Probing the evolutionary dynamics of whole-body regeneration within planarian flatworms

Abstract

Why some animals can regenerate while many others cannot remains a fascinating question. Even amongst planarian flatworms, well-known for their ability to regenerate complete animals from small body fragments, species exist that have restricted regeneration abilities or are entirely regeneration incompetent. Towards the goal of probing the evolutionary dynamics of regeneration, we have assembled a diverse live collection of planarian species from around the world. The combined quantification of species-specific head regeneration abilities and comprehensive transcriptome-based phylogeny reconstructions reveals multiple independent transitions between robust whole-body regeneration and restricted regeneration in the freshwater species. Our demonstration that the RNAi-mediated inhibition of canonical Wnt signalling can nevertheless bypass all experimentally tractable head regeneration defects in the current collection indicates that the pathway may represent a hot spot in the evolution of planarian regeneration defects. Combined with our finding that Wnt signalling has multiple roles in the reproductive system of the model species S. mediterranea, this raises the possibility of a trade-off between egg-laying and asexual reproduction by fission/regeneration as a driver of regenerative trait evolution. Although initial quantitative comparisons of Wnt signalling levels, reproductive investment, and regenerative abilities across the collection confirm some of the model's predictions, they also highlight the diversification of molecular mechanisms amongst the divergent planarian lineages. Overall, our study establishes a framework for the mechanistic evolution of regenerative abilities and planarians as model taxon for comparative regeneration research.

A genetic and microscopy toolkit for live imaging of whole-body regeneration inMacrostomum lignano

“…Unlike the planarian Schmidtea mediterranea, which regenerates a head in place of a tail after β-catenin RNAi (Gurley et al, 2008;Petersen & Reddien, 2008), M. lignano simply failed to regenerate anything. Furthermore, in planarian species that exhibit compromised anterior regeneration, β-catenin RNAi can often rescue this deficiency (Sikes & Newmark, 2013;Vila-Farré et al, 2023); however, we observed no such rescue in non-regenerative M. lignano tails (Figure S7B-C). Another key difference is observed in the expression of wnt-1.…”

Investigation into gene regulatory networks governing the development and maintenance of the planarian reproductive system

“…Furthermore, recent findings highlighting the differential Wnt signaling activity be-1.3. STUDYING GENE REGULATORY NETWORKS IN PLANARIA tween sexual and asexual S. mediterranea, along with the enrichment of pathway components in sexual tissues, suggest the involvement of heightened Wnt signaling in sexual reproduction (Vila-Farré et al, 2023). Notably, the knockdown of beta-catenin-1 in sexual planarians resulted in the loss of vitellaria and shell glands.…”

“…Additionally, a clustered heatmap of the Euclidean distances between samples was done using pheatmap function from pheatmap 1.0.12. The normalized counts of several marker genes for sexual tissues identified in the literature (Chong et al, 2011;Issigonis et al, 2022; U. W. Rouhana et al, 2017;Steiner et al, 2016;Vila-Farré et al, 2023;Y. Wang et al, 2010Zayas et al, 2005) were then assessed for each condition and compared to the asexual, ophis and egfp controls using boxplots in ggplot2.…”

“…I next tried to assess whether any specific reproductive organ was affected by knock-down of a candidate TF by looking at the expression level of several published markers for each type of reproductive organs (Chong et al, 2011;Issigonis et al, 2022; U. W. Rouhana et al, 2017;Steiner et al, 2016;Vila-Farré et al, 2023;Y. Wang et al, 2010Zayas et al, 2005) (Figure 3.31 until 3.33).…”