Eve activates en by repressing slp. Expression of en, absent in eve mutants, is restored in odd-numbered PSs in eve, slp double mutants. Wild-type embryos (C–P, left side) or embryos null mutant for eve (A), slp (B), or both eve and slp (C–P, right side) were stained (blue) by in situ hybridization to RNA from either en(A–F), odd (G–L), prd (M, N), or ftz (O, P); those in C–L were simultaneously stained for lacZ RNA from the hb-lacZ transgene on the balancer chromosome to identify the mutants (wild-type embryos have light blue staining throughout the head region). Those in G–P were then antibody-stained (brown) for En protein. Note that en expressionis absent inthe trunk region of eve mutants (A) butis restored (in an abnormal pattern) when slp function is simultaneously removed (D, F). Note also that odd expression is expanded in the double mutants (H, J), that odd and En expression are essentially complementary in these mutants (L), and that the En expression overlaps with that of prd (N), but not ftz (P), indicating that it is in odd-numbered PSs.