Patterning and morphogenesis of the insect head - origin of epicranial sutures and Tc-homeobrain

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Insect head morphology is extremely diverse and many crucial adaptations to different life styles have shaped the anatomy of insect heads (e.g. predating, licking on rotten fruit, sucking blood). It is a composite structure built by several segments and non-segmental tissue and it is formed by complex morphogenetic movements. Several sutures mark the insect head, which function in stabilization of the head capsule, in muscle attachment or ecdysis. It is well accepted that most of the sutures do not reflect segment boundaries, but their developmental and evolutionary origin remains obscure. Anterior insect head patterning does not involve pair rule or Hox cluster gene expression. Hence, it must be different from the trunk but the gene regulatory network of head patterning remains poorly understood. Strikingly, a set of highly conserved genes pattern the anterior region of all bilaterian animals. We use the red flour beetle Tribolium castaneum with its insect typical non-involuted head as a model for understanding the development of an insect head and the underlying genetic principles. The insights we gather in Tribolium are compared to Drosophila, other insects and arthropods and also vertebrates in order to trace back the evolution of anterior patterning. In the past, we have identified novel genes required for head pattern formation and have established a provisional fate map of the head. The latter led us to propose the hypothesis that the coronal and frontal sutures (the lines of ecdysis) are derived from embryonic epithelial fusion events. In this project, we want to perform in vivo imaging and non-invasive marking of cells with fluorescent proteins in order to generate an exact fate map and to better understand the morphogenetic movements of the head. Using these tools, we will then test, whether the sutures do indeed derive from embryonic fusion events. Further, we want to analyze the function of Tc-homeobrain, a novel head patterning gene, which is expressed in an anterior cap in the early blastoderm and later in the head anlagen. This is similar to Drosophila indicating a conserved function. However, no functional data is available in the fly. In RNAi in Tribolium, the entire dorsal head is missing. Several transgenic lines will be constructed as part of this project, which will be valuable for other studies. This includes a system to genetically permanently mark epidermal cells, several Gal4 drivers and responder constructs with fluorescent proteins, which mark nuclei or cell outlines.