Women have bigger pupils than men

From an anatomical point of view, a normal, non-pathological eye is known as an emmetropic eye, and has been studied very little until now in comparison with myopic and hypermetropic eyes. The results show that healthy emmetropic women have a wider pupil diameter than men. 

The pupil regulates the amount of light that reaches the retina [Credit: Michael Dawes]

Normal, non-pathological emmetropic eyes are the most common type amongst the population (43.2%), with a percentage that swings between 60.6% in children from three to eight years and 29% in those older than 66. 

Therefore, a study determines their anatomical pattern so that they serve as a model for comparison with eyes that have refractive defects (myopia, hypermetropia and stigmatism) pathological eyes (such as those that have cataracts). 

"We know very little about emmetropic eyes even though they should be used for comparisons with myopic and hypermetropic eyes" Juan Alberto Sanchis-Gimeno, researcher at the University of Valencia and lead author of the study explains to SINC. 

The project, published in the journal 'Surgical and Radiologic Anatomy' shows the values by gender for the central corneal thickness, minimum total corneal thickness, white to white distance and pupil diameter in a sample of 379 emmetropic subjects. 

"It is the first study that analyses these anatomical indexes in a large sample of healthy emmetropic subjects" Sanchis-Gimeno states. In recent years new technologies have been developed, such as corneal elevation topography, which allows us to increase our understanding of in vivo ocular anatomy. 

Although the research states that there are no big differences between most of the parameters analysed, healthy emmetropic women have a wider pupil diameter than men. 

"It will be necessary to investigate as to whether there are differences in the anatomical indexes studied between emmetropic, myopic and hypermetropic eyes, and between populations of different ethnic origin" the researcher concludes. 

How the human eye works 

Light penetrates through the pupil, crosses the crystalline lens and is projected onto the retina, where the photoreceptor cells turn it into nerve impulses, and it is transferred through the optic nerve to the brain. Rays of light should refract so that they can penetrate the eye and can be focused on the retina. Most of the refraction occurs in the cornea, which has a fixed curvature. 

The pupil is a dilatable and contractile opening that regulates the amount of light that reaches the retina. The size of the pupil is controlled by two muscles: the pupillary sphincter, which closes it, and the pupillary dilator, which opens it. Its diameter is between 3 and 4.5 millimetres in the human eye, although in the dark it could reach up to between 5 and 9 millimetres. 

The study is published in 'Surgical and Radiologic Anatomy' 

Source: Plataforma SINC via AlphaGalileo [April 26, 2012]

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Researchers discover bats may be a common source of many viral diseases

International researchers under the aegis of the University of Bonn have discovered the probable cause of not just one, but several infectious agents at the same time. Paramyxoviruses originate from ubiquitous bats, from where the pathogens have spread to humans and other mammals. This could make eradicating many dangerous diseases significantly more difficult than had been thought. The results of this study have just been published in the current issue of Nature Communications. 

[Image (c) Florian Gloza-Rausch/Uni Bonn/Noctalis Bad Segeberg]

Where do viruses dangerous to humans come from, and how have they evolved? Scientists working with Prof. Dr. Christian Drosten, Head of the Institute for Virology at the Universitätsklinikum Bonn, have made significant progress in answering this question. "We already knew from prior studies that bats and rodents play a role as carriers of paramyxoviruses," said Prof. Drosten. The many varied members of this large virus family cause, e.g., measles, mumps, pneumonias and colds. The highly dangerous Hendra and Nipah viruses cause types of encephalitis that result in death for one out of two patients. Paramyxoviruses also play a role in veterinary medicine, causing e.g., canine distemper or rinderpest. 

Researchers double the number of known paramyxovirus species 

With support from numerous scientific institutes in Germany and around the world, they tested a total of 9,278 animals from Europe, South America and Asia, including 86 bat and 33 rodent species. "These animals live in very large social communities with millions of individuals in some cases," reported the Bonn virologist. "Their close contact promotes mutual infection and provides for great variety in circulating viruses." Using molecular biology methods, the scientists identified which virus species are rampant in bats and rodents. According to their own estimates, they discovered more than 60 new paramyxovirus species. "That is about as many as the number that was already known," said Drosten. 

Bats are the original paramyxovirus hosts 

Using computational biology methods, the scientists calculated a common evolutionary tree for the new and the known viruses. They then deduced, using mathematical methods, in which host animals the viruses have most likely taken up residence during their evolutionary history. "Our analysis shows that almost all of the forebears of today's paramyxoviruses have existed in bats," explained Prof. Drosten. "Just as with influenza, where we are keeping an eye on birds as a source of new pandemic viruses, we will now have to study the bat viruses to see if they are a danger to humans." So, the current data might play a useful role in early detection and prevention of epidemics – a major new goal in virus research. 

Mumps viruses have jumped to humans 

The findings also included that the Hendra and Nipah viruses that cause encephalitis in Asia and Australia really came from Africa. "This results in an urgent need to conduct medical studies in Africa," said the Bonn virologist, adding that many disease cases on this continent remain unexplained and might possibly have been caused by such new viruses. In one case, the scientists have already found proof that bat viruses transfer directly to humans. "Our data show that the human mumps virus comes directly from bats – and can be found there to this day," reported Prof. Drosten. 

Dangerous viruses cannot be eradicated anytime soon 

These results indicate that it may not be as easy to eradicate dangerous viruses as had been assumed. For eliminating an infectious agent permanently from the population by means of vaccination requires that there are no animal hosts from which a new infection might come. "In bats, we assume that there is a vast reservoir of such agents," said Drosten. "If the vaccination campaigns are stopped once a virus has been eradicated, this might present a potential risk - maybe we will have to rethink." This is why Drosten advocates taking into account ecological data when planning vaccination campaigns. Eradicating bats or other wild animals would be neither possible nor sensible. "Bats and other small wild mammals are of immeasurable value for our planet's ecosystems," Drosten summarized his and his colleagues' unanimous opinion. 

Source: University of Bonn [April 24, 2012]

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Researchers create synthetic DNA/RNA that can evolve

Researchers have created artificial genetic material known as Xenonucleic acids, or XNAs, that can store information and evolve over generations in a comparable way to DNA. 

The research, reported Friday in the journal Science, has implications for the fields of molecular medicine and biotechnology, and sheds new light on how molecules first replicated and assembled into life billions of years ago. 

Living systems owe their existence to the information-carrying molecules DNA and RNA.  These fundamental chemical forms have two features essential for life: they display heredity, meaning they can encode and pass on genetic information, and they can adapt over time. 

Whether these traits could be performed by molecules other than DNA and RNA has been a long-debated issue. 

For the current study, an international team of researchers developed chemical procedures to convert DNA and RNA into six genetic polymers known as XNAs.  The process switches the deoxyribose and ribose (the “d” and “r” in DNA and RNA) for other molecules. 

The researchers demonstrated for the first time that all six XNAs could form a double helix with DNA, and were more stable than natural genetic material.  Moreover, one of these XNAs, a molecule known as anhydrohexitol nucleic acid, or HNA, was capable of undergoing directed evolution and folding into biologically useful forms. 

Philipp Holliger of MRC Laboratory of Molecular Biology in Cambridge, the study’s senior author, said the work demonstrated that heredity and evolution were possible using alternatives to natural genetic material. 

“There is nothing Goldilocks about DNA and RNA,” he told Science. 

“There is no overwhelming functional imperative for genetic systems or biology to be based on these two nucleic acids.” 

Both RNA and DNA embed data in their sequences of four nucleotides.  This information is vital for conferring hereditary traits and for supplying the coded recipe essential for building proteins from the 20 naturally occurring amino acids.  However, precisely how and when this system began remains one of the most perplexing and hotly contested areas of biology. 

According to one hypothesis, the simpler RNA molecule preceded DNA as the original informational conduit. The RNA world hypothesis proposes that the earliest examples of life were based on RNA and simple proteins.  Because of RNA’s great versatility—it is not only capable of carrying genetic information but also of catalyzing chemical reactions like an enzyme—it is believed by many to have supported pre-cellular life. 

Nevertheless, the spontaneous arrival of RNA through a sequence of purely random mixing events of primitive chemicals was, at the very least, an unlikely occurrence. 

“This is a big question,” said study leader John Chaput, a researcher at Arizona State University’s Biodesign Institute. 

“If the RNA world existed, how did it come into existence? Was it spontaneously produced, or was it the product of something that was even simpler than RNA?” 

This pre-RNA world hypothesis has been gaining ground, primarily through study of XNAs, which provide plausible alternatives to the current biological system and could have acted as chemical stepping-stones to the eventual emergence of life. 

Threose nucleic acid, or TNA, for example, is one candidate for this critical intermediary role. 

“TNA does some interesting things,” Chaput said, noting the molecule’s capacity to bind with RNA through antiparallel Watson-Crick base pairing. 

“This property provides a model for how XNAs could have transferred information from the pre-RNA world to the RNA world.” 

Nucleic acid molecules, including DNA and RNA, consist of 3 chemical components: a sugar group, a triphosphate backbone and combinations of the four nucleic acids.  By manipulating these structural elements, researchers can engineer XNA molecules with unique properties. 

However, in order for any of these molecules to have acted as a precursor to RNA in the pre-biotic epoch, they would need to have been able to transfer and recover their information from RNA. To do this, specialized enzymes, known as polymerases are required. 

And while nature has made DNA and RNA polymerases capable of reading, transcribing and reverse transcribing normal nucleic acid sequences, no naturally occurring polymerases exist for XNA molecules. 

So the researchers, led by Holliger, painstakingly evolved synthetic polymerases that could copy DNA into XNA, and other polymerases that could copy XNA back into DNA. 

Ultimately, polymerases were found that transcribe and reverse-transcribe six different genetic systems: HNA, CeNA, LNA, ANA, FANA and TNA. The experiments demonstrated that these unnatural DNA sequences could be rendered into various XNAs when the polymerases were fed the appropriate XNA substrates. 

Using these enzymes as tools for molecular evolution, the team evolved the first example of an HNA aptamer through iterative rounds of selection and amplification.  Starting from a large pool of DNA sequences, a synthetic polymerase was used to copy the DNA library into HNA. The pool of HNA molecules was then incubated with an arbitrary target. The small fraction of molecules that bound the target were then separated from the unbound pool, reverse transcribed back into DNA with a second synthetic enzyme, and amplified by PCR. After many repeated rounds, HNAs were generated that bound HIV trans-activating response RNA (TAR) and hen egg lysosome (HEL), which were used as binding targets. 

“This is a synthetic Darwinian process,” Chaput said. 

“The same thing happens inside our cells, but this is done in vitro.” 

The method for producing XNA polymerases draws on Holliger’s pervious, path-breaking work, and uses cell-like synthetic compartments of water/oil emulsion to conduct directed evolution of enzymes, particularly polymerases. 

By isolating self-replication reactions from each other, the process greatly improves the accuracy and efficiency of polymerase evolution and replication. 

“What nobody had really done before,” Chaput said, “is to take those technologies and apply them to unnatural nucleic acids. ” 

Chaput said the study advances the case for a pre-RNA world, while revealing a new class of XNA aptamers capable of fulfilling many useful roles. 

And while many questions surrounding the origins of life remain, he is optimistic that solutions are coming into view. 

“Further down the road, through research like this, I think we’ll have enough information to begin to put the pieces of the puzzle together.” 

In an article accompanying the study in the journal Science, Gerald Joyce of the Scripps Research Institute wrote that “the work heralds the era of synthetic genetics, with implications for exobiology (life elsewhere in the Universe), biotechnology, and understanding of life itself”. 

However, he stressed that the work does not yet represent a full synthetic genetics platform. For that, a self-replicating system that does not require the DNA intermediary must be developed. 

If that happens, “construction of genetic systems based on alternative chemical platforms may ultimately lead to the synthesis of novel forms of life”. 

Source: RedOrbit [April 20, 2012]

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Teamwork linked to intelligence

Learning to work in teams may explain why humans evolved a bigger brain, according to a new study published on Wednesday. 

Learning to work in teams may explain why humans evolved a bigger brain [Credit: AFP]

Compared to his hominid predecessors, Homo sapiens is a cerebral giant, a riddle that scientists have long tried to solve. 

The answer, according to researchers in Ireland and Scotland, may lie in social interaction. 

Working with others helped Man to survive, but he had to develop a brain big enough to cope with all the social complexities, they believe. 

In a computer model, the team simulated the human brain, allowing a network of neurons to evolve in response to a series of social challenges. 

There were two scenarios. The first entailed two partners in crime who had been caught by the police, each having to decide whether or not to inform on the other. 

The second had two individuals trapped in a car in a snowdrift and having to weigh whether to cooperate to dig themselves out or just sit back and let the other do it. 

In both cases, the individual would gain more from selfishness. 

But the researchers were intrigued to find that as the brain evolved, the individual was likelier to choose to cooperate. 

"We cooperate in large groups of unrelated individuals quite frequently, and that requires cognitive abilities to keep track of who is doing what to you and change your behaviour accordingly," co-author Luke McNally of Dublin's Trinity College told AFP. 

McNally pointed out, though, that cooperation has a calculating side. We do it out of reciprocity. 

"If you cooperate and I cheat, then next time we interact you could decide: 'Oh well, he cheated last time, so I won't cooperate with him.' So basically you have to cooperate in order to receive cooperation in the future." 

McNally said teamwork and bigger brainpower fed off each other. 

"Transitions to cooperative, complex societies can drive the evolution of a bigger brain," he said. 

"Once greater levels of intelligence started to evolve, you saw cooperation going much higher." 

The study appears in Proceedings of the Royal Society B, a journal published by Britain's de-facto academy of sciences. 

Commenting on the paper, Robin Dunbar, an evolutionary anthropologist at Oxford University, said the findings were a valuable add to understanding brain evolution. 

But he said there were physiological limits to cooperation. 

Man would need a "house-sized brain" to take cooperation to a perfect level on a planet filled with humans. 

"Our current brain size limits the community size that we can manage ... that we feel we belong to," he said. 

Our comfortable "personal social network" is limited to about 150, and boosting that to 500 would require a doubling of the size of the brain. 

"In order to create greater social integration, greater social cohesion even on the size of France, never mind the size of the EU, never mind the planet, we probably have to find other ways of doing it" than wait for evolution, said Dunbar. 

Source: AFP [April 11, 2012]

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