Clock-related neuropeptides in Acyrthosiphon pisum

The pea aphid (Acyrthosiphon pisum) is a strongly photoperiodic insect. Although the involvement of the circadian clock in insect photoperiodism is well established, the neuronal and molecular mechanisms by which clock neurons convey photoperiodic information remain largely unknown. Neuropeptides commonly act as neuromessengers in circadian clock neurons, yet little is known about the neuropeptidergic organization of the circadian clock in the pea aphid.

Here, we characterized the complete set of neuropeptides in the aphid brain and, using a combination of transcriptomic and peptidomic approaches, and investigated the neuropeptides expressed in the circadian clock neurons using immunohistochemistry.

We confirmed a large number of peptides, including several peptides described for the first time in this species. Furthermore, we found that circadian clock neurons express a variety of these neuropeptides, some of which overlapped within the same clock neuron type. In the lateral clock neurons, we found Pigment-Dispersing Factor, FMRFamide, Orcokinin a and Allatotropin, a neuropeptide profile that closely resembles that of cockroach clock neurons but differs markedly from that of the fruit fly, with the exception of Pigment-Dispersing Factor. In dorsal clock neurons, which are homologous to those that are presynaptic to insulin-producing cells in Drosophila, we detected Allatostatin A, Diuretic Hormone 31, FMRFamide, and Myoinhibitory peptide.

Together, our findings provide the first comprehensive map of neuropeptides associated with the pea aphid circadian clock, offering new insights into how clock neurons may regulate seasonal responses and establishing a foundation for future functional studies of neuropeptide-mediated photoperiodism.