* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download EVOLUTIONARY DEVELOPMENT AND THE INSECT BODY PLAN
Gene desert wikipedia , lookup
Long non-coding RNA wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Genome evolution wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Genomic imprinting wikipedia , lookup
Ridge (biology) wikipedia , lookup
Minimal genome wikipedia , lookup
Microevolution wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Genome (book) wikipedia , lookup
Gene expression programming wikipedia , lookup
Designer baby wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Gene expression profiling wikipedia , lookup
EVOLUTIONARY DEVELOPMENT AND THE INSECT BODY PLAN Sean Beplate Bio 348 2/5/10 The Study of “Evo‐Devo”…What Is It? • EvoluQonary development (aka phylontogeneQcs) is a product of both evoluQonary and developmental biology. • This field uQlizes phylogenies and ancestral relaQonships to examine the course of evoluQon for developmental processes of interest. (Embryonic development is a common component) • With respect to arthropods, evo‐devo has also drawn from the fields of entomology, carcinology, and geneQcs What is THE GOAL of Arthropod Evo‐ Devo? • Arthropods exhibit extreme diversity of both morphology and body plans • The evo‐devo approach aaempts to provide a framework for the development of this diversity, looking at both molecular and morphological evidence The Concept of a Body Plan • Richard Owen originally described “body plan” as “a paaern of anatomical organizaQon shared by a group of animals.” • The term “bauplan” was coined by Joseph Henry Woodger to describe “a collecQon of homologous anatomical features seen across the natural history of a group.” • Currently, “body plan” has expanded to include both of these. WHAT ARE THE FEATURES OF THE ARTHROPOD BODY PLAN? Arthropod Body Plan • Protostomes with segmented bodies • Appendages are also segmented; each segment has its own muscular structure and individual innervaQon • Have a cuQcle that is shed during growth • Exhibit tagmosis, providing the capability for specialized behaviors • Insects exhibit the most consistent tagmaQc paaern: head composed of fused segments, thorax of three segments, and an abdomen of 11/12 segments Hox Genes • Hox genes= homeoQc complex genes • Are transcripQon factors with sequences well conserved throughout most animals • Serve as regulators of segment idenQty within the arthropods. Because of this, they dictate organizaQon of body plan in embryonic ectoderm. • Overlap of these genes code for a different segment than if read separately. • Arthropods have 10 ancestral Hox genes Paaerns of Hox Gene Expression • Looking at the spider, a nested paaern (large amounts of overlap) is present in both the prosoma and opisthosoma. Looking at the Mandibulata (insect and crustacean examples,) there is much less overlap. It is likely that that this facilitates the specialized head appendages – less overlap in crustaceans corresponding to a greater number of feeding appendages. Difference in Chelicerata (prosoma and opisthosoma) body plan and Insecta (head, thorax, and abdomen) body plan. Increased Hox gene overlap likely contributed to the fewer segments seen in the Chelicerata. example of the obvious difference in number of head appendages between insects and crustaceans (Australian bull ant vs. cardinal shrimp) Drosophila melanogaster (DmUbx) and Artemia franciscana (AfUbx) Ubx protein sequence. The uncolored regions demonstrate blocks of differences in sequence MutaQon of Hox Genes and Hexapod Limb Paaern • Averof & Akam postulated that the hexapod body plan resulted from mutaQons restricQng Ubx and AbdA expression to proto‐abdomen region. Secondly, mutaQon of these genes caused their expression to suppress limb development. • Ronshaugen study first looked at Ubx protein sequence in Drosophila melanogaster and Artemia franciscana (a crustacean) Results of the Ronshaugen Study • Ubx from Artemia and Drosophila both demonstrated similar suppression of the development of head structures in the thorax of embryonic Drosophila • Big difference: Drosophila Ubx suppressed all embryonic limb development on thorax, while Artemia Ubx only suppressed 15% • Proposal: Hexapod body plan resulted from mutaQons located at C‐terminal residues. DISCUSSION TIME! • The Ronshaugen paper suggested that the removal of Ser/Thr residues produced novel phenotypes. How might such a development have been evoluQonarily propagated? (keep in mind the phylogenies presented in these readings) • Amer reading these papers, can you think of any reasons that six would have been an advantageous number of limbs for early insects to possess? Hox Gene Expression and Insect‐ Specific Development Hox Gene Expression and Insect‐ Specific Development • Because insects are unique in their ability to fly, wing evoluQon is currently being studied extensively • Two main hypotheses: – 1) Wings developed as dorsolateral outgrowths before arQculaQon and muscle connecQon. – 2)Wings developed from dorsal projecQons proximally located on legs and appendages of early insects. Which Hypothesis is More Accurate? • Averof & Cohen study tested this, using the proteins derived from the genes Pdm and Ap • Pdm and Ap proteins were detected in distal epipods in Artemia franciscana (a branchiopod) • Pdm protein was also detected in the epipod of Pacifastacus lenisculus (a crawfish) Hox Genes and Modern Insect Wings • Early wings were present on all segments of the thorax and abdomen. Juvenile insects also possessed wings. • Since the emergence of wings, they have become reduced in the insect body plan, resulQng from Hox gene induced repression • Scr has been found to suppress wing development in prothorax of Drosophila embryos, and Ubx and Abd‐A suppress in the abdomen DISCUSSION TIME! • Another key feature of the insect body plan is the lack of abdominal limbs in addiQon to the lack of abdominal wings. Arachnids also do not have any limbs on their “abdomen‐like” segment. What kind of Hox gene interacQons and expression paaerns could underlie this? Winglessness of Hymenoptera • Hymenoptera are social insects, meaning that they live in colonies with castes that fulfill different roles. • What makes this interesQng? Ants with wings and acts that lack wings exhibit the same genes! Background – Ant Castes • Queen – Female. Possesses wings. One job– to mate and lay eggs. • Male – Possesses wings. ReproducQve. • Soldiers – Non‐ reproducQve. Protect the nest • Workers– Non‐ reproducQve. Forage, maintain nest, and care for eggs. JH and Ant Development • As larvae, if enough nutriQon is available to an individual, juvenile hormone (jh) accumulates to a level high enough to develop wings during the pupal stage. If not enough jh gets produced, the ant will be non‐reproducQve. • In ants with soldier castes, a second JH checkpoint determines caste. Forewing discs develop in the pupal stage of soldiers, but are programmed to die FINAL DISCUSSION QUESTIONS • How do you think that Hox gene organizaQon could have aaributed to the development of insect heads from fused segments? • If the Ronshaugen study was to be repeated, what organisms/developed structures would it be helpful to include as a comparison? • Synthesizing the informaQon presented in each paper, what developments in insect body plan do you think may have followed the “hopeful monster” method? What do you think followed a more gradual progression?