Correlation between distal-less expression patterns and structures of appendages in development of the two-spotted cricket, Gryllus bimaculatus

A million of insect species have been identified so far, displaying a staggering variety of adult morphologies. To elucidate mechanism how such insect morphologies are developed at a molecular level, we investigated developmental process of the two-spotted crick:et, Gryllus bimaculatus, as a typical hemimetabola, and compared with that of Drosophila as an extensively studied typical holometabola. We analyzed expression patterns of homeobox genes of engrailed (en) and Distal-less (Dll) during development. In early embryos, an is expressed in the posterior compartments of body segments and developing appendages, while Dll is expressed in the distal region corresponding to the telopodite of developing appendages. Interestingly, these expression patterns are very similar to those observed in Drosophila imaginal discs. In the case of Dll, we found that its expression pattern, which is similar to each other in various appendages at early stages, changes in progress with elongation and segmentation, depending on the type of appendages. Late expression patterns of Dll are classified into three types: Dll expression in the entire region of the antenna, in a distal region of the cercus, and in distal and middle regions of the leg, maxillary and labial palpus, indicating that Dll expression patterns are closely related to segmentation patterns of the appendages. Furthermore, since Dll is intensely expressed in both sides of the femur-tibia articulation of the leg, we considered that Dll is involved in positioning of articulation during the late appendage development. Hence, our results indicated that although common molecules are involved in development of insect appendages, the variety of the morphologies depends on pattern and timing of their expressions.