An amphioxus neurula stage cell atlas supports a complex scenario for the emergence of vertebrate head mesoderm
Ontology highlight
ABSTRACT:
ORGANISM(S): Branchiostoma lanceolatum
PROVIDER: GSE255742 | GEO | 2024/04/10
REPOSITORIES: GEO
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Project description:An amphioxus neurula stage cell atlas supports a complex scenario for the emergence of vertebrate head mesoderm
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Project description:An important question in biology is why some animals are able to regenerate, whereas others are not. The basal chordate amphioxus is uniquely positioned to address the evolution of regeneration. We report here the high regeneration potential of the European amphioxus Branchiostoma lanceolatum. Adults regenerate both anterior and posterior structures, including neural tube, notochord, fin, and muscle. Development of a classifier based on tail regeneration profiles predicts the assignment of young and old adults to their own class with >94% accuracy. The process involves loss of differentiated characteristics, formation of an msx-expressing blastema, and neurogenesis. Moreover, regeneration is linked to the activation of satellite-like Pax3/7 progenitor cells, the extent of which declines with size and age. Our results provide a framework for understanding the evolution and diversity of regeneration mechanisms in vertebrates.
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Project description:BACKGROUND: A common feature of chemosensory systems is the involvement of G protein-coupled receptors (GPCRs) in the detection of environmental stimuli. Several lineages of GPCRs are involved in vertebrate olfaction, including trace amine-associated receptors, type 1 and 2 vomeronasal receptors and odorant receptors (ORs). Gene duplication and gene loss in different vertebrate lineages have lead to an enormous amount of variation in OR gene repertoire among species; some fish have fewer than 100 OR genes, while some mammals possess more than 1000. Fascinating features of the vertebrate olfactory system include allelic exclusion, where each olfactory neuron expresses only a single OR gene, and axonal guidance where neurons expressing the same receptor project axons to common glomerulae. By identifying homologous ORs in vertebrate and in non-vertebrate chordates, we hope to expose ancestral features of the chordate olfactory system that will help us to better understand the evolution of the receptors themselves and of the cellular components of the olfactory system. RESULTS: We have identified 50 full-length and 11 partial ORs in Branchiostoma floridae. No ORs were identified in Ciona intestinalis. Phylogenetic analysis places the B. floridae OR genes in a monophyletic clade with the vertebrate ORs. The majority of OR genes in amphioxus are intronless and many are also tandemly arrayed in the genome. By exposing conserved amino acid motifs and testing the ability of those motifs to discriminate between ORs and non-OR GPCRs, we identified three OR-specific amino acid motifs common in cephalochordate, fish and mammalian and ORs. CONCLUSION: Here, we show that amphioxus has orthologs of vertebrate ORs. This conclusion demonstrates that the receptors, and perhaps other components of vertebrate olfaction, evolved at least 550 million years ago. We have also identified highly conserved amino acid motifs that may be important for maintaining receptor conformation or regulating receptor activity. We anticipate that the identification of vertebrate OR orthologs in amphioxus will lead to an improved understanding of OR gene family evolution, OR gene function, and the mechanisms that control cell-specific expression, axonal guidance, signal transduction and signal integration.
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Project description:Central to the story of vertebrate evolution is the origin of the vertebrate head, a problem difficult to approach using paleontology and comparative morphology due to a lack of unambiguous intermediate forms. Embryologically, much of the vertebrate head is derived from two ectodermal tissues, the neural crest and cranial placodes. Recent work in protochordates suggests the first chordates possessed migratory neural tube cells with some features of neural crest cells. However, it is unclear how and when these cells acquired the ability to form cellular cartilage, a cell type unique to vertebrates. It has been variously proposed that the neural crest acquired chondrogenic ability by recruiting proto-chondrogenic gene programs deployed in the neural tube, pharynx, and notochord. To test these hypotheses we examined the expression of 11 amphioxus orthologs of genes involved in neural crest chondrogenesis. Consistent with cellular cartilage as a vertebrate novelty, we find that no single amphioxus tissue co-expresses all or most of these genes. However, most are variously co-expressed in mesodermal derivatives. Our results suggest that neural crest-derived cartilage evolved by serial cooption of genes which functioned primitively in mesoderm.
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Project description:Vertebrates have greatly elaborated the basic chordate body plan and evolved highly distinctive genomes that have been sculpted by two whole-genome duplications. Here we sequence the genome of the Mediterranean amphioxus (Branchiostoma lanceolatum) and characterize DNA methylation, chromatin accessibility, histone modifications and transcriptomes across multiple developmental stages and adult tissues to investigate the evolution of the regulation of the chordate genome. Comparisons with vertebrates identify an intermediate stage in the evolution of differentially methylated enhancers, and a high conservation of gene expression and its cis-regulatory logic between amphioxus and vertebrates that occurs maximally at an earlier mid-embryonic phylotypic period. We analyse regulatory evolution after whole-genome duplications, and find that-in vertebrates-over 80% of broadly expressed gene families with multiple paralogues derived from whole-genome duplications have members that restricted their ancestral expression, and underwent specialization rather than subfunctionalization. Counter-intuitively, paralogues that restricted their expression increased the complexity of their regulatory landscapes. These data pave the way for a better understanding of the regulatory principles that underlie key vertebrate innovations.
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Project description:We performed single-cell transcriptome analysis (using MARS-seq) in the stony coral Stylophora pistillata.
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Project description:R-spondins are a family of secreted proteins that play important roles in embryonic development and cancer. R-spondins have been shown to modulate the Wnt pathway; however, their involvement in other developmental signaling processes have remained largely unstudied. Here, we describe a novel function of Rspo2 in FGF pathway regulation in vivo Overexpressed Rspo2 inhibited elongation of Xenopus ectoderm explants and Erk1 activation in response to FGF. By contrast, the constitutively active form of Mek1 stimulated Erk1 even in the presence of Rspo2, suggesting that Rspo2 functions upstream of Mek1. The observed inhibition of FGF signaling was accompanied by the downregulation of the FGF target genes tbxt/brachyury and cdx4, which mediate anterioposterior axis specification. Importantly, these target genes were upregulated in Rspo2-depleted explants. The FGF inhibitory activity was mapped to the thrombospondin type 1 region, contrasting the known function of the Furin-like domains in Wnt signaling. Further domain analysis revealed an unexpected intramolecular interaction that might control Rspo2 signaling output. We conclude that, in addition to its role in Wnt signaling, Rspo2 acts as an FGF antagonist during mesoderm formation and patterning.
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