Fig. 3. Expression pattern of the rblA::pgal during development. (A) In a tight mound (14 hours), the central core, which is occupied by stalk precursors, remains unstained. (B) In the slug stage (17 hours), staining is confined to the rear two-thirds; the anterior prestalk region is negative. (C) In a fruiting body (22 hours), staining is almost exclusively found in the future spore mass. For clarity, the prestalk region and the stalk have been outlined in B and C.