Neuronal expression of tachykinin-related peptides and gene transcript during postembryonic development of Drosophila.

The gene Dtk, encoding the prohormone of tachykinin-related peptides (TRPs), has been identified from Drosophila. This gene encodes five putative tachykinin-related peptides (DTK-1 to 5) that share the C-terminal sequence FXGXRamide (where X represents variable residues) as well as an extended peptide (DTK-6) with the C-terminus FVAVRamide). By mass spectrometry (MALDI-TOF-MS), we identified ion signals with masses identical to those of DTK-1 to 5 in specific brain regions. We have analyzed the distribution of the Dtk transcript and peptides, by in situ hybridization and immunocytochemistry during postembryonic development of the central nervous system (CNS) of Drosophila. Antiserum against a cockroach TRP that cross-reacts with the DTKs was used for immunocytochemistry. Expression of transcript and peptides was detected from first to third instar larvae, through metamorphosis to adult flies. Throughout postembryonic development, we were able to follow the strong expression of TRPs in a pair of large descending neurons with cell bodies in the brain. The number of TRP-expressing neuronal cell bodies in the brain and ventral nerve cord increases during larval development. In the early pupa (stage P8), the number of TRP-expressing cell bodies is lower than in the third instar larvae. The number drastically increases during later pupal development, and in the adult fly about 200 TRP-expressing neurons can be seen in the CNS. The continuous expression of TRPs in neurons throughout postembryonic development suggests specific functional roles in both larval and imaginal flies and possibly also in some neurons during pupal development.