Project description:The Chinese tapertail anchovy, Coilia nasus, is a socioeconomically important anadromous fish that migrates from near ocean waters to freshwater to spawn every spring. The analysis of genomic architecture and information of C. nasus were hindered by the previously released versions of reference genomes with gaps. Here, we report the assembly of a chromosome-level gap-free genome of C. nasus by incorporating high-coverage and accurate long-read sequence data with multiple assembly strategies. All 24 chromosomes were assembled without gaps, representing the highest completeness and assembly quality. We assembled the genome with a size of 851.67 Mb and used BUSCO to estimate the completeness of the assembly as 92.5%. Using a combination of de novo prediction, protein homology and RNA-seq annotation, 21,900 genes were functionally annotated, representing 99.68% of the total predicted protein-coding genes. The availability of gap-free reference genomes for C. nasus will provide the opportunity for understanding genome structure and function, and will also lay a solid foundation for further management and conservation of this important species.
Project description:Background:SINEs are a type of nonautonomous retrotransposon that can transpose from one site to be integrated elsewhere in an organism genome. SINE insertion can give rise to genetic variants and regulate gene expression, allowing organisms to acquire new adaptive capacity. Studies on this subject have focused on the impacts of SINEs on genes. However, ecological disparities in fish have not yet been explained by SINEs. Results:New SINEs were isolated from Coilia nasus, which has two ecotypes-migratory and resident-that differ in their spawning and migration behaviors. The SINEs possess two structures that resemble a tRNA gene and a LINE retrotransposon tail. Comparison of olfactory tissue transcriptomes, intact SINE transcript copies were detected in only the migratory fish at the initial retrotransposition stage. The SINE DNA copy numbers were higher in the resident type than in the migratory type, while the frequency of SINE insertion was higher in the migratory type than in the resident type. Furthermore, SINE insertions can lead to new repeats of short DNA fragments in the genome, along with target site duplications. SINEs in the resident type have undergone excision via a mechanism in which predicted cleavage sites are formed by mutations, resulting in gaps that are then filled by microsatellites via microhomology-induced replication. Conclusions:Notably, SINEs in the resident type have undergone strong natural selection, causing genomic heteroplasmy and driving ecological diversity of C. nasus. Our results reveal possible evolutionary mechanisms underlying the ecological diversity at the interface between SINE mobilization and organism defense.