Sascha Hoogendoorn is a newly appointed tenure-track assistant professor in the department of Organic Chemistry at the University of Geneva. In her lab she uses an interdisciplinary approach to study and perturb cellular signaling, with a particular interest in the primary cilium and the Hedgehog signaling pathway. Her research combines organic chemistry with cell biology and CRISPR/Cas9-based gene editing to develop molecules that enable further dissection and manipulation of ciliary signaling. In this article, she briefly describes the potential of a CRISPR-based screen for Hedgehog signaling.

During my postdoc at Stanford I worked on the development of a genetic screening platform for the Hedgehog (Hh) signaling pathway. At that point the first pooled, growth-based CRISPR screens had just been published, and these proved to be very powerful for the detection of essential genes or drug targets for cytotoxic drugs. We engineered a cell line that converted Hh signal transduction into resistance to the antibiotic blasticidin, thereby effectively converting Hh signaling to growth. We then conducted a genome-wide screen to find genes that affect this pathway, using CRISPR-KO. We retrieved many known and novel components of the Hh pathway as well as the organelle it depends on, the primary cilium. Alternative screens for Hh signaling and cilia had been done in the past, using siRNAs and various detection methods, and we could show that our CRISPR methodology clearly outperformed those. This screen provided us, and the larger community, with a great resource on factors involved in signal transduction and we discovered some exciting new biology.

In my lab at the University of Geneva, I want to extend the platform and use it for mechanism-of-action studies of molecules that affect the Hh pathway. Furthermore, CRISPR is a very useful and easy tool to create individual cell lines with a knockout of a gene of interest, or to knock-in a reporter in an endogenous gene. I also want to explore alternative CRISPR technologies such as CRISPR interference and activation, but for those the sgRNA libraries are not as robust as for CRISPR-KO. Those will hopefully improve in the coming years. Off-targets will remain a concern and you should always thoroughly validate your CRISPR cells. Overall, I think it is very clear that the impact of this technology is huge, and with that also comes a great responsibility for us researchers to think about the ethics and how we implement it.