Project Summary

The genetic regulation of head patterning in insects is poorly understood. We use the red flour beetle Tribolium as model system because head involution hampers analysis of head development in Drosophila. In previous work we have identified a signaling center in the head (Insect head boundary, IHB) where the wingless/Wnt1, Wnt5 and hedgehog morphogens are expressed, along which several head genes are activated and the location of which corresponds to the mid-hindbrain-boundary (MHB) of vertebrates. We study autoregulation and mutual interactions of the Tc-wingless, Tc-Wnt5 and Tc-hedgehog morphogens and their influence on candidate target genes at the IHB. We will first repress and ectopically activate the pathways by RNAi against positive and negative regulators, respectively. In parallel we want to generate head specific Gal4 drivers in order to allow local activation and repression the pathways. The analysis of mutants will identify novel targets of the IHB. This project will lead to insights into the function of an important signaling center in the Tribolium head which (because of its insect typical development) likely represents the situation in arthropods. The correspondence of positions of the IHB and the MHB allows for comparisons with the vertebrate situation. From our past candidate gene approach using genes involved in Drosophila head and vertebrate neural plate patterning we have identified several genes that are most likely activated by the IHB morphogens. However, it is likely that there are more such genes because mutagenesis screens for head mutants in Drosophila have been hampered by head involution. Hence, no comprehensive list of genes required for head development is available in Drosophila. Moreover, insect specific head genes are likely to exist which cannot be found by testing genes known from vertebrate neural plate patterning. In order to identify a comprehensive list of target genes of the Wnt and Hedgehog pathways at the IHB we want to use RNA-seq to compare the mRNA complement found in wildtype and in RNAi embryos in which pathway activity is downregulated. A subset of confirmed genes specifically regulated by this treatment will be further analyzed for their function. This will reveal a comprehensive view on the role of the morphogens at the IHB (both different and overlapping sets of target genes) and novel players required for head development will be identified.