Fig. 4. Expression of ecmB during development. (A) Northern analysis of the developmental expression of the prestalk/stalk-specific ecmB gene. The upper band in both panels represents hybridization to the highly similar ecmA gene. (B) An ecmB/lacZ reporter gene was used to visualize ecmB expression at a cellular level. Structures were fixed at 16 hours (upper panels) and 24 hours (lower panels) of development and stained for ß-galactosidase activity to visualize expression of the reporter gene. More cells appear to express ecmB in the tagA mutant, and many of the additional cells accumulate in the anterior of the slug, but their localization within fruiting bodies appears relatively normal.