Involved in the morphogenesis of proximal and distal pattern elements in a subset of appendages. Also has a role in early imaginal disk development. Expressed during embryonic development, in distinct epidermal patterns in head, thorax and abdomen and in an endodermal pattern in the anterior intestinal tract. First expressed in 4-8 hours old embryos, peaks in 8-12 hours old embryos and continues through development up to late larval stage. In the head region, detected at stage 10 in the maxillary and labial segment primordia, and in later stages, in the prospective antennal and mandibular segment. In the epidermis, expression is seen from stage 11 in thoracic and abdominal lateral patches. Expression in the intestinal tract begins at stage 13, continues through stages 14 and 15 in the endoderm of the anterior midgut and at stage 16, is found in the posterior end. Expression in the imaginal disks is seen from late third-instar larvae in the prospective thorax, claw organ, antenna, scutellum and wing blade. Flies display a reduction in size of the arista and scutellum, a reduction or complete absence of the tarsal claws, irregularities of the sternopleural bristles and of the wing vein, and a bending of the wing blade. Belongs to the paired homeobox family.