Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, United States of America.
Department of Evolution and Ecology, University of California-Davis, Davis, CA, United States of America.
PLoS Genet. 2018 Apr 10;14(4):e1007320. doi: 10.1371/journal.pgen.1007320. eCollection 2018 Apr.
Hox genes are involved in the patterning of animal body parts at multiple levels of regulatory hierarchies. Early expression of Hox genes in different domains along the embryonic anterior-posterior (A/P) axis in insects, vertebrates, and other animals establishes segmental or regional identity. However, Hox gene function is also required later in development for the patterning and morphogenesis of limbs and other organs. In Drosophila, spatiotemporal modulation of Sex combs reduced (Scr) expression within the first thoracic (T1) leg underlies the generation of segment- and sex-specific sense organ patterns. High Scr expression in defined domains of the T1 leg is required for the development of T1-specific transverse bristle rows in both sexes and sex combs in males, implying that the patterning of segment-specific sense organs involves incorporation of Scr into the leg development and sex determination gene networks. We sought to gain insight into this process by identifying the cis-and trans-regulatory factors that direct Scr expression during leg development. We have identified two cis-regulatory elements that control spatially modulated Scr expression within T1 legs. One of these enhancers directs sexually dimorphic expression and is required for the formation of T1-specific bristle patterns. We show that the Distalless and Engrailed homeodomain transcription factors act through sequences in this enhancer to establish elevated Scr expression in spatially defined domains. This enhancer functions to integrate Scr into the intrasegmental gene regulatory network, such that Scr serves as a link between leg patterning, sex determination, and sensory organ development.
Hox 基因参与动物体部分在多个层次的调控层次上的模式形成。在昆虫、脊椎动物和其他动物的胚胎前后（A/P）轴的不同区域，Hox 基因的早期表达建立了节段或区域的身份。然而，Hox 基因的功能在发育后期也需要用于四肢和其他器官的模式形成和形态发生。在果蝇中，Sex comb reduced (Scr) 表达在第一胸（T1）腿内的时空调节是产生节段和性别特异性感觉器官模式的基础。在两性中，T1 腿的特定区域高表达 Scr 是 T1 特异性横生刚毛行和雄性中的性梳发育所必需的，这意味着节段特异性感觉器官的模式形成涉及将 Scr 纳入腿发育和性别决定基因网络。我们试图通过鉴定在腿发育过程中指导 Scr 表达的顺式和反式调节因子来深入了解这一过程。我们已经鉴定出两个控制 T1 腿内空间调制 Scr 表达的顺式调节元件。其中一个增强子指导性别二态性表达，是形成 T1 特异性刚毛模式所必需的。我们表明，Distalless 和 Engrailed 同源域转录因子通过该增强子中的序列作用，在空间上确定的区域建立升高的 Scr 表达。该增强子将 Scr 整合到节段内基因调控网络中，使得 Scr 成为腿模式形成、性别决定和感觉器官发育之间的联系。
