A modular cis-regulatory system controls isoform-specific pitx expression in ascidian stomodaeum.
Pituitary homeobox (pitx) genes have been identified in vertebrates as critical molecular determinants of various craniofacial ontogenetic processes including pituitary organogenesis. Accordingly, a prominent conserved feature of pitx genes in chordates is their early expression in the anterior neural boundary (ANB) and oral ectoderm, also known as the stomodaeum. Here we used the ascidian model species Ciona intestinalis to investigate pitx gene organization and cis-regulatory logic during early stages of oral development. Two distinct Ci-pitx mRNA variants were found to be expressed in mutually exclusive embryonic domains. Ci-pitx and vertebrate pitx2 genes display remarkably similar exon usage and organization, suggesting ancestry of the pitx transcriptional unit and regulation in chordates. We next combined phylogenetic footprinting, transient transgenesis, and confocal imaging methods to study the Ci-pitx cis-regulatory system, with special emphasis on the regulation of isoform-specific ANB/stomodaeal expression. Among 10 conserved noncoding sequences (CNSs) interspersed in C. intestinalis and Ciona savignyi pitx loci, we identified two separate cis-regulatory modules (CRMs) that drive ANB/stomodaeal expression in complementary spatiotemporal patterns. We discuss the developmental relevance of these data that provide an entry point to investigate the gene regulatory networks (GRNs) that position and shape oral structures in chordates.
Christiaen
Lionel
L
INRA junior group, UPR2197 DEPSN, INAF, CNRS, 1 Avenue De La Terrasse, F-91198 Gif-sur-Yvette, France.
Bourrat
Franck
F
Joly
Jean-Stéphane
JS
D000818:Animals; D001483:Base Sequence; D002938:Ciona intestinalis / Q000196:embryology* / Q000378:metabolism; D003001:Cloning, Molecular; D019295:Computational Biology; D004247:DNA / Q000235:genetics; D030541:Databases, Genetic; D004475:Ectoderm / Q000378:metabolism*; D005453:Fluorescence; D040461:Gene Components; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D009055:Mouth / Q000196:embryology* / Q000378:metabolism; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000097577:Homeobox Protein PITX2
D004247:DNA; D018398:Homeodomain Proteins; D020033:Protein Isoforms; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2