Direct and pleiotropic effects of the Masou Salmon Delta-5 Desaturase transgene in F1 channel catfish (Ictalurus punctatus)

CRISPR/Cas9-mediated knock-in of masu salmon (Oncorhyncus masou) elongase gene in the melanocortin-4 (mc4r) coding region of channel catfish (Ictalurus punctatus) genome

Channel catfish, Ictalurus punctatus, have limited ability to synthesize Ω-3 fatty acids. The ccβA-msElovl2 transgene containing masu salmon, Oncorhynchus masou, elongase gene driven by the common carp, Cyprinus carpio, β-actin promoter was inserted into the channel catfish melanocortin-4 receptor (mc4r) gene site using the two-hit two-oligo with plasmid (2H2OP) method. The best performing sgRNA resulted in a knockout mutation rate of 92%, a knock-in rate of 54% and a simultaneous knockout/knock-in rate of 49%. Fish containing both the ccβA-msElovl2 transgene knock-in and mc4r knockout (Elovl2) were 41.8% larger than controls at 6 months post-hatch (p = 0.005). Mean eicosapentaenoic acid (EPA, C20:5n-3) levels in Elov2 mutants and mc4r knockout mutants (MC4R) were 121.6% and 94.1% higher than in controls, respectively (p = 0.045; p = 0.025). Observed mean docosahexaenoic acid (DHA, C22:6n-3) and total EPA + DHA content was 32.8% and 45.1% higher, respectively, in Elovl2 transgenic channel catfish than controls (p = 0.368; p = 0.025). To our knowledge this is the first example of genome engineering to simultaneously target transgenesis and knock-out a gene in a commercially important aquaculture species for multiple improved performance traits. With a high transgene integration rate, improved growth, and higher omega-3 fatty acid content, the use of Elovl2 transgenic channel catfish appears beneficial for application on commercial farms.

CRISPR-Based Transcriptional Activation in Drosophila

Overexpression is one of the classical approaches to study pleiotropic functions of genes of interest. To achieve overexpression, we often increase the transcription by introducing genes on exogenous vectors or by using the CRISPR/dCas9-based transcriptional activation system. To date, the most efficient CRISPR/dCas9-based transcriptional activator is the Synergistic Activation Mediator (SAM) system whereby three different transcriptional activation domains are directly fused to dCas9 and MS2 phage Coat Protein (MCP), respectively, and the system in Drosophila is named flySAM. Here we describe the effective and convenient transcriptional activation system, flySAM, starting from vector construction, microinjection, and transgenic fly selection to the phenotypic analysis.