Fig. 2. Homeotic transformations in _promscs and scs_prom. Wholemounts of abdominal cuticles (see Materials and Methods for description of the abdominal segments). (A) In homozygous _promscs males, the presence of bristles on the sixth sternite (shown by arrows in wild type, left) indicates a homeotic transformation of A6 towards a more anterior segment. On the dorsal side, A5 and A6 tergites have a patchy pigmentation, indicating a transformation into a more anterior abdominal segment. This could reflect a transformation into A4. However, dissection of whole abdomen revealed that they contain only rudimentary gonads. As the somatic part of the gonads is derived from A3 (Bender and Hudson, 2000), rudimentary gonads reflect a transformation towards a more anterior segment. Taken altogether, these homeotic transformations indicate that A3, A4, A5 and A6 are transformed into a more anterior abdominal segment [a mixture of A2 and A3 (2-3)]. (B) A wild-type male has six abdominal segments. The seventh abdominal segment (A7), which is present in larvae, is suppressed during metamorphosis. In Fab-7², iab-7 (left) is ectopically activated in most cells of A6. As a consequence, A6 assumes A7 identity and most of the sixth tergite and sternite are absent. There are, however, cells of A6 in which ectopic activation of iab-7 does not take place. These cells, which are visible as a small tergite (shown by an arrow), adopt A5 identity, indicating that not only iab-7 is inactive, but also iab-6. In Fab-7¹² homozygotes (right), iab-7 is ectopically expressed in all cells of A6, giving rise to a fly with no apparent tissue in A6 (open arrow). In scs_prom homozygotes, A6 is completely transformed into A7, as revealed by the complete absence of tergite or sternite tissue in A6 (open arrow). (C) The derepression of iab-8 in A6 and A7 (Fab-7 and Fab-8 phenotype). The A7 into A8 transformation is detectable in females where A7 develops. scs_prom homozygous females show a phenotype reminiscent of an Fab-8 boundary deletion, as revealed by the strong reduction of the seventh tergite. Because in scs_prom, the Fab-7 boundary function is also affected, the sixth tergite is also reduced in size.

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