BIOCHEMISTRY
▸ Fetal genome sequenced at five weeks Just five weeks into gestation, a fetus can have its DNA collected during its mother’s routine Pap smear and accurately genotyped, according to a study (Sci. Transl. Med. 2016, DOI: 10.1126/scitranslmed. aah4661). The development holds promise for early genetic testing for thousands of birth defects. To obtain such information currently, pregnant women must undergo invasive and risky procedures such as chorionic villus sampling (CVS), a tissue analysis technique, at around 10–12 weeks’ gestation or amniocentesis at 16–18 weeks. Progress has also been made in the development of tests that detect snippets of fetal DNA in a mother’s blood. However, it can be difficult to generate an accurate picture of a fetal genome from these methods. Now, a team led by Chandni V. Jain, Sascha Drewlo, and D. Randall Armant of Wayne State University School of Medicine isolated placental cells known as trophoblasts from cervical canal swabs of 20 pregnant women at five to 19 weeks’ gestation. Trophoblasts carry fetal DNA, which the team was able to isolate and distinguish from the mothers’ DNA. They also showed that the fetal DNA quality is on par with DNA obtained through CVS or amniocentesis. The authors say tests can be developed for this source of fetal DNA that could identify single gene mutations, such as those responsible for some metabolic syndromes.—ELIZABETH WILSON
BIOTECHNOLOGY
CREDIT: NAT. METHODS
▸ Protein evolution’s CRISPR way forward Directed evolution is a powerful tool that allows researchers to simulate natural selection. Many such experiments place human genes into bacteria or yeast. Researchers then randomly mutate those genes in hopes of improving a protein’s function. But Gaelen T. Hess and colleagues of Stanford University wanted to give directed evolution experiments more guidance and do the entire process in cultured human cells. So they turned to CRISPR gene editing for
CATALYSIS
Onward to simpler C–H functionalizations Selective C–H activation and functionalization has emerged as an integral strategy for organic synthesis. Chemists have already developed an abundant set of methods, and many researchers are now turning to finding ways of simplifying those strategies. In one of the latest examples, a team led by Kenichiro Itami of Nagoya University and Djamaladdin G. Musaev of Emory University has used a computational-experimental approach to create a predictive regioselective reaction for C–H imidation of aromatic compounds (Chem. Sci. NFSI, CuBr, bipyridine ligand
N
0.053
0.017 0.018
.
CuII
N
F
F
. CuII
F
Charge predicts selectivity
N
SO2C6H5
N N
SO2C6H5
(C6H5SO2)2N
Active catalyst 2016, DOI: 10.1039/c6sc04145k). One hurdle for C–H functionalization has been that it’s a two-electron oxidation process, but inexpensive first-row transition metals used as catalysts typically are capable of one-electron redox activity. The way around this problem is to use two concurrent one-electron oxidations, which typically requires two catalysts. Itami, Musaev, and their team have found that treating copper bromide and a bipyridine ligand with the commercially available oxidizing reagent N-fluorobenzenesulfonimide (NFSI) leads to a new class of dinuclear copper catalysts in which the two Cu(II) centers work collectively to guide NFSI-promoted aromatic C–H imidation. As a bonus to the process, the researchers developed a way to calculate the charge on carbon atoms in aromatic molecules to predict which C–H bond is favored for imidation (shown above).—STEVE RITTER
inspiration and developed a new method called CRISPR-X, which allows scientists to study effects of random mutations in small stretches of DNA (Nat. Methods 2016, DOI: 10.1038/nmeth.4038). First, a
Fused MS2 and AID proteins are recruited to the dCas9 site where AID induces DNA mutations (stars).
catalytically dead version of the protein Cas9, called dCas9, is directed to a location along the genome matching its guide RNA. To induce mutations in the region, the team appended two hairpin loops that bind a viral protein called MS2 to the guide RNA. Finally, the MS2 protein, which the researchers fused to a mutation-inducing enzyme called AID, is expressed in the cell. There, it is recruited to the dCas9, enabling hypermutation at that site. “This is much more targeted than what people have done before,” Hess says. He foresees researchers using the system to mutate two different protein binding sites to study protein-protein interactions and to study mammalian regulatory elements that turn genes on and off.—RYAN CROSS NOVEMBER 7, 2016 | CEN.ACS.ORG | C&EN
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