Spontaneous and MNNG-induced reversion of an EGFP construct in HeLa cells: an assay for observing mutations in living cells by fluorescent microscopy

Label-free molecular probe based on G-quadruplex and strand displacement for sensitive and selective detection and naked eye discrimination of exon 2 deletion of AIMP2

Exon 2 deletion of aminoacyl tRNA synthetase complex-interacting multifunctional protein 2 (AIMP2) is a genetic deletion related to various cancers, for instance ovarian and lung cancers. It can be worked as an indicator of cancer for diagnosis of diseases. Here, we developed a label-free method based on the formation of split G-quadruplex in the presence of target DNA combined with strand displacement to detect exon 2 deletion of AIMP2 (DE2) sensitively and selectively. This method is easy-operating and cost-saving. Moreover, it has observed discrimination of gene deletion from wild-types by naked eyes. The results demonstrate that this strategy can be further used for the detection of different gene deletions to achieve early diagnosis of diseases and allow better prognosis.

Switching on transgene expression by correcting aberrant splicing using multi-targeting steric-blocking oligonucleotides

BACKGROUND

Mutations leading to aberrant splicing are found as a cause of numerous pathologies. Splice-switching oligonucleotides (SSOs), which modify aberrant expression patterns of alternatively spliced mRNAs, are a novel means of potentially controlling such diseases.

METHODS

We used an experimental model in which a mutated beta-globin intron, carrying an aberrant splice site at nucleotide 705, interrupts the coding region of the luciferase reporter gene inserted in HeLa pLuc/705 cells. We have optimized delivery of splice correcting, steric-blocking 2'-O-methyl SSOs targeting the 705 mutated region (2'-O-Me SSO(705)) with DLS (DLS: delivery liposomal system) lipoplexes.

RESULTS

Optimal luciferase activity for DLS/2'-O-Me SSO(705) was achieved at 100 nM and was detectable at concentrations as low as 10 nM in serum-containing culture medium, confirming the potential of DLS lipoplex-mediated nuclear SSO delivery as observed in cellular uptake studies. We confirmed by cytofluorometry and epifluorescence microscopy the high potential of the DLS lipoplex for cellular and nuclear oligonucleotide uptake. The DLS lipoplex was then used to directly compare the intracellular efficacy of various SSO chemistries and sequences in correction of aberrant splicing. 2'-O-Methoxyethyl-oligodeoxyribonucleoside phosphorothioates had a greater activity than 2'-O-methyl phosphodiester or 2'-O-methyl-phosphorothioate oligoribonucleotides. Targeting the splicing enhancer 623 region upstream was as efficient as targeting the 705 splice site, and, remarkably, simultaneous targeting of both sites was more efficient than treatment of the cells either with 2'-O-Me SSO(705) or 2'-O-Me SSO(623) alone.

CONCLUSIONS

We demonstrated that SSOs can switch on luciferase activity in HeLa cells previously transfected with the pLuc/705 plasmid via the same DLS vector and provides a novel approach to modulate the expression of a transgene.

High-level expression of hemoglobin A in human thalassemic erythroid progenitor cells following lentiviral vector delivery of an antisense snRNA

Mutations at nucleotides 654, 705, or 745 in intron 2 of the human beta-globin gene activate aberrant 3' and 5' splice sites within the intron and prevent correct splicing of beta-globin pre-mRNA, resulting in inhibition of beta-globin synthesis and in consequence beta-thalassemia. Transfection of HeLa cells expressing the 3 thalassemic mutants with modified U7 snRNA (U7.623), containing a sequence antisense to a region between the aberrant splice sites, reduced the incorrect splicing of pre-mRNA and led to increased levels of the correctly spliced beta-globin mRNA and protein. A lentiviral vector carrying the U7.623 gene was effective in restoration of correct splicing in the model cell lines for at least 6 months. Importantly, the therapeutic value of this system was demonstrated in hematopoietic stem cells and erythroid progenitor cells from a patient with IVS2-745/IVS2-1 thalassemia. Twelve days after transduction of the patient cells with the U7.623 lentiviral vector, the levels of correctly spliced beta-globin mRNA and hemoglobin A were approximately 25-fold over background. These results should be regarded as a proof of principle for lentiviral vector-based gene therapy for beta-thalassemia.

A:T --> G:C base pair substitutions occur at a higher rate than other substitution events in Pms2 deficient mouse cells

The mismatch repair pathway involves multiple proteins that are required to correct DNA polymerase generated mismatches before they become mutations. It has been shown recently, that the predominant base-pair substitution events leading to loss of endogenous Aprt activity in Pms2 null mouse cells are A:T --> G:C mutations (Oncogene 21 (2002) 1768, Oncogene 21 (2002) 2840). To determine if this observation could be explained by an increased rate of A:T --> G:C mutations relative to other base-pair substitutions, we developed a reversion assay to examine G:C --> A:T, C:G --> A:T, and A:T --> G:C mutations within mouse Aprt in a Pms2 null mouse kidney cell line. The results demonstrated a 6-50-fold increase in the rate of the A:T --> G:C mutations relative to the other base-pair substitutions. Additional work demonstrated that growth of the Pms2 null cells in antioxidant containing medium reduced the rate of the A:T --> G:C mutations. The results are discussed with regards to the role of mismatch repair proteins in preventing base-pair substitutions, including those induced by oxidative stress.

Repair of a splicing defect in erythroid cells from patients with beta-thalassemia/HbE disorder

A HeLa cell line stably expressing the human beta-globin gene carrying thalassemic mutations beta(E)/IVS1-6 served as a thalassemia model for repair of aberrant splicing of beta(E)-globin pre-mRNA with antisense oligonucleotides. Treatment of beta(E)/IVS1-6 HeLa cells with a morpholino oligonucleotide targeted immediately upstream of the aberrant 5' splice site activated by the mutations resulted in an increase in the amount of correctly spliced beta(E)-globin mRNA in a dose-dependent and sequence-specific fashion. The repaired beta(E)-globin mRNA was stable and could be translated into full-length beta(E)-globin polypeptide. Application of the same oligonucleotide to erythroid progenitor cells from two beta-thalassemia/HbE patients resulted in an approximately 70% increase in correct beta(E)-globin mRNA and 36% increase in hemoglobin E. The erythroid progenitor cells represent the actual targets for the clinical application of antisense repair of defective pre-mRNAs.

Temperature-dependent splicing of beta-globin pre-mRNA

A T-->G mutation at nucleotide 705 of human beta-globin intron 2 creates an aberrant 5' splice site and activates a cryptic 3' splice site upstream. In consequence, the pre-mRNA is spliced via aberrant splice sites, despite the presence of the still functional correct sites. Surprisingly, when IVS2-705 HeLa or K562 cells were cultured at temperatures below 30 degrees C, aberrant splicing was inhibited and correct splicing was restored. Similar temperature effects were seen for another beta-globin pre-mRNA, IVS2-745, and in a construct in which a beta-globin intron was inserted into a coding sequence of EGFP. Temperature-induced alternative splicing was affected by the nature of the internal aberrant splice sites flanking the correct sites and by exonic sequences. The results indicate that in the context of thalassemic splicing mutations and possibly in other alternatively spliced pre-mRNAs, temperature is one of the parameters that affect splice site selection.