Abstract

Regeneration is an essential process for all multicellular organisms, allowing them to recover effectively from internal and external injury. This process has been studied extensively in a medical context in vertebrates, with pathways often investigated mechanistically, both to derive increased understanding and as potential drug targets for therapy. Several species from other parts of the metazoan tree of life, including Hydra, planarians and echinoderms, noted for their regenerative capabilities, have previously been targeted for study. Less well-documented for their regenerative abilities are sponges. This is surprising, as they are both one of the earliest-branching extant metazoan phyla on Earth, and are rapidly able to respond to injury. Their sessile lifestyle, lack of an external protective layer, inability to respond to predation and filter-feeding strategy all mean that regeneration is often required. In particular the demosponge genus Halisarca has been noted for its fast cell turnover and ability to quickly adjust its cell kinetic properties to repair damage through regeneration. However, while the rate and structure of regeneration in sponges has begun to be investigated, the molecular mechanisms behind this ability are yet to be catalogued.Here we describe the assembly of a reference transcriptome for Halisarca caerulea, along with additional transcriptomes noting response to injury before, shortly following (2h post-), and 12h after trauma. RNAseq reads were assembled using Trinity, annotated, and samples compared, to allow initial insight into the transcriptomic basis of sponge regenerative processes. These resources are deep, with our reference assembly containing >92.6% of the BUSCO Metazoa set of genes, and well-assembled (N50s of 836, 957, 1688 and 2032 for untreated, 2h, 12h and reference transcriptomes respectively), and therefore represent excellent qualitative resources as a bedrock for future study. The generation of transcriptomic resources from sponges before and following deliberate damage has allowed us to study particular pathways within this species responsible for repairing damage. We note particularly the involvement of the Wnt cascades in this process in this species, and detail the contents of this cascade, along with cell cycle, extracellular matrix and apoptosis-linked genes in this work.This resource represents an initial starting point for the continued development of this knowledge, given H. caerulea's ability to regenerate and position as an outgroup for comparing the process of regeneration across metazoan lineages. With this resource in place, we can begin to infer the regenerative capacity of the common ancestor of all extant animal life, and unravel the elements of regeneration in an often-overlooked clade.

Highlights

  • In order to survive the often-hostile conditions in which they live, multicellular organisms have evolved the ability to regenerate their tissues, allowing them to recover if injured

  • While almost all multicellular organisms can regenerate throughout their lives (Sánchez Alvarado 2000), some clades are adept at this process, and have been subjected to particular scrutiny

  • While we already have a deeper understanding of the drivers of these processes in many phyla, in poriferans we still have little to no understanding of the molecular mechanisms underlying these regenerative processes

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Summary

Introduction

In order to survive the often-hostile conditions in which they live, multicellular organisms have evolved the ability to regenerate their tissues, allowing them to recover if injured. Sponges are well known for their regeneration abilities (Wulff 2010), capable of regenerating a lost fragment, regrowing from a small piece, or even regenerating entirely from disaggregated cells (Korotkova 1997) They are capable of regenerating at rates of as much as 2900 times the normal growth rates (Ayling 1983) this rate is by no means universal (Kahn and Leys 2016) and comes at the expense of standard cell cycling (Henry & Hart, 2005). This is perhaps a response to their niche, as they are benthic, non-motile organisms, which can be exposed to damage in a variety of ways. The advent of next-generation sequencing techniques allows us to solve this knowledge gap efficiently and effectively, and bring sponges into consideration as model organisms for understanding regeneration, given their peculiar advantages as described above

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