My research aims to understand the underlying genetic basis, how a repeated body unit or segment forms in the field cricket Gryllus bimaculatus. This is one of the few hemimetabolous insects, where RNA interference has been shown to work efficiently allowing me to carry out functional studies in an insect branching basal in the phylogenetic tree.
Although the insect body plan is well conserved, the developmental mechanisms of segmentation are surprisingly varied. The fruit fly Drosophila melanogaster has long served as the model organism, how a fertilized egg generates a structured segmented body. A cascade of transcription factors defines the body into smaller and smaller units in this species, specifying all segments essentially simultaneously.
Less evolutionary derived insects however, develop their posterior segments during a later secondary growth phase in a sequential fashion, similar to non-insect arthropods. This mode of segmentation (the so-called short-germ segmentation) is poorly understood, although most genes of the Drosophila-network are conserved in all insects despite the different modes of embryogenesis.
Therefore I hope to contribute to our understanding how short-germ insects pattern their body. On a broader scale, my thesis addresses the question as to whether there is any evidence for a common origin of segmentation in invertebrates and vertebrates.
1. Cell signalling in short-germ insects
Unlike Drosophila, short germ insects develop their posterior segments in a cellularized environment. I work on different cell-signalling pathways to understand which pathway might be crucial for cellular communication during this patterning process.
2. Evolution of the odd-skipped family in primitive insects
Gene duplication is one of the fundamental processes how a protein can retain an ancestral function, while its paralog or paralogs evolve to new functions. An example for such gene duplications is most likely the odd-skipped gene family, which is characteristic through its C2H2-Zn-finger encoding transcription factors and consists in Drosophila of: odd-skipped, sob, bowl and drm.
odd-skipped was first identified on the basis of a pair-rule segmentation phenotype, affecting every second segment in Drosophila melanogaster mutant embryos. Interestingly, sob is expressed in a strikingly similar fashion in this species, but its mutant does not affect the segmental pattern. In the centipede Strigamia maritima, a homologue of sob is expressed in a dynamic fashion, similar to genes (e.g. hairy in chicken embryos) involved in the segmentation of vertebrates.
My project addresses the evolution of this gene family by investigating the role of the sob homologue in the field cricket Gryllus bimaculatus through expression and functional analysis. This data will allow comparing its expression and function with higher insects on the one hand and non-insect arthropods, such as centipedes and spiders, on the other hand.
|Gryllus bimaculatus egg during germband elongation injected with A488-coupled dextrans (10,000 MW)