A promoter trap in embryonic stem (ES) cells selects for integration of DNA into CpG islands

Abstract

An analysis of several G418-resistant ES cell lines produced by electroporation of a promoterless neo gene (NASTI), shows an enrichment for integrations within, or adjacent to, CpG islands. A detailed analysis of two of the cell lines reveals short regions of homology between the genomic target DNA and the construct ends, and that recombination may be mediated by DNA Topoisomerase I. The DNA flanking the insert detects transcription of endogenous genes, and in one cell line divergent transcripts are detected. This use of ES cells should provide an effective and efficient means of creating insertional mutations in mice.