The analysis of body axis formation in the common house spider Parasteatoda tepidariorum

• Applicant: Dr. Matthias Pechmann
• Subject Area: Evolutionary Cell and Developmental Biology (Zoology) ; Developmental Biology
• Term: from 2012 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 226588632

Setting up the dorsoventral and the anteroposterior body axes is a fundamental process during the embryonic development of all bilaterian animals. In spider embryos, a cellular structure called the cumulus is the main organizer of the embryonic axes. While other arthropods do not have such a structure, the cumulus is remarkably similar to the organizer that specifies the axes of amphibian embryos (Spemann organizer). Both organizers function via BMP signalling, and are able to induce a secondary body axis in the respective embryos. The function of the cumulus has been best studied in the common-house spider Parasteatoda tepidariorum. It is known that the cumulus acts as a source of BMP signalling required to specify the dorsoventral body axis of the spider embryo. The cumulus arises in the center of the radially-symmetric germ-disc and migrates to its periphery. Through this migration the cumulus breaks the radial symmetry of the germ-disc. However, the molecular basis of germ-disc formation, cumulus specification and dpp activation in the cells of the cumulus are completely unknown. In the initial research proposal, I analysed germ-disc formation via embryonic injection of cytoskeleton and RNA polymerase inhibitors, and via parental RNA interference with candidate genes of the Toll- and the EGF-signalling pathways as well as many other candidate transcription factors. While I could show that germ-disc formation requires the actin (but not the tubulin) cytoskeleton and zygotic transcription, the candidate gene approach did not result in germ-disc or axial patterning phenotypes. Therefore, the new approach of the renewal proposal is based on genes that have been selected from new transcriptome data. A pilot RNAi screen with ten new candidate genes already resulted in two striking dorsoventral patterning phenotypes and one gap-gene like phenotype. These results demonstrate that the selection of the new candidate genes is accurate, and that this is an excellent approach for identifying the genes most important for spider axis determination. The dorsoventral phenotypes are especially interesting, as one of the genes is a completely novel regulator of cumulus migration, and the other gene may be upstream of BMP signalling (something that has never been described before). Given these exciting preliminary results, a functional screen of the remaining genes from the transcriptome data will likely yield many more interesting and novel phenotypes.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Siegfried Roth