Adenovirus-mediated Cre deletion of floxed sequences in primary mouse cells is an efficient alternative for studies of gene deletion.

This study evaluates the utility of Cre-expressing adenovirus for deletion of floxed genes in primary cells using primary murine hepatocytes. Adenovirus infection was very efficient, even at very low MOI (>95% infection at a MOI of 6) and did not reduce viability. High level LacZ expression was cytotoxic to hepatocytes but Cre expression had no effect on viability. Cre-mediated recombination was completed within a timespan that permits experimentation during primary culture (>95% recombination after 24 h), independently of the number of floxed alleles per cell. Recombination did not induce p53 or produce cytological nuclear abnormalities (even in polyploid cells). Contrary to expectation, deletion of DNA ligase 1 did not alter cell cycle progression, although Cre expression hastens entry to S phase from G(1), independently of the presence of floxed sequences. We conclude that adenovirus-mediated deletion of floxed alleles in primary cells is a straightforward and highly efficient tool for conducting preliminary studies of conditional gene targeting. Primary cells have advantages of differentiation, relative purity and ease of experimentation within controlled conditions, while avoiding confounding problems encountered in vivo (i.e. target cell specificity, kinetics and level of recombination, and elicitation of inflammatory and immune responses). This system could help identify important phenotypic effects and design and interpret in vivo studies.

Gene transfer to adult human lung tissue ex vivo.

The potential of gene therapy for treatment of lung disease remains unrealised. Early model systems often resulted in promising efficiency of gene transfer, only to prove irreproducible in the clinic. While problems such as induction of host immune responses and duration of expression also need to be addressed, it is now widely believed that alternative, relevant models which more accurately reflect gene transfer efficiencies in human lungs are urgently required. We report here on a human lung slice culture system to assess gene transfer to adult lung epithelium. A lacZ-expressing adenovirus (AdCA35lacZ) was used as a reporter vector. A solution of AdCA35lacZ was instilled via bronchioles into resected lung tissue, a route analogous to clinical administration. Following a 1 h incubation, the tissue was inflated with a 0.4% agarose solution, instilled via the same bronchioles. Once solidified, 500 microm slices of the tissue were prepared and cultured for 4 days. beta-Galactosidase staining revealed lacZ transgene expression in bronchiolar and alveolar cells of the lung slices throughout the 4 days in culture. This system, which can also be used to study other viral and liposome vectors, could prove to be a useful alternative model for assessing gene delivery to adult human lung epithelium.

Efficient BLG-Cre mediated gene deletion in the mammary gland.

Using the phage P1-derived Cre/loxP recombination system, we have developed a strategy for efficient mammary tissue specific inactivation of floxed genes. Transgenic mice were generated which express Cre DNA-recombinase under the control of the mammary gland specific promoter of the ovine beta-lactoglobulin (BLG) gene. To test the specificity of Cre mediated recombination, we crossed these mice to animals harbouring a floxed DNA ligase I allele. We show that the BLG-Cre construct specifies mammary specific gene deletion, and furthermore that it is temporally regulated, predominantly occurring during lactation. We fully characterised the extent of gene deletion in one line (line 74). In this strain the virgin gland is characterised by low levels (7%) of Cre mediated deletion, whereas 70-80% of cells within the lactating mammary gland have undergone recombination. Immunohistochemistry and indirect in situ PCR were used respectively to demonstrate that both Cre protein and Cre activity were evenly distributed throughout the population of secretory epithelial cells. The level of background recombination in non-mammary tissues was found to be < or = 1.1%, irrespective of mammary gland developmental status. Crossing the transgenic BLG-Cre strain described here to mice harbouring other floxed alleles will facilitate the functional analysis of those genes during differentiation and development of the mammary gland.