Development of optogenetically controlled gene expression tools for the characterization of neuronal circuits involved in insect reproduction

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Reproductive behaviors and their regulation are most fundamental to all animals, but have been exploited little for population control in insects. Since they are hard-wired into the brain we can learn how this behavioral program is encoded in the brain and shaped by perception and decision-making processes. Understanding how behavior is encoded in the brain is one of the big challenges in biology and requires a behaviorally and genetically tractable model organism, but also tools to manipulate localized neurons. One of the key tools to achieve this aim are light-manipulateable molecules, such ion channels, where light can be used to control neuronal activity in space and time. Due to the small size of insects, however, this technology has its limitation. Here, we want to adapt light-inducible transcription factors derived from bacteria and plants already used in mammalian cell culture to Drosophila to characterize the neuronal circuits involved in reproduction. For this analysis we will capitalize on gene expression regulatory sequences known to characterize neuronal populations involved in reproduction, but these gene expression patterns are complex. To be able to assign functions to localized neurons therefore requires spatial dissection of these gene expression patterns, which can be achieved by light-controlled transcription factors.To develop such light-controlable tools to manipulate gene expression, we will capitalize on the robust post-mating responses (PMRs) of the fruit fly Drosophila melanogaster. Here, male-derived sex-peptide (SP) transferred during mating is the key molecule leading to refusal to remate and induction of egg laying. The very robust behavioral response of Drosophila females to sex-peptide provides the essential prerequisites to map SP responsive neurons and eventually learn how complex behaviors such as mating choice and control of egg laying are encoded in the brain.Our recent studies showed that there are several distinct neuronal populations that can via exposure to SP induce refusal to remate and egg laying. We currently do not know where in the fly these neurons are located, however, we could show that these two post-mating responses can be separated. Candidate neurons for SP induced post-mating responses include sensory neurons in the genital tract and in the legs, but also neurons in the abdominal ganglion and the central brain. To identify the neuronal circuitry underlying the sex-peptide response, we will use light induced gene expression directed to neurons in specific parts of the female fly body to express membrane-tethered SP. Such optogentic manipulation of gene expression has the advantage to be fully controllable in space and time. With these experiments we will test the hypothesis that the response to SP is comprised of a modular assembly of individual elements, e.g. refusal to remate or induction of egg laying. Compared to the previous model arguing for central induction of all PMRs, a modular assembly of individual PMRs holds evolutionary flexibility during speciation and adaptation to diverse habitats, but can maintain basic regulatory principles such as the control of egg laying. We therefore anticipate that the knowledge obtained from our studies will be applicable to a wide range of pest insects pinpointing towards novel strategies for pest management to protect crop and control insect born diseases by interfering with egg laying. In particular, our findings are directly transferable to the close relative Drosophila suzukii, one of the few species able to lay eggs into fruits, which is currently invading Europe including the UK and causing damage worth billions of pounds to fruit production.