Wratten Naomi S, McGregor Alistair P, Shaw Philip J, Dover Gabriel A
Department of Genetics, University of Leicester, Leicester LE1 7RH, UK.
Evol Dev. 2006 Jan-Feb;8(1):6-15. doi: 10.1111/j.1525-142X.2006.05070.x.
To further understand the evolutionary dynamics of the regulatory interactions underlying development, we expand on our previous analysis of hunchback and compare the structure and function of the tailless enhancer between Musca domestica and Drosophila melanogaster. Our analysis shows that although the expression patterns and functional protein domains of tll are conserved between Musca and Drosophila, the enhancer sequences are unalignable. Upon closer investigation, we find that these highly diverged enhancer sequences encode the same regulatory information necessary for Bicoid, Dorsal, and the terminal system to drive tll expression. The binding sites for these transcription factors differ in the sequence, number, spacing, and position between the Drosophila and Musca tll enhancers, and we were unable to establish homology between binding sites from each species. This implies that the Musca and Drosophila Bcd-binding sites have evolved de novo in the 100 million years since these species diverged. However, in transgenic Drosophila embryos the Musca tll enhancer is able to drive the same expression pattern as endogenous Drosophila tll. Therefore, during the rapid evolution of enhancer sequences individual binding sites are continually lost and gained, but the transcriptional output is maintained by compensatory mutations in cis and in trans.
为了进一步了解发育过程中调控相互作用的进化动态，我们扩展了之前对驼背基因的分析，并比较了家蝇和黑腹果蝇中无尾增强子的结构和功能。我们的分析表明，尽管无尾基因在表达模式和功能蛋白结构域上家蝇和果蝇之间是保守的，但增强子序列却无法比对。经过更仔细的研究，我们发现这些高度分化的增强子序列编码了由双胸蛋白、背蛋白和末端系统驱动无尾基因表达所需的相同调控信息。这些转录因子的结合位点在果蝇和家蝇无尾基因增强子之间的序列、数量、间距和位置上存在差异，并且我们无法在每个物种的结合位点之间建立同源性。这意味着自这些物种分化以来的一亿年里，家蝇和果蝇的双胸蛋白结合位点是重新进化而来的。然而，在转基因果蝇胚胎中，家蝇无尾基因增强子能够驱动与内源性果蝇无尾基因相同的表达模式。因此，在增强子序列的快速进化过程中，单个结合位点不断丢失和获得，但转录输出通过顺式和反式的补偿性突变得以维持。
