We have compared the dorsoventral development of hemichordates and chordates to deduce the organization of their common ancestor, and hence to identify the evolutionary modifications of the chordate body axis after the lineages split. In the hemichordate embryo, genes encoding bone morphogenetic proteins (Bmp) 2/4 and 5/8, as well as several genes for modulators of Bmp activity, are expressed in a thin stripe of ectoderm on one midline, historically called “dorsal.” On the opposite midline, the genes encoding Chordin and Anti-dorsalizing morphogenetic protein (Admp) are expressed. Thus, we find a Bmp-Chordin developmental axis preceding and underlying the anatomical dorsoventral axis of hemichordates, adding to the evidence from Drosophila and chordates that this axis may be at least as ancient as the first bilateral animals. Numerous genes encoding transcription factors and signaling ligands are expressed in the three germ layers of hemichordate embryos in distinct dorsoventral domains, such as pox neuro, pituitary homeobox, distalless, and tbx2/3 on the Bmp side and netrin, mnx, mox, and single-minded on the Chordin-Admp side. When we expose the embryo to excess Bmp protein, or when we deplete endogenous Bmp by small interfering RNA injections, these expression domains expand or contract, reflecting their activation or repression by Bmp, and the embryos develop as dorsalized or ventralized limit forms. Dorsoventral patterning is independent of anterior/posterior patterning, as in Drosophila but not chordates. Unlike both chordates and Drosophila, neural gene expression in hemichordates is not repressed by high Bmp levels, consistent with their development of a diffuse rather than centralized nervous system. We suggest that the common ancestor of hemichordates and chordates did not use its Bmp-Chordin axis to segregate epidermal and neural ectoderm but to pattern many other dorsoventral aspects of the germ layers, including neural cell fates within a diffuse nervous system. Accordingly, centralization was added in the chordate line by neural-epidermal segregation, mediated by the pre-existing Bmp-Chordin axis. Finally, since hemichordates develop the mouth on the non-Bmp side, like arthropods but opposite to chordates, the mouth and Bmp-Chordin axis may have rearranged in the chordate line, one relative to the other.
References
[1]
De Robertis EM, Sasai Y (1996) A common plan for dorsoventral patterning in Bilateria. Nature 380: 37–40.
[2]
Lichtneckert R, Reichert H (2005) Insights into the urbilaterian brain: Conserved genetic patterning mechanisms in insect and vertebrate brain development. Heredity 94: 465–477.
[3]
Gerhart J, Lowe C, Kirschner M (2005) Hemichordates and the origin of chordates. Curr Opin Genet Dev 15: 461–467.
[4]
Finnerty JR, Pang K, Burton P, Paulson D, Martindale MQ (2004) Origins of bilateral symmetry: Hox and dpp expression in a sea anemone. Science 304: 1335–1337.
[5]
Martindale MQ, Finnerty JR, Henry JQ (2002) The Radiata and the evolutionary origins of the bilaterian body plan. Mol Phylogenet Evol 24: 358–365.
[6]
Ferguson EL (1996) Conservation of dorsal-ventral patterning in arthropods and chordates. Curr Opin Genet Dev 6: 424–431.
[7]
Dorfman R, Shilo BZ (2001) Biphasic activation of the BMP pathway patterns the Drosophila embryonic dorsal region. Development 128: 965–972.
[8]
De Robertis EM, Kuroda H (2004) Dorsal-ventral patterning and neural induction in Xenopus embryos. Annu Rev Cell Dev Biol 20: 285–308.
[9]
Delaune E, Lemaire P, Kodjabachian L (2005) Neural induction in Xenopus requires early FGF signalling in addition to BMP inhibition. Development 132: 299–310.
[10]
Rusten TE, Cantera R, Kafatos FC, Barrio R (2002) The role of TGF beta signaling in the formation of the dorsal nervous system is conserved between Drosophila and chordates. Development 129: 3575–3584.
[11]
Jessell TM (2000) Neuronal specification in the spinal cord: Inductive signals and transcriptional codes. Nat Rev Genet 1: 20–29.
[12]
Timmer JR, Wang C, Niswander L (2002) BMP signaling patterns the dorsal and intermediate neural tube via regulation of homeobox and helix-loop-helix transcription factors. Development 129: 2459–2472.
[13]
Liem KF Jr., Tremml G, Roelink H, Jessell TM (1995) Dorsal differentiation of neural plate cells induced by BMP-mediated signals from epidermal ectoderm. Cell 82: 969–979.
[14]
Skeath JB (1998) The Drosophila EGF receptor controls the formation and specification of neuroblasts along the dorsal-ventral axis of the Drosophila embryo. Development 125: 3301–3312.
[15]
von Ohlen T, Doe CQ (2000) Convergence of dorsal, DPP, and EGFR signaling pathways subdivides the Drosophila neuroectoderm into three dorsal-ventral columns. Dev Biol 224: 362–372.
[16]
Kishimoto Y, Lee KH, Zon L, Hammerschmidt M, Schulte-Merker S (1997) The molecular nature of zebrafish swirl: BMP2 function is essential during early dorsoventral patterning. Development 124: 4457–4466.
[17]
Bachiller D, Klingensmith J, Shneyder N, Tran U, Anderson R, et al. (2003) The role of chordin/Bmp signals in mammalian pharyngeal development and DiGeorge syndrome. Development 130: 3567–3578.
[18]
Rossi JM, Dunn NR, Hogan BL, Zaret KS (2001) Distinct mesodermal signals, including BMPs from the septum transversum mesenchyme, are required in combination for hepatogenesis from the endoderm. Genes Dev 15: 1998–2009.
[19]
Holland ND (2003) Early central nervous system evolution: An era of skin brains? Nat Rev Neurosci 4: 617–627.
[20]
Bourlat SJ, Nielsen C, Lockyer AE, Littlewood DT, Telford MJ (2003) Xenoturbella is a deuterostome that eats molluscs. Nature 424: 925–928.
[21]
Bullock TH, Horridge GA (1965) Structure and function in the nervous systems of invertebrates. San Francisco: W. H. Freeman. 919 p.
[22]
Hyman LH (1940) The invertebrates. New York: McGraw-Hill. 572 p.
[23]
Morgan T (1894) Development of Balanoglossus. J Morphol 9: 1–86.
Nubler-Jung K, Arendt D (1996) Enteropneusts and chordate evolution. Curr Biol 6: 352–353.
[26]
Geoffroy St.-Hilaire E (1822) Considérations générales sur les vertebrés. Mem HIst Nat 9: 89–119.
[27]
Arendt D, Nubler-Jung K (1994) Inversion of dorsoventral axis? Nature 371: 26.
[28]
Karaulanov E, Knochel W, Niehrs C (2004) Transcriptional regulation of BMP4 synexpression in transgenic Xenopus. Embo J 23: 844–856.
[29]
Niehrs C, Pollet N (1999) Synexpression groups in eukaryotes. Nature 402: 483–487.
[30]
Martin AP (2000) Choosing among alternative trees of multigene families. Mol Phylogenet Evol 16: 430–439.
[31]
Marques G, Musacchio M, Shimell MJ, Wunnenberg-Stapleton K, Cho KW, et al. (1997) Production of a DPP activity gradient in the early Drosophila embryo through the opposing actions of the SOG and TLD proteins. Cell 91: 417–426.
[32]
Blader P, Rastegar S, Fischer N, Strahle U (1997) Cleavage of the BMP-4 antagonist chordin by zebrafish tolloid. Science 278: 1937–1940.
[33]
Onichtchouk D, Chen YG, Dosch R, Gawantka V, Delius H, et al. (1999) Silencing of TGF-beta signalling by the pseudoreceptor BAMBI. Nature 401: 480–485.
[34]
Grotewold L, Plum M, Dildrop R, Peters T, Ruther U (2001) Bambi is co-expressed with Bmp-4 during mouse embryogenesis. Mech Dev 100: 327–330.
[35]
Chang C, Holtzman DA, Chau S, Chickering T, Woolf EA, et al. (2001) Twisted gastrulation can function as a BMP antagonist. Nature 410: 483–487.
[36]
Oelgeschlager M, Larrain J, Geissert D, De Robertis EM (2000) The evolutionarily conserved BMP-binding protein Twisted gastrulation promotes BMP signalling. Nature 405: 757–763.
[37]
Ross JJ, Shimmi O, Vilmos P, Petryk A, Kim H, et al. (2001) Twisted gastrulation is a conserved extracellular BMP antagonist. Nature 410: 479–483.
[38]
Conley CA, Silburn R, Singer MA, Ralston A, Rohwer-Nutter D, et al. (2000) Crossveinless 2 contains cysteine-rich domains and is required for high levels of BMP-like activity during the formation of the cross veins in Drosophila. Development 127: 3947–3959.
[39]
Coffinier C, Ketpura N, Tran U, Geissert D, De Robertis EM (2002) Mouse Crossveinless-2 is the vertebrate homolog of a Drosophila extracellular regulator of BMP signaling. Mech Dev 119 Suppl 1: S179–S184.
[40]
Binnerts ME, Wen X, Cante-Barrett K, Bright J, Chen HT, et al. (2004) Human Crossveinless-2 is a novel inhibitor of bone morphogenetic proteins. Biochem Biophys Res Commun 315: 272–280.
[41]
Rentzsch F, Zhang J, Kramer C, Sebald W, Hammerschmidt M (2006) Crossveinless 2 is an essential positive feedback regulator of BMP signaling during zebrafish gastrulation. Development 133: 801–811.
[42]
Kuroda H, Wessely O, De Robertis EM (2004) Neural induction in Xenopus: requirement for ectodermal and endomesodermal signals via Chordin, Noggin, beta-Catenin, and Cerberus. PLoS Biol 2: e92.. DOI: 10.1371/journal.pbio.0020092.
[43]
Lele Z, Nowak M, Hammerschmidt M (2001) Zebrafish ADMP is required to restrict the size of the organizer and to promote posterior and ventral development. Dev Dyn 222: 681–687.
[44]
Reversade B, De Robertis EM (2005) Regulation of ADMP and BMP2/4/7 at opposite embryonic poles generates a self-regulating morphogenetic field. Cell 123: 1147–1160.
[45]
Lowe CJ, Wu M, Salic A, Evans L, Lander E, et al. (2003) Anteroposterior patterning in hemichordates and the origins of the chordate nervous system. Cell 113: 853–865.
[46]
Merlo GR, Zerega B, Paleari L, Trombino S, Mantero S, et al. (2000) Multiple functions of Dlx genes. Int J Dev Biol 44: 619–626.
[47]
Wada H (2001) Origin and evolution of the neural crest: A hypothetical reconstruction of its evolutionary history. Dev Growth Differ 43: 509–520.
[48]
Carreira S, Dexter TJ, Yavuzer U, Easty DJ, Goding CR (1998) Brachyury-related transcription factor Tbx2 and repression of the melanocyte-specific TRP-1 promoter. Mol Cell Biol 18: 5099–5108.
[49]
Hayata T, Kuroda H, Eisaki A, Asashima M (1999) Expression of Xenopus T-box transcription factor, tbx2 in Xenopus embryo. Dev Genes Evol 209: 625–628.
[50]
Takabatake Y, Takabatake T, Takeshima K (2000) Conserved and divergent expression of T-box genes Tbx2-Tbx5 in Xenopus. Mech Dev 91: 433–437.
[51]
Yamada M, Revelli JP, Eichele G, Barron M, Schwartz RJ (2000) Expression of chick Tbx-2, Tbx-3, and Tbx-5 genes during early heart development: Evidence for BMP2 induction of Tbx2. Dev Biol 228: 95–105.
[52]
Gross JM, Peterson RE, Wu SY, McClay DR (2003) LvTbx2/3: A T-box family transcription factor involved in formation of the oral/aboral axis of the sea urchin embryo. Development 130: 1989–1999.
[53]
Grimm S, Pflugfelder GO (1996) Control of the gene optomotor-blind in Drosophila wing development by decapentaplegic and wingless. Science 271: 1601–1604.
[54]
Filippi A, Tiso N, Deflorian G, Zecchin E, Bortolussi M, et al. (2005) The basic helix-loop-helix olig3 establishes the neural plate boundary of the trunk and is necessary for development of the dorsal spinal cord. Proc Natl Acad Sci U S A 102: 4377–4382.
[55]
Lu QR, Yuk D, Alberta JA, Zhu Z, Pawlitzky I, et al. (2000) Sonic hedgehog–regulated oligodendrocyte lineage genes encoding bHLH proteins in the mammalian central nervous system. Neuron 25: 317–329.
[56]
Sun H, Rodin A, Zhou Y, Dickinson DP, Harper DE, et al. (1997) Evolution of paired domains: Isolation and sequencing of jellyfish and hydra Pax genes related to Pax-5 and Pax-6. Proc Natl Acad Sci U S A 94: 5156–5161.
[57]
Dambly-Chaudiere C, Jamet E, Burri M, Bopp D, Basler K, et al. (1992) The paired box gene pox neuro: A determinant of poly-innervated sense organs in Drosophila. Cell 69: 159–172.
[58]
Christiaen L, Burighel P, Smith WC, Vernier P, Bourrat F, et al. (2002) Pitx genes in Tunicates provide new molecular insight into the evolutionary origin of pituitary. Gene 287: 107–113.
[59]
Duboc V, Rottinger E, Lapraz F, Besnardeau L, Lepage T (2005) Left-right asymmetry in the sea urchin embryo is regulated by nodal signaling on the right side. Dev Cell 9: 147–158.
[60]
Shapiro MD, Marks ME, Peichel CL, Blackman BK, Nereng KS, et al. (2004) Genetic and developmental basis of evolutionary pelvic reduction in threespine sticklebacks. Nature 428: 717–723.
[61]
Goodrich ES (1917) "Proboscis pores” in craniate vertebrates, a suggestion concerning the premandibular somites and hypophysis. Quart J Microscop Sci 62: 539–553.
[62]
Holland ND, Venkatesh TV, Holland LZ, Jacobs DK, Bodmer R (2003) AmphiNk2-tin, an amphioxus homeobox gene expressed in myocardial progenitors: Insights into evolution of the vertebrate heart. Dev Biol 255: 128–137.
[63]
Ranganayakulu G, Elliott DA, Harvey RP, Olson EN (1998) Divergent roles for NK-2 class homeobox genes in cardiogenesis in flies and mice. Development 125: 3037–3048.
[64]
Balser E, Ruppert E (1990) Structure, ultrastructure, and function of the preoral heart-kidney in Saccoglossus kowalevskii (Hemichchordata, Enteropneusta) including new data on the stomochord. Acta Zoologica 71: 235–249.
[65]
Brickman JM, Jones CM, Clements M, Smith JC, Beddington RS (2000) Hex is a transcriptional repressor that contributes to anterior identity and suppresses Spemann organiser function. Development 127: 2303–2315.
[66]
Martinez Barbera JP, Clements M, Thomas P, Rodriguez T, Meloy D, et al. (2000) The homeobox gene Hex is required in definitive endodermal tissues for normal forebrain, liver, and thyroid formation. Development 127: 2433–2445.
[67]
Harris R, Sabatelli LM, Seeger MA (1996) Guidance cues at the Drosophila CNS midline: Identification and characterization of two Drosophila Netrin/UNC-6 homologs. Neuron 17: 217–228.
[68]
Kennedy TE, Serafini T, de la Torre JR, Tessier-Lavigne M (1994) Netrins are diffusible chemotropic factors for commissural axons in the embryonic spinal cord. Cell 78: 425–435.
[69]
Keleman K, Dickson BJ (2001) Short- and long-range repulsion by the Drosophila Unc5 netrin receptor. Neuron 32: 605–617.
[70]
Serafini T, Colamarino SA, Leonardo ED, Wang H, Beddington R, et al. (1996) Netrin-1 is required for commissural axon guidance in the developing vertebrate nervous system. Cell 87: 1001–1014.
[71]
Shimeld S (2000) An amphioxus netrin gene is expressed in midline structures during embryonic and larval development. Dev Genes Evol 210: 337–344.
[72]
Arber S, Han B, Mendelsohn M, Smith M, Jessell TM, et al. (1999) Requirement for the homeobox gene Hb9 in the consolidation of motor neuron identity. Neuron 23: 659–674.
[73]
Ferrier DE, Brooke NM, Panopoulou G, Holland PW (2001) The Mnx homeobox gene class defined by HB9, MNR2 and amphioxus AmphiMnx. Dev Genes Evol 211: 103–107.
[74]
William CM, Tanabe Y, Jessell TM (2003) Regulation of motor neuron subtype identity by repressor activity of Mnx class homeodomain proteins. Development 130: 1523–1536.
[75]
Cameron CB, Mackie GO (1996) Conduction pathways in the nervous system of . (Enteropneusta). Canadian J Zool 74: 15–19.
[76]
Nambu JR, Lewis JO, Wharton KA Jr., Crews ST (1991) The Drosophila single-minded gene encodes a helix-loop-helix protein that acts as a master regulator of CNS midline development. Cell 67: 1157–1167.
[77]
Mazet F, Shimeld SM (2002) The evolution of chordate neural segmentation. Dev Biol 251: 258–270.
[78]
Coumailleau P, Penrad-Mobayed M, Lecomte C, Bollerot K, Simon F, et al. (2000) Characterization and developmental expression of Sim, a Xenopus bHLH/PAS gene related to the Drosophila neurogenic master gene single-minded. Mech Dev 99: 163–166.
[79]
Moffett P, Dayo M, Reece M, McCormick MK, Pelletier J (1996) Characterization of msim, a murine homologue of the Drosophila sim transcription factor. Genomics 35: 144–155.
[80]
Hinman VF, Degnan BM (2002) Mox homeobox expression in muscle lineage of the gastropod : Evidence for a conserved role in bilaterian myogenesis. Dev Genes Evol 212: 141–144.
[81]
Minguillon C, Garcia-Fernandez J (2002) The single amphioxus Mox gene: Insights into the functional evolution of Mox genes, somites, and the asymmetry of amphioxus somitogenesis. Dev Biol 246: 455–465.
[82]
Roelink H, Augsburger A, Heemskerk J, Korzh V, Norlin S, et al. (1994) Floor plate and motor neuron induction by shh-1, a vertebrate homolog of hedgehog expressed by the notochord. Cell 76: 761–775.
[83]
Briscoe J, Ericson J (2001) Specification of neuronal fates in the ventral neural tube. Curr Opin Neurobiol 11: 43–49.
[84]
Liu Y, Helms AW, Johnson JE (2004) Distinct activities of Msx1 and Msx3 in dorsal neural tube development. Development 131: 1017–1028.
[85]
Cornell RA, Ohlen TV (2000) Vnd/nkx, ind/gsh, and msh/msx: Conserved regulators of dorsoventral neural patterning? Curr Opin Neurobiol 10: 63–71.
[86]
Shimeld SM (1999) The evolution of the hedgehog gene family in chordates: insights from amphioxus hedgehog. Dev Genes Evol 209: 40–47.
[87]
Hara Y, Katow H (2005) Exclusive expression of hedgehog in small micromere descendants during early embryogenesis in the sea urchin, . Gene Expr Patterns 5: 503–510.
[88]
Holland LZ, Venkatesh TV, Gorlin A, Bodmer R, Holland ND (1998) Characterization and developmental expression of AmphiNk2–2, an NK2 class homeobox gene from Amphioxus. (Phylum Chordata; Subphylum Cephalochordata). Dev Genes Evol 208: 100–105.
[89]
Darras S, Nishida H (2001) The BMP/CHORDIN antagonism controls sensory pigment cell specification and differentiation in the ascidian embryo. Dev Biol 236: 271–288.
[90]
Biehs B, Francois V, Bier E (1996) The Drosophila short gastrulation gene prevents Dpp from autoactivating and suppressing neurogenesis in the neuroectoderm. Genes Dev 10: 2922–2934.
Bullock TH (1945) The anatomical organization of the nervous system of enteropneusta. Quart J Microscrop Sci 86: 55–112.
[93]
Bateson W (1886) The ancestry of the chordata. Quart J Microscrop Sci 26: 535–571.
[94]
Hyman LH (1955) The invertebrates. New York: McGraw-Hill. 572 p.
[95]
Ashe HL, Levine M (1999) Local inhibition and long-range enhancement of DPP signal transduction by Sog. Nature 398: 427–431.
[96]
Echelard Y, Epstein DJ, St-Jacques B, Shen L, Mohler J, et al. (1993) Sonic hedgehog, a member of a family of putative signaling molecules, is implicated in the regulation of CNS polarity. Cell 75: 1417–1430.
[97]
Hemmati-Brivanlou A, Melton D (1997) Vertebrate embryonic cells will become nerve cells unless told otherwise. Cell 88: 13–17.
[98]
Colwin AL, Colwin LH (1950) The developmental capacities of separated early blastomeres of an enteropneust, . J Experimental Zool 115: 263–296.
[99]
Colwin AL, Colwin LH (1962) Induction of spawning in (Enteropneusta) at Woods Hole. Biological Bulletin 123: 493.
[100]
Bateson W (1884) Early stages in the development of Balanoglossus (sp. incert.). Quart J Microscrop Sci 24: 208–236.
[101]
Bateson W (1885) Later stages in the development of with a suggestion as to the affinities of the Enteropneusta. Quart J Microscrop Sci 25: 81–128.
[102]
Bateson W (1886) Continued account of the later stages in the development of , with a suggestion as to the affinities of the enteropneusta. Quart J Microscrop Sci 26: 511–534.
[103]
Colwin AL, Colwin LH (1953) The normal embryology of . J Morphol 92: 401–453.
[104]
Jaffe LA, Terasaki M (2004) Quantitative microinjection of oocytes, eggs, and embryos. Methods Cell Biol 74: 219–242.
[105]
Benito J, Pardos F (1997) Hemichordata. In: Harrison FW, Ruppert EE, editors. Microscopic anatomy of invertebrates. New York: Wiley-Liss. pp. 15–101. pp.
