into prestalk cells. This impression is confirmed by the transformation of the paxB^– strains with lacZ expression constructs under the control of the prestalk-specific ecmA, ecmB and the prespore-specific PsA promoters. This shows that many of the cells, especially in the base of the structures express prestalk-specific markers.