Marker counter-selection via CRISPR/Cas9 co-targeting for efficient generation of genome edited avian cell lines and germ cells

Enrichment strategies to enhance genome editing

Genome editing technologies hold great promise for numerous applications including the understanding of cellular and disease mechanisms and the development of gene and cellular therapies. Achieving high editing frequencies is critical to these research areas and to achieve the overall goal of being able to manipulate any target with any desired genetic outcome. However, gene editing technologies sometimes suffer from low editing efficiencies due to several challenges. This is often the case for emerging gene editing technologies, which require assistance for translation into broader applications. Enrichment strategies can support this goal by selecting gene edited cells from non-edited cells. In this review, we elucidate the different enrichment strategies, their many applications in non-clinical and clinical settings, and the remaining need for novel strategies to further improve genome research and gene and cellular therapy studies.

Harnessing Intronic microRNA Structures to Improve Tolerance and Expression of shRNAs in Animal Cells

Exogenous RNA polymerase III (pol III) promoters are commonly used to express short hairpin RNA (shRNA). Previous studies have indicated that expression of shRNAs using standard pol III promoters can cause toxicity in vivo due to saturation of the native miRNA pathway. A potential way of mitigating shRNA-associated toxicity is by utilising native miRNA processing enzymes to attain tolerable shRNA expression levels. Here, we examined parallel processing of exogenous shRNAs by harnessing the natural miRNA processing enzymes and positioning a shRNA adjacent to microRNA107 (miR107), located in the intron 5 of the Pantothenate Kinase 1 (PANK1) gene. We developed a vector encoding the PANK1 intron containing miR107 and examined the expression of a single shRNA or multiple shRNAs. Using qRT-PCR analysis and luciferase assay-based knockdown assay, we confirmed that miR30-structured shRNAs have resulted in the highest expression and subsequent transcript knockdown. Next, we injected Hamburger and Hamilton stage 14–15 chicken embryos with a vector encoding multiple shRNAs and confirmed that the parallel processing was not toxic. Taken together, this data provides a novel strategy to harness the native miRNA processing pathways for shRNA expression. This enables new opportunities for RNAi based applications in animal species such as chickens.