Evolution of Novel Ontogenies

Indiana University, Bloomington IN

Investigators

Abstract

0234576 Raff The goal of this project is to understand the mechanisms by which development evolves, and how developmental processes influence or constrain the direction of evolution. Two related species of sea urchins with highly different modes of early development are being used in this study. Heliocidaris tuberculata develops in the ancestral indirect mode via a feeding larva, whereas H. erythrogramma develops directly from embryo to juvenile adult. Eggs of H. erythrogramma fertilized by H. tuberculata sperm develop via a novel pathway in which a number of the primitive pluteus features are restored by the action of dominant factors derived from the paternal genome. Dr. Raff has exploited the restoration of pluteus-like gene expression in a restored pluteus tissue, oral ectoderm, to identify candidate regulatory genes involved in evolution of developmental mode. A hypothesis for evolutionary change in larval form of H. erythrogramma will be tested, and genes underlying evolution of both larval and maternal features will be studied through functional assays. The specific aims are (1) Determine the functional roles of regulatory genes in indirect, direct, and hybrid embryos. Gain of function studies will be done with presumptive dominant regulatory genes selected for known roles in organization of indirect-developers. These will be expressed in H. erythrogramma embryos as injected mRNAs to determine which larval features are restored by transcription factor mRNAs. (2) Determine the functional roles of genes affecting primary larval axes and their evolution. Functions of candidate genes will be studied by misexpression of mRNAs that include those encoding signal system components, transcription factors, and knockout/knockdown constructs for these components. (3) Use cross-species hybrids to investigate cell lineage transformations and novel gene expression patterns. He will use cell lineage tracing in hybrids to define which blastomeres shift fate to become oral ectoderm, as well as other cell lineage changes. Meeting NSF Review Criteria: (1) Intellectual merit of the proposed activity: The project will advance knowledge by determining how the function of developmental regulatory genes influences the evolution of development. The project will contribute to a new discipline in biology. The project makes use of unique organisms and resources in Australia, and includes long-term collaborations with Australian scientists. (2) Broader impacts of the proposed activity: The main societal impact is to help create a more integrated view of biological evolution. This is important in teaching evolution in a realistic way in biology classes at secondary and college levels. In addition, the work itself has been cited in college text books, (Freeman and Herron, Evolutionary Analysis, Prentice Hall, 2001; Wilt and Hake, Principles of Developmental Biology, Norton, 2001, and Gilbert, Developmental Biology, Sinauer, 2000), and the popular press (Washington Post, October, 2000, and National Geographic, May 2000), which helps create a greater public understanding of research in biology.