A chromosome-level genome assembly for the bowfin, a ray-finned fish with ancestral and derived phenotypes, is presented in this week's Nature Genetics, giving new insights into vertebrate biology and diversity. Because of its phylogenetic position as a representative of neopterygian fishes, its archetypical body plan, and its unduplicated and slowly evolving genome, the bowfin is a central species for the genomic exploration of ray-finned fishes. In the study, a team led by scientists from Michigan State University generated and analyzed their genome assembly to study chromatin accessibility and gene expression through bowfin development to investigate the evolution of immune, scale, respiratory, and fin skeletal systems. Among the findings are hundreds of gene-regulatory loci conserved across vertebrates. "The inclusion of the bowfin genomic landscape permits translation of genetic and genomic changes underlying vertebrate evolution and its regulation," the researchers write.
While CRISPR-Cas13 systems are being used for programmable RNA editing and other research applications, delivering Cas13-based RNA editing systems for therapeutic applications is a challenge, in part because the size of existing Cas13-based RNA editors exceeds adeno-associated virus-based delivery vectors. To address this, scientists from Harvard University performed a scan of Cas13 enzymes in prokaryotic and viral genomes and metagenomes. Among the thousands of candidate systems they identified, the researchers discovered one family of ultrasmall Casb13b proteins — dubbed Cas13bt — capable of mediating mammalian transcript knockdown. As reported in Nature Biotechnology, the team functionalized Cas13bt with adenosine and cytosine deaminase domains into compact RNA editors, which they could package into a single adeno-associated virus. "The small size of Cas13bt proteins provides new opportunities for programmable RNA modulation, particularly in vivo," they write.