Acoel Single-Cell Transcriptomics: Cell Type Analysis of a Deep Branching Bilaterian

Abstract

Bilaterian animals display a wide variety of cell types, organized into defined anatomical structures and organ systems, which are mostly absent in prebilaterian animals. Xenacoelomorpha are an early-branching bilaterian phylum displaying an apparently relatively simple anatomical organization that have greatly diverged from other bilaterian clades. In this study, we use whole-body single-cell transcriptomics on the acoel Isodiametra pulchra to identify and characterize different cell types. Our analysis identifies the existence of ten major cell type categories in acoels all contributing to main biological functions of the organism: metabolism, locomotion and movements, behavior, defense, and development. Interestingly, although most cell clusters express core fate markers shared with other animal clades, we also describe a surprisingly large number of clade-specific marker genes, suggesting the emergence of clade-specific common molecular machineries functioning in distinct cell types. Together, these results provide novel insight into the evolution of bilaterian cell types and open the door to a better understanding of the origins of the bilaterian body plan and their constitutive cell types.

Acoel single-cell atlas reveals expression dynamics and heterogeneity of adult pluripotent stem cells

“…S1b–d ). These cell types and their associated biological functions correspond to cell types identified in the single-cell sequencing data of another acoel species, Isodiametra pulchra , suggesting these cell types are shared across acoels 41 . Genes enriched in the neoblast cluster included the known neoblast marker piwi-1 22 , and similar to the expression pattern of that gene in I. pulchra , they lacked expression anteriorly and labeled cells with an even distribution from the midsection along the anterior-posterior axis, to the posterior-most region of Hofstenia .…”

Single cell atlas of Xenoturbella bocki highlights the limited cell-type complexity of a non-vertebrate deuterostome lineage

“…We find Xenoturbella neurons to be significantly less diverse than those characterized in acoelomorphs 31 , another of the Xenacoelomorph lineages. Interestingly, Xenoturbella neurons express hallmarks of metazoan neurons including islet-1, brn3/pouIV and the proneural bHLH transcription factor achaete-scute , indicating that they share some features of an ancestral neural regulatory program.…”

Evolution of homology: From archetype towards a holistic concept of cell type

“…The following references are intended to acquaint the interested reader with the recent single‐cell evidence on animal cell diversity in both model and nonmodel species, which would not be appropriate to detail in a single review but is still citable in terms of the number of publications. The wealth of scRNA‐Seq data already generated is expected to grow rapidly and already covers major animal lineages: Porifera (Musser et al, 2021; Sebé‐Pedrós, Chomsky, et al, 2018), Ctenophora and Placozoa (Sebé‐Pedrós, Chomsky, et al, 2018), Cnidaria (Chari et al, 2021; Hu et al, 2020; Levy et al, 2021; Sebé‐Pedrós, Saudemont, et al, 2018; Siebert et al, 2019), Acoela (Duruz et al, 2021; Hulett et al, 2022), Plathelminthes (Fincher et al, 2018; Li et al, 2021; Plass et al, 2018), Annelida (Achim et al, 2018; Shao et al, 2020), Arthropoda (Allen et al, 2020; Brückner et al, 2021; Croset et al, 2018; Davie et al, 2018; Dillon et al, 2022; Hung et al, 2020; Karaiskos et al, 2017; Rust et al, 2020; Slaidina et al, 2020), Nematoda (J. Cao et al, 2017; Packer et al, 2019), Echinodermata (Foster et al, 2020; Massri et al, 2021; Meyer et al, 2022; Paganos et al, 2021), Urochordata (C. Cao et al, 2019; Horie et al, 2018; Sladitschek et al, 2020), as well as the most densely sampled Craniota (Briggs et al, 2018; J. Cao et al 2019, 2020; Farrell et al, 2018; Han et al, 2020; Hodge et al, 2019; Pijuan‐Sala et al, 2019; Regev et al, 2017; Shafer et al, 2022; The Tabula Muris Consortium, 2018; Tosches et al, 2018; D. E. Wagner et al, 2018).…”