| dc.description.abstracteng | Embryonic segmentation of arthropods is a dynamic biological process that produces an organism by pattern formation, morphogenesis and specification of corresponding cells. The involved genes have mostly been identified by their phenotypes in systematic mutagenesis screens in few model systems, such as Drosophila melanogaster. The candidate gene approach based on RNAi was used to compare the function of those genes in other arthropods but was not able to detect novel and unsuspected functions. The detection of novel gene functions by a hypothesis independent screen has been a major endeavor to fill this gap.
In this work, a large collection of knock-down experiments was analyzed for cuticle phenotypes indicating a function in embryogenesis and a subset was re-screened to confirm the phenotypes. However, respective systematic searches may have remained incomplete, because interference of some patterning genes caused embryonic death before cuticle formation. Therefore, such "empty egg phenotypes" without any recognizable cuticle structures had been screened for defects in red flour beetle Tribolium castaneum embryogenesis and two glycogen metabolism genes had been shown to produce patterning defects. Here, I showed that RNAi targeting two genes involved in glucose synthesis Tc-GlyS and Tc-AGBE led to segmentation and appendage defects ultimately leading to empty egg phenotypes. Indeed, loss of Tc-GlyS and Tc-AGBE resulted in malformed and asymmetrically absent stripes of segment polarity genes indicating issues with maintaining segmental boundaries. More specifically, the defects first affected posterior abdominal segments but later extended to the entire trunk while the growth zone and pair-rule gene expression appeared to remain intact. Tc-dac and Tc-Sp8 expression marked medial portions of the appendages and were strongly affected while Tc-Dll and Tc-Sp8 expression marked distal parts and remained intact in RNAi phenotypes. I tested the hypothesis that this effect of glycogen metabolism enzymes was via the Glycogen synthase kinase 3 (GSK-3), which is known to be required for Wnt, Hh and Notch pathways, as well. I found that the effect was not exclusively by one of these pathways. Taken together, I found that Tc-GlyS and Tc- AGBE functions were required for segmental boundary maintenance, axis elongation and appendages outgrowth thereby linking metabolism and patterning formation. | de |