Nodal-related signals establish mesendodermal fate and trunk neural identity in zebrafish.
The vertebrate body plan arises during gastrulation, when morphogenetic movements form the ectoderm, mesoderm, and endoderm. In zebrafish, mesoderm and endoderm derive from the marginal region of the late blastula, and cells located nearer the animal pole form the ectoderm [1]. Analysis in mouse, Xenopus, and zebrafish has demonstrated that Nodal-related proteins, a subclass of the TGF-beta superfamily, are essential for mesendoderm development [2], but previous mutational studies have not established whether Nodal-related signals control fate specification, morphogenetic movements, or survival of mesendodermal precursors. Here, we report that Nodal-related signals are required to allocate marginal cells to mesendodermal fates in the zebrafish embryo. In double mutants for the zebrafish nodal-related genes squint (sqt) and cyclops (cyc) [3] [4] [5], dorsal marginal cells adopt neural fates, whereas in wild-type embryos, cells at this position form endoderm and axial mesoderm. Involution movements characteristic of developing mesendoderm are also blocked in the absence of Nodal signaling. Because it has been proposed [6] that inhibition of Nodal-related signals promotes the development of anterior neural fates, we also examined anteroposterior organization of the neural tube in sqt;cyc mutants. Anterior trunk spinal cord is absent in sqt;cyc mutants, despite the presence of more anterior and posterior neural fates. These results demonstrate that nodal-related genes are required for the allocation of dorsal marginal cells to mesendodermal fates and for anteroposterior patterning of the neural tube.
Feldman
B
B
Developmental Genetics Program, Division of Developmental Biology, Skirball Institute of Biomolecular Medicine, New York University School of Medicine, The National Institute for Medical Research, New York, London, New York 10016, NW7 1AA, USA, UK.
Dougan
S T
ST
Schier
A F
AF
Talbot
W S
WS
D000818:Animals; D002490:Central Nervous System / Q000196:embryology; D047908:Intracellular Signaling Peptides and Proteins; D016296:Mutagenesis; D055457:Nodal Protein; D055456:Nodal Signaling Ligands; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins
D047908:Intracellular Signaling Peptides and Proteins; D055457:Nodal Protein; D055456:Nodal Signaling Ligands; C526008:Nodal protein, mouse; D016212:Transforming Growth Factor beta; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; C485171:ndr1 protein, zebrafish; C512832:ndr2 protein, zebrafish; C512833:nodal1 protein, Xenopus