Fig. 3. Abd-B expression patterns in the central nervous system of homozygous scs^min, wild type and scs_prom embryos. Central nervous systems (CNS) were dissected out from embryos stained with an antibody directed against ABDB as described elsewhere (Hogga et al., 2001). In wild type, the typical graded ABDB expression pattern from PS10 to PS14 is visible. In scs^min CNS, a partial block between iab-5/iab-6 and Abd-B is visible by the weaker signal in PS10 and PS11. In scs_prom, the same impediment appears in PS10. Note however, that in PS11 and PS12, the ABDB expression patterns are similar (unlike in scs^min). The PS11 and PS12 levels and patterns of ABDB expression are not a reiteration of the PS12-specific pattern in wild type (as it would be expected in a Fab-7 embryo). They reach a level intermediate between the PS10 and PS11 from wild type. The regulatory output of the fused iab-6-iab-7 domain may be shared between the scs_prom and Abd-B promoters (see text).