Correlation of wing-leg identity in ectopic FGF-induced chimeric limbs with the differential expression of chick Tbx5 and Tbx4.
It has been reported that members of the fibroblast growth factor (FGF) family can induce additional limb formation in the flank of chick embryos. The phenotype of the ectopic limb depends on the somite level at which it forms: limbs in the anterior flank resemble wings, whereas those in the posterior flank resemble legs. Ectopic limbs located in the mid-flank appear chimeric, possessing characteristics of both wings and legs; feather buds are present in the anterior halves with scales and claws in the posterior halves. To study the mechanisms underlying the chimerism of these additional limbs, we cloned chick Tbx5 and Tbx4 to use as forelimb and hindlimb markers and examined their expression patterns in FGF-induced limb buds. We found that Tbx5 and Tbx4 were differentially expressed in the anterior and posterior halves of additional limb buds in the mid-flank, respectively, consistent with the chimeric patterns of the integument. A boundary of Tbx5/Tbx4 exists in all ectopic limbs, indicating that the additional limbs are essentially chimeric, although the degree of chimerism is dependent on the position. The boundary of Tbx5/Tbx4 expression is not fixed at a specific position within the interlimb region, but dependent upon where FGF was applied. Since the ectopic expression patterns of Tbx5/Tbx4 in the additional limbs are closely correlated with the patterns of their chimeric phenotypes, it is likely that Tbx5 and Tbx4 expression in the limb bud is involved in determination of the forelimb and hindlimb identities, respectively, in vertebrates.
Ohuchi
H
H
Department of Biological Science and Technology, Faculty of Engineering, The University of Tokushima, Japan.
Takeuchi
J
J
Yoshioka
H
H
Ishimaru
Y
Y
Ogura
K
K
Takahashi
N
N
Ogura
T
T
Noji
S
S
D000595:Amino Acid Sequence; D000818:Animals; D030161:Avian Proteins; D019521:Body Patterning; D002642:Chick Embryo; D005121:Extremities / Q000196:embryology*; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D051519:Fibroblast Growth Factor 4; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000235:genetics / Q000494:pharmacology*; D005347:Fibroblasts; D018507:Gene Expression Regulation, Developmental; D005819:Genetic Markers; D006133:Growth Substances / Q000235:genetics; D006801:Humans; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D010641:Phenotype; D011518:Proto-Oncogene Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D011994:Recombinant Proteins / Q000494:pharmacology; D016415:Sequence Alignment; D020825:T-Box Domain Proteins; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics*; D014162:Transfection; D014921:Wings, Animal / Q000196:embryology*
D030161:Avian Proteins; C496445:FGF4 protein, human; D051519:Fibroblast Growth Factor 4; D005819:Genetic Markers; D006133:Growth Substances; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; D020825:T-Box Domain Proteins; C103172:T-box transcription factor 5; C491196:TBX4 protein, Gallus gallus; C491193:TBX4 protein, human; D014157:Transcription Factors; D016222:Fibroblast Growth Factor 2; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors