In third instar larvae, btd-GAL4 is expressed throughout the medial and distal regions of the leg disc but is excluded from the body wall and the distal tip of the leg. In prepupal leg discs, it is expressed in the tarsal segments and more proximally with a gap in the region corresponding to the tibia.
btd reporter is expressed in the entire leg imaginal disc except in the most proximal ring of cells that will become the body wall. In the antennal disc it is expressed in a medial ring of cells along the proximal-distal axis. No expression is observed in the wing, haltere, or eye discs. btd expression overlaps the expression of Sp1. In third instar larval leg discs, btd reporter is expressed at a low level in the trochanter, strongly in the coxa, and is not detected in the body wall. In an everting pupal leg disc, btd expression divides the hth expression domain into presumptive coxa and body wall.
Expression is observed in the ventral derivatives of the adult body, including the legs, proboscis, antennae and genitalia. The embryonic expression pattern recapitulates that of native btd expression (ventral expression during germ band extension, in the ventral imaginal disc primordia during germ band retraction). Expression in the leg and antennal imaginal discs partially overlaps the expression of both Dll and hth.
