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Title: Efficient CRISPR/Cas9 gene editing in a tilapia cell line model using endogenous promoters
Cell cultures are effective supplemental models to study specific biochemical pathways used for environmental adaption in animals. They enable isolation from system influence and facilitate control the extracellular environment. For work focusing on fish species many representative cell lines now exist, including a tilapia brain cell line (OmB) developed in our lab. CRISPR/Cas9 gene editing is an additional tool aiding these studies by allowing manipulation of specific genetic loci and evaluating their causal relationship between phenotypes of interest. However, established CRISPR/Cas9 gene targeting tools and methods often have not functioned as efficiently in fish cells as seen in other animal cell models such as mammalian cell lines, consistent with our initial attempts to apply CRISPR/Cas9 in OmB cells that failed to indicate genomic alteration at the targeted sites. Poor expression of heterologous promoters in OmB cells was hypothesized to be a primary cause for this occurrence so we constructed a custom plasmid vector based system utilizing tilapia endogenous promoters (EF1 alpha to express Cas9 and a U6 to express gRNAs). This system demonstrated substantial editing of most target sites attempted with mutational efficiency as high 80%. This work specifically highlighted the importance of phylogenetic proximity in selection of a polymerase more » III promoter for gRNA expression as commonly used interspecies U6 promoters (human and zebrafish) yielded no detectable gene editing when applied in this system with a common gRNA target sequence. These new tools will allow generation of knockout cell lines for gene targeting studies in tilapia and other phylogenetically close fish species. « less
Authors:
;
Award ID(s):
1656371
Publication Date:
NSF-PAR ID:
10227858
Journal Name:
SICB Virtual Annual Meeting 2021
Volume:
P29
Issue:
7
Page Range or eLocation-ID:
1
Sponsoring Org:
National Science Foundation
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  1. Abstract

    CRISPR/Cas9 gene editing is effective in manipulating genetic loci in mammalian cell cultures and whole fish but efficient platforms applicable to fish cell lines are currently limited. Our initial attempts to employ this technology in fish cell lines using heterologous promoters or a ribonucleoprotein approach failed to indicate genomic alteration at targeted sites in a tilapia brain cell line (OmB). For potential use in a DNA vector approach, endogenous tilapia beta Actin (OmBAct), EF1 alpha (OmEF1a), and U6 (TU6) promoters were isolated. The strongest candidate promoter determined by EGFP reporter assay, OmEF1a, was used to drive constitutive Cas9 expression in a modified OmB cell line (Cas9-OmB1). Cas9-OmB1 cell transfection with vectors expressing gRNAs driven by the TU6 promoter achieved mutational efficiencies as high as 81% following hygromycin selection. Mutations were not detected using human and zebrafish U6 promoters demonstrating the phylogenetic proximity of U6 promoters as critical when used for gRNA expression. Sequence alteration to TU6 improved mutation rate and cloning efficiency. In conclusion, we report new tools for ectopic expression and a highly efficient, economical system for manipulation of genomic loci and evaluation of their causal relationship with adaptive cellular phenotypes by CRISPR/Cas9 gene editing in fish cells.

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