Biology subjects

Steger, R. J.

Publications and source records attributed to Steger, R. J..

3 recordsLinked to original sources

bioRxiv2026

Combinatorial CRISPR/Cas12a excises targeted loci in the mammalian genome at very low efficiency

The CRISPR/Cas12a system has emerged as a highly useful tool for genomic editing due to its ability to process multiple guide RNAs (gRNAs) from a single promoter. In this study, we explored the potential of combinatorial CRISPR/Cas12a to excise targeted loci in the mammalian genome by inducing double-strand breaks (DSBs) upstream and downstream of targeted exons. We designed a library of gRNA pairs targeting introns flanking 54 exons of 18 essential genes and 17 exons of 10 nonessential genes, aiming to assess the efficiency of Cas12 in excising targeted loci. While single gRNAs directly targeting essential exons produced expected fitness defects in cells, pairs of guides targeting flanking intronic regions resulted in only trivial viability effects, suggesting that excision rarely occurred. Further analysis showed no meaningful correlation between gRNA efficiency, orientation, GC content, or cut site geometry and the success of locus excision. These findings indicate that, under the conditions tested, the Cas12a system does not yield locus excision at the efficiency required for sensitive negative selection assays.

systems biology↗

bioRxiv2024

Activity-based selection for enhanced base editor mutational scanning

Base editing is a CRISPR-based technology that enables high-throughput, nucleotide-level functional interrogation of the genome, which is essential for understanding the genetic basis of human disease and informing therapeutic development. Base editing screens have emerged as a powerful experimental approach, yet significant cell-to-cell variability in editing efficiency introduces noise that may obscure meaningful results. Here, we develop a co-selection method that enriches for cells with high base editing activity, substantially increasing editing efficiency at a target locus. We evaluate this activity-based selection method against a traditional screening approach by tiling guide RNAs across TP53, demonstrating its enhanced capacity to pinpoint specific mutations and protein regions of functional importance. We anticipate that this modular selection method will enhance the resolution of base editing screens across many applications.

genetics↗

bioRxiv2023

Modular vector assembly enables rapid assessment of emerging CRISPR technologies

The diversity of CRISPR systems, coupled with scientific ingenuity, has led to an explosion of applications; however, to test newly-described innovations in their model systems, researchers typically embark on cumbersome, one-off cloning projects to generate custom reagents that are optimized for their biological questions. Here, we leverage Golden Gate cloning to create the Fragmid toolkit, a modular set of CRISPR cassettes and delivery technologies, along with a web portal, resulting in a combinatorial platform that enables scalable vector assembly within days. We further demonstrate that multiple CRISPR technologies can be assessed in parallel in a pooled screening format using this resource, enabling the rapid optimization of both novel technologies and cellular models. These results establish Fragmid as a robust system for the rapid design of CRISPR vectors, and we anticipate that this assembly approach will be broadly useful for systematic development, comparison, and dissemination of CRISPR technologies.

genomics↗