Dorsoventral axis formation in the cricket Gryllus bimaculatus as example of convergent evolution of Toll’s morphogen function

• Applicant: Professor Dr. Siegfried Roth
• Subject Area: Evolutionary Cell and Developmental Biology (Zoology)
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 516937640

Toll and BMP signaling are essential for dorsoventral (DV) axis formation in all insects studied so far. The Toll signaling gradient in Drosophila represents moreover, one of the best-understood morphogen systems determining cell fates in a concentration-dependent manner. While BMP is crucial for the establishment of the DV axis in most bilaterian animals, Toll’s DV function appears to be an evolutionary novelty of insects. In the past we have studied DV axis formation in representatives of major insect lineages and found a diminishing requirement for Toll in insects more distantly related to Drosophila. Concomitantly, the importance of BMP signaling increases approaching the BMP dominated patterning networks known from other bilateria. Surprisingly, the cricket, Gryllus bimaculatus, an orthopteran species representing the basal-most insect lineage we have studied so far, did not conform to this trend. The Gryllus DV system rather has striking similarities to that of Drosophila. In this proposal, we want to unravel molecular mechanisms of Gryllus DV pattering and thereby explore the possibility of convergent evolution of Toll’s morphogen function. Our work programme is based on recent advances in Gryllus live-imaging, transgenesis, CRISPR/Cas9 mediated genome editing and genome sequencing, and it encompasses four specific objectives. We plan (1) to study the spatiotemporal profile of Toll signaling by visualizing the nuclear accumulation of the transcription factor Dorsal/NF-κB, (2) to identify Toll and BMP target genes by differential transcriptome analysis, (3) to characterize cis-regulatory elements of target genes by ATAC-seq, computational motif searches and ATAC-seq based footprinting, (4) to tag target genes for live imaging and perform reporter assays to confirm the functionality of predicted cis-regulatory elements. Together, these data will provide molecular insights into the unexpected parallels between fly and cricket DV patterning and complement our picture of the complex evolutionary history of DV axis formation in insects.

• DFG Programme: Research Grants
• Co-Investigators: Dr. Justin Crocker; Dr. Philipp Schiffer