Potential of small extracellular vesicles as Cas9 delivery tool: A promising approach for gene editing livestock gametes and embryos.

Genome editing is a rapidly advancing technology with transformative potential in livestock, offering opportunities that range from enhanced production traits to the generation of biomedical models for human disease and xenotransplantation. The CRISPR/Cas9 system, originally identified as a bacterial defense mechanism, has become the most widely used tool for precise genome editing. In this review, we first summarize the potential applications of CRISPR/Cas9 in livestock and highlight notable successes to date. We then address the ongoing challenges associated with delivering CRISPR/Cas9 into gametes and embryos, as current methods such as microinjection and electroporation often result in high mosaicism and cellular damage. We subsequently introduce extracellular vesicles (EVs) as a promising alternative delivery system. Secreted by virtually all cell types, EVs can efficiently transport bioactive molecules and are readily internalized by gametes and embryos. Although EV-mediated delivery of CRISPR/Cas9 has shown success in somatic cells, its use in reproductive cells remains largely unexplored. We review emerging strategies for loading EVs with CRISPR/Cas components and discuss the potential advantages of combining this approach with recently developed smaller Cas variants to overcome delivery barriers. Collectively, these innovations support the promise of EVs as a biologically compatible, efficient, and minimally invasive system for targeted genome editing in livestock reproduction.