| dc.description.abstracteng | The insect head is a composite structure of several segments and an anterior non-segmental region. Due to head involution, the Drosophila larval head is strongly reduced and for technical reasons the developmental basis of head formation has not been comprehensively studied in Drosophila. In order to elucidate this process I used the red flour beetle Tribolium castaneum as model, focussing on the anterior median region (AMR) of the head, which harbors labrum and stomodeum. This region is patterned by a different set of genes than the surrounding tissues. The AMR development has already been studied using the candidate approach, which focused on genes previously identified in Drosophila. In order to identify a comprehensive list of genes involved in the formation of the AMR independent from previous knowledge, I used the unbiased large scale RNA interference screen (iBeetle-screen).
From the iBeetle results, I was able to identify three interesting genes which are required for proper labrum formation. Both Tc-Serrate and Tc-mib1 are components of the Notch signaling pathway, which is known to be required e.g. for the formation of the joints and growth of adult legs and appendages in Drosophila and Tribolium. I showed that Tc-Ser is expressed during early AMR formation, but is not necessary for the early pattering process. During early labrum formation Notch signaling is required for the regulation of cell proliferation like in the Drosophila eye and wing imaginal discs. The labrum was suggested to be an appendage like structure, patterned by the same regulatory gene network. However, the results in this work indicate that Notch-signaling is acting upstream of the leg patterning network in the labrum in contrast to its function in the legs.
Another novel gene required for labrum development is the GATA transcription factor Tc-grain. In Drosophila, grain is required for neurogenesis by regulating the axon guidance and in morphogenesis of the adult legs and the larval posterior spiracles. I showed that the expression of Tc-grn is conserved to Drosophila. Additionally, I showed that Tc-grn in Tribolium is likely to be involved in amnion development and is required for proper labrum formation probably by regulating morphogenesis. | de |