Nodal signals mediate interactions between the extra-embryonic and embryonic tissues in zebrafish.
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.
Fan
Xiang
X
Department of Cellular Biology, The University of Georgia, Athens, GA 30602, USA.
Hagos
Engda G
EG
Xu
Bo
B
Sias
Christina
C
Kawakami
Koichi
K
Burdine
Rebecca D
RD
Dougan
Scott T
ST
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*
D047908:Intracellular Signaling Peptides and Proteins; D055456:Nodal Signaling Ligands; D029961:Zebrafish Proteins; C485171:ndr1 protein, zebrafish; C512832:ndr2 protein, zebrafish