Christensen Randolph N, Weinstein Michael, Tassava Roy A
Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210, USA.
Dev Dyn. 2002 Mar;223(2):193-203. doi: 10.1002/dvdy.10049.
Members of the fibroblast growth factor (FGF) family of molecules are critical to limb outgrowth. Here, we examine the expression of Fgfs in three types of limbs-embryonic (developing), mature (differentiated), and regenerating-as well as in the surrounding non-limb tissues in the Mexican axolotl, Ambystoma mexicanum. We have previously cloned partial cDNAs of Fgf4, 8, and 10 from the axolotl (Christensen et al., 2001); the complete Fgf10 cDNA sequence is presented here. Axolotl Fgf10 showed deduced amino acid sequence identity with all other vertebrate Fgf10 coding sequences of >62%, and also included conserved 5' and 3' untranslated regions in nucleotide sequence comparisons. Semiquantitative reverse transcriptase-polymerase chain reaction showed that fibroblast growth factors are differentially expressed in axolotl limbs. Only Fgf8 and 10 were highly expressed during axolotl limb development, although Fgf4, 8, and 10 are all highly expressed during limb development of other vertebrates. Fgf4 expression, however, was highly expressed in the differentiated salamander limb, whereas expression levels of Fgf8 and 10 decreased. Expression levels of Fgf8 and 10 then increased during limb regeneration, whereas Fgf4 expression was completely absent. In addition, axolotl limb regeneration contrasted to limb development of other vertebrates in that Fgf8 did not seem to be as highly expressed in the distal epithelium; rather, its highest expression was found in the blastema mesenchyme. Finally, we investigated the expression of these Fgfs in non-limb tissues. The Fgfs were clearly expressed in developing flank tissue and then severely downregulated in mature flank tissue. Differential Fgf expression levels in the limb and shoulder (limb field) versus in the flank (non-limb field) suggest that FGFs may be instrumental during limb field specification as well as instrumental in maintaining the salamander limb in a state of preparation for regeneration.
成纤维细胞生长因子（FGF）家族分子的成员对肢体生长至关重要。在此，我们研究了墨西哥钝口螈（Ambystoma mexicanum）三种类型肢体（胚胎期（发育中的）、成熟（分化的）和再生的）以及周围非肢体组织中Fgfs的表达情况。我们之前已从钝口螈中克隆出Fgf4、8和10的部分cDNA（克里斯滕森等人，2001年）；本文展示了完整的Fgf10 cDNA序列。钝口螈Fgf10推导的氨基酸序列与所有其他脊椎动物Fgf10编码序列的同一性>62%，并且在核苷酸序列比较中还包含保守的5'和3'非翻译区。半定量逆转录 - 聚合酶链反应表明，成纤维细胞生长因子在钝口螈肢体中差异表达。虽然Fgf4、8和10在其他脊椎动物的肢体发育过程中均高表达，但在钝口螈肢体发育期间只有Fgf8和10高表达。然而，Fgf4在分化的蝾螈肢体中高表达，而Fgf8和10的表达水平下降。在肢体再生过程中，Fgf8和10的表达水平随后升高，而Fgf4的表达完全缺失。此外，钝口螈肢体再生与其他脊椎动物的肢体发育不同之处在于，Fgf8在远端上皮中似乎没有那么高的表达；相反，其最高表达出现在芽基间充质中。最后，我们研究了这些Fgfs在非肢体组织中的表达。Fgfs在发育中的胁腹组织中明显表达，然后在成熟的胁腹组织中严重下调。肢体和肩部（肢体场）与胁腹（非肢体场）中Fgf表达水平的差异表明，FGFs可能在肢体场特化过程中起作用，并且有助于使蝾螈肢体保持在为再生做准备的状态。
