Fig. 3. Sgs4 is not properly repressed in the presence of elevated levels of Fkh and in mutants of the BR-C function 2Bc. (A) Maintenance of fkh expression by heat shock induction of a Fkh-encoding transgene leads to high levels of Sgs4 mRNA in early prepupae. The expression of Sgs4 in the salivary glands of Oregon R animals (ORN) and animals of the transformant line P [hs-Fkh111] was analyzed by northern blot hybridization after a 1 hour heat shock applied 3-4 hours before dissection of the glands, or without prior heat shock. Sgs4 expression in prepupae is only maintained only in salivary glands of P[hs-Fkh111] animals after heat shock application. Equivalent results were obtained after reducing the heat shock period to 30 minutes (not shown). (B) Sgs4 expression extends into the prepupal stage in mutants of the BR-C function 2Bc. Expression of Sgs4 in males hemizygous for the 2Bc alleles 2Bc1, 2Bc2 and 2Bc4, or control males hemizygous for the balancer chromosome present in the corresponding stock, was assayed by northern blot analysis. Hybridization to rp49 was used as a control for loading and transfer. Note that, although fkh mRNA levels remain completely or nearly unchanged at pupariation in the 2Bc mutants (see Fig. 4), the amount of Sgs4 mRNA is lower in prepupae of these mutants than in prepupae expressing the ectopic Fkh. This difference is probably due to the strong heat shock induction mediated by the hsp70 promoter, leading to a high level of ectopic Fkh and enhanced Sgs4 expression. m3L and 3L, mid-third instar larvae; l3L, late-third instar larvae; PP, white prepupae.
