Structural model of the Cascade surveillance machine. Credit: Ryan Jackson, Montana State University. Click for larger image
To dismantle the viruses that infect them, bacteria have evolved an immune system that identifies invading viral DNA and signals for its destruction. This gene-editing system is called CRISPR, and it’s being harnessed as a tool for modifying human genes associated with disease.
Taking another important step toward this potential application, researchers now know the structure of a key CRISPR component: a multi-subunit surveillance machine called Cascade that identifies the viral DNA. Shaped like a sea horse, Cascade is composed of 11 proteins and CRISPR-related RNA. A research team led by Blake Wiedenheft of Montana State University used X-ray crystallography and computational analysis to determine Cascade’s configuration. In a complementary study, Scott Bailey of Johns Hopkins University and his colleagues determined the structure of the complex bound to a viral DNA target.
Like blueprints, these structural models help scientists understand how Cascade assembles into an efficient surveillance machine and, more broadly, how the CRISPR system functions and how to adapt it as a tool for basic and clinical research.
Montana State University News Release
Johns Hopkins University News Release
Genetically engineered human stem cells hold promise for basic biomedical research as well as for regenerative medicine. Credit: Jeff Miller, University of Wisconsin-Madison.
Human pluripotent stem cells (hPSCs) can multiply indefinitely and give rise to virtually all human cell types. Manipulating the genomes of these cells in order to remove, replace or correct specific genes holds promise for basic biomedical research as well as medical applications. But precisely engineering the genomes of hPSCs is a challenge. A research team led by Erik Sontheimer of Northwestern University and James Thomson of the Morgridge Institute for Research at the University of Wisconsin-Madison developed a technique that could be a great improvement over existing, labor-intensive methods. Their approach uses an RNA-guided enzyme from Neisseria meningitidis bacteria—part of a recently discovered bacterial immune system—to efficiently target and modify specific DNA sequences in the genome of hPSCs. The technique could eventually enable the repair or replacement of diseased or injured cells in people with some types of cancer, Parkinson’s disease and other illnesses.
This work also was funded by NIH’s National Center for Advancing Translational Sciences.
Northwestern University News Release
After deriving induced pluripotent stem cells (iPSC) from the cells of a person with Down syndrome, researchers inserted the XIST gene to silence the third chromosome 21 copy. Credit: Lawrence lab.
Each year about 1 in 700 babies is born with Down syndrome, a condition that occurs when cells contain three copies of chromosome 21. A new technique offers a proof of principle for silencing the extra copy. Using induced pluripotent stem cells derived from a person with Down syndrome, a research team led by Jeanne Lawrence of the University of Massachusetts Medical School inserted a gene called XIST into the extra chromosome 21. The gene, which normally turns off one whole X chromosome in females, rendered the chromosome copy and most of its genes inactive. The researchers plan to test the approach in a mouse model of Down syndrome and use it to further explore the biology of chromosome errors. The findings could eventually aid the development of therapies to mitigate resulting medical problems.
This work also was funded by NIH’s National Cancer Institute and Eunice Kennedy Shriver National Institute of Child Health and Human Development.
University of Massachusetts Medical School News Release