Casares F, Mann R S
Department of Biochemistry and Molecular Biophysics, Center for Neurobiology and Behavior, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
Nature. 1998 Apr 16;392(6677):723-6. doi: 10.1038/33706.
During the evolution of insects from a millipede-like ancestor, the Hox genes are thought to have promoted the diversification of originally identical body structures. In Drosophila melanogaster, antennae and legs are homologous structures that differ from each other as a result of the Hox gene Antennapedia (Antp), which promotes leg identities by repressing unknown antennal-determining genes. Here we present four lines of evidence that identify extradenticle (exd) and homothorax (hth) as antennal-determining genes. First, removing the function of exd or hth, which is required for the nuclear localization of Exd protein, transforms the antenna into leg; such transformations occur without activation of Antp. Second, hth is expressed and Exd is nuclear in most antennal cells, whereas both are restricted to proximal cells of the leg. Third, Antp is a repressor of hth. Fourth, ectopic expression of Meis1, a murine hth homologue, can trigger antennal development elsewhere in the fly. Taken together, these data indicate that hth is an antennal selector gene, and that Antp promotes leg development by repressing hth and consequently nuclear Exd.
在昆虫从类似千足虫的祖先进化过程中，Hox基因被认为促进了原本相同身体结构的多样化。在黑腹果蝇中，触角和腿是同源结构，由于Hox基因触角足基因（Antp）的作用，它们彼此不同，该基因通过抑制未知的触角决定基因来促进腿部特征的形成。在此，我们提供了四条证据，确定了额外齿（exd）和同胸（hth）为触角决定基因。第一，去除exd或hth的功能（这是Exd蛋白核定位所必需的）会将触角转变为腿；这种转变在没有激活Antp的情况下发生。第二，hth在大多数触角细胞中表达，Exd在细胞核中存在，而两者都局限于腿部的近端细胞。第三，Antp是hth的抑制因子。第四，小鼠hth同源物Meis1的异位表达可在果蝇其他部位触发触角发育。综上所述，这些数据表明hth是一种触角选择基因，并且Antp通过抑制hth从而抑制细胞核中的Exd来促进腿部发育。
