Finding the Genes That Matter: Profiling Gene Expression in Strongylocentrotid Sea Urchins with Different Biogeographic and Temperature Distributions

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The goal of this project is: (1) to test the hypothesis that temperature contributes to setting species distribution patterns in marine ecosystems and (2) to employ genomic approaches and other molecular techniques to assess changes in gene expression in congeneric sea urchins that are adapted to different temperatures and have different biogeographical distributions in nature. The project will use four congeneric species of temperate sea urchin (genus Strongylocentrotus) as study organisms: S. purpuratus, S. droebachiensis, S. franciscanus, and S. pallidus. These marine invertebrates are ideal study organisms for this study because (1) the congeners are closely-related yet have different ecological temperature ranges that facilitate comparative studies, (2) it is possible to work on early life history stages as well adults with relative ease and the embryos have intraspecific differences in response to temperature, and (3) there are significant, readily-available molecular resources for the purple sea urchin, S. purpuratus, as a result of the Sea Urchin Genome Project. Gene expression profiles will be assessed in order to address how the differentially thermally adapted sea urchin species respond to ecologically relevant temperatures at the genomic level. The strategy for the genomics approach entails using DNA macroarrays to screen for differentially expressed genes that will then be analyzed using other genomics techniques -- DNA microarrays and real time PCR. The objectives of the research component are focused around the following three questions: Question 1: Are early life history stages of strongylocentrotid sea urchins differentially sensitive to temperature with respect to patterns gene expression and thermotolerance? This aspect of the project will test whether embryos of the sea urchin congener are differentially sensitive to temperature. Embryos will be raised using standard procedures and thermotolerance of different stages will be assessed in thermal trials. Different embryo stages for each species will be exposed to a range of temperatures and then sampled in order to profile temperature-dependent gene expression in the embryos. Gene expression patterns in larval stage sea urchins will be assessed using the genomics strategy where macroarrays are used to screen for gene expression patterns. Question 2: Do adults display differential responses to temperature as detected at the genomic scale? Adult specimens from each species will be acclimated to the same temperatures and molecular techniques will be used to assess differential gene expression patterns. Congeneric adults will be acclimated in aquaria at 5 and 15 C for 4 weeks. Samples (dissected tube feet) will be analyzed for expression pattern variations in the acclimated sea urchins immediately following acclimation and in the 2 h heat challenge samples. cDNA macroarray, followed by DNA microarray experiments on targeted genes, will be used to compare the expression in the sea urchins. Question 3: How do temperature-dependent patterns of gene expression vary on a latitudinal scale in two Strongylocentrotus congeners with distinctly different distributions in nature? The hypothesis that differential gene expression will be tested, i.e. variable transcript abundance and species, correlates with the different distributions of the sea urchin congeners. Specimens will be collected at different points in the biogeographic range and the transcript profile, as measured using DNA microarrays, will be assessed and correlated to thermal range of the species. Broader Impacts & Education: The ultimate contribution of this study is to bring techniques of functional genomics to bear on questions in marine systems. The results will provide insight into how marine organisms function in the marine environment, and how they respond to variation in their physical environment. Regarding education and training, in addition to the standard training of undergraduates and graduate students in biological research, the PI will collaborate with Oceans Alive!, an on-going educational outreach program at UCSB's Marine Science Institute and the Research Experience and Education Facility (REEF). REEF is a learning lab committed to formal and informal educational activities for K-12 students and the public. The PI.s lab will work with the REEF manager and the MSI educational director to develop interpretive displays of local intertidal organisms and educational and training materials for REEF docents.