Guest lecture by Francis Mojica: "The Story of CRISPR: From Brines to Brains"
Guest lecture by Francis Mojica, PhD, University of Alicante.
Dr. Mojica pioneered the work that led to the identification of the CRISPR locus. He also described its biological function as an adaptive immune system in prokaryotes. His work laid the foundations for the subsequent development of CRISPR/Cas, the genome editing technology that has revolutionized the field of Biomedicine.
Arrays of CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) were discovered three decades ago. Soon after, during the early 1990s, the first functional analyses were carried in extremely halophilic archaea, where these repeats were shown to interfere with DNA replicon maintenance when manipulated. Afterwards, CRISPR were reported in additional, distantly related prokaryotes, leading to the recognition of a new family of short regularly spaced repeats, widespread in bacteria and archaea. The identification of CRISPR-associated (Cas) proteins and the revelation that repeat-intervening sequences (referred to as spacers) seemed to be incompatible with matching sequences in mobile genetic elements (notably, in viruses, suggesting a defensive function), fueled research on CRISPR-Cas. As a result, their role as an adaptive immune system was soon demonstrated for a variety of model microorganisms, and the mechanism of action unveiled. Subsequently, a three-step (i.e., adaptation, expression and interference) general scheme was conceived, involving the common elements of active CRISPR-Cas systems: repeats, spacers, Cas proteins and the “leader” sequences (AT-rich stretches flanking CRISPR arrays). In brief, during adaptation, new spacers are integrated at the leader-proximal end of a CRISPR cassette. Transcription from the leader, and processing of the CRISPR transcript (expression stage), generates single-spacer CRISPR RNA (crRNA) molecules that guide a Cas endonuclease to targeted sequences (complementary to the carried spacer), leading to target cleavage (interference). The unique combination of versatility and feasibility of the diverse CRISPR-Cas components enables a variety of applications, not only in the native carrier organism but also in heterologous (prokaryotic or eukaryotic) hosts. Hitherto, native and engineered interference-related elements of CRISPR-Cas have been harnessed for host immunization, cell dormancy, regulation of gene expression, locus labelling, molecular diagnostics and genome editing, in almost any cell type, from prokaryotes and plant cells to neurons. More recently, the adaptation capability of CRISPR has also been exploited, utilizing the repeat-spacer arrays as data storage devices in bacteria. Thanks to the prokaryotes, we have on our hands the most powerful tools ever available for biological and biomedical research, revolutionizing biotechnology, agriculture and medicine. Still, the use of CRISPR-Cas as therapeutic agents in humans, looks very promising to tackle major challenges in clinical practice.