Morphological and functional examination of neuropeptides in the circadian system of Rhyparobia maderae with focus on myoinhibitory peptides

FG Tierphysiolgie

Figure 1: In running wheel assays MIP-specific changes in locomotor activity patterns were evaluated. Double plot actogramm demonstrates that the injection of MIP 1 (arrowhead) phase delayed the onset of activity (dots), while the period length (red line) of the freerunning animal did not change.

Project members: Thordis Arnold, Philipp Renk, Huleg Zolmon, Prof. Dr. Monika Stengl

The cockroach Rhyparobia maderae is an established model organism for circadian research. Transplantation experiments located the circadian clock that controls rest-activity cycles to the accessory medulla (AME) with innervating pigment-dispersing factor (PDF) expressing neurons. The AME is a small optic lobe neuropil innervated by about 240 neurons belonging to 8 soma groups that are enriched in neuropeptides. Among all AME clock neurons the 12 anterior PDF expressing cells are studied best. Two of them co-express myoinhibitory peptides (MIPs).

We want to understand the function of MIP in the circadian system of the cockroach. In running wheel experiments injections of MIP 1 phase delayed and MIP 2 phase-advanced locomotor activity rhythms depending on the time of the day. Thus, MIPs are involved in input pathways to the circadian clock. But, MIP expressing neurons arborize also in different target areas of circadian pacemaker neurons and in most midbrain neuropils involved in higher order sensory processing. Thus, MIPs have many different functions, most likely also as clock output pathways to neurosecretory control areas and premotor areas. However, details about functional pathways or signal transduction are still missing. With multi-label- immunocytochemistry combined with backfills we examine the morphology of individual MIP-expressing neurons in the circadian network. Furthermore, we examine agonistic or antagonistic interactions of MIP with other neuropeptides of the circadian clock such as with PDF in different physiological and behavioral assays. With RNA interference we perform knockdowns of the MIP- and/or PDF-precursor, as well as MIP and/or PDF receptor and analyze effects on locomotor activity patterns in running wheel assays (Figure 1). We cloned a candidate for a MIP receptor and examine it via heterologous expression and BRET or calcium-imaging assays to examine its MIP-sensitivity and respective signaling cascades.

Based upon findings in Drosophila (Hussain et al., 2016, PLoS Biology) we hypothesize that MIPs play a role in a behavioral switch between mating and feeding activity. We are currently testing this hypothesis in newly developed behavioral assays.