Axial patterning in cephalochordates and the evolution of the organizer

Yu, Jr-Kai; Satou, Yutaka; Holland, Nicholas D.; Shin-I, Tadasu; Kohara, Yuji; Satoh, Noriyuki; Bronner‐Fraser, Marianne; Holland, Linda Z.

doi:10.1038/nature05472

“…Recent results have shown that the dorsal side of a juvenile hemichordate is determined by a stripe of expression of bone morphogenetic protein (BMP) gene expressed dorsally, and its ventral side by an expression stripe of BMP antagonists, including chordin , just as has been reported for the arthropods (Sasai & De Robertis 1997). By contrast, in vertebrates, BMP is expressed ventrally, and chordin is expressed dorsally (Sasai & De Robertis 1997;Yu et al 2007), suggesting that the chordate D-V axis is inverted compared with a hemichordate or Deuterostome phylogeny B. J. Swalla & A.…”

Section: Conserved Gene Network Pattern Deuterostome Axes and Germ Lmentioning

confidence: 98%

Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives

Swalla

¹

,

Smith

²

2008

Phil. Trans. R. Soc. B

View full text Add to dashboard Cite

Deuterostomes are a monophyletic group of animals that include the vertebrates, invertebrate chordates, ambulacrarians and xenoturbellids. Fossil representatives from most major deuterostome groups, including some phylum-level crown groups, are found in the Lower Cambrian, suggesting that evolutionary divergence occurred in the Late Precambrian, in agreement with some molecular clock estimates. Molecular phylogenies, larval morphology and the adult heart/kidney complex all support echinoderms and hemichordates as a sister grouping (Ambulacraria). Xenoturbellids are a relatively newly discovered phylum of worm-like deuterostomes that lacks a fossil record, but molecular evidence suggests that these animals are a sister group to the Ambulacraria. Within the chordates, cephalochordates share large stretches of chromosomal synteny with the vertebrates, have a complete Hox complex and are sister group to the vertebrates based on ribosomal and mitochondrial gene evidence. In contrast, tunicates have a highly derived adult body plan and are sister group to the vertebrates based on the analyses of concatenated genomic sequences. Cephalochordates and hemichordates share gill slits and an acellular cartilage, suggesting that the ancestral deuterostome also shared these features. Gene network data suggest that the deuterostome ancestor had an anterior-posterior body axis specified by Hox and Wnt genes, a dorsoventral axis specified by a BMP/chordin gradient, and was bilaterally symmetrical with left-right asymmetry determined by expression of nodal.

show abstract

“…In echinoderms and hemichordates, BMP is expressed on the aboral side of the embryo and chordin on the oral side [62,63]. By contrast, in cephalochordate embryos, BMP is expressed on the ventral side and chordin on the dorsal side [64]. Saccoglossus kowalevskii is an acorn worm in which fertilized eggs develop directly into adults without a tornaria larval stage.…”

Section: (C) the Inversion Hypothesismentioning

confidence: 99%

Chordate evolution and the three-phylum system

Satoh

¹

,

Rokhsar

²

,

Nishikawa

³

2014

Self Cite

View full text Add to dashboard Cite

Traditional metazoan phylogeny classifies the Vertebrata as a subphylum of the phylum Chordata, together with two other subphyla, the Urochordata (Tunicata) and the Cephalochordata. The Chordata, together with the phyla Echinodermata and Hemichordata, comprise a major group, the Deuterostomia. Chordates invariably possess a notochord and a dorsal neural tube. Although the origin and evolution of chordates has been studied for more than a century, few authors have intimately discussed taxonomic ranking of the three chordate groups themselves. Accumulating evidence shows that echinoderms and hemichordates form a clade (the Ambulacraria), and that within the Chordata, cephalochordates diverged first, with tunicates and vertebrates forming a sister group. Chordates share tadpole-type larvae containing a notochord and hollow nerve cord, whereas ambulacrarians have dipleurula-type larvae containing a hydrocoel. We propose that an evolutionary occurrence of tadpole-type larvae is fundamental to understanding mechanisms of chordate origin. Protostomes have now been reclassified into two major taxa, the Ecdysozoa and Lophotrochozoa, whose developmental pathways are characterized by ecdysis and trochophore larvae, respectively. Consistent with this classification, the profound dipleurula versus tadpole larval differences merit a category higher than the phylum. Thus, it is recommended that the Ecdysozoa, Lophotrochozoa, Ambulacraria and Chordata be classified at the superphylum level, with the Chordata further subdivided into three phyla, on the basis of their distinctive characteristics.

show abstract

“…Recent results have shown that the dorsal side of a juvenile hemichordate is determined by a stripe of expression of bone morphogenetic protein (BMP) gene expressed dorsally, and its ventral side by an expression stripe of BMP antagonists, including chordin , just as has been reported for the arthropods (Sasai & De Robertis 1997). By contrast, in vertebrates, BMP is expressed ventrally, and chordin is expressed dorsally (Sasai & De Robertis 1997;Yu et al 2007), suggesting that the chordate D-V axis is inverted compared with a hemichordate or arthropod D-V axis . As the mouth is ventral in both the chordate and non-chordate groups, evolution of the chordates must have entailed moving the mouth from the opposite side of the gill slits to the same side as the gill slits, while also evolving a notochord and a dorsal central nervous system from a ventral enteropneust-like nerve net.…”

Section: Conserved Gene Network Pattern Deuterostome Axes and Germ Lmentioning

confidence: 98%

Deciphering deuterostome phylogeny: molecular, morphological, and palaeontological perspectives

Smith¹,

Swalla²

2009

View full text Add to dashboard Cite

Deuterostomes are a monophyletic group of animals that include the vertebrates, invertebrate chordates, ambulacrarians and xenoturbellids. Fossil representatives from most major deuterostome groups, including some phylum-level crown groups, are found in the Lower Cambrian, suggesting that evolutionary divergence occurred in the Late Precambrian, in agreement with some molecular clock estimates. Molecular phylogenies, larval morphology and the adult heart/kidney complex all support echinoderms and hemichordates as a sister grouping (Ambulacraria). Xenoturbellids are a relatively newly discovered phylum of worm-like deuterostomes that lacks a fossil record, but molecular evidence suggests that these animals are a sister group to the Ambulacraria. Within the chordates, cephalochordates share large stretches of chromosomal synteny with the vertebrates, have a complete Hox complex and are sister group to the vertebrates based on ribosomal and mitochondrial gene evidence. In contrast, tunicates have a highly derived adult body plan and are sister group to the vertebrates based on the analyses of concatenated genomic sequences. Cephalochordates and hemichordates share gill slits and an acellular cartilage, suggesting that the ancestral deuterostome also shared these features. Gene network data suggest that the deuterostome ancestor had an anterior-posterior body axis specified by Hox and Wnt genes, a dorsoventral axis specified by a BMP/chordin gradient, and was bilaterally symmetrical with left-right asymmetry determined by expression of nodal.

show abstract

Axial patterning in cephalochordates and the evolution of the organizer

Cited by 238 publications

References 36 publications

Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives

Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives

Chordate evolution and the three-phylum system

Deciphering deuterostome phylogeny: molecular, morphological, and palaeontological perspectives

Contact Info

Product

Resources

About