TFAP2A and obesity due to melanocortin 4 receptor deficiency: Another study revealed that the Drosophila obesity-linked homologs Transcription factor AP-2 (TfAP-2) and Tiwaz (Twz) regulate octopamine signaling to initiate feeding and then octopamine, in a negative feedback loop, induces expression of Dsk to inhibit consummatory behavior (15).