Genetic and Genomic tools for C. briggsae research: Project Summary Research using the microscopic nematode Caenorhabditis elegans has produced many foundational discoveries in the genetic basis of cell death, organismal aging, the biological roles for microRNAs, as well as other fundamental topics that are relevant to human health. An important complement to studies on C. elegans is those on the related nematode Caenorhabditis briggsae, which shares many of the experimental strengths of C. elegans, but from which it diverged approximately 30 million years ago. C. briggsae provides a platform for comparative genetic studies, leading to efficient analysis of conserved processes, as well as discoveries on the evolution of genes, pathways and networks. These comparative studies are important in establishing research rigor and validating findings. In addition, differences between C. elegans and C. briggsae in terms of life history traits and global distribution of populations means that many studies addressing population biology questions, polygenic traits, or host-pathogen, commensal, and opportunistic relationships with viruses, bacteria, and insects are better done with C. briggsae than with C. elegans. Despite these important features, many genetic resources that are essential for standard C. elegans research are not available for studies using C. briggsae. With the increasing efficiency of genetic editing and engineering using CRISPR-mediated methods, the availability of important genomic and genetic tools is a key limitation for these important comparative studies. This project will produce these research resources to address this gap. As a first aim, two telomere-to- telomere C. briggsae reference genomes with validated gene models will be produced, using sets of complementary long and short sequence read methods and validation techniques. These data will be incorporated into NCBI and Wormbase, the online database used by researchers who use C. elegans and related nematodes. A second aim will produce and validate a set of genetic balancers, or rearranged chromosomes that prevent meiotic crossing over. These genetic tools are critical for the maintenance and evaluation of mutations that are homozygous lethal or sterile and that are currently maintained through laborious processes. Genetic balancers will also permit more complex genetic experiments not currently feasible in C. briggsae. Finally, strains with "safe harbor" landing sites for the introduction of DNA into defined locations in the C. briggsae genome will be produced and validated. These strains will permit controlled, reproducible introduction of single copy insertion clones into C. briggsae, and permit a range of experimental manipulation including gene "node swaps" between the two species, and the testing of reagents developed for C. elegans directly in C. briggsae. Together, these aims will produce key tools that remove important barriers to genetic analysis in this research organ...