Nymphal RNAi analysis reveals novel function of scalloped in antenna, cercus and caudal filament formation in the firebrat, Thermobia domestica

Scalloped (Sd) and Vestigial (Vg) form a transcription factor complex that plays a central role in the wing development of Drosophila melanogaster. Sd provides DNA-binding ability through a conserved TEF-1, TEC-1, ABAA domain (TEAD), whereas Vg is required in order to confer transcription activity to the Sd-Vg complex. The present study reported the results of functional analysis of the sd orthologue (Td-sd) in the firebrat, Thermobia domestica. As T. domestica is a basal apterygote insect, analysis of its wing genes could potentially provide clues to understanding insect wing evolution. Initially, embryonic RNAi analysis was performed using previously established techniques. Unfortunately, the effect of Td-sd RNAi during embryonic development could not be analyzed due to phenotype lethality. Therefore, in order to explore Td-sd function during post-embryonic development, double-stranded RNA was injected into a T. domestica nymph. This resulted in specific reduction of the antenna, cercus and caudal filament, although formation of the paranotum was not affected. These results demonstrated novel function of sd in two types of ventral appendages, the antenna and the cercus, as well as in a non-appendage outgrowth, the caudal filament. The nymphal RNAi method established for use in T. domestica in the present study could serve as a helpful tool in understanding the evolution of characteristic traits in insects.