Munoz-Sanjuan I, Simandl B K, Fallon J F, Nathans J
Department of Molecular Biology and Genetics, Department of Anatomy, University of Wisconsin, Madison, Wisconsin 53706, USA.
Development. 1999 Jan;126(2):409-21. doi: 10.1242/dev.126.2.409.
Members of the fibroblast growth factor (FGF) family have been identified as signaling molecules in a variety of developmental processes, including important roles in limb bud initiation, growth and patterning. This paper reports the cloning and characterization of the chicken orthologues of fibroblast growth factor homologous factors-1 and -2 (cFHF-1/cFGF-12 and cFHF-2/cFGF-13, respectively). We also describe the identification of a novel, conserved isoform of FHF-2 in chickens and mammals. This isoform arises by alternative splicing of the first exon of the FHF-2 gene and is predicted to encode a polypeptide with a distinct amino-terminus. Whole-mount in situ hybridization reveals restricted domains of expression of cFHF-1 and cFHF-2 in the developing neural tube, peripheral sensory ganglia and limb buds, and shows that the two cFHF-2 transcript isoforms are present in non-overlapping spatial distributions in the neural tube and adjacent structures. In the developing limbs, cFHF-1 is confined to the posterior mesoderm in an area that encompasses the zone of polarizing activity and cFHF-2 is confined to the distal anterior mesoderm in a region that largely overlaps the progress zone. Ectopic cFHF-2 expression is induced adjacent to grafts of cells expressing Sonic Hedgehog and the zone of cFHF-2 expression is expanded in talpid2 embryos. In the absence of the apical ectodermal ridge or in wingless or limbless mutant embryos, expression of cFHF-1 and cFHF-2 is lost from the limb bud. A role for cFHF-2 in the patterning and growth of skeletal elements is implied by the observation that engraftment of developing limb buds with QT6 cells expressing a cFHF-2 isoform that is normally expressed in the limb leads to a variety of morphological defects. Finally, we show that a secreted version of cFHF-2 activates the expression of HoxD13, HoxD11, Fgf-4 and BMP-2 ectopically, consistent with cFHF-2 playing a role in anterior-posterior patterning of the limb.
成纤维细胞生长因子（FGF）家族成员已被确定为多种发育过程中的信号分子，在肢芽起始、生长和模式形成中发挥重要作用。本文报道了成纤维细胞生长因子同源因子-1和-2（分别为cFHF-1/cFGF-12和cFHF-2/cFGF-13）的鸡直系同源物的克隆和特征。我们还描述了在鸡和哺乳动物中鉴定出的一种新的、保守的FHF-2异构体。这种异构体通过FHF-2基因第一个外显子的可变剪接产生，预计编码一种具有独特氨基末端的多肽。全胚胎原位杂交显示cFHF-1和cFHF-2在发育中的神经管、外周感觉神经节和肢芽中的表达受限区域，并表明两种cFHF-2转录异构体在神经管和相邻结构中以不重叠的空间分布存在。在发育中的肢体中，cFHF-1局限于包含极化活性区的后中胚层，而cFHF-2局限于在很大程度上与进展区重叠的远端前中胚层。在表达音猬因子的细胞移植附近诱导异位cFHF-2表达，并且在talpid2胚胎中cFHF-2表达区扩大。在没有顶端外胚层嵴或在无翅或无肢突变胚胎中，cFHF-1和cFHF-2的表达从肢芽中消失。将表达通常在肢体中表达的cFHF-2异构体的QT6细胞移植到发育中的肢芽中会导致多种形态缺陷，这暗示了cFHF-2在骨骼元件的模式形成和生长中的作用。最后，我们表明分泌形式的cFHF-2异位激活HoxD13、HoxD11、Fgf-4和BMP-2的表达，这与cFHF-2在肢体前后模式形成中发挥作用一致。
