Sara Khadjeh

Role of Hox genes in walking leg morphology specification in insects and spiders


Hox genes encode homeodomain containing transcription factors which provide positional information along the primary body axis and are responsible for specification of segment identity and cellular fates. Potential sites of evolutionary change in the Hox gene pathway could be the expression domain, the biochemical function and downstream targets, finally affecting the developmental role of a given Hox gene. However, the Hox gene Antp is known to specify walking leg morphology in Drosophila. If Antp is misexpressed in other appendage types, e.g. the antenna, the appendage is homeotically transformed into walking leg identity. Thus, Antp is the factor that can confer walking leg identity onto appendages in insects. Intriguingly, however, in spiders Antp is not expressed in the walking legs. This strongly suggests that Antp has a different role in spiders and flies and indicates that another Hox gene is taking up the role of Antp.


Fig.: The common house spider Achaearanea tepidariorum.


Deformed (Dfd) is the Hox gene that is expressed in the walking leg segments in spiders. In the present project we want to test the idea that Dfd and not Antp can confer walking leg identity in spiders. Therefore, we want to generate transgenic Drosophila lines that express the spider Dfd and Antp genes under the control of the Gal4/UAS system. Misexpression experiments of the spider genes in Drosophila lines should reveal whether spider Antp and Dfd are able to generate walking leg morphology. The present project would be among the first studies to link the evolution of a morphological character to the evolution of gene regulation.