Measuring transcriptional and chromatin position effects on recombinant adeno-associated virus mediated homologous recombination by targeted integration of barcoded vectors at engineered target sites genome wide
Recombinant AAV vectors have the unique ability to promote targeted integration of transgenes via homologous integration at specified genomic sites reaching frequencies of 0.1-1%. We studied genomic parameters that influence targeting efficiencies on a large scale. To do this, we generated more than 1000 engineered, doxycycline-inducible target sites in the human HAP1 cell line and infected this polyclonal population with a library of AAV-DJ targeting vectors each carrying a unique barcode. The heterogeneity of barcode integration at each target site provided an assessment of the targeting efficiency at that locus. We compared targeting efficiency with and without target site transcription for identical chromosomal positions, finding that targeting efficiency was enhanced by target site transcription. Chromatin states associated with active transcription were also predictive of higher targeting efficiency. Furthermore, there was an effect on the amenability of a site to targeting due to other factors such as the level of transcription from intersecting genes. These results define important parameters that may not only assist in designing optimal targeting vectors for genome editing, but also provide new insights into the mechanism of AAV-mediated homologous recombination. Overall design: 2 independent biological replicates induced with doxycycline (100ng/mL) at time of AAV transduction, 2 independent biological replicates uninduced at time of AAV transduction. Each biological replicate with 2 technical replicates.