In the aquaculture industry, selective breeding has played an important role in increasing aquaculture production significantly. To meet the global growing demand for high quality proteins, it is essential to apply novel technologies to accelerate breeding to facilitate the increase in aquaculture production. Gene and genome editing technologies, including ZFNs, TALLENS and Crispr/Cas9, are promising tools to speed up genetic improvement. Among all the genome editing approaches, the CRISPR/Cas9 system is faster, cheaper and precise in editing genes/genomes. Therefore, the application of CRISPR/Cas9 technology in the editing of genomes in aquaculture species is emerging rapidly. It has been applied to precisely edit genes to identify gene functions and generate the preferred traits in over 20 aquaculture species. This review summarises the genome editing technologies and their applications in the rapid improvement of economic traits in the aquaculture industry. Challenges and future directions of genome editing are also discussed.
Background Fishes are the one of the most diverse groups of animals with respect to their modes of sex determination, providing unique models for uncovering the evolutionary and molecular mechanisms underlying sex determination and reversal. Here, we have investigated how sex is determined in a species of both commercial and ecological importance, the Siamese fighting fish Betta splendens. Results We conducted association mapping on four commercial and two wild populations of B. splendens. In three of the four commercial populations, the master sex determining (MSD) locus was found to be located in a region of ~ 80 kb on LG2 which harbours five protein coding genes, including dmrt1, a gene involved in male sex determination in different animal taxa. In these fish, dmrt1 shows a male-biased gonadal expression from undifferentiated stages to adult organs and the knockout of this gene resulted in ovarian development in XY genotypes. Genome sequencing of XX and YY genotypes identified a transposon, drbx1, inserted into the fourth intron of the X-linked dmrt1 allele. Methylation assays revealed that epigenetic changes induced by drbx1 spread out to the promoter region of dmrt1. In addition, drbx1 being inserted between two closely linked cis-regulatory elements reduced their enhancer activities. Thus, epigenetic changes, induced by drbx1, contribute to the reduced expression of the X-linked dmrt1 allele, leading to female development. This represents a previously undescribed solution in animals relying on dmrt1 function for sex determination. Differentiation between the X and Y chromosomes is limited to a small region of ~ 200 kb surrounding the MSD gene. Recombination suppression spread slightly out of the SD locus. However, this mechanism was not found in the fourth commercial stock we studied, or in the two wild populations analysed, suggesting that it originated recently during domestication. Conclusions Taken together, our data provide novel insights into the role of epigenetic regulation of dmrt1 in sex determination and turnover of SD systems and suggest that fighting fish are a suitable model to study the initial stages of sex chromosome evolution.
Genomic resources, including nuclear DNA markers, mitochondrial DNA markers, highresolution linkage maps, transcriptomes, reference genome sequences and their annotations, are critically important in aquaculture. Their potential applications are plenty, such as enabling the analysis of genetic diversity in population structures, mating and spawning behaviour; genetic traceability; reconstructing pedigrees; mapping quantitative trait loci (QTL) for important phenotypic traits; marker-assisted selection and genomic selection; and to understand genetic and epigenetic regulation of traits. Asian seabass (Lates calcarifer) is becoming a popular aquaculture species. In the past 30 years, many genomic resources have been developed and used to understand the genetic diversity of wild and cultured populations, setting up mating schemes, genetic traceability, mapping QTL and genome-wide association studies for growth, omega-3 fatty acid content, resistance to diseases and genetic improvement of important traits in breeding programmes. In this review, we systematically synthesize the status of available genomic resources and their applications in enhancing the genetic improvement and aquaculture production of Asian seabass. We also critically discuss the challenges and future research directions of developing, optimizing and applying genomic resources in Asian seabass aquaculture.
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