Fig. 10. PaxB expression is needed both in prespore and prestalk cells to rescue development. To assess the requirement of paxB for development we expressed the paxB GFP construct under the control of the actin15 promoter, the prestalk-specific ecmA and ecmB promoters, and the prespore-specific psA promoter. The outcome of these experiments was that expression of paxB under the control of the A15 promoter gave a fairly good but not complete rescue, followed by expression under the ecmA promoter, the ecmB promoter and the psA promoter. This was also reflected in the rescue of migration of slugs formed (not shown). The lower row of three images shows from left to right the expression of the PaxB-GFP constructs at the slug stage under the control of the psA, ecmA and ecmB promoters in the paxB^– strain.