Taekjip Ha is the Bloomberg Distinguished Professor of Biophysics and Biophysical Chemistry, Biophysics, and Biomedical Engineering at Johns Hopkins University School of Medicine, and he is also an investigator with the Howard Hughes Medical Institute. Dr. Ha will deliver a seminar entitled, "Light, CRISPR and DNA repair." Hosted by Glen Hocky.
For more information about Taekjip Ha, click here.
Abstract: CRISPR is a revolutionary technology for genome editing, manipulation and diagnostics. We developed a light-on control for CRISPR, termed very fast (vf) CRISPR that can control Cas9 activity at seconds and micrometer precision. Using vfCRISPR and time-resolved ChIP-seq, we discovered surprisingly rapid detection and repair of Cas9-generated DNA breaks, and ultrafast spreading of damage-induced chromatin modification. Using vfCRISPR and live cell imaging, we found that the first round of repair takes much longer than subsequent rounds and that repair of two alleles in the same cell occur on a similar time scale despite large cell to cell heterogeneity. Using imaging-guided vfCRISPR, we achieved the ultimate resolution of CRISPR control, the single allele resolution.
We also developed a light-off control for CRISPR with unprecedent 99% efficacy. Combining light on and light off controls with multitarget CRISPR, we discovered the extent and time scale of chromatin opening (~1-2 kb and ~30 min, and time scale of chromatin restoration after repair completion. The multitarget CRISPR also allowed us to show that Cas9 is selectively evicted from the PAM-distal side of a break, leading to the loading of a repair factor at the same side.
We used the exquisite sequence specificity of CRISPR with our own superhelicases to create a new genome imaging method called GOLD FISH with a single nucleotide sensitivity, a feat never been achieved for direct hybridization-based imaging.