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For Those Long Legs

Researchers have homed in on the genes that give daddy longlegs their characteristically long legs, New Scientist reports.

A University of Wisconsin-Madison-led team sequenced the genome of Phalangium opilio, alternatively known as daddy longlegs or harvestmen,which are spider relatives. As they report in the Proceedings of the Royal Society B, the researchers found that its genome shows no signs of having undergone a whole-genome duplication and only harbors a single Hox gene cluster. They investigated the functions of three Hox genes — Deformed (Dfd), Sex combs reduced (Scr), and a homolog of Epidermal growth factor receptor (Egfr) — through RNAi knockdown studies.

Knocking down Dfd affected the length of P. opilio's first two legs, while knocking down Dfd as well as Scr led legs one through three to develop as pedipalps, though Scr knockdown on its own had no noticeable effect. Meanwhile, Egfr knockdown affected leg segmentation, a trait that usually allows daddy longlegs to wrap their legs around objects.

"We've shown… how the combinations of these genes create a blueprint in the embryo to differentiate between what's going to be a leg that is used for walking and what is going to be a pedipalp, which can be used to manipulate food and assess the surroundings," first author Guilherme Gainett from Wisconsin-Madison tells New Scientist.

The Scan

Booster for At-Risk

The New York Times reports that the US Food and Drug Administration has authorized a third dose of the Pfizer-BioNTech SARS-CoV-2 vaccine for people over 65 or at increased risk.

Preprints OK to Mention Again

Nature News reports the Australian Research Council has changed its new policy and now allows preprints to be cited in grant applications.

Hundreds of Millions More to Share

The US plans to purchase and donate 500 million additional SARS-CoV-2 vaccine doses, according to the Washington Post.

Nature Papers Examine Molecular Program Differences Influencing Neural Cells, Population History of Polynesia

In Nature this week: changes in molecular program during embryonic development leads to different neural cell types, and more.