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This Week in PNAS: Feb 19, 2019

Editor's Note: Some of the articles described below are not yet available at the PNAS site, but they are scheduled to be posted some time this week.  

In a study scheduled to appear in the Proceedings of the National Academy of Sciences this week, researchers from the US, Russia, and Portugal present a whole-genome assembly for the white shark, Carcharodon carcharias. Using short read sequence data for a female shark from the Atlantic Ocean and Dovetail Genomics scaffolds produced from DNA for a male white shark in the Pacific, the team put together a more than 4.6 billion base white shark genome assembly, identifying 24,520 predicted protein-coding genes that were annotated with the help of RNA sequence data on several tissues from the Atlantic and two Pacific sharks. By comparing the white shark genome to sequences from the whale shark and the elephant shark, the investigators got a look at shark adaptations, including signs of positive selection on wound healing genes and expansions to a family of vomeronasal type 2 genes suspected of contributing to sharks' scent detection.

A team from the UK, China, and Uganda propose a paper-based microfluidic method for detecting DNA from the malaria-causing parasite Plasmodium falciparum. The approach brings together paper folding-assisted blood sample preparation, a microfluidic lateral flow assay, loop-mediated isothermal DNA amplification (LAMP), and detection steps, according to the study's authors. They validated the low-cost approach by testing P. falciparum samples in the lab before applying it to dozens of samples from Ugandan village schools, where the multiplex LAMP approach appeared to compare favorably with existing detection strategies used in the field such as optical microscopy and rapid immunodiagnostic tests.

Researchers from the California Institute of Technology describe a synthetic, "selfish," chromosomal genetic element known as "Cleave and Rescue," or ClvR, with potential promise for gene drive applications. The element is comprised of germline-expressed Cas9 and guide RNAs, the team explains, along with a recoded, cleavage-resistant essential gene and a "Rescue" gene that restores essential gene functions. The Cas9 and guide RNAs expressed in the germline are meant to "cleave and disrupt version of an essential gene located elsewhere in the genome," the authors write, while "a version of the essential gene resistant to cleavage, provides essential gene function." They demonstrate that four guide RNAs and a Cas9 endonuclease enzyme in a ClvR element on chromosome 3 of Drosophila melanogaster genome could knock out an essential X-linked gene in the germline, spreading the edit to fruit fly offspring.