Correlation of diversity of leg morphology in Gryllus bimaculatus (cricket) with divergence in dpp expression pattern during leg development

Insects can be grouped into mainly two categories, holometabolous and hemim etabolous, according to the extent of their morphological change during met amorphosis. The three thoracic legs, for example, are known to develop thro ugh two overtly different pathways: holometabolous insects make legs throug h their imaginal discs, while hemimetabolous legs develop from their leg bu ds. Thus, how the molecular mechanisms of leg development differ from each other is an intriguing question. In the holometabolous long-germ insect, th ese mechanisms have been extensively studied using Drosophila melanogaster, However, little is known about the mechanism in the hemimetabolous insect. Thus, we studied leg development of the hemimetabolous short-germ insect, Gryllus bimaculatus (cricket), focusing on expression patterns of the three key signaling molecules, hedgehog (hh), wingless (wg) and decapentaplegic (dpp), which are essential during leg development in Drosophila, In Gryllus embryos, expression of hh is restricted in the posterior half of each leg bud, while dpp and wg are expressed in the dorsal and ventral sides of its anteroposterior (A/P) boundary, respectively. Their expression patterns are essentially comparable with those of the three genes in Drosophila leg ima ginal discs, suggesting the existence of the common mechanism for leg patte rn formation. However, we found that expression pattern of dpp was signific antly divergent among Glyllus, Schistocerca (grasshopper) and Drosophila em bryos, while expression patterns of hh and wg are conserved. Furthermore, t he divergence was found between the pro/mesothoracic and metathoracic Gryll us leg buds, These observations imply that the divergence in the dpp expres sion pattern may correlate with diversity of leg morphology.