title: Gremlin1 induces anterior-posterior limb bifurcations in developing Xenopus limbs but does not enhance limb regeneration.
abstract: Gremlin1 (grem1) has been previously identified as being significantly up-regulated during regeneration of Xenopus laevis limbs. Grem1 is an antagonist of bone morphogenetic proteins (BMPs) with a known role in limb development in amniotes. It forms part of a self-regulating feedback loop linking epithelial (FGF) and mesenchymal (shh) signalling centres, thereby controlling outgrowth, anterior posterior and proximal distal patterning. Spatiotemporal regulation of the same genes in developing and regenerating Xenopus limb buds supports conservation of this mechanism. Using a heat shock inducible grem1 (G) transgene to created temperature regulated stable lines, we have shown that despite being upregulated in regeneration, grem1 overexpression does not enhance regeneration of tadpole hindlimbs. However, both the regenerating and contralateral, developing limb of G transgenics developed skeletal defects, suggesting that overexpressing grem1 negatively affects limb patterning. When grem1 expression was targeted earlier in limb bud development, we saw dramatic bifurcations of the limbs resulting in duplication of anterior posterior (AP) pattern, forming a phenotypic continuum ranging from duplications arising at the level of the femoral head to digit bifurcations, but never involving the pelvis. Intriguingly, the original limbs have AP pattern inversion due to de-restricted Shh signalling. We discuss a possible role for Grem1 regulation of limb BMPs in regulation of branching pattern in the limbs.
authors.affiliation: Department of Zoology, University of Otago, Dunedin, New Zealand.
authors.forename: Yi-Hsuan
authors.initials: YH
authors.lastname: Wang
authors.affiliation: Department of Zoology, University of Otago, Dunedin, New Zealand.
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Keenan
authors.affiliation: Department of Zoology, University of Otago, Dunedin, New Zealand.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Lynn
authors.affiliation: Department of Zoology, University of Otago, Dunedin, New Zealand.
authors.forename: James C
authors.initials: JC
authors.lastname: McEwan
authors.affiliation: Department of Zoology, University of Otago, Dunedin, New Zealand; Genetics Otago, University of Otago, Dunedin, New Zealand. Electronic address: caroline.beck@otago.ac.nz.
authors.forename: Caroline W
authors.initials: CW
authors.lastname: Beck
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D019521:Body Patterning / Q000235:genetics / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology; D016207:Cytokines; D005121:Extremities / Q000196:embryology* / Q000502:physiology; D051524:Fibroblast Growth Factor 8 / Q000235:genetics / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D018869:Heat-Shock Response / Q000235:genetics / Q000502:physiology; D053823:Hedgehog Proteins / Q000235:genetics / Q000502:physiology; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology*; D017880:Limb Deformities, Congenital / Q000196:embryology / Q000235:genetics; D012038:Regeneration / Q000235:genetics / Q000502:physiology; D015854:Up-Regulation; D029867:Xenopus Proteins / Q000235:genetics / Q000502:physiology*; D014982:Xenopus laevis / Q000196:embryology* / Q000235:genetics / Q000502:physiology*; D000099176:Noggin Protein
chemical_list: D002352:Carrier Proteins; D016207:Cytokines; D051524:Fibroblast Growth Factor 8; D053823:Hedgehog Proteins; D036341:Intercellular Signaling Peptides and Proteins; D029867:Xenopus Proteins; D000099176:Noggin Protein; C576319:FGF8 protein, Xenopus; C486400:GREM1 protein, Xenopus; C558166:Shh protein, Xenopus
keywords: Branching morphogenesis; Digit identity; Ectopic limbs; Grem1; Limb bud; Polydactyly; Regeneration; Xenopus