Gαi and GƔ30A act downstream of Tre1 in Drosophila courtship

Abstract

The role of genes in morphological development is well understood for a variety of model organisms, but there remains a gap in our understanding of how genetics mediate behavior. Are there master genes that regulate behavior? Answering this question will lead to a better understanding of the development and function of the central nervous system, eventually allowing us to map out the pathways that regulate specific behaviors. We are using Drosophila melanogaster as a model organism and the male courtship ritual as the behavior of interest to study the relationships between genes, neural development, and behavior. Trapped in endoderm 1 (Tre1), a gene encoding an orphan G-protein coupled receptor (GPCR), is required for normal courtship behavior in fruit flies, but how this receptor regulates behavior is not yet understood. Here, we characterize the signaling cascade downstream of Tre1 by testing mutations in the Drosophila G-proteins for courtship defects similar to those seen in Tre1. Our results demonstrate that Gαi is a candidate downstream effector for Tre1, while also implicating Gγ30A in courtship behavior. Future goals include completing the characterization of the G-protein mutations and conducting experiments to explore the complex interaction between Gprotein signaling and courtship initiation. 2 McNair Research Journal SJSU, Vol. 15 [2019], Art. 8 https://scholarworks.sjsu.edu/mcnair/vol15/iss1/8 79 INTRODUCTION Genes are responsible for the development of the central nervous system (CNS), which, in turn, mediates behavior. Many of the genetic pathways underlying morphological development in animals have been identified and well-characterized. In contrast, there is still much to be understood about how a gene or genes specify behavior (Demir and Dickson 2005). Elucidating the roles of genes with regard to particular behaviors has the potential to be a powerful set of tools to map out the molecular pathways that direct the wiring of the CNS. Courtship behavior is observable and well characterized in Drosophila melanogaster, making it a practical model for the purposes of this study. In addition, the behavior is innate – it is “hard wired” into the brain. Only males perform the courtship ritual – and they are able to perform it even if they have been socially isolated since “birth.” The courtship ritual is a stereotyped set of six distinct steps that must be executed correctly, and in the proper order, to ensure reproductive success (Baker et al. 2001). Because innate behaviors such as this do not have to be learned, they are ideal models for the study of how genes pattern the nervous system to elicit specific behavioral responses. We seek to expand our knowledge on this particular trait as it is so evolutionarily favored it is programmed into the Drosophila nervous system. We previously demonstrated that the gene Trapped in endoderm-1 (Tre1) is required for normal courtship behavior in fruit flies. Specifically, male flies in which Tre1-expressing cells are silenced, or with loss of function mutations in Tre1, initiate courtship much more rapidly than wild-type males (Luu et al. 2016). Tre1 encodes an orphan G-protein coupled receptor (GPCR). In this work, we aimed to identify components of the G-protein signaling cascade downstream of Tre1. To accomplish this goal, we tested mutations disrupting subunits of heterotrimeric Gproteins for courtship initiation defects. Here, we show that both Gαi and Gγ30A are involved in courtship initiation, and that these genes may reveal a complex role for G-protein signaling in the programming of this behavior.