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UBC Theses and Dissertations

3D genomic insights of an early branching metazoan : a chromosome scale assembly of Mnemiopsis leidyi and differential expression in early development Barclay, Charlotte


The transition to multicellularity is widely considered a crucial evolutionary process, yet the precise mechanisms are still being uncovered. Advancements in bioinformatic techniques and high-throughput DNA sequencing provide increasing opportunities to better understand complex phenomena like multicellularity, through the study of early branching model organisms. However, to fully leverage the available tools, high quality reference genomes are required. As a result an increasing number of studies combine long read and HiC sequence data to generate a high quality, chromosome scale assembly with high contiguity. This study utilises PacBio's novel long and accurate HiFi reads, in conjunction with Hi-C sequencing technology, to produce a chromosome-scale assembly for the ctenophore Mnemiopsis leidyi. The final assembly demonstrates remarkable contiguity, with an N50 value of 15.6MB and a computationally derived karyotype of n=13. These findings demonstrate an improvement of greater than two orders of magnitude when compared to the previous short read assembly for this species. Further structural genomic organisation was identified, using Arrowhead as part of the Juicer pipeline, to provide the first evidence of topologically associating domains (TADs) and loops in this organism. These findings highlight the importance of utilizing advanced sequencing technologies to improve existing assemblies in our understanding of genomic organisation and structure, and the considerations that should be taken when comparing results derived from different bioinformatic tools. Mnemiopsis leidyi is phylogenetically well placed to answer evolutionary questions surrounding the origins of multicellularity and the addition of a high-quality reference assembly will prove imperative to future molecular and genomics research.

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