embryo-microinjection-electroporation-chordate-ciona

Embryo Microinjection and Electroporation in the Chordate <em>Ciona intestinalis</em>

Simple model organisms are instrumental for in vivo studies of developmental and cellular differentiation processes. Currently, the evolutionary distance ...

University Innsbruck

Transcription factors of the TCF family are key mediators of the Wnt/β-catenin pathway. TCF usually activates transcription on cis-regulatory elements containing TCF binding sites when the pathway is active and represses transcription when the pathway is inactive. However, some direct targets display an opposite regulation (activated by TCF in the absence of Wnt), but the mechanism behind this atypical regulation remains poorly characterized. Here, we use the cis-regulatory region of an opposite target gene, ttx-3, to dissect the mechanism of this atypical regulation. Using a combination of genetic, molecular, and biochemical experiments, we establish that, in the absence of Wnt pathway activation, TCF activates ttx-3 expression via a Zic binding site by forming a complex with a Zic transcription factor. This mechanism is later reinforced by specific bHLH factors. This study reveals an atypical mode of action for TCF that may apply to other binary decisions mediated by Wnt signaling.

Atypical Transcriptional Activation by TCF via a Zic Transcription Factor in C. elegans Neuronal Precursors.

Maternal factors initiate the zygotic developmental program in animal embryos. In embryos of the chordate, Ciona intestinalis, three maternal factors-Gata.a, β-catenin, and Zic-r.a-are required to establish three domains of gene expression at the 16-cell stage; the animal hemisphere, vegetal hemisphere, and posterior vegetal domains. Here, we show how the maternal factors establish these domains. First, only β-catenin and its effector transcription factor, Tcf7, are required to establish the vegetal hemisphere domain. Second, genes specifically expressed in the posterior vegetal domain have additional repressive cis-elements that antagonize the activity of β-catenin/Tcf7. This antagonizing activity is suppressed by Zic-r.a, which is specifically localized in the posterior vegetal domain and binds to DNA indirectly through the interaction with Tcf7. Third, Gata.a directs specific gene expression in the animal hemisphere domain, because β-catenin/Tcf7 weakens the Gata.a-binding activity for target sites through a physical interaction in the vegetal cells. Thus, repressive regulation through protein-protein interactions among the maternal transcription factors is essential to establish the first distinct domains of gene expression in the chordate embryo.

Article	Year
Atypical Transcriptional Activation by TCF via a Zic Transcription Factor in C. elegans Neuronal Precursors. Developmental cell\| PubMed ID: 26073017	2015
A Maternal System Initiating the Zygotic Developmental Program through Combinatorial Repression in the Ascidian Embryo. PLoS genetics\| PubMed ID: 27152625	2016

Willi Kari

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