Comparison of early phase 3 segmentation gene expression in wild-type and
opa mutant embryos. The horizontal axis represents an idealised portion of the AP axis (~12 nuclei across). The grey vertical lines demarcate a double parasegment repeat (~8 nuclei across), of an odd- followed by an even-numbered parasegment (see
Figure 6). The pattern of protein (intense colour) and transcript expression (paler colour) of the pair-rule genes, and the segment-polarity genes
en and
wg, are shown for each genotype. Wild-type patterns are the same as in
Figure 6B. Transcript distributions for
opa mutant embryos were inferred from our double in situ data, while protein distributions were extrapolated from transcript data. Fading expression of Eve and Runt is represented by lighter sections at the posterior of the stripes. In
opa mutant embryos, expression of
eve and
runt fades prematurely, while the expression of
odd, prd and
slp remains double segmental. Only the even-numbered stripes of
wg emerge, with
en expression delayed until mid-germband extension (
Benedyk et al., 1994;
Figure 10). Stronger expression in the posterior of the Eve stripes in
opa mutants is inferred from the observation that the
eve stripes remain broad at a time when they would have already narrowed in wild-type (compare panels
A and
F in
Appendix 2—figure 2, or see
Figure 8—figure supplement 5). For simplicity, the low-level or residual expression of
eve and
runt observed in
opa mutant embryos is not included in the schematic. See text for further details.