Optimal LentiCRISPR-Based System for Sequential CRISPR/Cas9 Screens.

The advent of genome-wide clustered regularly interspaced short palindromic repeats (CRISPR) screening has advanced the understanding of molecular systems within cells. Here, we demonstrate the utility of sequentially performed CRISPR knockout screens that use an existing library to explore a biological question across the human genome, and then the remaining cells are used to examine each gene candidate against one common gene of interest. We call this approach "Many vs One" CRISPR screening, made possible by a modified 7SK promoter in place of the U6 promoter to drive expression of a single guide RNA. Inserting this novel 7SK promoter into the ubiquitously used lentiCRISPRv2 backbone is crucial, because it overcomes the need for a substantial increase in CRISPR library coverage during screening, sample processing, and next generation sequencing. This new 7SK vector equals the original lentiCRISPRv2 in lentiviral titer, knockout efficiency, and ease of use.

Burkitt Lymphomas Evolve to Escape Dependencies on Epstein-Barr Virus.

Epstein-Barr Virus (EBV) can transform B cells and contributes to the development of Burkitt lymphoma and other cancers. Through decades of study, we now recognize that many of the viral genes required to transform cells are not expressed in EBV-positive Burkitt lymphoma (BL) tumors, likely due to the immune pressure exerted on infected cells. This recognition has led to the hypothesis that the loss of expression of these viral genes must be compensated through some mechanisms. Recent progress in genome-wide mutational analysis of tumors provides a wealth of data about the cellular mutations found in EBV-positive BLs. Here, we review common cellular mutations found in these tumors and consider how they may compensate for the viral genes that are no longer expressed. Understanding these mutations and how they may substitute for EBV's genes and contribute to lymphomagenesis can serve as a launchpad for more mechanistic studies, which will help us navigate the sea of genomic data available today, and direct the discoveries necessary to improve the treatment of EBV-positive BLs.