A coelectroporation method for the isolation of cryptic plasmids from Lactococcus lactis

Coexpression after electroporation of plasmid mixtures into muscle in vivo

AIM

Muscle is perhaps the most frequently considered tissue for non-viral gene therapy, in particular after gene transfer by electroporation. Expression in muscle is stable, but since the cell turnover is so slow incorporation in the host genome is not required. This raises interesting practical and theoretical questions related to the behaviour of the transgenic DNA under such conditions.

METHODS

We have investigated expression of reporter genes from plasmid mixtures electroporated into the extensor digitorum longus (EDL) muscle in mice in order to assess the degree of coexpression.

RESULTS

Under conditions where the reporter is easily identified the coexpression rate was 100%, as none of 287 fibres from five different muscles expressing blue fluorescent protein (BFP) failed to express green fluorescent protein (GFP). With other reporter combinations the rate was lower, but this we attribute to marginal sensitivity for fluorescent proteins, or from reporter protein degradation for beta-galactosidase.

CONCLUSIONS

The high degree of coexpression suggests that a large copy number takes part in the final transcription with this system. The finding also enhances the usefulness of muscle and electroporation for gene therapy and experimental biology.

A food-grade approach for functional analysis and modification of native plasmids in Lactococcus lactis

While plasmids from lactic acid bacteria possess many traits that are of industrial value, their exploitation is often frustrated by an inability to conduct food-grade engineering of native plasmids or to readily screen for their transfer. Here we describe a system that uses a RepA(+) temperature-sensitive helper plasmid and a RepA(-) cloning vector to overcome these problems while maintaining the food-grade status of the native plasmid. This strategy was used to precisely delete ltnA1 alone, or in conjunction with ltnA2 (encoding the structural proteins of the lantibiotic lacticin 3147), from the native 60.2-kb plasmid pMRC01 and to select for the transfer of pMRC01 between Lactococcus lactis strains.