A group of scientists in Oregon has successfully modified the genes of embryos using CRISPR, a cut-and-paste gene-editing tool.
The experiments, which have not yet been subject to peer review, were conducted by biologist Shoukhrat Mitalipov and colleagues at Oregon Health & Science University in Portland, MIT Technology Review reported. Mitalipov conducted the experiments on dozens of single-celled embryos, which were discarded before they could progress very far in development, according to Technology Review. This is the first time that scientists in the United States have used this approach to edit the genes of embryos.
The CRISPR/Cas9 gene-editing system is a simple “cut and replace” method for editing precise spots on the genome. CRISPRS are long stretches of DNA that are recognized by molecular “scissors” called Cas9; by inserting CRISPR DNA near target DNA, scientists can theoretically tell Cas9 to cut anywhere in the genome. Scientists can then swap a replacement gene sequence in the place of the snipped sequence. The replacement sequence then gets automatically incorporated into the genome by natural DNA repair mechanisms.
In 2015, a group in China used CRISPR to edit several human embryos that had severe defects, though none were allowed to gestate very long before being discarded. If rumors are to be believed, the new results are more promising than those earlier efforts, according to Technology Review. The Chinese technique led to genetic changes in some, but not all of the cells in the embryos, and CRISPR sometimes snipped out the wrong place in the DNA. According to Technology Review, the new technique was used in dozens of embryos that were created for in vitro fertilization (IVF), using the sperm of men who had severe genetic defects.
In general, editing the germ line — meaning sperm, eggs or embryos — has been controversial, because it means permanently changing the DNA that is passed on from one generation to the next. Some scientists have called for a ban on germ-line editing, saying the approach is incredibly risky and ethically dubious.