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PLOS Biology ICYMI: February’s Five

Welcome to the second edition of the ICYMI (In Case You Missed It) blog, where we highlight recent PLOS Biology articles that may have passed you by. This time around we’ve brought you papers on topics as wide-ranging as attracting white blood cells to an infection site, how monkey brains stabilise images and the evolution of wild tomatoes!


190,000,000 Years of Plodding: Tetrapod Evolution was Slow

Image credit: Leandra Walters, 10.1371/journal.pone.0144036.g005
Image credit: Leandra Walters, 10.1371/journal.pone.0144036.g005

There are nearly 30,000 different species of tetrapod in existence today. Previous examinations of both fossil records and molecular evidence show that their origins can be traced back to the Mesozoic era, however it is not clear when major increases in the numbers of species (“speciation”) took place.

In this paper, Roger Benson, Graeme Lloyd and colleagues survey more than 27,000 fossils to argue that, over the 190 million years that made up the Mesozoic, the expansion in the number of species was relatively slow – and certainly not rapid enough to account for the numbers seen today. Instead they hypothesise short bursts of rapid species diversification, such as after the famous mass extinction event at the end of the Cretaceous (see this PLOS Biology article for an analogous post-apocalyptic expansion in birds).


Wuho Minds the Gap

Hsieh thumb
Image credit: 10.1371/journal.pbio.1002349.g010

DNA replication is an essential step towards passing on genetic information, however there are a number of potential errors that can drastically affect this process. A key area where faults can occur is at the replication fork, where the double-stranded DNA splits to allow free nucleotides to be incorporated into new copies of the two strands.

Flap endonuclease 1 (FEN1) is an enzyme present at the replication fork that’s needed to act as a “flap endonuclease”, trimming the ends of small Okazaki fragments of DNA so they can be joined together. However, FEN1 can also convert to a potentially damaging “gap endonuclease,” which may break strands of DNA and disrupt the replication process. This paper, from I-Cheng Cheng, Tao-shih Hsieh and colleagues, shows that a newly identified protein, Wuho (WH), regulates the activity of FEN1 when around a replication fork, ensuring it does more good acting as a flap endonuclease than damage as a gap endonuclease.


Exosomes Protect and Perpetuate Chemical Attractants

Image credit: 10.1371/journal.pbio.1002336.g008
Image credit: 10.1371/ journal.pbio.1002336.g008

Neutrophils, a type of white blood cell, are an important part of the body’s response to infection. They are able to locate their target by following chemical signals released at the site of an inflammation (“primary attractants”). The neutrophils themselves will then release their own chemicals (“secondary attractants”) which amplifies the signal and mobilises a greater number of these immune cells.

However, the secondary attractant chemical released by neutrophils, Leukotriene B4 (LTB4), is rather a delicate flower, and doesn’t last long outside the cell. This article from Ritankar Majumdar, Aidin Tameh and Carole Parent shows that neutrophils package LTB4 – and the enzymes needed to continue making it – inside a membrane before being released from the cell as an exosome. This protects the signal from the potentially harmful environment outside of the white blood cell, ultimately leading to an increased immune response.


When Tomatoes were Wild

Image credit: David Haak
Image credit: David Haak

Wild tomatoes have shown remarkable adaptive evolution over a relatively short time frame, creating thirteen distinct species in 2.5 million years. However the factors that have caused this rapid progression are still being debated.

James Pease, Leonie Moyle and colleagues examined the genetic differences of all thirteen wild tomato species and found evidence for three sources of variation that have driven the radiation of this group. These are post-speciation hybridization, where distinct species interbreed; de novo mutation, where random mutations arise during DNA replication; and ancestral variation, where variants are carried through from the ancestral population.


Reducing the ‘Blair Witch’ effect

We’ve all seen video footage where shaky camera movements make focussing on an image hard work. It is perhaps surprising then that in our everyday lives we view images stably, despite the continual movement of our eyes , head and body shifting images on our retinas.

Authors Tao Yao, Stefan Treue and Suresh Krishna analysed a key motion-processing area in the brains of macaque monkeys (see our featured image), and found evidence that a mechanism called “transsaccadic remapping” aids image stability. This is where certain neurons anticipate the quick, automatic eye movements know as saccades, and compensate accordingly.


Featured Image credit: Flickr user madrerik

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