Chromosomal-Level Genome Assembly of the Painted Sea Urchin Lytechinus pictus: A Genetically Enabled Model System for Cell Biology and Embryonic Development.

The painted urchin Lytechinus pictus is a sea urchin in the family Toxopneustidae and one of several sea urchin species that are routinely used as an experimental research organism. Recently, L. pictus has emerged as a tractable model system for establishing transgenic sea urchin lines due to its amenability to long term laboratory culture. We present the first published genome of L. pictus. This chromosomal-level assembly was generated using Illumina sequencing in conjunction with Oxford Nanopore Technologies long read sequencing and HiC chromatin conformation capture sequencing. The 998.9-Mb assembly exhibits high contiguity and has a scaffold length N50 of 46.0 Mb with 97% of the sequence assembled into 19 chromosomal-length scaffolds. These 19 scaffolds exhibit a high degree of synteny compared with the 19 chromosomes of a related species Lytechinus variegatus. Ab initio and transcript evidence gene modeling, combined with sequence homology, identified 28,631 gene models that capture 92% of BUSCO orthologs. This annotation strategy was validated by manual curation of gene models for the ABC transporter superfamily, which confirmed the completeness and accuracy of the annotations. Thus, this genome assembly, in conjunction with recent high contiguity assemblies of related species, positions L. pictus as an exceptional model system for comparative functional genomics and it will be a key resource for the developmental, toxicological, and ecological biology scientific communities.