Innsbruck, 18/06/2020 Ciona intestinalis developmental program: - PowerPoint PPT Presentation

Innsbruck, 18/06/2020

Ciona intestinalis developmental program: Maternal factors establish three domains of gene expression • Gata.a  AD • β -catenin  VD • Zic-r.a  PVD Modified from Satoh et al, 2003 Posterior vegetal domain 16-cell stage

Ciona intestinalis : simple and conserved lineage and body plan Fujii et al. 2008 Marletàz et al, 2003 • AD  epidermal and neural cells • Invariant cells division • VD  mesendodermal tissues and the • Sequenced and compact genome nerve cord • Primitive chordate body plan • PVD  Muscles and mesenchymal

Maternal factors crosstalk to initiate the zygotic genetic program AD VD AD VD

Open Questions • How β -catenin and Zic-r.a cooperate to activate Tbx6.b specifically in Tbx6.b CO the PVD? • Why Tbx6.b is not activated in the anterior vegetal cells by β -catenin? CO β -catenin MO • how β -catenin represses Gata.a activity in the VD?

Fgf Enhancer activity: Tcf sites are essential for specific expression in VD In situ hybridization CO β -catenin MO

Tbx6.b Enhancer activity: Tcf sites are required for expression in PVD In situ hybridization CO β -catenin MO Zic-r.a MO

Fgf vs Tbx6.b Enhancer expression: additional repressive elements? Tbx6.b Fgf ? VD PVD

Efna.d Enhancer activity: GATA sites are necessary for expression in AD In situ hybridization CO Gata.a MO β -catenin MO CO

β -catenin, Tcf and Gata.a interact to create different gene expression patterns in AD and VD Efna.d regulatory • region doesn’t bind Tcf/ β -catenin complex How β -catenin suppress • the activity in VD? Hypothesis: β -catenin might prevent Gata.a from binding to its target sites? Gata.a Tcf7 Gata.a specific binding was not disrupted by co-incubation ß-catenin • with either Tcf7 or β -catenin Co- incubation with both Tcf7 and β -catenin reduced Gata.a X • binding GATA In the VD of normal embryos, β -catenin and Tcf7 interact with Gata.a and suppress the binding activity of Gata.a.

Discussion β -catenin and Tcf7 activate gene expression in the VD. This complex may • interferes with Gata.a binding to GATA sites reducing target genes expression in the VD Genes specifically expressed in the PVD posses elements that prevent • activation of these genes by β -catenin and Tcf7. Zic-r.a can function in regulatory regions to overcome the repressive • activity indirectly through Tcf. Insertion of repressor elements in reporter constructs usually expressed • independently of Zic-r.a, evoked Zic-r.a-dependent expression in the PVD.

Conclusion Three maternal factors coordinate to establish three distinct expression domains. Negative regulatory mechanisms of the animal fate in the vegetal hemisphere and those of the posterior vegetal fate in the anterior vegetal hemisphere are important. Present analysis Gata.a Tcf7 Tcf repress GATA sites independently of β -catenin? X • GATA GATA site signature influence repression? • incomplete Tcf site masks GATA sites? • aGATAAAGTATCt

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