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This Week in Science: Mar 20, 2015

In Science this week, researchers from the University of California, San Diego, report on the use of the genome-editing technology CRISPR/Cas9 to convert a heterozygous mutation into a homozygous one. To do so, they developed a method called mutagenic chain reaction, or MCR, which uses CRISPR/Cas9 to create autocatalytic mutations to generate homozygous loss-of-function mutations. In Drosophila, they demonstrated that MCR mutations spread from their chromosome of origin to the homologous chromosome, triggering homozygosity in the "vast majority of somatic and germline cells."

Also in Science, California Institute of Technology researcher and Nobel Laureate David Baltimore and colleagues call for a dialogue on the responsible application of CRISPR/Cas9 genome engineering and germline gene modification. In a Perspective piece, the scientists argue the need for open dialogue between scientists, bioethicists, legal experts, and the general public. They also recommend steps to ensure that the technology is used responsibly.

Finally, a team of US and European investigators describes TRICK — short for "translating RNA imaging by coat protein knock-off" — a fluorescence microscopy technique that can provide insights into the translation of single messenger RNAs both in vitro and in vivo. The method involves labeling reporter mRNAs with both red and green fluorescent proteins so that they appear yellow. When these reporters undergo translation, the green fluorescent proteins are displaced by the ribosomes, leaving the translated mRNA molecules red. The team used the technique to visualize protein synthesis in human tumor cells and in Drosophila, and determined that mRNA are not translated in the nucleus of a cell, but that they can be translated at different times throughout a cell's cytoplasm.