Akiyama-Oda Yasuko, Oda Hiroki
JT Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka 569-1125, Japan.
Development. 2006 Jun;133(12):2347-57. doi: 10.1242/dev.02400.
The mechanism by which Decapentaplegic (Dpp) and its antagonist Short gastrulation (Sog) specify the dorsoventral pattern in Drosophila embryos has been proposed to have a common origin with the mechanism that organizes the body axis in the vertebrate embryo. However, Drosophila Sog makes only minor contributions to the development of ventral structures that hypothetically correspond to the vertebrate dorsum where the axial notochord forms. In this study, we isolated a homologue of the Drosophila sog gene in the spider Achaearanea tepidariorum, and characterized its expression and function. Expression of sog mRNA initially appeared in a radially symmetrical pattern and later became confined to the ventral midline area, which runs axially through the germ band. RNA interference-mediated depletion of the spider sog gene led to a nearly complete loss of ventral structures, including the axial ventral midline and the central nervous system. This defect appeared to be the consequence of dorsalization of the ventral region of the germ band. By contrast, the extra-embryonic area formed normally. Furthermore, we showed that embryos depleted for a spider homologue of dpp failed to break the radial symmetry, displaying evenly high levels of sog expression except in the posterior terminal area. These results suggest that dpp is required for radial-to-axial symmetry transformation of the spider embryo and sog is required for ventral patterning. We propose that the mechanism of spider ventral specification largely differs from that of the fly. Interestingly, ventral specification in the spider is similar to the process in vertebrates in which the antagonism of Dpp/BMP signaling plays a central role in dorsal specification.
据推测，果蝇胚胎中Decapentaplegic（Dpp）及其拮抗剂Short gastrulation（Sog）确定背腹模式的机制与脊椎动物胚胎中组织体轴的机制有着共同的起源。然而，果蝇的Sog对腹侧结构发育的贡献很小，这些腹侧结构假设对应于脊椎动物形成轴向脊索的背部。在本研究中，我们在蜘蛛温驯络新妇中分离出果蝇sog基因的同源物，并对其表达和功能进行了表征。sog mRNA的表达最初呈现出径向对称模式，随后局限于沿轴向穿过胚带的腹侧中线区域。RNA干扰介导的蜘蛛sog基因缺失导致包括轴向腹侧中线和中枢神经系统在内的腹侧结构几乎完全丧失。这种缺陷似乎是胚带腹侧区域背化的结果。相比之下，胚外区域正常形成。此外，我们表明，缺失蜘蛛dpp同源物的胚胎未能打破径向对称，除了后末端区域外，sog表达水平均匀较高。这些结果表明，dpp是蜘蛛胚胎从径向对称转变为轴向对称所必需的，而sog是腹侧模式形成所必需的。我们提出，蜘蛛腹侧特化的机制与果蝇的机制有很大不同。有趣的是，蜘蛛的腹侧特化类似于脊椎动物中的过程，其中Dpp/BMP信号的拮抗作用在背侧特化中起核心作用。
