Abstract
During gastrulation, diffusible "organizer" signals, including members of the TGFbeta Nodal subfamily, pattern dorsal mesoderm and the embryonic axes. Simultaneously, negative regulators of these signals, including the Nodal inhibitor Lefty, an atypical TGFbeta factor, are induced by Nodal. This suggests that Lefty-dependent modulation of organizer signaling might regulate dorsal mesoderm patterning and axial morphogenesis. Here, Xenopus Lefty (Xlefty) function was blocked by injection of anti-Xlefty morpholino oligonucleotides (MO). Xlefty-deficient embryos underwent exogastrulation, an aberrant morphogenetic process not predicted from deregulation of the Nodal pathway alone. In the absence of Xlefty, both Nodal- (Xnr2, gsc, cer, Xbra) and Wnt-responsive (gsc, Xnr3) organizer gene expression expanded away from the dorsal blastopore lip. Conversely, coexpression of Xlefty with Nodal or Wnt reduced the ectopic expression of Nodal- (Xbra) and Wnt-responsive (Xnr3) genes in a dose-dependent manner. Furthermore, Xlefty expression in the ectodermal animal pole inhibited endogenous Nodal- and Wnt-responsive gene expression in distant mesoderm cells, indicating that Xlefty inhibition can spread from its source. We hypothesize that Xlefty negatively regulates the spatial extent of Nodal- and Wnt-responsive gene expression in the organizer and that this Xlefty-dependent inhibition is essential for normal organizer patterning and gastrulation.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Activins / genetics
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Activins / metabolism
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Animals
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Embryo, Nonmammalian / drug effects
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Gastrula / metabolism
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Gastrula / physiology
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Gene Expression Regulation, Developmental / physiology*
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Goosecoid Protein
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Homeodomain Proteins / genetics
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Homeodomain Proteins / metabolism
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Intercellular Signaling Peptides and Proteins
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Left-Right Determination Factors
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Mesoderm / metabolism
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Nodal Protein
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Nodal Signaling Ligands
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Oligonucleotides, Antisense / pharmacology
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Organizers, Embryonic / physiology*
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Proteins / genetics
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Proteins / metabolism
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Proto-Oncogene Proteins / genetics
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Proto-Oncogene Proteins / metabolism*
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Repressor Proteins*
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Signal Transduction
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T-Box Domain Proteins / genetics
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T-Box Domain Proteins / metabolism
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Transcription Factors*
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Transforming Growth Factor beta / genetics
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Transforming Growth Factor beta / metabolism*
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Wnt Proteins
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Xenopus / embryology*
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Xenopus / genetics*
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Xenopus Proteins / genetics
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Xenopus Proteins / metabolism
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Zebrafish Proteins*
Substances
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Goosecoid Protein
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Homeodomain Proteins
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Intercellular Signaling Peptides and Proteins
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Left-Right Determination Factors
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Ndr2 protein, vertebrate
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Nodal Protein
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Nodal Signaling Ligands
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Oligonucleotides, Antisense
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Proteins
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Proto-Oncogene Proteins
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Repressor Proteins
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STK38L protein, Xenopus
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T-Box Domain Proteins
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TBXT protein, Xenopus
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Transcription Factors
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Transforming Growth Factor beta
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Wnt Proteins
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Xenopus Proteins
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Zebrafish Proteins
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cer1 protein, Xenopus
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nodal3.1 protein, Xenopus
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Activins