Editing of DNA methylation using CRISPR/Cas9 and a ssDNA template in human cells

Optimization of the intron sequences combined with the CMV promoter increases recombinant protein expression in CHO cells

To meet the requirements of the biopharmaceutical industry, improving the yield of recombination therapeutic protein (RTP) from Chinese hamster ovary (CHO) cells is necessary. The human cytomegalovirus (CMV) promoter is widely used for RTP expression in CHO cells. To further improve RTP production, we truncated the human CMV intron and further evaluated the effect of four synthetic introns, including ctEF-1α first, EF-1α first, chimeric, and β-globin introns combined with the CMV promoter on recombinant expression levels in transient and stably recombinant CHO cells. The results showed that the truncated, EF-1α first, chimeric, and β-globin introns can significantly improve stable transgene expression in CHO cells. The qPCR results indicated that the mRNA level of transgene increased through optimizing intron sequences combined with the CMV promoter. Transcriptomics analysis was performed and found that differential expression of genes involved in mRNA processing, RNA export from nucleus, cytoplasmic translation, transcriptional activation and cell cycle regulation. In conclusion, optimization of the intron sequences combined with the CMV promoter can achieve a higher yield of recombinant proteins in CHO cells. This will be valuable for generating CHO cell lines with high productivity for industrial applications.

Interlaboratory consistency of SDC2 promoter methylation detection in colorectal cancer using the post-optimized materials

Fecal DNA-based Syndecan 2 (SDC2) methylation detection is a promising non-invasive strategy for early colorectal cancer (CRC) screening. In China, commercial assays for SDC2 methylation detection vary in sensitivity and specificity, yet there is no standardized external quality assessment (EQA) to ensure accuracy. This study utilized CRISPR-Cas9 and homology-directed repair (HDR) technologies to edit the SDC2 promoter in 293T cells, creating hypermethylated and heterogeneous cell lines. These cell lines were used to develop an EQA panel for SDC2 methylation. We established a 10-sample panel, encompassing a range of methylation levels, and conducted an EQA across 140 laboratories. Among 1,400 results, 0.57% were incorrect. The optimized EQA materials effectively monitor the accuracy of SDC2 methylation detection in CRC, supporting reliable and consistent clinical testing and contributing to early CRC screening and diagnosis in China.

Engineering of Zinc Finger Nucleases Through Structural Modeling Improves Genome Editing Efficiency in Cells

Genome Editing is widely used in biomedical research and medicine. Zinc finger nucleases (ZFNs) are smaller in size than transcription activator-like effector (TALE) nucleases (TALENs) and CRISPR-Cas9. Therefore, ZFN-encoding DNAs can be easily packaged into a viral vector with limited cargo space, such as adeno-associated virus (AAV) vectors, for in vivo and clinical applications. ZFNs have great potential for translational research and clinical use. However, constructing functional ZFNs and improving their genome editing efficiency is extremely difficult. Here, the efficient construction of functional ZFNs and the improvement of their genome editing efficiency using AlphaFold, Coot, and Rosetta are described. Plasmids encoding ZFNs consisting of six fingers using publicly available zinc-finger resources are assembled. Two functional ZFNs from the ten ZFNs tested are successfully obtained. Furthermore, the engineering of ZFNs using AlphaFold, Coot, or Rosetta increases the efficiency of genome editing by 5%, demonstrating the effectiveness of engineering ZFNs based on structural modeling.

A more efficient method for generating glioblastoma-multiforme model in mice using genome editing technology

The elucidation of the properties of malignant glioma and development of therapeutic methods require glioblastoma-multiforme mice model with characteristics such as invasiveness, multinuclearity, and ability for mitosis. A previous study has shown that overexpression of active HRas (HRasL61) in neural stem/progenitor cells (NSCs) isolated from p53 knockout (KO) mice could induce glioma-initiating cells (GICs). The orthotopically transplantation of 10 cells into the forebrain of immunodeficient mice resulted in the development of glioblastoma multiforme-like malignant brain tumors. In this study, we successfully induced GICs from wild-type fetal NSCs. Using CRISPR/Cas9, we obtained p53 KO NSCs. HRasL61 was additionally overexpressed in p53 KO NSCs. p53-/HRasL61+ cells were cloned and then transplanted into immunodeficient mice. p53-/HRasL61+ cells formed glioblastoma multiforme-like tumors. Further, GIC markers were strongly expressed in p53-/HRasL61+ cells. Therefore, p53-/HRasL61+ cell is an induced GIC. A CRISPR/Cas9-based method for inducing GIC is much more efficient than a KO mice-based method. This study provides a promising framework for easily creating glioblastoma model in mice.

In search of an ideal template for therapeutic genome editing: A review of current developments for structure optimization

Gene therapy is a fast developing field of medicine with hundreds of ongoing early-stage clinical trials and numerous preclinical studies. Genome editing (GE) now is an increasingly important technology for achieving stable therapeutic effect in gene correction, with hematopoietic cells representing a key target cell population for developing novel treatments for a number of hereditary diseases, infections and cancer. By introducing a double strand break (DSB) in the defined locus of genomic DNA, GE tools allow to knockout the desired gene or to knock-in the therapeutic gene if provided with an appropriate repair template. Currently, the efficiency of methods for GE-mediated knock-in is limited. Significant efforts were focused on improving the parameters and interaction of GE nuclease proteins. However, emerging data suggests that optimal characteristics of repair templates may play an important role in the knock-in mechanisms. While viral vectors with notable example of AAVs as a donor template carrier remain the mainstay in many preclinical trials, non-viral templates, including plasmid and linear dsDNA, long ssDNA templates, single and double-stranded ODNs, represent a promising alternative. Furthermore, tuning of editing conditions for the chosen template as well as its structure, length, sequence optimization, homology arm (HA) modifications may have paramount importance for achieving highly efficient knock-in with favorable safety profile. This review outlines the current developments in optimization of templates for the GE mediated therapeutic gene correction.

DNA Methylation: Genomewide Distribution, Regulatory Mechanism and Therapy Target

DNA methylation is the most important epigenetic modification involved in the regulation of transcription, imprinting, establishment of X-inactivation, and the formation of a chromatin structure. DNA methylation in the genome is often associated with transcriptional repression and the formation of closed heterochromatin. However, the results of genome-wide studies of the DNA methylation pattern and transcriptional activity of genes have nudged us toward reconsidering this paradigm, since the promoters of many genes remain active despite their methylation. The differences in the DNA methylation distribution in normal and pathological conditions allow us to consider methylation as a diagnostic marker or a therapy target. In this regard, the need to investigate the factors affecting DNA methylation and those involved in its interpretation becomes pressing. Recently, a large number of protein factors have been uncovered, whose ability to bind to DNA depends on their methylation. Many of these proteins act not only as transcriptional activators or repressors, but also affect the level of DNA methylation. These factors are considered potential therapeutic targets for the treatment of diseases resulting from either a change in DNA methylation or a change in the interpretation of its methylation level. In addition to protein factors, a secondary DNA structure can also affect its methylation and can be considered as a therapy target. In this review, the latest research into the DNA methylation landscape in the genome has been summarized to discuss why some DNA regions avoid methylation and what factors can affect its level or interpretation and, therefore, can be considered a therapy target.