Neuroactive molecules such as neurotransmitters, neuromodulators and neuropeptides are extensively used by neural networks to generate and modulate behaviors of the organisms. However the mechanisms of how the function of these molecules is translated into specific behaviors as well as how the neurochemical specificity within the nervous system is achieved are still poorly understood.
Octopamine is a biogenic amine structurally similar to the catecholamines dopamine and noradrenaline. It is known to be among the major neuroactive molecules in invertebrate species but it also exists, in a lesser extent, in the nervous system of vertebrates. In mammals, it is thought to be a cotransmitter with noradrenaline but its physiological role is not understood. On the other hand, Octopamine acts as neurotransmitter/ neuromodulator/ neurohormone in invertebrate species affecting several aspects of their physiology and behaviour, combining many of the roles of noradrenaline and adrenaline in vertebrates. For instance, in peripheral tissues, it acts as a stress hormone, stimulates glycogenolysis, increases muscle contraction and in the central nervous system its action appears to be responsible for the initiation of various behaviours while the small number of neurons that produce it innervate all major parts of the brain.
We aim to develop a model system in order to study the molecular mechanisms underlying the action of Octopamine and we focus our research on the molecular genetics of the Drosophila Tßh(Tyramine-ß hydroxylase) gene in the biosynthetic pathway of Octopamine.
Studies on Tßh mutants
Mutations in the Tßh locus have been generated and the physiology and behaviour of the mutants that represent octopamine-less flies is studied. Phenotypic analysis has revealed (a) a memory defect (Schwaerzel et al. 2003) (b) abnormalities in stress reactivity components (Gruntenko et al. 2000,2004) (c) a profound female sterility phenotype (Monastirioti et al.1996).
We have established that due to defective ovulation, octopamine-less flies retain their mature eggs within their ovaries. Immunocytochemical analysis and GAL4-UAS rescue experiments identified a specific Octopamine cell subpopulation as a neural focus that controls the ovulation step of the egg laying process, with Octopamine being the necessary functional molecule (Monastirioti 2003).
We currently continue our research with genetic experiments (screenings, interactions, GAL-UAS expression assays) that target the egg laying phenotype of octopamine-less flies, aiming to identify signaling molecules, regulators of Tßh/Octopamine expression and intrinsic/extrinsic factors regulating Drosophila female fecundity.
Studies on Tßh gene regulation
By using standard molecular and genetic techniques we develop molecular tools (GAL4-UAS binary systems, inducible and RNAi transgenes expressing lines) and we focus on the analysis of a functional Tßh gene promoter in order to study the regulatory mechanisms that establish the octopamine cell phenotype during development. Moreover a functional promoter is a valuable tool for driving expression of marker genes for better imaging of octopamine neuronal networks, mutated forms of Tßh gene, toxins, or genes that would potentially alter chemical integrity of neurons in order to study alterations in the behaviour of the organism.
Octopamine in insects of economic interest
The objective of the project is to explore the Octopamine system in insects of economic interest as the important role of Octopamine in insect physiology/behaviour and the sterility phenotype of
the octopamine-less flies that demonstrates the essential role of the molecule in the reproductive process, suggest the potential of this system in pest management. The aim of the project is (a) cloning and inactivation of genes in the Octopamine biosynthetic pathway from different insects (C. capitata Medfly, Anopheles-Mosquitos) in order to induce depletion of Octopamine in these species (b) analysis of mutant phenotypes relevant to the reproductive process or to other physiological processes that could serve as potential targets in pest control.
The advantage of the research group is its expertise in molecular genetics and the experience on Octopamine research and neuronal function. In addition, the research Institute (IMBB) offers excellent infrastructure and facilities for insect rearing and insect transformation as well as research groups experienced in insect transgenic technology and biology of pest insects that will allow scientific interactions and fruitful collaborations.