Project description:The notochord is a defining feature of the chordates. The transcription factor Brachyury (Bra) is a key regulator of notochord fate but here we show that it is not a unitary master regulator in the model chordate Ciona. Ectopic Bra expression only partially reprograms other cell types to a notochord-like transcriptional profile and a subset of notochord-enriched genes are unaffected by CRISPR Bra disruption. We identify Foxa.a and Mnx as potential co-regulators and find that combinatorial cocktails are more effective at reprograming other cell types than Bra alone. We reassess the network relationships between Foxa.a, and other components of the notochord gene regulatory network and find that Foxa.a expression in the notochord is regulated by vegetal FGF signaling. It is a direct activator of Bra expression and has a binding motif that is significantly enriched in the regulatory regions of notochord-enriched genes. These and other results indicate that Bra and Foxa.a act together in a regulatory network dominated by positive feed-forward interactions, with neither being a classically-defined master regulator.er
Project description:The notochord is a defining feature of the chordates. The transcription factor Brachyury (Bra) is a key regulator of notochord fate but here we show that it is not a unitary master regulator in the model chordate Ciona. Ectopic Bra expression only partially reprograms other cell types to a notochord-like transcriptional profile and a subset of notochord-enriched genes are unaffected by CRISPR Bra disruption. We identify Foxa.a and Mnx as potential co-regulators and find that combinatorial cocktails are more effective at reprograming other cell types than Bra alone. We reassess the network relationships between Foxa.a, and other components of the notochord gene regulatory network and find that Foxa.a expression in the notochord is regulated by vegetal FGF signaling. It is a direct activator of Bra expression and has a binding motif that is significantly enriched in the regulatory regions of notochord-enriched genes. These and other results indicate that Bra and Foxa.a act together in a regulatory network dominated by positive feed-forward interactions, with neither being a classically-defined master regulator.er
Project description:The notochord is a defining feature of the chordates. The transcription factor Brachyury (Bra) is a key regulator of notochord fate but here we show that it is not a unitary master regulator in the model chordate Ciona. Ectopic Bra expression only partially reprograms other cell types to a notochord-like transcriptional profile and a subset of notochord-enriched genes are unaffected by CRISPR Bra disruption. We identify Foxa.a and Mnx as potential co-regulators and find that combinatorial cocktails are more effective at reprograming other cell types than Bra alone. We reassess the network relationships between Foxa.a, and other components of the notochord gene regulatory network and find that Foxa.a expression in the notochord is regulated by vegetal FGF signaling. It is a direct activator of Bra expression and has a binding motif that is significantly enriched in the regulatory regions of notochord-enriched genes. These and other results indicate that Bra and Foxa.a act together in a regulatory network dominated by positive feed-forward interactions, with neither being a classically-defined master regulator.
Project description:The notochord is a defining feature of the chordates. The transcription factor Brachyury (Bra) is a key regulator of notochord fate but here we show that it is not a unitary master regulator in the model chordate Ciona. Ectopic Bra expression only partially reprograms other cell types to a notochord-like transcriptional profile and a subset of notochord-enriched genes are unaffected by CRISPR Bra disruption. We identify Foxa.a and Mnx as potential co-regulators and find that combinatorial cocktails are more effective at reprograming other cell types than Bra alone. We reassess the network relationships between Foxa.a, and other components of the notochord gene regulatory network and find that Foxa.a expression in the notochord is regulated by vegetal FGF signaling. It is a direct activator of Bra expression and has a binding motif that is significantly enriched in the regulatory regions of notochord-enriched genes. These and other results indicate that Bra and Foxa.a act together in a regulatory network dominated by positive feed-forward interactions, with neither being a classically-defined master regulator.er
Project description:The key notochord transcription factor Brachyury was ectopically expressed in Ciona embryos under the control of the FoxAa cis-regulatory region (which drives expression in neural, endodermal and mesenchymal lineages in addition to notochord). Misexpression of Brachyury induced 925 genes compared to a control reporter plasmid (Bra>GFP). There was only modest overlap with a set of notochord-enriched genes previously identified by RNAseq of flow-sorted notochord cells, indicating that Brachyury is not a notochord master regulator gene as strictly defined.
Project description:The notochord is the eponymous feature of the chordates and an essential organ in chordate development. The notochord of the invertebrate chordate Ciona consists of only 40 cells, and is a longstanding model for studying differentiation and morphogenesis in a small, simple embryo. Here we perform RNAseq analysis on flow-sorted notochord cells from multiple stages of development to define a comprehensive Ciona notochord transcriptome. We identify 1364 genes with enriched expression in the notochord and extensively validate the results by in situ hybridization. This notochord gene set is highly enriched for Gene Ontology codes related to the extracellular matrix, cell adhesion and cytoskeleton, and contains numerous genes with intriguing potential functions in morphogenesis. Orthologs of 112 of the Ciona notochord genes have known notochord expression in vertebrates, more than twice as many as would be predicted by chance alone. This set of putative effector genes with notochord expression conserved from tunicates to vertebrates will be invaluable for testing hypotheses about the evolution of the notochord.