title: Hox cluster disintegration with persistent anteroposterior order of expression in Oikopleura dioica.
abstract: Tunicate embryos and larvae have small cell numbers and simple anatomical features in comparison with other chordates, including vertebrates. Although they branch near the base of chordate phylogenetic trees, their degree of divergence from the common chordate ancestor remains difficult to evaluate. Here we show that the tunicate Oikopleura dioica has a complement of nine Hox genes in which all central genes are lacking but a full vertebrate-like set of posterior genes is present. In contrast to all bilaterians studied so far, Hox genes are not clustered in the Oikopleura genome. Their expression occurs mostly in the tail, with some tissue preference, and a strong partition of expression domains in the nerve cord, in the notochord and in the muscle. In each tissue of the tail, the anteroposterior order of Hox gene expression evokes spatial collinearity, with several alterations. We propose a relationship between the Hox cluster breakdown, the separation of Hox expression domains, and a transition to a determinative mode of development.
authors.affiliation: Sars Centre for Marine Molecular Biology, Bergen High Technology Centre, Thormøhlensgaten 55, 5008 Bergen, Norway.
authors.forename: Hee-Chan
authors.initials: HC
authors.lastname: Seo
authors.forename: Rolf Brudvik
authors.initials: RB
authors.lastname: Edvardsen
authors.forename: Anne Dorthea
authors.initials: AD
authors.lastname: Maeland
authors.forename: Marianne
authors.initials: M
authors.lastname: Bjordal
authors.forename: Marit Flo
authors.initials: MF
authors.lastname: Jensen
authors.forename: Anette
authors.initials: A
authors.lastname: Hansen
authors.forename: Mette
authors.initials: M
authors.lastname: Flaat
authors.forename: Jean
authors.initials: J
authors.lastname: Weissenbach
authors.forename: Hans
authors.initials: H
authors.lastname: Lehrach
authors.forename: Patrick
authors.initials: P
authors.lastname: Wincker
authors.forename: Richard
authors.initials: R
authors.lastname: Reinhardt
authors.forename: Daniel
authors.initials: D
authors.lastname: Chourrout
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000235:genetics*; D019143:Evolution, Molecular; D005306:Fertilization; D018507:Gene Expression Regulation, Developmental; D023061:Gene Order / Q000235:genetics; D005801:Genes, Homeobox / Q000235:genetics*; D023281:Genomics; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014561:Urochordata / Q000033:anatomy & histology / Q000196:embryology* / Q000235:genetics*
chemical_list: D012333:RNA, Messenger