Abstract
BackgroundUnderstanding how genes change during evolution to direct the development of diverse body plans is a major goal of the evo-devo field. Achieving this will require the establishment of new model systems that represent key points in phylogeny. These new model systems must be amenable to laboratory culture, and molecular and functional approaches should be feasible. To date, studies of insects have been best represented by the model system Drosophila melanogaster. Given the enormous diversity represented by insect taxa, comparative studies within this clade will provide a wealth of information about the evolutionary potential and trajectories of alternative developmental strategies.ResultsHere we established the beetle Dermestes maculatus, a member of the speciose clade Coleoptera, as a new insect model system. We have maintained a continuously breeding culture in the lab and documented Dermestes maculatus embryogenesis using nuclear and phalloidin staining. Anterior segments are specified during the blastoderm stage before gastrulation, and posterior segments are added sequentially during germ band elongation. We isolated and studied the expression and function of the pair-rule segmentation gene paired in Dermestes maculatus. In this species, paired is expressed in stripes during both blastoderm and germ band stages: four primary stripes arise prior to gastrulation, confirming an intermediate-germ mode of development for this species. As in other insects, these primary stripes then split into secondary stripes. To study gene function, we established both embryonic and parental RNAi. Knockdown of Dmac-paired with either method resulted in pair-rule-like segmentation defects, including loss of Engrailed expression in alternate stripes.ConclusionsThese studies establish basic approaches necessary to use Dermestes maculatus as a model system. Methods are now available for use of this intermediate-germ insect for future studies of the evolution of regulatory networks controlling insect segmentation, as well as of other processes in development and homeostasis. Consistent with the role of paired in long-germ Drosophila and shorter-germ Tribolium, paired functions as a pair-rule segmentation gene in Dermestes maculatus. Thus, paired retains pair-rule function in insects with different modes of segment addition.Electronic supplementary materialThe online version of this article (doi:10.1186/s13227-015-0028-0) contains supplementary material, which is available to authorized users.
Highlights
Understanding how genes change during evolution to direct the development of diverse body plans is a major goal of the evo-devo field
Embryogenesis in D. maculatus Since little was known about the early stages of D. maculatus embryonic development, we tracked nuclear and cytoskeletal dynamics using SYTOX Green, DAPI and phalloidin staining (Fig. 1)
In D. maculatus, we were able to capture embryos in which dividing cells with two nuclei still sharing cytoplasm were visible at the cellular blastoderm surface, while cells that had finished cytokinesis each exhibited one nucleus enclosed by its own, individual membrane (Fig. 1i)
Summary
Understanding how genes change during evolution to direct the development of diverse body plans is a major goal of the evo-devo field. Achieving this will require the establishment of new model systems that represent key points in phylogeny. Understanding the basis for the diversity of plant and animal systems on our planet will require studies of the mechanistic basis of body patterning and developmental. The most sophisticated coleopteran model system developed to date is the flour beetle, Tribolium castaneum (T. castaneum; [9,10,11]), providing a frame of reference for the development of additional beetle systems to represent the diversity of this large clade
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