Generating a New sgRNA Vector, pGL3-U6-sgRNA-PGK-mRFP-T2A-PuroR, to Improve Base Editing

CRSPR/Cas9-mediated base editing introduces point mutations in cellular DNA by exploiting target-specific single guide RNA (sgRNA) along with a genetically modified Cas9. Existing plasmid vectors for sgRNA expression in base editing contain either a fluorescent marker or an antibiotic resistance cassette but not both, preventing simultaneous monitoring and enrichment of transfected host cells. In this study, we introduced a fluorescent marker into pGL3-U6-sgRNA-PGK-puromycin, a popular sgRNA expression vector available at Addgene. Specifically, the cDNAs of mRFP and a T2A linker were inserted in between the hPGK promoter and the puromycin resistance gene (PuroR). After correct insertion was verified by DNA sequencing, this new plasmid, pGL3-U6-sgRNA-PGK-mRFP-T2A-PuroR, was utilized to generate a stop codon in the second exon of the Munc13-1 gene in RBL-2H3 cells. Both the mRFP fluorescent marker and the puromycin resistance marker functioned accordingly in the process. This new sgRNA vector therefore represents a useful addition to the CRISPR tool kit.

The establishment of a novel high-throughput screening system using RNA-guided genome editing to identify chemicals that suppress aldosterone synthase expression

Aldosterone is synthesized in the adrenal by the aldosterone synthase CYP11B2. Although the control of CYP11B2 expression is important to maintain the mineral homeostasis, its overexpression induced by the depolarization-induced calcium (Ca2+) signaling activation has been reported to increase the synthesis of aldosterone in primary aldosteronism (PA). The drug against PA focused on the suppression of CYP11B2 expression has not yet been developed, since the molecular mechanism of CYP11B2 transcriptional regulation activated via Ca2+ signaling remains unclear. To address the issue, we attempted to reveal the mechanism of the transcriptional regulation of CYP11B2 using chemical screening. We generated a cell line by inserting Nanoluc gene as a reporter into CYP11B2 locus in H295R adrenocortical cells using the CRSPR/Cas9 system, and established the high-throughput screening system using the cell line. We then identified 9 compounds that inhibited the CYP11B2 expression induced by potassium-mediated depolarization from the validated compound library (3399 compounds). Particularly, tacrolimus, an inhibitor of phosphatase calcineurin, strongly suppressed the CYP11B2 expression even at 10 nM. These results suggest that the system is effective in identifying drugs that suppress the depolarization-induced CYP11B2 expression. Our screening system may therefore be a useful tool for the development of novel medicines against PA.

Generation and validation of recombinant herpes simplex type 1 viruses (HSV-1) using CRISPR/Cas9 genetic disruption

Herpes simplex virus type 1 (HSV-1) is a large DNA virus that has been popular for oncolytic virus development in pre-clinical research and clinical trials. An oncolytic HSV-1 encoding granulocyte-macrophage colony stimulating factor (GM-CSF), designated talimogene laherparepvec (T-VEC) was approved for the treatment of patients with advanced melanoma in 2015. There are numerous advantages of HSV-1 for oncolytic development, including the ease of recombinant engineering, presence of non-essential genes allowing attenuation of pathogenicity and space for foreign transgene expression. In addition, most recombinants retain sensitivity to acyclovir providing an additional safety feature. In this chapter, we will focus on the key methods for the development of oncolytic HSV-1 vectors and some of the commonly utilized laboratory protocols used to characterize and assess the structure and oncolytic activity of recombinant HSV-1 viruses.