Figure 2.

Pair-rule and en expression patterns in runt null mutants, and maintenance of odd expression by ftz. Wild-type embryos (A–K, left side, and Q, S) or embryos null mutant for runt (all others except R and T, which are null for ftz) were stained (blue) by in situ hybridization to RNA for either odd (A–J, O,P, S, T) or slp (K–N, Q, R; those in Q and R were simultaneously stained for lacZ RNA from the hb-lacZ transgene on the balancer chromosome to identify the mutants, as in Fig. 1), and then antibody-stained (brown) for either Eve (A–H, M, N, P–T) or En (I–L, O). Note the stripe-specific effects of runt on odd expression at the blastoderm stage (B), with the 1st, 4th, and 5th stripes being the most normal (corresponding to PSs 2, 8, and 10). The subsequent evolution of these incipient PSs diverges from that of PSs 4, 6, and 12, in that they remain of approximately normal width (seen as gaps between Eve stripes in F, where odd expression is “replaced” by that of slp, as shown in M–P), while 4, 6, and 12 are abnormally narrow. Note also that in runt mutants, abnormally wide secondary odd stripes come up within Eve stripes 2–4, 6, and 7 (seen in F; these are in PSs 3, 5, 7, 11, and 13). By stage 8 (G–L), odd RNA is seen clearly only in odd-numbered PSs in runt mutants, while slp is expressedin even-numbered PSs: the positions of the originally strong, wide stripes of odd are now those of the wide stripes of slp, that is, PSs 2, 8,and 10. The odd-numberedEn stripes are marked with dots in J and L (stripes 1–2and 9–10 are fused), while ftz domain 4is marked with arrows in M–T. Note that in runt mutants (M–P) and in ftz mutants (R, T) odd expression is fading ventrally as slp is activated, and that in ftz mutants, slp is expressed throughout the ftz domains, while odd is lost there (although still present dorsally in T, odd is also lost there by stage 9, well before it fades in the wild type; not shown).