Institute of Evolutionary Biology, Consejo Superior de Investigaciones Cientificas-Universitat Pompeu Fabra, 08003 Barcelona, Spain.
Institute of Evolutionary Biology, Consejo Superior de Investigaciones Cientificas-Universitat Pompeu Fabra, 08003 Barcelona, Spain
Proc Natl Acad Sci U S A. 2014 May 13;111(19):7024-9. doi: 10.1073/pnas.1401478111. Epub 2014 Apr 28.
All immature animals undergo remarkable morphological and physiological changes to become mature adults. In winged insects, metamorphic changes either are limited to a few tissues (hemimetaboly) or involve a complete reorganization of most tissues and organs (holometaboly). Despite the differences, the genetic switch between immature and adult forms in both types of insects relies on the disappearance of the antimetamorphic juvenile hormone (JH) and the transcription factors Krüppel-homolog 1 (Kr-h1) and Broad-Complex (BR-C) during the last juvenile instar. Here, we show that the transcription factor E93 is the key determinant that promotes adult metamorphosis in both hemimetabolous and holometabolous insects, thus acting as the universal adult specifier. In the hemimetabolous insect Blattella germanica, BgE93 is highly expressed in metamorphic tissues, and RNA interference (RNAi)-mediated knockdown of BgE93 in the nymphal stage prevented the nymphal-adult transition, inducing endless reiteration of nymphal development, even in the absence of JH. We also find that BgE93 down-regulated BgKr-h1 and BgBR-C expression during the last nymphal instar of B. germanica, a key step necessary for proper adult differentiation. This essential role of E93 is conserved in holometabolous insects as TcE93 RNAi in Tribolium castaneum prevented pupal-adult transition and produced a supernumerary second pupa. In this beetle, TcE93 also represses expression of TcKr-h1 and TcBR-C during the pupal stage. Similar results were obtained in the more derived holometabolous insect Drosophila melanogaster, suggesting that winged insects use the same regulatory mechanism to promote adult metamorphosis. This study provides an important insight into the understanding of the molecular basis of adult metamorphosis.
所有未成熟的动物都会经历显著的形态和生理变化，从而成为成熟的个体。在有翅昆虫中，变态变化要么局限于少数组织（半变态），要么涉及大多数组织和器官的完全重组（完全变态）。尽管存在差异，但这两种类型的昆虫中，未成熟和成虫形式之间的遗传转换都依赖于变态期结束时抗变态的保幼激素（JH）和转录因子 Krüppel-homolog 1（Kr-h1）和 Broad-Complex（BR-C）的消失。在这里，我们表明转录因子 E93 是促进半变态和完全变态昆虫成虫变态的关键决定因素，因此是成虫的通用指定因子。在半变态昆虫德国小蠊中，BgE93 在变态组织中高度表达，在若虫期通过 RNA 干扰（RNAi）介导的 BgE93 敲低阻止了若虫-成虫转变，诱导若虫发育的无休止重复，即使在没有 JH 的情况下也是如此。我们还发现，BgE93 在德国小蠊的最后一个若虫龄期间下调了 BgKr-h1 和 BgBR-C 的表达，这是适当成虫分化所必需的关键步骤。E93 的这种重要作用在完全变态昆虫中是保守的，因为在 TcE93 在 T. castaneum 中的 RNAi 阻止了蛹-成虫转变，并产生了多余的第二个蛹。在这种甲虫中，TcE93 也在蛹期抑制 TcKr-h1 和 TcBR-C 的表达。在更衍生的完全变态昆虫黑腹果蝇中也获得了类似的结果，表明有翅昆虫使用相同的调节机制来促进成虫变态。这项研究为理解成虫变态的分子基础提供了重要的见解。
