Sox2 regulatory region 2 sequence works as a DNA nuclear targeting sequence enhancing the efficiency of an exogenous gene expression in ES cells

CRISPR/Cas9 Deletion of SOX2 Regulatory Region 2 (SRR2) Decreases SOX2 Malignant Activity in Glioblastoma

Simple Summary

Understanding how SOX2, a major driver of cancer stem cells, is regulated in cancer cells is relevant to tackle tumorigenesis. In this study, we deleted the SRR2 regulatory region in glioblastoma cells. Our data confirm that the SRR2 enhancer regulates SOX2 expression in cancer and reveal that SRR2 deletion halts malignant activity of SOX2.

Abstract

SOX2 is a transcription factor associated with stem cell activity in several tissues. In cancer, SOX2 expression is increased in samples from several malignancies, including glioblastoma, and high SOX2 levels are associated with the population of tumor-initiating cells and with poor patient outcome. Therefore, understanding how SOX2 is regulated in cancer cells is relevant to tackle tumorigenesis. The SOX2 regulatory region 2(SRR2) is located downstream of the SOX2 coding region and mediates SOX2 expression in embryonic and adult stem cells. In this study, we deleted SRR2 using CRISPR/Cas9 in glioblastoma cells. Importantly, SRR2-deleted glioblastoma cells presented reduced SOX2 expression and decreased proliferative activity and self-renewal capacity in vitro. In line with these results, SRR2-deleted glioblastoma cells displayed decreased tumor initiation and growth in vivo. These effects correlated with an elevation of p21^CIP1 cell cycle and p27^KIP1 quiescence regulators. In conclusion, our data reveal that SRR2 deletion halts malignant activity of SOX2 and confirms that the SRR2 enhancer regulates SOX2 expression in cancer.

Cytoplasmic transport and nuclear import of plasmid DNA

Productive transfection and gene transfer require not simply the entry of DNA into cells and subsequent transcription from an appropriate promoter, but also a number of intracellular events that allow the DNA to move from the extracellular surface of the cell into and through the cytoplasm, and ultimately across the nuclear envelope and into the nucleus before any transcription can initiate. Immediately upon entry into the cytoplasm, naked DNA, either delivered through physical techniques or after disassembly of DNA-carrier complexes, associates with a large number of cellular proteins that mediate subsequent interactions with the microtubule network for movement toward the microtubule organizing center and the nuclear envelope. Plasmids then enter the nucleus either upon the mitotic disassembly of the nuclear envelope or through nuclear pore complexes in the absence of cell division, using a different set of proteins. This review will discuss our current understanding of these pathways used by naked DNA during the transfection process. While much has been elucidated on these processes, much remains to be discerned, but with the development of a number of model systems and approaches, great progress is being made.

Cell-specific targeting strategies for electroporation-mediated gene delivery in cells and animals

The use of electroporation to facilitate gene transfer is an extremely powerful and useful method for both in vitro and in vivo applications. One of its great strengths is that it induces functional destabilization and permeabilization of cell membranes throughout a tissue leading to widespread gene transfer to multiple cells and cell types within the electric field. While this is a strength, it can also be a limitation in terms of cell-specific gene delivery. The ability to restrict gene delivery and expression to particular cell types is of paramount importance for many types of gene therapy, since ectopic expression of a transgene could lead to deleterious host inflammatory responses or dysregulation of normal cellular functions. At present, there are relatively few ways to obtain cell-specific targeting of nonviral vectors, molecular probes, small molecules, and imaging agents. We have developed a novel means of restricting gene delivery to desired cell types based on the ability to control the transport of plasmids into the nuclei of desired cell types. In this article, we discuss the mechanisms of this approach and several applications in living animals to demonstrate the benefits of the combination of electroporation and selective nuclear import of plasmids for cell-specific gene delivery.

Targeted delivery of a decoy oligodeoxynucleotide to a single ES cell by femtoinjection

Femtoinjection has been proposed as a feasible approach for the targeted delivery of a decoy oligodeoxynucleotide (ODN) into a single ES cell for the study of transcription factor activity. Here, we evaluated the utility of decoy ODN delivery via femtoinjection in an ES cell model in which Venus fluorescent protein was expressed under the control of the tet-off system. Femtoinjection of a control decoy (Con-decoy) and a tetracycline response element decoy (TRE-decoy) into the cytoplasm had no apparent effect on Venus fluorescent protein expression; however, femtoinjection of the TRE-decoy into the nucleus successfully suppressed expression of the Venus fluorescent protein. We therefore conclude that it is feasible to suppress the activity of a transcription factor in a single ES cell by the delivery of a decoy ODN into the nucleus using the femtoinjection technique.

FROM THE CLINICAL EDITOR

The authors of this novel basic science study successfully demonstrate a femtoinjection technique to deliver a decoy oligodeoxynucleotide into a single ES cell.

Application of a novel strategy of engineering conditional alleles to a single exon gene, Sox2

BACKGROUND

The Conditional by Inversion (COIN) method for engineering conditional alleles relies on an invertible optimized gene trap-like element, the COIN module, for imparting conditionality. The COIN module contains an optimized 3' splice site-polyadenylation signal pair, but is inserted antisense to the target gene and therefore does not alter transcription, until it is inverted by Cre recombinase. In order to make COIN applicable to all protein-coding genes, the COIN module has been engineered within an artificial intron, enabling insertion into an exon.

METHODOLOGY/PRINCIPAL FINDINGS

Therefore, theoretically, the COIN method should be applicable to single exon genes, and to test this idea we engineered a COIN allele of Sox2. This single exon gene presents additional design challenges, in that its proximal promoter and coding region are entirely contained within a CpG island, and are also spanned by an overlapping transcript, Sox2Ot, which contains mmu-miR1897. Here, we show that despite disruption of the CpG island by the COIN module intron, the COIN allele of Sox2 (Sox2(COIN)) is phenotypically wild type, and also does not interfere with expression of Sox2Ot and miR1897. Furthermore, the inverted COIN allele of Sox2, Sox2(INV) is functionally null, as homozygotes recapitulate the phenotype of Sox2(βgeo/βgeo) mice, a well-characterized Sox2 null. Lastly, the benefit of the eGFP marker embedded in the COIN allele is demonstrated as it mirrors the expression pattern of Sox2.

CONCLUSIONS/SIGNIFICANCE

Our results demonstrate the applicability of the COIN technology as a method of choice for targeting single exon genes.