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Showing posts with label Biology. Show all posts
Showing posts with label Biology. Show all posts

Monday, 27 January 2020

A new type of evolutionary process has been highlighted


Evolution and natural selection takes place at the DNA level, because genes mutate and genetic traits persist or get lost over time. But now biologists believe that evolution can take place on a whole new scale - transmitted not by genes, but by molecules linked to their surface and responsible for their methylation. This mechanism would allow the conservation of an epigenome by enzymatic processes through several tens of millions of years, according to a process analogous to that of the Darwinian evolution of the genome.

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These molecules, known as "methyl groups", modify the structure of DNA and can turn genes on and off. The alterations are known as "epigenetic changes". Many organisms, including humans, have DNA dotted with methyl groups, but creatures like Drosophila and roundworms have lost the genes necessary to do so during the evolutionary period.

Another organism, the yeast Cryptococcus neoformans , also lost key genes for methylation during the Cretaceous, about 50 to 150 million years ago. But remarkably, in its current form, the fungus still has methyl groups in its genome. Now, scientists theorize that C. neoformans was able to conserve epigenetic changes for tens of millions of years, thanks to a new mode of evolution. The study was published in the journal Cell.


Methyl groups present in C. neoformans

The authors generally study C. neoformans to better understand how yeast causes fungal meningitis in humans. The fungus tends to infect people with weak immune systems and causes about 20% of all AIDS-related deaths.

Hiten Madhani, professor of biochemistry and biophysics at the University of California, and his colleagues, spend part of their days researching the genetic code of C. neoformans , looking for critical genes that help yeast invade human cells.

But the team was surprised when reports emerged, suggesting that the genetic material was adorned with methyl groups. In vertebrates and plants, cells add methyl groups to DNA using two enzymes. The first, de novo methyltransferase, links methyl groups to unadorned genes.

Diagram explaining the functioning of methylation via the intervention of de novo methyltransferase and maintenance methyltransferase. Credits: Nature


The enzyme adds to each half of the helical DNA strand the same methyl group pattern, creating a symmetrical design. During cell division, the double helix unwinds and builds two new strands of DNA from the corresponding halves. At this stage, an enzyme called "maintenance methyltransferase" intervenes to copy all the methyl groups from the original strand to the newly constructed half.

De novo methyltransferase loss and maintenance of methyltransferase compensation

Madhani and his colleagues examined existing evolutionary trees to trace the history of C. neoformans over time and found that, during the Cretaceous period, the ancestor of the yeast had the two enzymes necessary for the methylation of l DNA. But somewhere along the line, C. neoformans lost the gene needed to make de novo methyltransferases

During its evolutionary process, C. neoformans lost de novo methyltransferase and retained the maintenance methyltransferase. Credits: Sandra Catania et al. 2020

Without the enzyme, the body could no longer add new methyl groups to its DNA - it could only copy existing methyl groups by using its maintenance enzyme. In theory, even when working alone, the maintenance enzyme could keep DNA covered with methyl groups indefinitely - if it could make a perfect copy every time.

Natural selection at the origin of the conservation of a methylation mechanism

In reality, the team discovered that the enzyme makes mistakes and loses track of methyl groups every time the cell divides. When grown in a petri dish, C. neoformans cells occasionally gain new methyl groups in the same way that random mutations occur in DNA. However, cells lost methyl groups about 20 times faster than they could gain new ones.

In about 7,500 generations, each last methyl group would disappear, leaving nothing to be copied by the maintenance enzyme, the team estimated. Given the speed at which C. neoformans multiplies, the yeast should have lost all of its methyl groups in about 130 years. Instead, it retained the epigenetic changes for tens of millions of years.

Despite the loss of DNMT, C. neoformans can still use methylation thanks to compensation by its maintenance methyltransferase. A process preserved by natural selection. Credits: Sandra Catania et al. 2020

“ Because the rate of loss is higher than the rate of gain, the system would slowly lose methylation over time if there were no mechanism to maintain it. This mechanism is natural selection, ”explains Madhani. In other words, even if C. neoformans gained new methyl groups much more slowly than it lost them, methylation considerably increased the endurance of the organism, which meant that it could surpass individuals with less methylation.

Use methylation to control transposons

Enduring individuals have prevailed over those with fewer methyl groups, and thus, methylation levels have remained higher over millions of years. But what evolutionary advantage could these methyl groups offer to C. neoformans ? Well, they could protect the yeast genome from life-threatening damage.

Transposons, also known as "jumping genes", jump into the genome at will and often fit into very impractical places. For example, a transposon could jump to the center of a gene necessary for cell survival; this cell could malfunction or die. Fortunately, the methyl groups can cling to the transposons and lock them in place. It may be that C. neoformans maintain a certain level of DNA methylation to control transposons.


Understanding methylation in C. neoformans

Many mysteries still surround DNA methylation in C. neoformans . Besides copying methyl groups between strands of DNA, maintenance methyltransferase appears to be important in terms of how yeast causes infection in humans, according to a 2008 study by Madhani. Without the intact enzyme, the body cannot attack cells as effectively.

The enzyme also requires large amounts of chemical energy to function and copies only the methyl groups on the pristine half of the replicated DNA strands. In comparison, the equivalent enzyme in other organisms does not require additional energy to function and sometimes interacts with naked DNA, devoid of any methyl group. Further research will reveal exactly how methylation works in C. neoformans and whether this new form of evolution occurs in other organisms.


Bibliography:

Evolutionary Persistence of DNA Methylation for Millions of Years after Ancient Loss of a De Novo Methyltransferase

Sandra Catania, Phillip A. Dumesic, Harold Pimentel,  Ammar Nasif
Caitlin I. Stoddard
Jordan E. Burke
Jolene K. Diedrich
Sophie Cook
Terrance Shea
Elizabeth Geinger
Robert Lintner
John R. Yates III
Petra Hajkova
Geeta J. Narlikar
Christina A. Cuomo
Jonathan K. Pritchard
Hiten D. Madhani

Published:January 16, 2020

DOI:https://doi.org/10.1016/j.cell.2019.12.012

Friday, 24 January 2020

Snakes are believed to be the cause of reported coronavirus disease in China



Since late December, a new coronavirus respiratory disease has emerged in China. It has already caused several hundred victims. Now, the new strain of coronavirus baptized 2019-nCoV by the WHO, has spread to several other countries. To better understand the virus, virologists must trace its origin and the animal host through which it first passed before infecting humans. A recent study shows that 2019-nCoV was transmitted to humans in the Wuhan market from snakes.

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Snakes - Chinese krait and Chinese cobra - may be the initial source of the newly discovered coronavirus that triggered the onset of a deadly infectious respiratory disease in China this winter. The disease was first reported in late December 2019 in Wuhan, a large city in central China, and quickly spread. Since then, sick travelers from Wuhan have infected people in China and other countries, including the United States.

Using samples from the virus isolated from patients, Chinese scientists determined the genetic code of the virus and observed it. The pathogen responsible for this pandemic is a new coronavirus. It belongs to the same family of viruses as the well-known severe acute respiratory syndrome coronavirus SARS-CoV, and the Middle East respiratory syndrome coronavirus (MERS-CoV), which have killed hundreds of people in the past 17 years. The World Health Organization (WHO) has named the new coronavirus “2019-nCoV”.


What is coronavirus?

The name of the coronavirus comes from its shape, which resembles a crown or a solar crown when imaged using an electron microscope. The coronavirus is transmitted by air and mainly infects the upper respiratory and gastrointestinal tracts of mammals and birds.

Although most members of the coronavirus family cause only mild flu-like symptoms during infection, SARS-CoV and MERS-CoV can infect the upper and lower respiratory tract, causing severe respiratory illness and other complications in humans.

The 2019-nCoV coronavirus observed under the electron microscope. Credits: CDC Chine

2019-nCoV causes symptoms similar to those of SARS-CoV and MERS-CoV. People infected with these coronaviruses suffer from a severe inflammatory reaction. Unfortunately, no approved antiviral vaccine or treatment is available for coronavirus infection. A better understanding of the 2019-nCoV life cycle, including the source of the virus, how it is transmitted and how it replicates is necessary to prevent and treat the disease.

2019-nCoV: an initial transmission from animals to humans

SARS and MERS are classified as zoonotic viral diseases, which means that the first infected patients acquired these viruses directly from animals. This was possible because, in the host animal, the virus had acquired a series of genetic mutations which allowed it to infect and multiply inside humans.

These viruses can now be transmitted between humans. Field studies have revealed that the original source of SARS-CoV and MERS-CoV is the bat and that masked palm civets (a mammal native to Asia and Africa) and camels , respectively, are used intermediate hosts between bats and humans.

This graph shows the origins of the different coronaviruses. The initial strains all come from bats. Credits: Science

In the case of this coronavirus epidemic in 2019, reports indicate that most of the patients in the first hospital group were workers or customers of a local wholesale seafood market which also sold processed meats and consumable animals living.

Including poultry, donkeys, sheep, pigs, camels, foxes, badgers, bamboo rats, hedgehogs and reptiles. However, as no one has ever reported finding a coronavirus infecting aquatic animals, it is plausible that the coronavirus may have originated from other animals sold in this market.

A disease transmitted by bats?

The hypothesis that nCoV 2019 comes from an animal on the market is strongly supported by a new publication in the journal Journal of Medical Virology . Virologists have analyzed and compared the genetic sequences of 2019-nCoV and all other known coronaviruses.

Study of the 2019-nCoV genetic code reveals that the new virus is most closely linked to two samples of bat SARS-type coronavirus from China, initially suggesting that, like SARS and MERS, the bald -mouse could also be behind 2019-nCoV.

The authors further found that the DNA coding sequence for the 2019-nCoV peak protein, which forms the crown of the viral particle that recognizes the receptor on a host cell, indicates that the bat virus may have mutated before infecting people. But when the researchers performed a more detailed bioinformatic analysis of the 2019-nCoV sequence, it suggested that this coronavirus could have come from snakes.

2019-nCoV: it would have gone from the bat to the snake

The researchers used an analysis of the protein codes favored by the new coronavirus and compared it to the protein codes of the coronaviruses found in different animal hosts, such as birds, snakes, marmots, hedgehogs, manis, bats and humans. Surprisingly, they found that the 2019-nCoV protein codes are most similar to those used in snakes.



Snakes often hunt bats in the wild. Reports indicate that the snakes were sold in the local seafood market in Wuhan, raising the possibility that 2019-nCoV has passed from the host species - bats - to snakes, and then to humans at the start of this. coronavirus epidemic. However, how the virus could adapt to both cold-blooded and warm-blooded hosts remains a mystery.

The authors of the report and other researchers must verify the origin of the virus by laboratory experiments. The first thing to do is to find the 2019-nCoV sequence in snakes. However, since the epidemic, the seafood market has been disinfected and closed, making it difficult to trace the source animal of the new virus.

DNA sampling from market animals and wild snakes and bats is necessary to confirm the origin of the virus. However, the results reported will also provide information on the development of prevention and treatment protocols.


Bibliography:

RESEARCH ARTICLE:  Homologous recombination within the spike glycoprotein of the newly identified coronavirus may boost cross‐species transmission from snake to human

Wei Ji  Wei Wang  Xiaofang Zhao  Junjie Zai  Xingguang Li

First published: 22 January 2020

https://doi.org/10.1002/jmv.25682

Unknown ancient viruses discovered in a Tibetan glacier


A set of unknown viruses has been discovered in a glacier in the northwest of the Tibetan plateau in China. Researchers recently dissolved samples after examining two ice cores from the site, revealing the existence of 28 groups of viruses never seen before.

Studying these mysterious viruses could provide researchers with crucial information to determine which viruses have thrived in different climates and environments over time.

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" However, in the worst case scenario, this melting ice [due to climate change] could release pathogens into the environment, " wrote the researchers in the study, which has not yet been peer reviewed. . If this happens, it's best to know as much as you can about these viruses, the researchers wrote. The results of the research have been available for consultation on the bioRxiv server since January 7.

Studying ancient glacial organisms can be difficult. Indeed, it is extremely easy to contaminate samples of ice cores with current bacteria. Thus, the researchers created a new microbial and viral sampling protocol.


A new sampling protocol to avoid contamination

In this case, the two samples of ice cores, from the Guliya ice cap on the Tibetan plateau, were collected in 1992 and 2015. However, at that time, no specific measures were taken to avoid microbial contamination during drilling, handling or transporting carrots.

In other words, the outside of these ice cores was contaminated. But the interior was still pristine, the researchers wrote in the study. To access the inner part of the carrots without contaminating it, the researchers installed themselves in a cold room (at -5 degrees Celsius) and used a sterilized band saw to cut 0.5 cm of the ice from the outer layer. They then washed the ice cores with ethanol to melt another 0.5 cm of ice. Finally, they washed the next 0.5 cm with sterile water.

After this work (removal of 1.5 cm of ice), the researchers reached an uncontaminated layer which they were able to study. This method has proven to be effective even during tests in which they had coated the outer layer of the ice with other bacteria and viruses.

The experiment revealed 33 groups of viruses (or genera) in ice cores. Of these, 28 were previously unknown to science, the researchers said. " The microbes differed considerably across the two ice cores, presumably representing very different climatic conditions at the time of deposition, " the document said. It is not surprising that the glacier has kept these mysterious viruses for so long, they add.

" We are very far from sampling all the diversity of viruses on Earth, " says Chantal Abergel to Vice , researcher in environmental virology at the National Center for Scientific Research, who did not participate in the study.



Since human-induced climate change is melting glaciers around the world, these viral archives could be lost, the researchers noted. The study of ancient viruses “offers a first window on viral genomes and their ecology linked to glaciers. It also highlights their likely impact on today's abundant microbial groups, ”the researchers wrote.


Bibliography:

Glacier ice archives fifteen-thousand-year-old viruses

Zhi-Ping Zhong, Natalie E. Solonenko, Yueh-Fen Li, Maria C. Gazitúa, Simon Roux, Mary E. Davis, James L. Van Etten, Ellen Mosley-Thompson, Virginia I. Rich, Matthew B. Sullivan, Lonnie G. Thompson

doi: https://doi.org/10.1101/2020.01.03.894675

Wednesday, 22 January 2020

This strange organism from the depth could hold secrets about the origins of complex life on Earth

Illustration of a eukaryotic cell. They evolved from single-celled organisms about 2 billion years ago. | Shutterstock

A mysterious microbe discovered in the depths of the Pacific Ocean could hold the secrets of the evolution of the first muticellular life forms. Indeed, according to a new study, the little “tentacle organism” could tell us about what allowed life to become more complex during the early stages of evolution.

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Long before complex living things existed, the world was home to simple single-celled organisms, archaea and bacteria. Between 2 and 1.8 billion years ago, these microorganisms began to evolve, leading to the emergence of more complex life forms, called eukaryotes.

The field of eukaryotes today includes humans, animals, plants and fungi. But this incredible evolution from aquatic life to life out of the water, then to walking - and for more advanced beings, thought and feeling, is still poorly understood by scientists.


The Asgard archaea, potential ancestors of eukaryotes

In a previous study, biologists hypothesized that an archival group called Asgard archaea (the archaea of ​​Asgård) regrouped the much sought-after ancestors of eukaryotes because they contain genes similar to their complex counterparts.

To analyze what these microbes looked like and how this transition could have happened, a group of Japanese researchers then spent a decade collecting and analyzing the mud from the bottom of Omine Ridge, off the coast of Japan. The results of the study were published on January 15 in the journal Nature.

The team stored the mud samples (and the microorganisms found there) in a special bioreactor, in a laboratory environment that mimics the conditions of the deep sea in which they were found.

Years later, they began to isolate the microorganisms in samples. The researchers' original goal was to find methane-consuming microbes that might be able to clean up the wastewater, according to the New York Times . But when they discovered that their samples contained an unknown strain of Asgard archaea, they decided to analyze it and grow it in the laboratory.

These images obtained by scanning electron microscopy show (A) an isolated archaea, (B) several cells developing together in the laboratory archaea, and (C&D) with tentacle-like protrusions, which develop towards the end of their growth. Credits: Japan Agency for Marine and Land Science and Technology (JAMSTEC)

Prometheoarchaeum syntrophicum , a new strain of Asgard archaea

They named the newly found strain of Asgard archaea “ Prometheoarchaeum syntrophicum “, after the Greek god Prometheus, who is said to have created humans out of mud, according to mythology.

The researchers found that these archaea were grown relatively slowly, doubling only every 14 to 25 days. Their analysis then confirmed that P. syntrophicum had a large number of genes similar to those of eukaryotes. In fact, these genes held the instructions to create certain proteins present inside these microbes. However, as expected, proteins did not create organelle-like structures like those found inside eukaryotes.

They also found that the microbes had long, branched, tentacle-like protrusions on the outside that could be used to catch passing bacteria. Indeed, the team discovered that microbes tended to stick to other bacteria in the petri dishes.


An elegant hypothesis explaining the changes in P. syntrophicum

The authors offer an interesting hypothesis for what happened in these ancient waters, which they explain in a recently published video (available at the end of the article): about 2.7 billion years ago, oxygen a started to accumulate on Earth. But having lived so long in a world without oxygen, this element would prove to be toxic for P. syntrophicum .

So P. syntrophicum may have developed a new adaptation: a way of forming bonds with oxygen-tolerant bacteria. These bacteria would have provided P. syntrophicum with the vitamins and compounds necessary to survive, while in turn feeding on archaeal waste.

As oxygen levels increased even more, P. syntrophicum could have become more aggressive, uprooting passing bacteria with its long tentacle-like structures and integrating them. Inside P. syntrophicum , this bacterium would eventually have evolved into an energy-producing organelle, the key to eukaryotic survival: the mitochondria.

The success of the team in the culture of Prometheoarchaeum , after efforts spanning more than a decade, “represents a huge breakthrough for microbiology”, writen by an accompanying editorial Christa Schleper and Filipa L. Sousa, two researchers from the University of Vienna, who did not participate in the study. " It opens the way to the use of molecular and imaging techniques to further elucidate the metabolism of Promethéoarché and the role of eukaryotic signature proteins in biology of Archean cells " they added.



Bibliography:

Isolation of an archaeon at the prokaryote–eukaryote interface

Hiroyuki Imachi, Masaru K. Nobu, Nozomi Nakahara, Yuki Morono, Miyuki Ogawara, Yoshihiro Takaki, Yoshinori Takano, Katsuyuki Uematsu, Tetsuro Ikuta, Motoo Ito, Yohei Matsui, Masayuki Miyazaki, Kazuyoshi Murata, Yumi Saito, Sanae Sakai, Chihong Song, Eiji Tasumi, Yuko Yamanaka, Takashi Yamaguchi, Yoichi Kamagata, Hideyuki Tamaki & Ken Takai

Nature volume 577, pages519–525(2020)

Thursday, 21 November 2019

First detection of sugars necessary for life found in meteorites



The origin of life on Earth is an open question and represents a field of active research. Although prebiotic models of the appearance of life have been proposed, the process of appearance of building blocks of life (amino acids, nucleic acids, sugars, etc.) is still very little constrained. One of the hypotheses currently proposed proposes an extraterrestrial origin of these components within the framework of a model called panspermia. In this model, the constituents of life would have been brought to the primitive Earth through the incessant bombardment of comets and meteorites. And recently, researchers have for the first time discovered ribose and other sugars necessary for life in two meteorites, thus reinforcing this hypothesis.

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An international team of researchers has found sugar molecules essential for life in meteorites. This new discovery adds to the growing list of biologically important compounds found in meteorites, furthering the hypothesis that chemical reactions in asteroids - the parent bodies of many meteorites - can make certain life ingredients. If this is correct, the bombardment of meteorites on the primitive Earth may have helped the appearance of life by providing the basic elements.


First direct evidence of the existence of extraterrestrial ribose

The team discovered ribose and other bio-essential sugars, including arabinose and xylose, in two carbon-rich meteorites, NWA 801 (CR2 type) and Murchison (CM2 type).

Ribose is a crucial component of RNA (ribonucleic acid). RNA serves as a messenger molecule, copying the genetic instructions of the DNA molecule (deoxyribonucleic acid) and transmitting them to molecular factories within the cell, called ribosomes, which read RNA to construct specific proteins.

Structures of sugars (pentoses) discovered in the two meteorites. Credits: Yoshihiro Furukawa et al. 2019

" Other important elements in life have already been discovered in meteorites, including amino acids (protein components) and nucleic bases (components of DNA and RNA), but sugars have been an element missing among the main building blocks of life, "said Yoshihiro Furukawa of Tohoku University, Japan. " The research provides the first direct evidence of ribose in space and the contribution of sugar to Earth. The extraterrestrial sugar could have contributed to the formation of RNA on the prebiotic Earth, which probably led to the origin of life .

" It's remarkable that a molecule as fragile as ribose can be detected in such an old material, " says Jason Dworkin, an astrobiologist at NASA's Goddard Center. " These results will help guide our sample analyzes of the original Ryugu and Bennu asteroids, which will be returned by Hayabusa 2 of the Japan Aerospace Exploration Agency and NASA's OSIRIS-REx space probe ."


Ribose: a sugar used in the composition of RNA

A persistent mystery about the origin of life is how biology could have come from non-biological chemical processes. DNA contains the genetic instructions necessary for the functioning of a living organism. However, RNA also contains information and many researchers believe that it evolved first and was later replaced by DNA. This is because RNA molecules have abilities that are lacking in DNA.

Structure of the RNA. RNA uses ribose as sugar, unlike DNA that uses deoxyribose. Credits: BioC

RNA can reproduce without the need for other molecules, and it can also initiate or accelerate chemical reactions as a catalyst. These results support the possibility that RNA has coordinated the mechanism of life before DNA.

" The sugar contained in DNA (2-deoxyribose) was not detected in any of the meteorites analyzed in this study. This is important because there may be a lack of extraterrestrial ribose delivery to the early Earth, which is consistent with the hypothesis that RNA evolved first, "explains Danny Glavin.

Sugars brought by meteorites from space

The team discovered sugars by analyzing powdered meteorite samples using gas chromatography mass spectrometry, which sorts and identifies molecules based on their mass and electrical charge. They found that the abundances of ribose and other sugars ranged from 2.3 to 11 parts per billion in NWA 801, and from 6.7 to 180 parts per billion in the Murchison meteorite.

With the Earth now full of life, the team had to take into account the possibility that meteorite sugars could have simply come from a terrestrial contamination. Several sources of data indicate that contamination is unlikely, including isotopic analysis. Isotopes are versions of a different mass element because of the number of neutrons in the nucleus of the atom.

The isotopic analysis of the sugars found in the meteorites confirmed that they came from space, not from the Earth. Credits: Yoshihiro Furukawa et al. 2019

Carbon chemistry on Earth uses carbon 12 compared to the heavier version (carbon 13). However, the carbon contained in meteorite sugars was significantly enriched in carbon 13, beyond the amount observed in terrestrial biology, which corroborates the conclusion that it comes from space.

Towards a better understanding of the emergence of life on Earth

The team plans to analyze more meteorites to get a better idea of ​​the abundance of extraterrestrial sugars. They also plan to determine whether extraterrestrial sugar molecules have a preferred left or right orientation. Some molecules come in two varieties that are inverted images of each other. On Earth, life uses left amino acids and straight sugars.

Since it is possible that the opposite works perfectly - right amino acids and left sugars - scientists want to know where this preference comes from. If some processes in asteroids favor the production of one variety over another, then perhaps the influx from space via meteorite impacts has made this variety more abundant on the ancient Earth.

Bibliography:

 Extraterrestrial ribose and other sugars in primitive meteorites

 Yoshihiro Furukawa, Yoshito Chikaraishi, Naohiko Ohkouchi,  View ORCID ProfileNanako O. Ogawa, Daniel P. Glavin,  View ORCID ProfileJason P. Dworkin, Chiaki Abe, and Tomoki Nakamur

PNAS first published November 18, 2019

https://doi.org/10.1073/pnas.1907169116


Tuesday, 5 November 2019

How do bacteria alter Drosophila behavior?

 Confronted with microorganisms that share their environment, eukaryotes have mechanisms to contain them. When this immune barrier is crossed and the animal is infected, other biological processes are triggered that limit the consequences of the infection. In a study published in the eLife journal , researchers show that Drosophila females infected with bacteria lay fewer eggs than healthy females. They provide evidence that this behavioral adaptation is due to the direct detection of a universal compound present in the bacterial wall , called peptidoglycan , by only a few neurons present in the brain of flies.

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Anyone who has been victim of a viral or bacterial infection knows the side effects that result in a loss of appetite , a fragmented sleep and, in extreme cases, a depressive state. While these "side effects" that reflect the impact of microorganisms on the host's nervous system have been clearly established, the nature of the microbial vectors of the effect and the precise identity of the targeted neurons remain, in most cases, unknown.

Figure: (Left): In the absence of infection, fertilized female Drosophila eggs. (Right): During an infection, the proliferating bacteria produce fragments of peptidoglycan, a component of their wall, in the extracellular medium. By unknown mechanisms, this compound of the bacterial wall enters the brain. Its detection by only one or two neurons (framed), of the 100,000 or so contained in the brain of a Drosophila, causes their inhibition (lowering of calcium levels) and, ultimately, a slowdown in egg deposition. It is likely that this drop in egg yield allows the infected Drosophila to allocate as much energy as possible.to fight against infection. Once infection is controlled, the level of spawning returns to normal. This is a case of behavioral immunity.
© Ambra Masuzzo.

The researchers had shown in a previous study that egg-laying behavior of fruit-infected Drosophila was modified, with infected females laying fewer eggs than their healthy counterparts. This work provided evidence that the detection of a major and universal component of the bacterial wall, the peptidoglycan, by infected Drosophila neurons alters their behavior. The next step was to identify precisely these neurons and to demonstrate how this bacterial compound could modify their activity.


In this new publication, researchers use the powergenetic and molecular tools available in Drosophila to demonstrate that by acting on only one or two of the 100,000 neurons contained in the Drosophila brain, the bacterial compound alters the behavior of the host. Using calcium imaging to measure intracellular calcium concentration, the authors demonstrate that direct application of bacterial peptidoglycan in vivo or ex vivo is sufficient to block the activity of these neurons. It remains to understand the mechanisms by which the detection of peptidoglycan and activationNF-kB signaling pathway block their activity. The cellular mechanisms that allow the peptidoglycan to reach these neurons by crossing the blood-brain barrier also remain to be elucidated.


The question now arises of the generalization of these discoveries to vertebrates . Several elements suggest that the mechanism could be conserved beyond invertebrates. On the one hand, the peptidoglycan of bacteria produced by the microbiota of mice was detected in the circulationblood and is able to cross the blood-brain barrier. In addition, mutant mice for peptidoglycan receptors exhibit behavioral disorders and social interactions. The recently published work adds an important piece to the complex puzzle that governs interactions between the microbial world and the nervous system of eukaryotes.

Source

Sunday, 3 November 2019

Brain recognizes familiar music at lightning speed


One snippet of music suffices: our brain recognizes familiar songs with surprising speed. It takes only 100 to 300 milliseconds to classify a piece of music as known, as experiments reveal. But the recognition does not only show in the brain: Our pupils react too. They widen with excitement when we hear a familiar and popular song.

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Music is deeply rooted in our human nature: There is hardly a culture worldwide that knows no music, and unborn children in the womb react to melodious sounds. Above all, the sound of music develops a strong emotional effect . It can make us cry, awaken memories - or cause uproar.

How certain music affects a person, however, is completely different. This is evidenced, for example, by the fact that everyone has a different favorite song. Where one of them turns off the radio annoyed, the other one turns up loud and sings along at the top of his voice.

Song recognized?

Interestingly enough, our most popular pieces of music seem to be anchored in the brain in a special way: often just a few notes are enough to recognize the song. But how fast can the thinking organ identify familiar melodies? Robert Jagiello from University College London and his colleagues have now taken the test.

For their study, the researchers recruited five men and five women, each of whom named five pop songs known to them, connecting them with positive feelings and memories. For each of these songs, Jagiello's team chose a counterpart - a song that sounded similar in tempo, melody, harmony, and song, but was unknown to the participants.

A matter of milliseconds

In the crucial experiment, the scientists then alternately played less than a second of the known and unknown songs to the study participants. They used electroencephalography (EEG) to observe how the brain responded to these musical snippets. They also measured the dilation of the pupils, which is considered a sign of excitement.

The results revealed that the mind recognized familiar songs surprisingly quickly. It took only 100 to 300 milliseconds to classify a music excerpt as known. This was shown on the one hand by a clear pupil reaction. On the other hand, Jagiello and his colleagues found an activation of cortical brain regions involved in recalling memories.

Benefit for the therapy

"Our results show that familiar music is recognized remarkably quickly. This points to a fast temporal circuit and underlines how deeply such pieces of music are anchored in our memory, "says Jagiello's colleague Maria Chait. The scientists suspect that this particular reaction to the music has to do with the positive emotions associated with it.

According to the team, the results may also be relevant to therapeutic approaches: "Understanding how the brain recognizes familiar melodies can be very useful for music therapy. For example, there is a growing interest in learning about people with dementia through music. Because the memory of music is often kept for a surprisingly long time, "explains Chait.

Identifying the neural processes that enable the recognition of music could thus help to better understand this and other phenomena.

Source

Saturday, 2 November 2019

New powerful ranavirus discovered that can spread among amphibians


Of the invasive pathogens that are decimating the reptile populations in various areas the United States we have already mentioned and now a new study, appeared in the journal Ecological Modeling and produced by researchers of the University of Tennessee, shows the existence of a new ranavirus similar to a Frog virus 3 (FV3).

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The new ranavirus, called RCV-Z2, can, according to researchers who have developed a specific model to predict its spread, spread just as quickly in a tadpole population of North American wood frogs ( Lithobates sylvaticus ) and transmission can occur in a very efficient through direct contact, through necrophagy (if the subjects feed on the bodies of other infected subjects) or even by water.

The ranaviruses are pathogens that are emerging globally and affect mainly reptiles, amphibians and fish threatening the ecological diversity of these species and therefore all the eco-environments in which they are found.
To combat the ranavirus emergency, which has become global, researcher Matt Gray founded and directs the Global Ranavirus Consortium.


The same Gray states in the press release published on the University of Tennessee website:
"In our previous work, we discovered that RCV-Z2 is a recombinant ranavirus that has the DNA of a strain in North America and one from Europe and Asia. We think these viruses mixed DNA on a frog farm in South Georgia: the result was a highly virulent hybrid virus. The point of this modeling effort was to demonstrate how this virus evolved with the DNA of the eastern hemisphere can infect and spread into a kind of amphibian. The news is not good ".

And this without counting the trade in amphibians and other wild animals that may be subject to these infections: with a trade of this type their pathogens can be moved around the world, something that could make the infection truly global.

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