Abstract
Like all known LIM class homeobox genes, Xlim-1 encodes a protein with two tandemly repeated cysteine-rich LIM domains upstream of the homeodomain. In Xenopus laevis, Xlim-1 is specifically expressed in the Spemann organizer, whose major functions include neural induction and dorsalization of ventral mesoderm. From RNA injection experiments we conclude here that: (1) the LIM domains behave as negative regulatory domains; (2) LIM domain mutants of Xlim-1 elicited neural differentiation in animal explants; (3) mutant, and to a lesser extent wild-type, Xlim-1 enhanced muscle formation after coinjection with Xbra; (4) both of these activities are mediated by extracellular signals as seen in combined explant experiments; (5) Xlim-1 mutants activated goosecoid (gsc) expression in animal explants, but not expression of noggin or follistatin; (6) mutant Xlim-1 elicited formation of partial secondary axes, and cooperated with gsc in notochord formation. Thus Xlim-1 has latent activities, implicating it in organizer functions.
MeSH terms
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Animals
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Base Sequence
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Carrier Proteins
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Cell Differentiation / genetics
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Cell Differentiation / physiology
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Culture Techniques
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DNA Primers
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DNA-Binding Proteins / biosynthesis
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / physiology*
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Embryonic Induction*
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Fetal Proteins / genetics
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Fetal Proteins / physiology
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Follistatin
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Glycoproteins / biosynthesis
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Goosecoid Protein
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Homeodomain Proteins*
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LIM-Homeodomain Proteins
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Molecular Sequence Data
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Muscles / embryology*
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Mutation
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Nervous System / embryology*
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Notochord / embryology
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Protein Biosynthesis
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Proteins*
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RNA, Messenger / genetics
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Repressor Proteins*
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Signal Transduction
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T-Box Domain Proteins*
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Transcription Factors*
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Xenopus Proteins
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Xenopus laevis
Substances
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Carrier Proteins
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DNA Primers
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DNA-Binding Proteins
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Fetal Proteins
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Follistatin
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Glycoproteins
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Goosecoid Protein
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Homeodomain Proteins
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LIM-Homeodomain Proteins
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Lhx1 protein, Xenopus
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Proteins
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RNA, Messenger
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Repressor Proteins
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T-Box Domain Proteins
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Transcription Factors
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Xenopus Proteins
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noggin protein
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Brachyury protein