Figure 1.

 Distribution of exd RNA and protein in maternal and zygotic exd mutants. All panels show embryos with anterior to the left and dorsal up. (A–D) Embryos of exd^Y012 genotype and therefore, have Exd product exclusively from maternal origin (mat⁺ zyg⁻). (E–H) Embryos containing only Exd product of zygotic origin (mat⁻ zyg⁺). (A) mat⁺ zyg⁻ embryo at the blastoderm stage stained for exd RNA. The maternal product is ubiquitously distributed throughout the embryo. (B) mat⁺ zyg⁻ embryo at stage 8–9 of embryogenesis. Maternal exd RNA is still present, but at lower levels. (C) Stage 10 embryo of the same genotype in which the maternal RNA is almost undetectable. (D) mat⁺ zyg⁻ embryo after germ-band retraction stained for Exd protein. Although no maternal RNA is detectable in the embryo from stage 11 onwards, the protein is still present in later stages of embryogenesis. Note the nuclear localization of Exd in the cells of thoracic segments. (E) Stage 8 mat⁻ zyg⁺ embryo lacking the maternal contribution stained for exd mRNA. The zygotic product is present throughout the body. (F) Stage 11 embryo showing a modulation in the levels of zygotic RNA along the A/P axis. In the ectoderm there is very little expression in the more posterior segments, but note that there is mesodermal exd expression (arrow) that is not in register with the ectoderm. (G) Embryo of approximately the same age as in F stained with the anti-Exd antibody. The Exd zygotic protein is still present in the posterior segments of the embryo, where the mRNA is not detected anymore. (H) Stage 14 mat⁻ zyg⁺ embryo stained with anti-Exd antibody. The zygotic protein shows high levels of nuclear distribution in the thoracic segments and lower levels in the abdominal segments. The distribution of the zygotic protein is the same as the maternal one, but the levels of the maternal protein are lower (cf. D and H).