title: Making very similar embryos with divergent genomes: conservation of regulatory mechanisms of Otx between the ascidians Halocynthia roretzi and Ciona intestinalis.
abstract: Ascidian embryos develop with a fixed cell lineage into simple tadpoles. Their lineage is almost perfectly conserved, even between the evolutionarily distant species Halocynthia roretzi and Ciona intestinalis, which show no detectable sequence conservation in the non-coding regions of studied orthologous genes. To address how a common developmental program can be maintained without detectable cis-regulatory sequence conservation, we compared in both species the regulation of Otx, a gene with a shared complex expression pattern. We found that in Halocynthia, the regulatory logic is based on the use of very simple cell line-specific regulatory modules, the activities of which are conserved, in most cases, in the Ciona embryo. The activity of each of these enhancer modules relies on the conservation of a few repeated crucial binding sites for transcriptional activators, without obvious constraints on their precise number, order or orientation, or on the surrounding sequences. We propose that a combination of simplicity and degeneracy allows the conservation of the regulatory logic, despite drastic sequence divergence. The regulation of Otx in the anterior endoderm by Lhx and Fox factors may even be conserved with vertebrates.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachiohji, Tokyo 192-0397, Japan.
authors.forename: Izumi
authors.initials: I
authors.lastname: Oda-Ishii
authors.forename: Vincent
authors.initials: V
authors.lastname: Bertrand
authors.forename: Isao
authors.initials: I
authors.lastname: Matsuo
authors.forename: Patrick
authors.initials: P
authors.lastname: Lemaire
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Saiga
mesh_terms: D000818:Animals; D001665:Binding Sites; D002938:Ciona intestinalis / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D002970:Cleavage Stage, Ovum / Q000378:metabolism; D051858:Forkhead Transcription Factors; D005786:Gene Expression Regulation / Q000502:physiology*; D018014:Gene Transfer Techniques; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D051857:Otx Transcription Factors; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D051858:Forkhead Transcription Factors; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D051857:Otx Transcription Factors; D014157:Transcription Factors