The role of myoinhibitory peptides (MIPs) in the circadian system of the Madeira cockroach Rhyparobia maderae

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The Madeira cockroach Rhyparobia maderae is an established model organism for circadian rhythm research. We identified the accessory medulla (AME) with associated pigment-dispersing factor-immunoreactive (PDF-ir) neurons as circadian pacemaker center controlling circadian locomotor activity rhythms. The AME neurons are abundant in partly colocalized neuropeptides. For example, PDF and myoinhibitory peptide (MIP) are colocalized in two neurons. The function of MIP in the cockroach clock is not known. In Drosophila melanogaster the sex peptide receptor (SPR) is a MIP receptor which controls a physiological/behavioral switch from the non-mated to the mated state. With transcriptome analysis we previously identified a SPR candidate in R. maderae. Using heterologous expression studies combined with BRET assays we want to examine its function. In Ca2+-imaging assays combined with immunocytochemistry, with application of MIPs to primary cell cultures of the AME we will characterize MIP signaling in the cockroach clock. We want to determine signal transduction cascades of MIP in the circadian clock and identify MIP-sensitive AME cells. Furthermore, in behavioral assays combined with immunocytochemistry we will examine whether MIP-signaling and mating/post-mating behaviors regulate each other. We expect to gain insights into specific functions of MIPs and into general principles of neuropeptide function in the circadian system and in insect brains in general.