title: Nodal signals mediate interactions between the extra-embryonic and embryonic tissues in zebrafish.
abstract: In many vertebrates, extra-embryonic tissues are important signaling centers that induce and pattern the germ layers. In teleosts, the mechanism by which the extra-embryonic yolk syncytial layer (YSL) patterns the embryo is not understood. Although the Nodal-related protein Squint is expressed in the YSL, its role in this tissue is not known. We generated a series of stable transgenic lines with GFP under the control of squint genomic sequences. In all species, nodal-related genes induce their own expression through a positive feedback loop. We show that two tissue specific enhancers in the zebrafish squint gene mediate the response to Nodal signals. Expression in the blastomeres depends upon a conserved Nodal response element (NRE) in the squint first intron, while expression in the extra-embryonic enveloping layer (EVL) is mediated by an element upstream of the transcription start site. Targeted depletion experiments demonstrate that the zebrafish Nodal-related proteins Squint and Cyclops are required in the YSL for endoderm and head mesoderm formation. Thus, Nodal signals mediate interactions between embryonic and extra-embryonic tissues in zebrafish that maintain nodal-related gene expression in the margin. Our results demonstrate a high degree of functional conservation between the extra-embryonic tissues of mouse and zebrafish.
authors.affiliation: Department of Cellular Biology, The University of Georgia, Athens, GA 30602, USA.
authors.forename: Xiang
authors.initials: X
authors.lastname: Fan
authors.forename: Engda G
authors.initials: EG
authors.lastname: Hagos
authors.forename: Bo
authors.initials: B
authors.lastname: Xu
authors.forename: Christina
authors.initials: C
authors.lastname: Sias
authors.forename: Koichi
authors.initials: K
authors.lastname: Kawakami
authors.forename: Rebecca D
authors.initials: RD
authors.lastname: Burdine
authors.forename: Scott T
authors.initials: ST
authors.lastname: Dougan
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D019521:Body Patterning; D004707:Endoderm / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D008648:Mesoderm / Q000378:metabolism; D008969:Molecular Sequence Data; D055456:Nodal Signaling Ligands; D020218:Response Elements; D015398:Signal Transduction; D015027:Zebrafish / Q000196:embryology / Q000502:physiology*; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D055456:Nodal Signaling Ligands; D029961:Zebrafish Proteins; C485171:ndr1 protein, zebrafish; C512832:ndr2 protein, zebrafish