A conserved role for arrow in posterior axis patterning across Arthropoda

Area of Science:

• Developmental Biology
• Evolutionary Biology
• Genetics

Background:

• Segmentation is crucial for arthropod evolution.
• Canonical Wnt (cWnt) signaling is known to regulate posterior segmentation in vertebrates and some insects.
• Data on Wnt signaling in diverse arthropod lineages, especially non-holometabolous insects and arachnids, are limited.

Purpose of the Study:

• To investigate the role of the Wnt co-receptor arrow (arr) in posterior axis elongation across different arthropod groups.
• To determine if cWnt signaling is required for maintaining Wnt8 expression during arthropod development.
• To characterize the effects of arr knockdown on segmentation and gene expression in spiders and insects.

Main Methods:

• RNA interference (RNAi) was used to knock down the arrow (arr) gene in the spider Parasteatoda tepidariorum, the cricket Gryllus bimaculatus, and the milkweed bug Oncopeltus fasciatus.
• Phenotypic analysis focused on posterior truncations and segmentation defects.
• RNA-sequencing (RNA-Seq) was employed for differential gene expression analysis in P. tepidariorum arr loss-of-function mutants.

Main Results:

• arr knockdown led to posterior truncations in O. fasciatus and G. bimaculatus, with varying severity.
• Spider embryos with disrupted arr showed defects along the entire axis, including germband segmentation.
• Knockdown of arr did not abolish Wnt8 expression in any species, and Caudal expression was retained in severe spider and cricket phenotypes.

Conclusions:

• Canonical Wnt signaling is not universally required for the maintenance of Wnt8 expression across Arthropoda.
• The findings suggest a conserved role for Wnt signaling in posterior development but highlight lineage-specific variations.
• Differential gene expression analysis is a powerful tool for studying severe developmental phenotypes in emerging model organisms.