Genome editing and broodstock technologies offer significant potential to accelerate genetic improvement in aquaculture species. However, several challenges persist, including low germline transmission rates of desired edits, limited multiplication rates of donor-to-recipients for certain gene modifications, and the extended waiting periods required for donor fish to grow when gonial cells are used as donor. Among germ cell types, gonial cells like spermatogonia or oogonia are commonly used as donors due to their relative abundance and plasticity which allow them to develop into either sperm or eggs depending on the phenotypic sex of the recipient gonads. While primordial germ cells (PGCs) represent an alternative donor cell type, their use is constrained by the limited quantity available per fish. Unlike in mammals, PGC specification in fish is directed by maternally deposited germ plasm, comprising mRNAs such as vasa, dnd1, nanos3, piwi-like, bucky ball, daz-like, tdrd.
Recent advancements by Wang et al (2023) demonstrated that PGC can be induced by injecting germ plasm mRNA cocktails into zebrafish zygotes. These induced PGCs (iPGCs) successfully migrated to the gonadal anlagen of recipients and matured into functional gametes. Building on this foundation, we aimed to validate and optimize this technique in Nile tilapia. We tested various combinations of germ plasm cocktail to induce PGCs and evaluated their colonization rates. In addition, we investigated the timing of PGC induction and harvesting, genome editing and genotyping of iPGCs, and their transplantation efficiencies.
iPGC technology offers numerous advantages, including the ability to achieve 100% germline editing albeit still mosaic, elimination of the need to grow donor fish, easier harvesting and transplantation into recipients, and increased multiplication rates for edits impacting gonial cell quantity. These advancements hold promise for accelerating the commercial application of genome editing and broodstock technologies in aquaculture, facilitating more efficient and precise genetic improvements.