Differential neuronal expression of three Drosophila ion transport peptide splice forms indicate multiple functions of peptidergic neurons

• We identified previously two long (DrmITPL1 and -L2) and one amidated short isoform (DrmITP) of insect ion transport peptides (ITPs) as products derived by alternatively splicing from the Drosophila itp-gene (CG13586). The peptides are members of a large family of arthropod neuropeptides incl. crustacean hyperglycemic hormones (CHH/ITP-family), but similar ITPs are only known in locusts to have antidiuretic bioactivity on the hindgut. We localised the peptides by in situ hybridisation and immunocytochemistry with isoform-specific antibodies in the nervous system of larval (L3) and adult Drosophila melanogaster and screened Gal4-lines specific for peptidergic cells. Four neurosecretory cells in brain-corpora cardiaca/allata putatively release DrmITP as a hormone in all stages. DrmITP also occurs in interneurons in the brain/ventral ganglia and in neurons efferent towards the hindgut. Some interneurons are identical to well-known circadian clock neurons for which the effector molecules were elusive but are responsible for the evening bouts of locomotor activity in flies. DrmITPL1 and -L2 were found only in peripheral lateral bipolar and putative sensory neurons which are likely to play a role in the control of growth, hindgut ion transport and heart beat. With DrmITP identified in brain neurosecretory cells, hindgut-innervating neurons in the abdominal ganglia and one pair in the abdomen close to the larval anal organ or innervating the adult rectal pads, both chloride-transporting organs, we are facing an enormous complexity in multiple functions of differentially expressed ITP/Ls derived from a single gene. Preliminary results using Gal4-driven RNAi in distinct peptidergic neurons look promising to find deficiency phenotypes.

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