T-DNA transfer and integration as a tool for insertional mutagenesis in the taxol-producing fungus

Agrobacterium tumefaciens-mediated DNA transiormation method was applied to transform Noclulisporium sylviforme fusant HDF-68, a taxol-produeing fungus. We constructed a binary vector pBI121-43 canting a hygromycin-resistant gene cassette between the right and left borders of T-DNA, Optimal co-cultivation of N.sylviforrne with A. tumefaciens containing pBI121-43 led to 110- 130 hygromycin-resistant transformants per＂ million eonidia. Putative transformants were found to be mitotically stable. The molecular analysis of transformants demonstrated the random integration of single copy of the T-DNA into the host genome. This transformation system serves as a basic tool for insertional mutagenesis in N. sylviforme fusant HDF-68, and the development of such svstem lays a solid foundation for constructing high-yied gene engineering strain and clarifying taxol biosynthesis pathway in this fungus.

Stem cell gene therapy:the risks of insertional mutagenesis and approaches to minimize genotoxicity

Virus-based vectors are widely used in hematopoietic stem cell(HSC)gene therapy,and have the ability to integrate permanently into genomic DNA,thus driving long-term expression of corrective genes in all hematopoietic lineages.To date,HSC gene therapy has been successfully employed in the clinic for improving clinical outcomes in small numbers of patients with X-linked severe combined immunodeficiency(SCID-X1),adenosine deaminase deficiency(ADA-SCID),adrenoleukodystrophy(ALD),thalassemia,chronic granulomatous disease(CGD),and Wiskott-Aldrich syndrome(WAS).However,adverse events were observed during some of these HSC gene therapy clinical trials,linked to insertional activation of proto-oncogenes by integrated proviral vectors leading to clonal expansion and eventual development of leukemia.Numerous studies have been performed to understand the molecular basis of vector-mediated genotoxicity,with the aim of developing safer vectors and lower-risk gene therapy protocols.This review will summarize current information on the mechanisms of insertional mutagenesis in hematopoietic stem and progenitor cells due to integrating gene transfer vectors,discuss the available assays for predicting genotoxicity and mapping vector integration sites,and introduce newlydeveloped approaches for minimizing genotoxicity as a way to further move HSC gene therapy forward into broader clinical application.

Establishment of Agrobacterium tumefaciens-Mediated Transformation System for Rice Sheath Blight Pathogen Rhizoctonia solani AG-1 IA

To construct the T-DNA insertional mutagenesis transformation system for rice sheath blight pathogen Rhizoctonia solani AG-1 IA,the virulent isolate GD118 of this pathogen was selected as an initial isolate for transformation.The conditions for transformation of isolate GD118 were optimized in five aspects,i.e.pre-induction time,co-culture time,acetosyringone(AS) concentration at the co-culture phase,co-culture temperature and pH value of induction solid medium(ISM) at the co-culture phase.Finally,a system of Agrobacterium tumefaciens-mediated transformation(ATMT) for R.solani AG-1 IA was established successfully.The optimal conditions for this ATMT system were as follows:the concentration of hygromycin B at 30 μg/mL for transformant screening,8 h of pre-induction,20 h of co-culture,200 μmol/L of AS in ISM,co-culture at 25 ℃ and pH 5.6 to 5.8 of ISM at the co-culture phase.The transformants still displayed high resistance to hygromycin B after subculture for five generations.A total of 10 randomly selected transformants were used for PCR verification using the specific primers designed for the hph gene,and the results revealed that an expected band of 500 bp was amplified from all of the 10 transformants.Moreover,PCR amplification for these 10 transformants was carried out using specific primers designed for the Vir gene of A.tumefaciens,with four strains of A.tumefaciens as positive controls for eliminating the false-positive caused by the contamination of A.tumefaciens.An expected band of 730 bp was amplified from the four strains of A.tumefaciens,whereas no corresponding DNA band could be amplified from the 10 transformants.The results of the two PCR amplifications clearly showed that T-DNA was indeed inserted into the genome of target isolate GD118.

Effective Expression-Independent Gene Trapping and Mutagenesis Mediated by Sleeping Beauty Transposon

Expression-independent gene or polyadenylation[poly（A）]trapping is a powerful tool for genome-wide mutagenesis regardless of whether a targeted gene is expressed.Although a number of poly（A）-trap vectors have been developed for the capture and mutation of genes across a vertebrate genome,further efforts are needed to avoid the 3＇-terminal insertion bias and the splice donor（SD） read-through,and to improve the mutagenicity.Here,we present a Sleeping Beauty（SB） transposon-based vector that can overcome these limitations through the inclusion of three functional cassettes required for gene-finding,gene-breaking and large-scale mutagenesis, respectively.The functional cassette contained a reporter/selective marker gene driven by a constitutive promoter in front of a strong SD signal and an AU-rich RNA-destabilizing element（ARE）,which greatly reduced the SD read-through events,except that the internal ribosomal entry site（IRES） element was introduced in front of the SD signal to overcome the phenomenon of 3＇-bias gene trapping.The breaking cassette consisting of an enhanced splicing acceptor（SA）,a poly（A） signal coupled with a transcriptional terminator（TT） effectively disrupted the transcription of trapped genes.Moreover,the Hsp70 promoter from tilapia genome was employed to drive the inducible expression of SB11,which allows the conditional remobilization of a trap insert from a non-coding region.The combination of three cassettes led to effective capture and disruption of endogenous genes in HeLa cells.In addition,the Cre/LoxP system was introduced to delete the Hsp70-SB11 cassette for stabilization of trapped gene interruption and biosafety. Thus,this poly（A）-trap vector is an alternative and effective tool for identification and mutation of endogenous genes in cells and animals.

Insights into Hepatitis B Virus DNA Integration-55 Years after Virus Discovery

Hepatitis B virus(HBV),which was discovered in 1965,is a threat to global public health.HBV infects human hepatocytes and leads to acute and chronic liver diseases,and there is no cure.In cells infected by HBV,viral DNA can be integrated into the cellular genome.HBV DNA integration is a complicated process during the HBV life cycle.Although HBV integration normally results in replication-incompetent transcripts,it can still act as a template for viral protein expression.Of note,it is a primary driver of hepatocellular carcinoma(HCC).Recently,with the development of detection methods and research models,the molecular biology and the pathogenicity of HBV DNA integration have been better revealed.Here,we review the advances in the research of HBV DNA integration,including molecular mechanisms,detection methods,research models,the effects on host and viral gene expression,the role of HBV integrations in the pathogenesis of HCC,and potential treatment strategies.Finally,we discuss possible future research prospects of HBV DNA integration.