Origins of the chordate bodyplan and mode of development will be sought in the hemichordates, the little studied sister taxon (with echinoderms) of chordates. Hemichordates possess: 1) a short stomacord which forms from the gut roof and contains vacuolated cells like a chordate notochord or prechordal plate, 2) a dorsal nerve cord formed by neurulation like a chordate dorsal hollow neural tube, 3) a long array of chordate-like gill slits, and 4) a transient post-anal tail in the juvenile of some species, like a chordate tail. They may also have left-right asymmetries like those of chordates. Except for the gill slits, none of these traits has been convincingly identified as chordate-like by anatomical scrutiny, and hemichordates also share traits with annelids and arthropods, such as a ventral nerve cord besides their dorsal cord. We are obtaining cDNA sequences from Saccoglossus kowalevskii, an enteropneust hemichordate, for in situ hybridization to assess hemichordate- chordate similarities more incisively. We find a set of chordate-homologous genes expressed in the dorsal midline of the hemichordate embryo (bmp2/4, twg) where the dorsal nerve cord forms and in the ventral midline (netrin, admp) where the ventral nerve cord forms. The animal's entire body wall contains an intraepidermal nerve net from which axons collect at the two midlines. It is like a chordate neural tube with bmp in the roofplate and netrin in the floorplate. We will continue to compare nervous systems and other traits. The three-part organization of hemichordates corresponds to the chordate anteroposterior axis in terms of expression domains of various homeobox genes (rtx, six3, pitx, otx, Hox3,4,9). The prosome is like the anterior head/ventral forebrain, the mesosome like the dorsal forebrain, midbrain and first branchial arch, and the metasome like the rest of the chordate body. These similarities are presumably conserved from a three-part common ancestor. Hemi-chordate development will be studied for the presence of one or more inductive parts of Spemann's organizer, which in chordates is involved in the development of all four specific traits. The stomochord region expresses otx and dkk genes, we find, as does the chordate head organizer. Knowledge of hemichordates will help to explain why chordates have certain aspects of their body plan and development, and by difference, what additions and modifications have been made only within the chordate line.

Agency
National Institute of Health (NIH)
Institute
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Type
Research Project (R01)
Project #
1R01HD042724-01
Application #
6530263
Study Section
Cell Development and Function Integrated Review Group (CDF)
Program Officer
Javois, Lorette Claire
Project Start
2002-07-01
Project End
2005-06-30
Budget Start
2002-07-01
Budget End
2003-06-30
Support Year
1
Fiscal Year
2002
Total Cost
$231,660
Indirect Cost
Name
University of California Berkeley
Department
Biochemistry
Type
Schools of Arts and Sciences
DUNS #
094878337
City
Berkeley
State
CA
Country
United States
Zip Code
94704
Simakov, Oleg; Kawashima, Takeshi; Marl├ętaz, Ferdinand et al. (2015) Hemichordate genomes and deuterostome origins. Nature 527:459-65
Freeman, Robert; Ikuta, Tetsuro; Wu, Michael et al. (2012) Identical genomic organization of two hemichordate hox clusters. Curr Biol 22:2053-8
Darras, Sebastien; Gerhart, John; Terasaki, Mark et al. (2011) *-catenin specifies the endomesoderm and defines the posterior organizer of the hemichordate Saccoglossus kowalevskii. Development 138:959-70
Lemons, Derek; Fritzenwanker, Jens H; Gerhart, John et al. (2010) Co-option of an anteroposterior head axis patterning system for proximodistal patterning of appendages in early bilaterian evolution. Dev Biol 344:358-62
Freeman Jr, R M; Wu, M; Cordonnier-Pratt, M-M et al. (2008) cDNA sequences for transcription factors and signaling proteins of the hemichordate Saccoglossus kowalevskii: efficacy of the expressed sequence tag (EST) approach for evolutionary and developmental studies of a new organism. Biol Bull 214:284-302
Gerhart, John (2006) The deuterostome ancestor. J Cell Physiol 209:677-85
Lowe, Christopher J; Terasaki, Mark; Wu, Michael et al. (2006) Dorsoventral patterning in hemichordates: insights into early chordate evolution. PLoS Biol 4:e291
Gerhart, John; Lowe, Christopher; Kirschner, Marc (2005) Hemichordates and the origin of chordates. Curr Opin Genet Dev 15:461-7
Lowe, Christopher J; Wu, Mike; Salic, Adrian et al. (2003) Anteroposterior patterning in hemichordates and the origins of the chordate nervous system. Cell 113:853-65