Lentiviral protein delivery of meganucleases in human cells mediates gene targeting and alleviates toxicity.

Site-specific endonucleases can be engineered for custom recognition of any genetic locus and used for gene targeting. Yet, the prolonged expression and accumulation of these nucleases in cells lead to toxic effect. Here we describe an efficient and quantitative method for introducing nucleases into cells as proteins packaged within lentiviral vector particles. I-CreI-derived meganucleases, which can be engineered as single-chain proteins, were incorporated into lentiviral vector particles either without modification or as fusions with cyclophilin A. The small amount of nuclease delivered by the viral particles is sufficient to induce efficient targeted mutagenesis in human HEK293H and primary T cells. When a repair template sequence was packaged in the lentiviral vector, high levels of homologous gene targeting were obtained and toxicity was markedly reduced.

Variable correction of Artemis deficiency by I-Sce1-meganuclease-assisted homologous recombination in murine hematopoietic stem cells.

The correction of genetic mutations by homologous recombination is an attractive approach to gene therapy. We used the DNA double-strand breaks introduced by the site-specific endonuclease I-Sce1 as a means of increasing homologous recombination of an exogenous DNA template in murine hematopoietic stem cells (mHSCs). To develop this approach, we chose an Artemis knockout (Art(-/-)) mouse in which exon 12 of the Artemis gene had been replaced by an I-Sce1 recognition site. The I-Sce1 enzyme and the Artemis correction template were each delivered by a self-inactivating (SIN)-integrase-defective lentiviral vector (SIN-IDLV-CMV-ISce1 and SIN-IDLV-Art, respectively). Transduction of Art(-/-) mHSCs with the two vectors successfully reverted the Art(-/-) phenotype in 2 of our 10 experiments. Even though the potential for genotoxicity has yet to be evaluated, this new approach to gene editing appears to be promising. Improving the efficacy of this approach will require further technical work.

Synchronous and regulated expression of two AU-binding proteins, AUF1 and HuR, throughout murine development.

The AUF1 (hnRNPD) and HuR (ELAV-like) proteins, potential trans-acting factors for regulated mRNA decay, bind in vitro to A+U-rich elements (AREs) found in the 3' untranslated region (3' UTR) of many labile transcripts. In an effort to determine whether these trans-acting factors are likely to play a role in embryogenesis, we have analysed their expression during mouse development both at the mRNA and protein levels. We show that AUF1 and HuR are expressed at all the developmental stages analysed from day 8.5 of embryonic development to adulthood. Expression levels are dynamic, varying between tissues and developmental stages. However, a strong positive correlation between AUF1 and HuR protein levels was observed in all examined tissues. Finally, we compared AUF1 and HuR expression with accumulation of one common target mRNA, c-myc. The similar spatio-temporal distribution of these proteins and of c-myc mRNA is in agreement with a potential concerted role in ARE-mediated control of mRNA stability.

Activation of constitutive 5-hydroxytryptamine(1B) receptor by a series of mutations in the BBXXB motif: positioning of the third intracellular loop distal junction and its G(o)alpha protein interactions.

Constitutive activity of the recombinant human 5-hydroxytryptamine(1B) (5-HT(1B)) receptor (RC code 2.1.5HT.01.B) was investigated by mutagenesis of the BBXXB motif (in which B represents a basic residue and X a non-basic residue) located in the C-terminal portion of the third intracellular loop. In contrast with wild-type 5-HT(1B) receptors, three receptor mutants (Thr(313)-->Lys, Thr(313)-->Arg and Thr(313)-->Gln) increased their agonist-independent guanosine 5'-[gamma-[(35)S]thio]triphosphate binding response by 26-41%. This activity represented approx. 30% of the maximal response induced by 5-HT and could be reversed by the inverse agonists methiothepin and 3-(3-dimethylaminopropyl)-4-hydroxy-N-(4-pyridin-4-yl phenyl)-benzenamide (GR 55562). Enhanced agonist-independent and agonist-dependent 5-HT(1B) receptor activation was provided by co-expression of a pertussis toxin-resistant rat G(o)alpha Cys(351)-->Ile protein. The wild-type 5-HT(1B) receptor displayed a doubling in basal activity, whereas a spectrum of enhanced basal activities (313-571%) was observed with a series of diverse amino acid substitutions (isoleucine, glycine, asparagine, alanine, lysine, phenylalanine, glutamine and arginine) at the 5-HT(1B) receptor position 313 in the presence of pertussis toxin (100 ng/ml). Consequently, the constitutive 5-HT(1B) receptor activity can be modulated by the mutation of Thr(313), and displays a graded range between 11% and 59% of maximal 5-HT(1B) receptor activation by 5-HT. No clear pattern is apparent in the framework of traditionally cited amino acid characteristics (i.e. residue size, charge or hydrophobicity) to explain the observed constitutive activities. The various amino acid substitutions that yielded enhanced activity are unlikely to make similar intramolecular interactions within the 5-HT(1B) receptor. It is hypothesized that the positioning of the junction between the third intracellular loop and transmembrane domain VI is altered by mutation of Thr(313) in the BBXXB motif and thereby unmasks G(alpha)-protein interaction points.