Fig. 3.

Molecular genetics of Cbx ¹. Modified from Fig. 4 of Peifer et al. 1987 and from Fig. 1.5 of Maeda and Karch (2009); DOI: 10.1016/S0070-2153(09)88001-0 with the permission of CSH Press and Elsevier, respectively. The abx/bx (orange) and bxd/pbx (red) regulatory regions, respectively active in PS5 and PS6 are represented on the top of each of the a, b, and c panels. A cartoon of the central nervous system in PS4, PS5, and PS6 is represented in the middle of each panel with the parasegmental borders on top and the corresponding segmental borders below. At the bottom of each panel, an adult thorax is shown with the PS5- and PS6-specific expression of Ubx drawn in orange and red, respectively. Note the PS5-PS6 boundary passing through the middle of the haltere. In panel a, enhancers A and B from the abx/bx regulatory domain turn on Ubx at a moderate level into the A and B cells of the CNS. These A and B enhancers remain active in the more posterior parasegments. Note that the C and D enhancers of the bxd/pbx regulatory region remain inactive in PS5. In PS6 however, these C and D enhancers activate Ubx at a higher level in the C and D cells. Panel b displays the pbx ¹ mutation deleting the D enhancer. As a consequence, the D cells located in the posterior part of T3 do not express Ubx, leading in adults to the transformation of the posterior part of the haltere into posterior wing. In the Cbx ¹ mutation (panel c), the D enhancer is relocated within the abx/bx regulatory, enabling them to function in PS5, as drawn in the cartoon of the CNS. This activity leads to the transformation of the posterior part of the wing into the posterior part of the haltere