Characterisation of hoxa gene expression in the chick limb bud in response to FGF.
We tested a diffusion gradient model for setting up overlapping domains of Hoxa gene expression in the chick limb bud. The model is based on morphogen production at the limb bud tip where the apical ridge is located and assumes that cells respond to a series of concentration thresholds. Consistent with the model, Hoxa13 gene expression rapidly switches off when the ridge is removed from stage 21/22 buds, while Hoxa11 and Hoxa10 expression is stable; Hoxa13 expression can be initiated and maintained in absence of the ridge by FGF soaked beads; the Hoxa13 domain first expands quickly and then slows up and the size is related to the dose of FGF4. Contrary to the model, addition of FGF4 to early limb buds does not activate Hoxa13 prematurely nor extend the Hoxa13 expression domain proximally. Therefore FGF4 signalling is necessary but not sufficient for Hoxa gene expression in the limb bud.
Vargesson
N
N
Department of Anatomy and Developmental Biology, University College London, London, United Kingdom.
Kostakopoulou
K
K
Drossopoulou
G
G
Papageorgiou
S
S
Tickle
C
C
D000818:Animals; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D051519:Fibroblast Growth Factor 4; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D000080905:Homeobox A10 Proteins; D018398:Homeodomain Proteins / Q000096:biosynthesis; D017403:In Situ Hybridization; D018878:Limb Buds / Q000196:embryology / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D013997:Time Factors; D015534:Trans-Activators / Q000096:biosynthesis*
D004268:DNA-Binding Proteins; D051519:Fibroblast Growth Factor 4; D000080905:Homeobox A10 Proteins; D018398:Homeodomain Proteins; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; C099959:homeobox protein HOXA13; C088144:HoxA protein; C092119:Hoxa10 protein, mouse; D005346:Fibroblast Growth Factors