Embryonic expression patterns of the Hox genes of the crayfish Procambarusclarkii (Crustacea, Decapoda)

Higher crustaceans (class Malacostraca) represent the most species-rich and morphologically diverse group of non-insect arthropods. The superorders Eu carida and Peracarida, two large groups that separated over 350 million yea rs ago, encompass most malacostracan diversity. Recently, the Hox genes of the peracarid woodlouse Porcellio scaber (Isopoda) were shown to be express ed in domains that coincide with morphological boundaries of body tagmata, which differ from those in insects (Abzhanov and Kaufman 1999a,b). Moreover , observed changes in Hox expression domains during ontogeny correlate with morphological remodeling, such as a transformation of the first thoracic l eg into mouthpart maxillipeds, which occurs in the trunk of the embryo. Dec apods have a different modification of the malacostracan bodyplan, with up to three pairs of maxillipeds and extensive fusion and cephalization of the thorax. Here we describe expression patterns of the trunk Hox genes Scr, A ntp, Ubx, abd-A and cad in the eucarid crayfish Procambarus clarkii(Decapod a). We find that the crayfish expression patterns, for the most part, resem ble those of the woodlouse Porcellio scaber(Isopoda), but are more modulate d and complex. Nevertheless, as in Porcellio the boundaries of the Hox expr ession domains do correlate with morphological features and their modulatio ns to transformations in the embryo. Thus we propose that the trunk Hox gen es were likely important in the evolution of and currently play an essentia l role in the development of the complex decapod bodyplan.