Abstract
Changes in developmental gene regulatory networks (dGRNs) underlie much of the diversity of life, but the evolutionary mechanisms that operate on regulatory interactions remain poorly understood. Closely related species with extreme phenotypic divergence provide a valuable window into the genetic and molecular basis for changes in dGRNs and their relationship to adaptive changes in organismal traits. Here we analyse genomes, epigenomes and transcriptomes during early development in two Heliocidaris sea urchin species that exhibit highly divergent life histories and in an outgroup species. Positive selection and chromatin accessibility modifications within putative regulatory elements are enriched on the branch leading to the derived life history, particularly near dGRN genes. Single-cell transcriptomes reveal a dramatic delay in cell fate specification in the derived state, which also has far fewer open chromatin regions, especially near conserved cell fate specification genes. Experimentally perturbing key transcription factors reveals profound evolutionary changes to early embryonic patterning events, disrupting regulatory interactions previously conserved for ~225 million years. These results demonstrate that natural selection can rapidly reshape developmental gene expression on a broad scale when selective regimes abruptly change. More broadly, even highly conserved dGRNs and patterning mechanisms in the early embryo remain evolvable under appropriate ecological circumstances.
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Data Availability
Genomes. Sequencing reads used to assemble the Heliocidaris genomes and the genome assemblies themselves are available on the Chinese National GeneBank (CNP0002233) and NCBI (PRJNA869508). Genome assemblies of Heliocidaris erythrogramma and Heliocidaris tuberculata are also available on NCBI (PRJNA827916 and PRJNA827769, respectively). Genome assembly of Lytechinus variegatus is previously published21 and available on NCBI (PRJNA657258). Genome annotations and files associated with whole genome alignments between species are available on Dryad (https://doi.org/10.5061/dryad.sj3tx966v). ATAC-seq. Raw sequencing reads for the ATAC-seq dataset are available on NCBI (PRJNA828607). Alignment files are available on Dryad (https://doi.org/10.5061/dryad.sj3tx966v). Result files associated with the ATAC-seq analyses are available as Supplementary Data 2–4. Bulk RNA-seq. Bulk RNA-seq data were retrieved from ref. 19. scRNA-seq. Raw sequencing reads for the Heliocidaris erythrogramma single-cell ATAC-seq dataset are available on NCBI (PRJNA833141). Sequencing reads from the Lytechinus variegatus scRNA-seq dataset were retrieved from ref. 34 and are available on NCBI (PRJNA765003). Results files associated with the scRNA-seq analyses are available as Supplementary Data 7 and 9.
Code Availability
Code and analyses associated with these result figures are available on GitHub at https://github.com/phillipdavidson/heliocidaris_analyses.
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Acknowledgements
We thank the Sydney Institute of Marine Science (SIMS) for facilities, as well as the SIMS staff for their assistance. This work was supported by the National Science Foundation Division of Integrative Organismal Systems (award no. 1929934 to G.A.W.), National Science Foundation Graduate Research Fellowships to H.R.D. and A.J.M., and an Australian Research Council Discovery Grant (award no. DP120102849 to M.B.).
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L.W., M.B., G.F. and G.A.W. conceived and designed the study. L.W., D.K. and P.C. collected tissues for genomic sequencing. Y.Z. performed genomic DNA extraction and sequencing library preparations. P.L.D., H.G. and H.Z. assembled the genomes. P.L.D. performed genome annotation, alignments and data analysis. P.L.D. and A.B. performed selection analyses. P.L.D. and H.R.D. collected, prepared and analysed ATAC-seq libraries. A.J.M. collected, prepared and analysed scRNA-seq libraries. J.S.S. and A.E. performed embryonic expression and injection assays. P.L.D. and G.A.W. wrote the manuscript, and all authors contributed to manuscript revisions.
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Extended data
Extended Data Fig. 1 Chromatin landscape and expression domain of foxN2/3 is conserved.
Chromatin accessibility nearby foxN2/3 in H. erythrogramma (top, orange) and H. tuberculata (bottom, green), including seven open chromatin regions (OCRs). In-situ hybridization of foxN2/3 in blastula-stage b, H. erythrogramma and c, H. tuberculata embryos. Micrographs derive from a single round of in-situ experiments for each species.
Extended Data Fig. 2 Scaling down number of L. variegatus cells does not substantially affect clustering.
UMAP of non-integrated single cell RNA-seq data from L. variegatus, in which the data has been randomly subsampled to 2065 cells so that the cell number is equivalent to the H. erythrogramma dataset. This subsampling does not change the number and general spatial relationship among clusters in L. variegatus (that is distinct cluster of skeletogenic cells separate from remainder of cells in the embryo).
Extended Data Fig. 3 Three independent methods of integrating single cell RNA-seq data recover similar clustering relationships among L. variegatus and H. erythrogramma cells.
Canonical correlation analysis (CCA), reciprocal principal component analysis (RPCA), and Harmony each recover more numerous, distinct transcriptional states in L. variegatus relative to H. erythrogramma following integration of single cell expression data. All three methods reveal a consistent number of clusters in both species. In particular, H. erythrogramma contains fewer clusters there is more extensive overlap of cells among clusters. These results suggesting that differentiation of discrete cell populations is delayed in the H. erythrogramma embryo.
Extended Data Fig. 4 hesC appears to have lost its ancestral role of repressing larval skeletal cell specification in H. erythrogramma.
Derived expression patterns of hesC in H. erythrogramma at a, cleavage; b, blastula; and c, d, larva stage embryos. Micrographs derive from a single round of in-situ experiments. e, f, Control and MASO knock-down of HesC in H. erythrogramma (early larva; scale bar 100 µm). Polarized light illuminates skeletal elements. HesC knockdown appears to show no phenotype, a dramatic change from the ancestral dGRN. Injection experiments were replicated twice.
Supplementary information
Supplementary Information
Supplementary Tables 1–3 and Figs. 1–9.
Supplementary Data 1
List of sea urchin dGRN genes.
Supplementary Data 2
List of putatively neutral sites for selection analyses, referenced to H. erythrogramma genome.
Supplementary Data 3
OCR tests for selection results.
Supplementary Data 4
OCR accessibility counts and statistics.
Supplementary Data 5
P values from coding selection analyses.
Supplementary Data 6
Results from bulk RNA-seq analyses.
Supplementary Data 7
scRNA-seq count data.
Supplementary Data 8
Gene models from each species’ genome annotations.
Supplementary Data 9
Marker genes for each cluster from single-cell analyses.
Supplementary Data 10
Putative orthology relationships between genes of H. erythrogramma and L. variegatus from OrthoFinder2.
Supplementary Data 11
Marker genes used to putatively assign cell type identity to scRNA-seq clusters.
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Davidson, P.L., Guo, H., Swart, J.S. et al. Recent reconfiguration of an ancient developmental gene regulatory network in Heliocidaris sea urchins. Nat Ecol Evol 6, 1907–1920 (2022). https://doi.org/10.1038/s41559-022-01906-9
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DOI: https://doi.org/10.1038/s41559-022-01906-9