title: Direct regulation of siamois by VegT is required for axis formation in Xenopus embryo.
abstract: The homeobox gene siamois is one of the earliest genes expressed in the Spemann organizer and plays a critical role in the formation of the dorsoventral axis. It is directly regulated by maternal Wnt signalling and functions as an essential zygotic intermediary between maternal factors and the formation of the Spemann organizer. The maternal T domain transcription factor VegT interacts with Wnt signalling and is also involved in the formation of the Spemann organizer. However, the molecular mechanism of this functional interaction is not fully understood. Here we show that VegT is required for siamois expression through direct binding to the T-box binding sites in the siamois promoter. Mutational analysis of each of the five consensus T-box binding sites suggests that the proximal site close to the transcription start site is essential for activation of siamois promoter by VegT, while individual mutation of the four distal sites has no effect. VegT and Wnt signalling also functionally interact and are mutually required for siamois expression. In particular, VegT synergizes with Tcf1, but not Tcf3 and Tcf4, to induce siamois expression, and this is independent of Tcf/Lef-binding sites or the proximal T-box binding site in the siamois promoter. We further extend previous observations by showing that VegT cooperates with maternal Wnt signalling in the formation of the dorsoventral axis. These results demonstrate that maternal VegT directly regulates siamois gene transcription in the formation of the Spemann organizer, and provide further insight into the mechanism underlying the functional interaction between VegT and Wnt signalling during development.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, Institut de Biologie Paris-Seine (IBPS), UMR 7622, Laboratory of Developmental Biology, Paris, France.
authors.forename: Hong-Yan
authors.initials: HY
authors.lastname: Li
authors.forename: Warif
authors.initials: W
authors.lastname: El Yakoubi
authors.forename: De-Li
authors.initials: DL
authors.lastname: Shi
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D019521:Body Patterning; D047369:Chromatin Immunoprecipitation; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D007124:Immunoenzyme Techniques; D008969:Molecular Sequence Data; D020897:Organizers, Embryonic; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism*; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D029867:Xenopus Proteins / Q000235:genetics* / Q000378:metabolism*; D014982:Xenopus laevis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D018398:Homeodomain Proteins; D012333:RNA, Messenger; C093133:SIA1 protein, Xenopus; D020825:T-Box Domain Proteins; C103966:VegT protein, Xenopus; D051153:Wnt Proteins; D029867:Xenopus Proteins