Komisarczuk Anna Z, Kawakami Koichi, Becker Thomas S
Sars Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, N-5008 Bergen, Norway.
Dev Biol. 2009 Dec 15;336(2):301-12. doi: 10.1016/j.ydbio.2009.09.029. Epub 2009 Sep 25.
The complex expression pattern of fibroblast growth factor 8 (Fgf8) and the cellular responses dependent on concentration of its mRNA in vertebrates suggest that Fgf8 should be tightly controlled at the transcriptional level. We found zebrafish conserved noncoding elements (CNEs) with pan-vertebrate as well as fish-specific orthologous sequences from across 200 kb of the zebrafish fgf8a genomic regulatory block to direct reporter expression in patterns consistent with the expression pattern of fgf8a. These included elements from inside the introns of the skin-specific slc2a15a and the ubiquitously expressed fbxw4 bystander genes. The fgf8a/fbxw4 gene pair, which has remained joined throughout three whole genome duplications in chordate evolution, is inverted in teleost genomes, but CNEs across both evolutionary breakpoints showed specific activity. While some CNEs directed highly reproducible expression patterns, others were subject to variation but showed, in a subset of transgenes, expression in the apical ectodermal ridge, the anterior boundaries of somites and the midbrain-hindbrain boundary, specific Fgf8 signaling domains, suggesting that their activity may be context specific. A human element with tetrapod-specific orthologous sequences directed reporter expression to the vasculature, possibly corresponding to a tetrapod innovation. We conclude that fgf8a transcriptional regulation employs pan-vertebrate and teleost-specific enhancers dispersed over three genes in the zebrafish genome.
成纤维细胞生长因子8（Fgf8）复杂的表达模式以及脊椎动物中依赖于其mRNA浓度的细胞反应表明，Fgf8在转录水平上应受到严格控制。我们在斑马鱼成纤维细胞生长因子8a（fgf8a）基因组调控区200 kb范围内发现了斑马鱼保守非编码元件（CNE），这些元件具有全脊椎动物以及鱼类特异性直系同源序列，可指导报告基因以与fgf8a表达模式一致的方式进行表达。这些元件包括来自皮肤特异性溶质载体家族2成员15a（slc2a15a）内含子内部以及普遍表达的旁观者基因F-盒蛋白4（fbxw4）的元件。在脊索动物进化过程中经历了三次全基因组复制后仍保持相连的fgf8a/fbxw4基因对，在硬骨鱼基因组中发生了倒置，但跨越两个进化断点的CNE均显示出特定活性。虽然一些CNE指导高度可重复的表达模式，但其他一些则存在变异，但在一部分转基因中，它们在顶端外胚层嵴、体节的前边界以及中脑-后脑边界（特定的Fgf8信号传导域）中表达，这表明它们的活性可能具有背景特异性。一个具有四足动物特异性直系同源序列的人类元件将报告基因表达导向脉管系统，这可能对应于四足动物的一种创新。我们得出结论，fgf8a的转录调控采用了分散在斑马鱼基因组中三个基因上的全脊椎动物和硬骨鱼特异性增强子。
