Fig. 8. Comparison of genetic interactions in embryonic epidermis and in the mature female genital disc, and organization of the A8 in the female genital disc. (A) Regulatory interactions between abd-A, Abd-B and Dll in the embryonic epidermis and in the mature genital discs. In the embryo, Abd-B represses abd-A in the A8, and abd-A represses Dll in the abdominal segments. In the third instar female genital disc, it seems that Abd-B maintains abd-A transcription, and that ectopic Dll can repress abd-A. (B) In the A8 of the female disc we can distinguish two regions (Estrada and Sánchez-Herrero, 2001) (this report). The anterior region (region I, purple) expresses buttonhead, abd-A and low levels of Abd-B, and can activate Dll in the absence of Abd-B. It represents the `appendage' part of the genitalia and corresponds mainly or exclusively to the internal genitalia. The lower region (region II) does not express abd-A or buttonhead, but expresses high levels of Abd-B. It corresponds to the `trunk' region of the female A8. In this region, Dll is not activated in the absence of Abd-B.