%0 Journal Article %A Simon Blanchoud %A Kim Rutherford %A Lisa Zondag %A Neil Gemmell %A Megan J Wilson %T De novo draft assembly of the Botrylloides leachii genome provides further insight into tunicate evolution %D 2017 %R 10.1101/152983 %J bioRxiv %P 152983 %X Tunicates are marine invertebrates that compose the closest phylogenetic group to the vertebrates. This chordate subphylum contains a particularly diverse range of reproductive methods, regenerative abilities and life-history strategies. Consequently, tunicates provide an extraordinary perspective into the emergence and diversity of chordate traits. Currently published tunicate genomes include three Phlebobranchiae, one Thaliacean, one Larvacean and one Stolidobranchian. To gain further insights into the evolution of the tunicate phylum, we have sequenced the genome of the colonial Stolidobranchian Botrylloides leachii.We have produced a high-quality (90% BUSCO genes) 159 Mb assembly, containing 82 % of the predicted 194 Mb. The B. leachii genome is much smaller than that of Botryllus schlosseri (725 Mb), but comparable to those of C. intestinalis and M. oculata (both 160 Mb). This difference is largely due to an increase in repetitive DNA content in B. schlosseri. By analyzing the structure and composition of the conserved homeobox gene clusters, we identified many examples of multiple cluster breaks and gene dispersion, suggesting that several lineage-specific genome rearrangements occurred during tunicate evolution.In addition, we investigate molecular pathways commonly associated with regeneration and development. We found lineage-specific gene gain and loss within the Wnt, Notch and retinoic acid pathways. Such examples of genetic changes to key evolutionary conserved pathways may underlie some of the diverse regenerative abilities observed in the tunicate subphylum. These results, combined with the relatively recent separation from their last common ancestor (630 MYA), supports the widely held view that tunicate genomes are evolving particularly rapidly. %U https://www.biorxiv.org/content/biorxiv/early/2017/06/21/152983.full.pdf