The Deparment of Ecology, Evolution and Behavior, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
Dev Biol. 2013 Aug 1;380(1):125-31. doi: 10.1016/j.ydbio.2013.04.030. Epub 2013 May 8.
The anterior and posterior ends of the insect embryo are patterned through the terminal patterning system, which is best known from the fruitfly Drosophila melanogaster. In Drosophila, the RTK receptor Torso and its presumed co-activator Torso-like initiate a signaling cascade, which activates two terminal gap genes, tailless and huckebein. These in turn interact with various patterning genes to define terminal structures. Work on other insect species has shown that this system is poorly conserved, and not all of its components have been found in all cases studied. We place the variability of the system within a broader phylogenetic framework. We describe the expression and knock-down phenotypes of the homologues of terminal patterning genes in the hemimetabolous Oncopeltus fasciatus. We have examined the interactions among these genes and between them and other patterning genes. We demonstrate that all of these genes have different roles in Oncopeltus relative to Drosophila; torso-like is expressed in follicle cells during oogenesis and is involved in the invagination of the blastoderm to form the germ band, and possibly also in defining the growth zone; tailless is regulated by orthodenticle and has a role only in anterior determination; huckebein is expressed only in the middle of the blastoderm; finally, torso was not found in Oncopeltus and its role in terminal patterning seems novel within holometabolous insects. We then use our data, together with published data on other insects, to reconstruct the evolution of the terminal patterning gene network in insects. We suggest that the Drosophila terminal patterning network evolved recently in the lineage leading to the Diptera, and represents an example of evolutionary "tinkering", where pre-existing pathways are co-opted for a new function.
昆虫胚胎的前后端通过终端模式系统进行模式化，该系统以果蝇 Drosophila melanogaster 最为知名。在果蝇中，RTK 受体 Torso 及其假定的共激活因子 Torso-like 启动信号级联反应，激活两个末端间隙基因 tailless 和 huckebein。反过来，它们与各种模式基因相互作用，定义末端结构。对其他昆虫物种的研究表明，该系统的保守性较差，并非所有成分都在所有研究案例中都有发现。我们将系统的可变性置于更广泛的系统发育框架内进行描述。我们描述了半变态昆虫 Oncopeltus fasciatus 中末端模式基因同源物的表达和敲低表型。我们检查了这些基因之间以及它们与其他模式基因之间的相互作用。我们证明，与果蝇相比，所有这些基因在 Oncopeltus 中都具有不同的作用；在卵子发生过程中，Torso-like 在滤泡细胞中表达，并参与胚盘的内陷以形成生殖带，并且可能还参与定义生长区；tailless 受 orthodenticle 调控，仅在前部决定中发挥作用；huckebein 仅在胚盘的中部表达；最后，在 Oncopeltus 中未发现 torso，其在末端模式形成中的作用在完全变态昆虫中是新颖的。然后，我们使用我们的数据以及其他昆虫的已发表数据，重建了昆虫末端模式基因网络的进化。我们认为，果蝇末端模式形成网络是在导致双翅目昆虫的谱系中最近进化而来的，代表了进化“修补”的一个例子，其中预先存在的途径被用于新的功能。
