Evolution of the insect neuropeptidergic system: function of the prohormone convertases PC1/3 and PC2 in the beetle Tribolium castaneum

• Applicant: Dr. Vera Terblanche
• Subject Area: Evolutionary Cell and Developmental Biology (Zoology)
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 433708322

The animal neuropeptidergic system regulates important biological functions ranging from physiology, behaviour, reproduction, development and growth. Besides their transcriptional regulation, the genetically encoded neuropeptide precursors are subject to posttranslational processing by a number of modifying enzymes required. Central to this processing is the internal cleavage of the precursors at dibasic recognition sites by prohormone convertases of the subtilisin-like family. In mice and humans two convertases, PC1/3 and PC2, have been shown to be responsible for cleaving neuropeptides. While this set of convertases is highly conserved in animals, Drosophila, the major insect model, only retained an orthologue of PC2, which is active in its neurosecretory pathway. However, nothing is known on principles of neuropeptide processing in an insect model that has retained the ancestral set of both PC1/3 and PC2. Considering the predicted central role of the processing enzymes in the production of neuropeptides, and the biological importance of the peptidergic signalling systems, understanding principles and target specificity of both these factors will yield valuable insights into neuropeptide regulation and its evolutionary variations in insects. Therefore, I suggest addressing these questions in the beetle Tribolium castaneum, which has retained PC2 and PC1/3. In addition, by contrast to the fly, Tribolium has retained a vasopressin/oxytocin ortholog which might be a conserved target of PC1/3, which is also suggested by specific co-expression of both factors in the beetle.I propose to test which neuropeptide targets are processed by which protease through a quantitative peptidomics approach. This will reveal principles of combinatorial processing, as well as ancestral functions such as a possible processing of inotocin by PC1/3. Once I have identified target peptides that require either of the prohormone convertase (or both) for their processing, I want to dissect the biological function of both factors exerted through their targets, and thus identify evolutionary pressures that may have led to the retention of PC1/3 processing. In addition, I will test the working hypotheses, that co-expression of a neuropeptide precursor with a protease defines whether or not it is processed by it. This puts the control of over the specific processing into the hands of higher order regulatory mechanisms that control cell type specific expression of both, the processing enzymes and the neuropeptide precursors. Therefore, I want to screen for transcriptional regulators involved in the genetic activation of the prohormone convertases. Taken together the planned work will uncover some of the genetic and enzymatic regulations of a prototypic insect neuropeptidergic system. It will reveal conserved elements of the system, but also offer insights on how such a system evolves in response to biological requirements associated with the life style of a species.

• DFG Programme: Research Grants