Phenotypic robustness conferred by apparently redundant transcriptional enhancers.
Phenotypic robustness conferred by apparently redundant transcriptional enhancers.
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基因包含含有转录增强子的顺式调控区域。近期的报道表明，发育基因通常拥有多个离散的增强子模块，它们以相似的时空模式驱动转录：位于基础启动子附近的主要增强子以及位于更远处的次要或“影子”增强子。有人假设主要增强子和次要增强子看似冗余的活性有助于表型的稳健性。我们通过产生一种缺失来检验这一假设，该缺失移除了刚毛幼虫（shavenbaby，svb）的两个新发现的增强子，svb是一个编码转录因子的基因，该转录因子指导幼虫刚毛的发育。在胚胎发育的最佳温度下，这种缺失会导致刚毛模式出现轻微缺陷。然而，在低温和高温极端温度下发育的胚胎中，这些次要增强子的缺失会导致刚毛大量缺失。这些温度依赖性缺陷可以通过携带一个驱动svb cDNA转录的次要增强子的转基因来挽救。最后，去除无翅基因（wingless）的一个拷贝，无翅基因是正常刚毛模式所必需的，仅在缺乏次要增强子的果蝇中会导致类似的刚毛缺失。这些结果支持了这样一种假设，即次要增强子在面对环境和遗传变异时有助于表型的稳健性。
Genes include cis-regulatory regions that contain transcriptional enhancers. Recent reports have shown that developmental genes often possess multiple discrete enhancer modules that drive transcription in similar spatio-temporal patterns: primary enhancers located near the basal promoter and secondary, or “shadow”, enhancers located at more remote positions. It has been hypothesized that the seemingly redundant activity of primary and secondary enhancers contributes to phenotypic robustness. We tested this hypothesis by generating a deficiency that removes two newly-discovered enhancers of shavenbaby (svb), a gene encoding a transcription factor that directs development of larval trichomes. At optimal temperatures for embryonic development, this deficiency causes minor defects in trichome patterning. In embryos that develop at both low and high extreme temperatures, however, absence of these secondary enhancers leads to extensive loss of trichomes. These temperature-dependent defects can be rescued by a transgene carrying a secondary enhancer driving transcription of the svb cDNA. Finally, removal of one copy of wingless, a gene required for normal trichome patterning, causes a similar loss of trichomes only in flies lacking the secondary enhancers. These results support the hypothesis that secondary enhancers contribute to phenotypic robustness in the face of environmental and genetic variability.
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