Wimmer E A, Cohen S M, Jäckle H, Desplan C
Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10021-6399, USA.
Development. 1997 Apr;124(8):1509-17. doi: 10.1242/dev.124.8.1509.
The Drosophila gap-like segmentation genes orthodenticle, empty spiracles and buttonhead (btd) are expressed and required in overlapping domains in the head region of the blastoderm stage embryo. Their expression domains correspond to two or three segment anlagen that fail to develop in each mutant. It has been proposed that these overlapping expression domains mediate head metamerization and could generate a combinatorial code to specify segment identity. To test this model, we developed a system for targeted gene expression in the early embryo, based on region specific promoters and the flp-out system. Misexpression of btd in the anterior half of the blastoderm embryo directed by the hunchback proximal promoter rescues the btd mutant head phenotype to wild-type. This indicates that, while btd activity is required for the formation of specific head segments, its ectopic expression does not disturb head development. We conclude that the spatial limits of btd expression are not instructive for metamerization of the head region and that btd activity does not contribute to a combinatorial code for specification of segment identity.
果蝇中与间隙样分割基因相关的正齿、空气门和钮头（btd）基因，在囊胚期胚胎头部区域的重叠区域表达且发挥作用。它们的表达区域对应于两到三个体节原基，每个突变体中这些原基无法发育。有人提出，这些重叠的表达区域介导头部体节形成，并可能产生一种组合密码来指定体节身份。为了验证该模型，我们基于区域特异性启动子和flp-out系统，开发了一种早期胚胎中靶向基因表达的系统。由驼背近端启动子引导的囊胚胚胎前半部分中btd的错误表达，将btd突变体头部表型挽救为野生型。这表明，虽然btd活性对于特定头部体节的形成是必需的，但其异位表达不会干扰头部发育。我们得出结论，btd表达的空间限制对头部区域的体节形成没有指导作用，并且btd活性对指定体节身份的组合密码没有贡献。
