Efficiency of chimeraplast gene targeting by direct nuclear injection using a GFP recovery assay.

Traditional RNA-DNA chimeric oligonucleotides (chimeraplasts), composed of a continuous stretch of RNA and DNA residues in a duplex conformation, have been shown to correct single-base mutations in episomal and genomic DNA both in vitro and in vivo. In the current study, we have compared the efficiency of single-base pair correction between a traditionally designed chimeraplast (covalently linked duplex) and hybrid chimeraplasts (noncovalent duplexes formed from stretches of RNA and DNA nucleotides synthesized individually and hybridized in vitro). Six hybrid chimeraplasts of identical length were constructed with various lengths of target homology and strand location of the desired nucleotide change. These constructs were evaluated for their ability to correct a point mutation in the gene encoding recombinant enhanced green fluorescent protein (eGFP) that rendered the protein nonfluorescent. A plasmid encoding this mutant eGFP gene and a chimeraplast were co-introduced directly into the nuclei of primary fibroblasts by microinjection. As shown by the recovery of eGFP fluorescence, three of the six hybrid chimeraplasts demonstrated the ability to mediate gene correction (0.4-2.4%). Covalent joining of RNA and DNA strands in chimeraplasts was not necessary for correction of DNA mutations. However, the strand placement of the desired nucleotide change and the length of nonhomologous sequences flanking target nucleotides played a crucial role in the efficiency of chimeraplast-mediated gene correction. Despite the ability of certain chimeraplast designs to correct point mutations in episomal plasmids, targeted correction of integrated copies of the mutant eGFP transgene was unsuccessful in primary fibroblasts. These results demonstrate that, although chimeraplasts are fairly effective at targeting episomal DNA in primary cells, further optimization is required to increase the efficiency for targeting integrated genes.

Conditions for in vitro maturation and artificial activation of ferret oocytes.

The ferret represents an attractive species for animal modeling of lung diseases because of the similarity between ferret and human lung biology and its relatively small size and short gestation time. In an effort to establish experimental protocols necessary for cloning ferrets, optimized conditions for in vitro maturation and artificial activation of ferret oocytes were examined. Cumulus-oocyte complexes were harvested from ovaries of superovulated ferrets, and in vitro maturation was evaluated in three different culture media: medium 1 (TCM-199 + 10% FBS), medium 2 (TCM-199 + 10% FBS with eCG [10 IU/ml] and hCG [5 IU/ml]), or medium 3 (TCM-199 + 10% FBS with eCG, hCG, and 17beta-estradiol [2 microg/ml]). After 24 h of maturation in vitro, the maturation rate of oocytes cultured in medium 2 (70%, n = 79) was significantly greater (P < 0.01) than those of oocytes cultured in the other two media (27%-36%, n = 67-73). At 48 h, similar maturation rates (56%-69%, n = 76-87) were observed for all three types of media. For activation experiments, oocytes cultured in medium 2 were stimulated with electrical and chemical stimuli either individually or in combination. Treatment with cycloheximide and 6-dimethylaminopurine (6-DMAP) following electrical stimulation resulted in 43% (n = 58) of the oocytes developing to the blastocyst stage. Such an activation rate represented a significant improvement over those obtainable under other tested conditions, including individual treatment with electrical pulses (10%, n = 41), cycloheximide (3%, n = 58), or 6-DMAP (5%, n = 59). Blastocysts derived from in vitro activation appeared to be normal morphologically and were composed of an appropriate number of both inner cell mass (mean +/- SEM, 10.3 +/- 1.1; n = 11) and trophectoderm (60.8 +/- 2.9, n = 11) cells. These results have begun to elucidate parameters important for animal modeling and cloning with ferrets.

Genistein restores functional interactions between Delta F508-CFTR and ENaC in Xenopus oocytes.

The cystic fibrosis transmembrane conductance regulator (CFTR), in addition to its Cl(-) channel properties, has regulatory interactions with other epithelial ion channels including the epithelial Na(+) channel (ENaC). Both the open probability and surface expression of wild type CFTR Cl(-) channels are increased significantly when CFTR is co-expressed in Xenopus oocytes with alphabetagamma-ENaC, and conversely, the activity of ENaC is inhibited following wild type CFTR activation. Using the Xenopus oocyte expression system, a lack of functional regulatory interactions between DeltaF508-CFTR and ENaC was observed following activation of DeltaF508-CFTR by forskolin and isobutylmethylxanthine (IBMX). Whole cell currents in oocytes expressing ENaC alone decreased in response to genistein but increased in response to a combination of forskolin and IBMX followed by genistein. In contrast, ENaC currents in oocytes co-expressing ENaC and DeltaF508-CFTR remained stable following stimulation with forskolin/IBMX/genistein. Furthermore, co-expression of DeltaF508-CFTR with ENaC enhanced the forskolin/IBMX/genistein-mediated activation of DeltaF508-CFTR. Our data suggest that genistein restores regulatory interactions between DeltaF508-CFTR and ENaC and that combinations of protein repair agents, such as 4-phenylbutyrate and genistein, may be necessary to restore DeltaF508-CFTR function in vivo.

Partial correction of endogenous DeltaF508 CFTR in human cystic fibrosis airway epithelia by spliceosome-mediated RNA trans-splicing.

Spliceosome-mediated RNA trans-splicing (SMaRT) was investigated as a means for functionally correcting endogenous DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) transcripts using in vitro human cystic fibrosis (CF) polarized airway epithelia and in vivo human CF bronchial xenografts. Recombinant adenovirus (Ad.CFTR-PTM) encoding a pre-therapeutic molecule (PTM) targeted to CFTR intron 9 corrected transepithelial cyclic AMP (cAMP)-sensitive short-circuit current (Isc) in DeltaF508 homozygous epithelia to a level 16% of that observed in normal human bronchial epithelia. Molecular analyses using RT-PCR and western blotting confirmed SMaRT-mediated partial correction of endogenous DeltaF508 messenger RNA (mRNA) transcripts and protein. In an in vivo model of DeltaF508 CF airway epithelia, human CF bronchial xenografts infected with Ad.CFTR-PTM also demonstrated partial correction of CFTR-mediated Cl- permeability at a level 22% of that seen in non-CF xenografts. These results provide functional evidence for SMaRT-mediated repair of mutant endogenous CFTR mRNA in intact polarized CF airway epithelial models.