Wednesday, January 27, 2010

BROKE A TOOTH? GROW ANOTHER!

0 comentarios
To all those who have made deals with the tooth fairy in the past: you probably sold your teeth below their fair value.

Dr. George Huang, Chair of Endodontics at the Boston University Henry M. Goldman School of Dental Medicine (GSDM), says those baby teeth and extracted third molars we are throwing away hold valuable dental stem cells.

“Our team found for the first team that we can reprogram dental stem cells into human embryonic-like cells called induced pluripotent stem (iPS) cells, which may be an unlimited source of cells for tissue regeneration,” Dr. Huang says.

So far, scientists have had luck creating iPS cells from various cells in mice easily, but this hasn’t been as easy in humans, until more recently. All three types of human dental stem cells the GSDM team tested are easier to reprogram than fibroblasts, which previously seemed to be the best way to make human iPS cells.

In a related study, Dr. Huang regenerated two major human tooth components—dental pulp and dentin—for the first time in a mouse experimental model. The mouse was used to supply nutrition for human tissue regeneration.

Using tissue engineering, researchers saw empty root canal space fill with pulp-like tissue with ample blood supplies. Dentin-like tissue regrew on the dentinal wall.

“The finding will revolutionize endodontic and dental clinical practice by helping to preserve teeth,” Dr. Huang says.”

The studies, iPS cells reprogrammed from mesenchymal-like stem/progenitor cells of dental tissue origin and Stem/progenitor cell–mediated de novo regeneration of dental pulp with newly deposited continuous layer of dentin in an in vivo model, appear in Stem Cells and Development and Tissue Engineering.

The mission of Boston University Henry M. Goldman School of Dental Medicine is to provide excellent education to dental professionals throughout their careers; to shape the future of dental medicine and dental education through research; to offer excellent health care services to the community; to participate in community activities; and to foster a respectful and supportive environment.

Boston University

STUDY SHEDS NEW LIGHT ON KEY TO LIFE ON EARTH

0 comentarios
University of Manchester scientists have discovered exactly how plants obtain energy from sunlight through chlorophyll production in a study that helps to explain the design and activity of all enzymes.

Professor Nigel Scrutton and his team at the Faculty of Life Sciences have not only gained a more detailed understanding of the production of the most abundant and life sustaining chemical on Earth, they also expect to apply their findings to all enzymes thus allowing the design of novel clinical and industrial processes.

The study, published in the latest edition of the Journal of Biological Chemistry (JBC), also takes in quantum tunnelling, a newly discovered enzyme mechanism where they use energy to blast through rather than climb a chemical reaction.

Professor Scrutton says: 'Chlorophyll is the most abundant and arguably the most important chemical on planet Earth. Without it, there would be no life on Earth as it allows plants to convert light into chemical energy.

'The enzyme that produces it, POR, is light-driven. Now we have a detailed understanding of how the light 'switches on' the chemistry.

This could be applied to other enzymes with a host of implications - we could design our own light-activated enzymes and use these to target disease, or we could harness light - a very cheap form of energy - to drive biocatalysis in general.

His colleague Dr Derren Heyes adds: 'There is only one other light-driven enzyme, DNA photolyase, which repairs genetic mutations. The insights we have gained into POR could be applied to this enzyme although we also hope to apply our findings to other enzymes.

"We were surprised to find that very small changes in the structure of the enzyme were crucial for the light-driven reaction - so we know we need to be very precise when engineering enzymes."

Professor Scrutton says: "The fact that the atoms involved in the enzyme reaction use unusual behaviour (quantum tunneling) found only in the 'quantum world' is creating a lot of interest in the scientific community.

"Ultimately this is very exciting research. We are developing a theory of how enzymes work. Enzymes drive all of life so the research potential is huge."

University of Manchester

BENEFITS OF OMEGA-3 FATTY ACIDS COME AT A COST

0 comentarios

For decades, omega-3 fatty acids have been praised for their myriad health benefits. Credited with helping treat or prevent degenerative illnesses such as heart disease, rheumatoid arthritis, diabetes, and even Alzheimer's disease, they also play a key role in brain development and cognitive function.

However, the benefits of omega-3s –– and DHA in particular –– also come at an inevitable cost, according to researchers at UC Santa Barbara. Over a lifetime, they can lead to cellular disease and a significant decrease in cognitive function. The scientists, the father and son team of Raymond C. and David L. Valentine, have compiled their work in a new book titled "Omega-3 Fatty Acids and the DHA Principle" (CRC Press, 2009).

In humans, omega-3s are essential fatty acids that are necessary for health, but cannot be manufactured from scratch by the body. They are obtained largely from fish and other marine organisms, such as algae and krill. The body uses several types of omega-3s, including two "fish oils": eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). "DHA and EPA sit atop a hierarchy of omega-3s and provide the most clear health benefits," said David Valentine, associate professor of earth science at UCSB. His father, Raymond Valentine, is a professor emeritus of plant sciences at UC Davis, and a visiting scholar at the Marine Science Institute at UCSB.

The elder Valentine's most recent research explores ways in which genes from ocean organisms can be engineered into crop plants so omega-3s can be harvested and made easily accessible in the same way other oils, such as olive and canola, are. David Valentine is studying the energetics of organisms, specifically the roles of omega-3s and other molecules in cellular membranes. The oils are used inside organisms as membranes that surround cells. They serve as the host phase for many critical functions, including respiration and photosynthesis.

The physical and chemical properties of DHA enable it to rapidly facilitate biochemical processes in the cell membrane. This effect provides numerous benefits, including those involved in the growth of bacteria, rapid energy generation, vision, brain impulse, and photosynthesis. The Valentines focus on the roles of omega-3 fatty acids in cellular membranes ranging from human neurons and swimming sperm to deep-sea bacteria, and they develop a principle by which to assess their benefits and risks.

While other oils are used in membranes all over the body, omega-3s are far more specific in their location. They are found most predominantly in the brain, in the eyes, in certain other brain-like cells, and in sperm, according to David Valentine. "They are precisely targeted," he said. "And the reasons for that are twofold. Their physical and chemical properties enable specialized cellular functions, such as the rapid firing of neurons and the rhythmic pulsing of sperm tails. However, omega-3s are so chemically unstable that they oxidize and go rancid very quickly, and are therefore excluded from all other cells."

That instability, he added, is their down side. "The brain is absolutely packed full of omega-3s. However, there's also oxygen in the brain, and that's going to cause a reaction. They're going to oxidize. And that gradual oxidation is, in essence, a losing battle against brain damage. After a lifetime, the damage takes its toll," he said.

Among the many ideas the Valentines explore in the book are the effects that the oxidation of omega-3s have on the brain. "One of the causes of brain aging is the oxidation of these compounds, which compose a large percentage of the brain. It's not too much of a stretch to think they're part of the gradual progression of brain aging and, possibly, some of the brain diseases that come later in life," David Valentine said.

Despite the hazards posed by a lifetime of omega-3s, Valentine does not encourage people to toss out their bottles of fish oil. In fact, the contrary is true. "I consume plenty of DHA because I think the benefits to human health far outweigh the down sides," he said. "There's no question, for example, that omega-3s help brain development in children. The brain relies heavily on DHA, and will perform better when it is plentiful," he said. "But it's an inevitable catch-22. Human intelligence is derived in part from DHA, but DHA itself is inherently unstable."

The effects of omega-3 oxidation are, in some ways, a function of the ever-increasing human life span. "The dangers have never been an issue in human evolution because humans didn't live to be 70 or 80 years old," said Valentine. "There was never this wall that people would hit, because they didn't live that long."

(Photo: UCSB)

University of California

CARBON-STORAGE RESEARCH GETS UPSIZED

0 comentarios

A U of A engineering professor researching carbon storage has been awarded funding to set up a one-of-a-kind lab that will simulate the harsh conditions that exist two kilometres beneath the Earth's surface.

Rick Chalaturnyk has been awarded $1.6 million in funding from both the Alberta Science and Research Investments Program and the federal Canada Foundation for Innovation for a $4-million research lab that will be the only one of its kind in Canada. The remainder of funding will come from the university and industry supporters.

Researchers at the lab, called the Geomechanical Reservoir Experimental Facility, will investigate carbon storage and enhanced oil recovery using leading-edge equipment that will give them a better understanding of how carbon dioxide behaves underground.

Using a large high-powered centrifuge, Chalaturnyk and his colleagues will be able to increase the size of their standard test samples from small cores to a half a cubic metre in size, apply up to 5,800 pounds per square inch of pressure to the sample and use highly sensitive acoustic imaging techniques to "see" the way carbon dioxide injected into the ground will behave in its liquid, gas and supercritical phases under different pressures and temperatures.

They will also be able to simulate steam-injection oil recovery methods, heating the samples to temperatures as high as 350 C, an experiment that is "not for the faint of heart," according to Chalaturnyk.

"At 350 degrees metal starts to change," he said. "It's hard to get sensors to measure what's going on. There aren't many plastics that can withstand that temperature. You can't stick electronics in there-even using fibre optics at that temperature is a very difficult thing to do. We'll have these tiny sensors, barely 3 millimetres in size, which we will be using to record what is going on in the sample."

The lab will also enable researchers to study the way cement behaves at certain depths and temperatures. Because carbon dioxide can be injected into the ground at abandoned oil and gas wells, it is essential to understand how well the cement borehole casings hold up if the storage site is to maintain its integrity.

While helping educate the next generation of geo-engineers, the lab will also advance Alberta's commitment to become a leader in carbon capture and storage, to reduce greenhouses gas emissions while allowing development of unconventional energy sources like oilsands, shale gas, bitumen carbonates and coal-bed methane.

(Photo: Jason University of Alberta)

University of Alberta

UM-LED TEAM SHINES COSMIC LIGHT ON MISSING ORDINARY MATTER

0 comentarios
An international team of scientists, led by University of Maryland astronomer Stacy McGaugh, has found that individual galactic objects have less ordinary matter, relative to dark matter, than does the Universe as a whole.

Scientists believe that all ordinary matter, the protons & neutrons that make up people, planets, stars and all that we can see, are a mere fraction -- some 17 percent -- of the total matter in the Universe. The protons and neutrons of ordinary matter are referred to as baryons in particle physics and cosmology.

The remaining 83 percent apparently is the mysterious "dark matter," the existence of which is inferred largely from its gravitational pull on visible matter. Dark matter, explains McGaugh "is presumed to be some new form of non-baryonic particle - the stuff scientists hope the Large Hadron Collider in CERN will create in high energy collisions between protons."

McGaugh and his colleagues posed the question of whether the "universal" ratio of baryonic matter to dark matter holds on the scales of individual structures like galaxies.

"One would expect galaxies and clusters of galaxies to be made of the same stuff as the universe as a whole, so if you make an accounting of the normal matter in each object, and its total mass, you ought to get the same 17 percent fraction," he says. "However, our work shows that individual objects have less ordinary matter, relative to dark matter, than you would expect from the cosmic mix; sometimes a lot less!"

Just how much less depends systematically on scale, according to the researchers. The smaller an object the further its ratio of ordinary matter to dark matter is from the cosmic mix. McGaugh says their work indicates that the largest bound structures, rich clusters of galaxies, have 14 percent of ordinary baryonic matter, close to expected 17 percent.

"As we looked at smaller objects - individual galaxies and satellite galaxies, the normal matter content gets steadily less," he says. "By the time we reach the smallest dwarf satellite galaxies, the content of normal matter is only ~1percent of what it should be. (Such galaxies' baryon content is ~0.2percent instead of 17percent). The variation of the baryon content is very systematic with scale. The smaller the galaxy, the smaller is its ratio of normal matter to dark matter. Put another way, the smallest galaxies are very dark matter dominated.

"This raises an obvious question," McGaugh says, "where are all these missing baryons? The short answer is, we don't know. There are various lines of speculation, most of which are either easily dismissed or are un-testable. So for now this is a problem without an obvious solution."

University of Maryland

BRAIN ACTIVITY LEVELS AFFECT SELF-PERCEPTION

0 comentarios
The less you use your brain's frontal lobes, the more you see yourself through rose-colored glasses, a University of Texas at Austin researcher says.

Those findings are being published in the February edition of the journal NeuroImage.

"In healthy people, the more you activate a portion of your frontal lobes, the more accurate your view of yourself is," says Jennifer Beer, an assistant professor of psychology, who conducted the research with graduate student Brent L. Hughes. "And the more you view yourself as desirable or better than your peers, the less you use those lobes."

The natural human tendency to see oneself in a positive light can be helpful and motivating in some situations but detrimental in others, Beer says.

Her research, conducted at the university's Imaging Research Center, gives new insight into the relationship among brain functions and human emotion and perceptions.

It may help scientists better understand brain functions in seniors or people who suffer from depression or other mental illnesses. It could also have implications for recovering methamphetamine addicts whose frontal lobes are often damaged by drug use and who can overestimate their ability to stay clean.

As part of the study, 20 subjects answered questions about how they compared to their peers on such positive traits as tact, modesty, likability and maturity and such negative traits as materialism, messiness, unreliability and narrow-mindedness. As the subjects answered those questions, a magnetic resonance imaging (MRI) machine scanned their brains.

The subjects who viewed themselves in a very positive light across those disparate areas used their orbitofrontal cortex less than the other subjects. This region of the frontal lobe is generally associated with reasoning, planning, decision-making and problem-solving

Some subjects who had accurate views of themselves showed four times more frontal lobe activation than the most extreme "rose-colored glasses" wearer in the study.

Among a separate set of subjects who were asked the same questions, those who were required to answer quickly saw themselves in a far more positive light than those who had unlimited time to answer. Those findings suggest that processing information in a more deliberate manner may be the way in which frontal lobe activation permits people to come to more realistic conclusions.

"Subjects made unrealistically positive judgments about themselves more quickly, suggesting these judgments require fewer mental resources," Beer says. "Perhaps, like the visual system, the social judgment system is designed to give us a quick 'good enough' perception for the sake of efficiency."

Beer is a leader in the emerging field of social neuroscience, which studies people's emotions, how they think about themselves and what's going on in the brain when they do.

University of Texas

DOG GENOME RESEARCHERS TRACK PAW PRINTS OF SELECTIVE BREEDING

0 comentarios

From the Dachshund's stubby legs to the Shar-Pei's wrinkly skin, breeding for certain characteristics has left its mark on the dog genome. Researchers have identified 155 regions on the canine genome that appear to have been influenced by selective breeding.

With more than 400 distinct breeds, dogs come in a wide range of shapes, sizes, fur-styles, and temperaments. The curly-haired toy poodle, small enough to sit in a teacup, barely looks or acts like the smooth-coated Great Dane tall enough to peer like a periscope out of a car's sunroof. Not so apparent are breed differences in how the dogs' bodies function and their susceptibility to various diseases.

Although domestication of dogs began over 14,000 years ago, according to Dr. Joshua Akey, University of Washington (UW) assistant professor of genome sciences, the spectacular diversity among breeds is thought to have originated during the past few centuries through intense artificial selection of and strict breeding for desired characteristics. Akey is the lead author of the effort to map canine genome regions that show signs of recent selection and that contain genes that are prime candidates for further investigation. Those genes are being examined for their possible roles in the most conspicuous variations among dog breeds: size, coat color and texture, behavior, physiology, and skeleton structure.

The researchers performed the largest genome-wide scan to date for targets of selection in purebred dogs. The genomes came from 275 unrelated dogs representing 10 breeds that were very unlike each other. The breeds were: Beagle, Border Collie, Brittany, Dachshund, German Shepherd, Greyhound, Jack Russell Terrier, Labrador Retriever, Shar-Pei, and Standard Poodle.

The study was conducted, the researchers said, because the canine genome, the product of centuries of strong selection, contains many important lessons about the genetic architecture of physical and behavioral variations and the mechanisms of rapid, short-term evolution. The findings, the researchers said, "provide a detailed glimpse into the genetic legacy of centuries of breeding practices."

Their results were published Jan. 11 in the Proceedings of the National Academy of Science, in the article "Tracking footprints of artificial selection in the dog genome."

The researchers catalogued more than 21,000 tiny variations in the genome. In investigating the relationships among the 10 breeds, they found that, genetically, the German Shepherd, Shar-Pei, Beagle, and Greyhound were especially distinct.

Their list of most differentiated regions of the dog genome included five genes already linked to hallmark traits of certain breeds: one for small size, one for short limbs like those in Dachshunds and other stubby-legged dogs, and three for coats.

In calculating the overlap of the signatures marking selection in the genome, the researchers found that approximately 66 percent occurred in only one or two breeds. They noted it was likely that these genome regions contain genes that confer qualities that distinguish a breed, such as skin wrinkling in the Shar-Pei. In contrast, signatures of selection found in five or more breeds tended to sort the dogs into classes, and include, for example, a gene that governs the miniature size of breeds in the toy group.

A gene associated with dwarfism in mice, the study reports, appears to mediate variations in dog breed size and weight. Small-size breeds, like Dachshund, Beagle, Jack Russell Terrier, and Brittany have enormous differentiation in this gene, compared to larger-size breeds. Another region of peak differentiation in the dog genome, in an area thought to regulate muscle cell formation in embryos, seems to separate the German Shepherd, Jack Russell Terrier, Border Collie and Greyhound from the Dachshund, Beagle, Brittany, and Shar-Pei.

The 155 regions of the genome that appear to have been influenced by selective breeding contain 1,630 known or predicted protein-coding genes. The researchers tried to obtain a broad overview of the molecular functions of these genes. They were surprised to discover that genes involved in immunity and defense were overrepresented in the 155 regions, a phenomenon also discovered in genome analysis of selection in natural populations. Natural and artificial selection were not expected to act on similar classes of genes, the researchers noted, but immune-related genes may be frequent targets of selection because of their critical role in defending against ever-changing infections.

The researchers honed in on a particular genome region in the Shar-Pei. Many of these dogs have excessive wrinkles, but some are smooth. The degree of skin folding correlates with levels of certain molecules whose production may be governed by a gene in this region. Rare mutations in this same gene also cause severe skin wrinkling in people. Tiny genetic variations in this gene seemed linked to whether a Shar-Pei would be smooth or wrinkled, and a rare genetic mutation was found in the Shar-Pei but not in other dogs.

The researchers explained, that, despite the many insights emerging from their data, there were several limitations to their study and in interpreting the findings. They pointed out that a pattern of variation that is unusual to the dog genome at large doesn't prove that specific genome region is under selection.

A major impetus behind studying dog genomics, the researchers pointed out, is its potential to advance knowledge about the genetic basis of human form variations and of differences in disease susceptibility among people. In many cases, the researchers said, it may be easier to locate the genetic targets of selection in dogs, and then map these to related regions in the human genome. Scientists are intrigued by the possibility that recent selection may have affected genome regions common to both human and dog lineages.

"This research has shown that artificial selection in dogs has acted on many of the same genes as natural selection in humans, and that many of these genes are regulators of gene activity," said Dr. Irene Eckstrand, who oversees evolution grants at the National Institute of General Medical Sciences at the National Institutes of Health. "The statistical and computational approaches used in this study will be of great value in deciphering the organization of human genetic variation, and in identifying the genetic basis of human characteristics."

The researchers also said that a better understanding of artificial selection in dogs may reveal the molecular mechanisms of rapid, short-term evolution. Future work, they hope, may uncover the gene activities responsible for shaping the incredible diversity among the world's dogs.

(Photo: Earl Steele)

University of Washington

SCIENTISTS MOVE A STEP CLOSER TO UNDERSTANDING WHY LEOPARDS CAN'T CHANGE THEIR SPOTS

0 comentarios
The leopard cannot change its spots, nor can the tiger change its stripes, but a new research report published in the January 2009 issue of the journal GENETICS tells us something about how cats end up with their spots and stripes. It demonstrates for the first time that at least three different genes are involved in the emergence of stripes, spots, and other markings on domestic cats. Researchers have also determined the genomic location of two of these genes, which will allow for further studies that could shine scientific light on various human skin disorders.

"We hope that the study opens up the possibility of directly investigating the genes involved in pattern formation (i.e., the establishment of stripes, spots, and other markings) on the skin of mammals, including their structure, function, and regulation," said Eduardo Eizirik, a researcher involved in the work from the Pontifical Catholic University of Rio Grande do Sul, Brazil. "From these studies, we hope to understand how the different coat patterns have evolved in different mammalian groups, and to be able to investigate their roles in adaptation to different environments, such as their importance for camouflage in wild cat species."

Scientists crossed domestic cats with different coat patterns, such as stripes and blotches, and tracked the inheritance of these patterns among their offspring. Genetic samples were collected and used to type various molecular markers. Results showed that specific markers were inherited by a kitten every time a given coat pattern appeared, suggesting that the marker and the gene causing the coat pattern were located in the same region of the genome. Using statistical procedures called linkage mapping, scientists determined the genomic location of two genes involved in these traits. By clarifying the inheritance of markings in one mammalian species, researchers hope to identify and characterize the implicated genes and then determine if they apply to other mammals, such as humans. The hope is that this discovery will shed new light on human skin diseases that appear to follow standardized patterns.

"Coat color and markings of animals are obvious traits that have long attracted the interest of geneticists" said Mark Johnston, Editor-in-Chief of the journal GENETICS, "and this study in cats may ultimately help us better understand the genetics behind hair and skin color in other mammals. In turn, this understanding could lead to new therapeutic strategies to correct skin problems in people."

The Genetics Society of America

UNLOCKING THE MYSTERY OF THE DUCK-BILLED PLATYPUS' VENOM

0 comentarios

Abandon any notion that the duck-billed platypus is a soft and cuddly creature -- maybe like Perry the Platypus in the Phineas and Ferb cartoon. This platypus, renowned as one of the few mammals that lay eggs, also is one of only a few venomous mammals. The males can deliver a mega-sting that causes immediate, excruciating pain, like hundreds of hornet stings, leaving victims incapacitated for weeks. Now scientists are reporting an advance toward deciphering the chemical composition of the venom, with the first identification of a dozen protein building blocks. Their study is in the Journal of the American Chemical Society, a weekly publication.

Masaki Kita, Daisuke Uemura, and colleagues note that spurs in the hind limb of the male platypus can deliver the venom, a cocktail of substances that cause excruciating pain. The scientists previously showed that the venom triggers certain chemical changes in cultured human nerve cells that can lead to the sensation of pain. Until now, however, scientists did not know the exact components of the venom responsible for this effect.

To unlock its secrets, the scientists collected samples of platypus venom and used high-tech analytical instruments to separate and characterize its components. They identified 11 new peptides, or protein subunits, in the venom. Studies using nerve cells suggest that one of these substances, called Heptapeptide 1, is the main agent responsible for triggering pain. The substance appears to work by interacting with certain receptors in the nerve cells, they suggest.

(Photo: Wikimedia Commons)

American Chemical Society

HOW GALAXIES CAME TO BE: ASTRONOMERS EXPLAIN HUBBLE SEQUENCE

0 comentarios

For the first time, two astronomers have explained the diversity of galaxy shapes seen in the universe. The scientists, Dr Andrew Benson of the California Institute of Technology (Caltech) and Dr Nick Devereux of Embry-Riddle University in Arizona, tracked the evolution of galaxies over thirteen billion years from the early Universe to the present day. Their results appear in the journal Monthly Notices of the Royal Astronomical Society.

Galaxies are the collections of stars, planets, gas and dust that make up most of the visible component of the cosmos. The smallest have a few million and the largest as many as a million million (a trillion) stars.

American astronomer Edwin Hubble first developed a taxonomy for galaxies in the 1930s that has since become known as the ‘Hubble Sequence’. There are three basic shapes: spiral, where arms of material wind out in a disk from a small central bulge, barred spirals, where the arms wind out in a disk from a larger bar of material and elliptical, where the galaxy’s stars are distributed more evenly in a bulge without arms or disk. For comparison, the galaxy we live in, the Milky Way, has between two and four hundred thousand million stars and is classified as a barred spiral.

Explaining the Hubble Sequence is complex. The different types clearly result from different evolutionary paths but until now a detailed explanation has eluded scientists.

Benson and Devereux combined data from the infrared Two Micron All Sky Survey (2MASS) with their sophisticated GALFORM computer model to reproduce the evolutionary history of the Universe over thirteen billion years. To their surprise, their computations reproduced not only the different galaxy shapes but also their relative numbers.

“We were completely astonished that our model predicted both the abundance and diversity of galaxy types so precisely”, said Devereux. “It really boosts my confidence in the model”, added Benson.

The astronomers’ model is underpinned by and endorses the ‘Lambda Cold Dark Matter’ model of the Universe. Here ‘Lambda’ is the mysterious ‘dark energy’ component believed to make up about 72% of the cosmos, with cold dark matter making up another 23%. Just 4% of the Universe consists of the familiar visible or ‘baryonic’ matter that makes up the stars and planets of which galaxies are comprised.

Galaxies are thought to be embedded in very large haloes of dark matter and Benson and Devereux believe these to be crucial to their evolution. Their model suggests that the number of mergers between these haloes and their galaxies drives the final outcome – elliptical galaxies result from multiple mergers whereas disk galaxies have seen none at all. Our Milky Way galaxy’s barred spiral shape suggests it has seen a complex evolutionary history, with only a few minor collisions and at least one episode where the inner disk collapsed to form the large central bar.

“These new findings set a clear direction for future research. Our goal now is to compare the model predictions with observations of more distant galaxies seen in images obtained with the Hubble and those of the soon to be launched James Webb Space Telescope (JWST)”, said Devereux.

(Photo: A. Benson (University of Durham), NASA / STScI)

Royal Astronomical Society

Y CHROMOSOMES EVOLVING RAPIDLY

0 comentarios

The Y chromosome is often considered somewhat of a genetic oddball. Short and stubby, it carries hardly any genes, most of which are related to traits associated with maleness. Most of the chromosome consists of highly repetitive sequences of DNA, known as massive palindrome sequences, whose function is unknown.

Evolutionary biologists have long believed that the mammalian Y chromosome is essentially stagnant, having lost most of its genes hundreds of millions of years ago. But new research from MIT's Whitehead Institute, published in this week's issue of Nature, overturns that theory. The research team, led by Whitehead Institute director and MIT biology professor David Page, showed that the Y chromosome is actually evolving rapidly and continuously remaking itself.

For the first time, the researchers sequenced the Y chromosome of the chimpanzee, allowing for the first interspecies comparison of the chromosome. They found significant differences between the two species' Y chromosomes, suggesting that those chromosomes have evolved faster than other chromosomes during the six million years since humans and chimpanzees emerged from a common ancestor.

The findings offer the first evidence that a Y chromosome as evolutionarily old as the human Y is in fact still evolving, says Andrew Clark, a genetics professor at Cornell University who studies Y chromosome evolution in fruit flies.

"There's a dramatic amount of turnover, and it's not just degeneration — it's gain and loss of genes that do something on the Y chromosome," says Clark, adding that the new sequence comparison may also help researchers study male infertility, which is often driven by defects in the Y chromosome.

Hundreds of millions of years ago, the Y diverged from its sister X chromosome and became specialized for male-specific traits. Evolutionary biologists have theorized that it quickly lost most of its genes through a process known as degeneration, then lapsed into a fairly static state.

However, this theory was difficult to test because all of those repetitive DNA stretches make the Y chromosome very tricky to sequence, says Jennifer Hughes, a postdoctoral associate at the Whitehead Institute and lead author of the Nature paper. Most genome sequencing studies completely exclude the Y chromosome.

In 2003, Page's laboratory and collaborators at the Genome Center at Washington University (who were also involved in the new chimpanzee study) were the first team to sequence the human Y chromosome. They found that the Y carries 78 genes, more than expected, but still far fewer than the 1,000 or so located on the X chromosome.

"Having the human sequence tells us quite a bit, but to obtain information about the evolution of the Y, we needed to do a comparative analysis," says Hughes.

As its next target, the Whitehead team chose the chimpanzee, humans' closest living relative. Human and chimpanzees genomes differ very little: 98.8 percent of DNA base pairs are identical between the two species.

Page's team expected that the chimpanzee and human Y chromosomes would also be very similar. To their surprise, they found that chimp and human Y chromosomes differ considerably — far more than the rest of the chromosomes. During the six million years of separation, the chimp Y has lost one-third to one-half of the human Y chromosome genes. However, the chimp Y has twice as many massive palindrome sequences as the human Y.

Page compares the Y chromosome changes to a home undergoing continual renovation. "People are living in the house, but there's always some room that's being demolished and reconstructed," says Page, who is also a Howard Hughes Medical Institute investigator. "And this is not the norm for the genome as a whole."

The researchers suspect several factors are at play in the divergent evolution of human and chimp Y chromosomes, including differences in mating behaviors. Because a female chimpanzee may mate with many male chimpanzees around the same time, any genes on the Y chromosome that lead to enhanced sperm production offer a distinct competitive advantage.

If a Y chromosome with genes for enhanced sperm production also carries mutations that alter or eliminate a gene not related to sperm production, those less advantageous mutations also get passed on, resulting in a Y chromosome with far fewer genes than the human Y.

"The gene loss seen in chimps and the possibility that this has been driven by the influence of sperm competition in chimps but not humans is interesting, and we will be able to judge this more readily once we have functional information about the gene products, which is still sketchy in many cases," says Mark Jobling, professor of genetics at the University of Leicester, who studies the evolution of the Y chromosome.

Researchers in the Page lab and the Washington University Genome Center are now sequencing and examining the Y chromosomes of several other mammals, to investigate whether rapid evolution is occurring in species other than humans and chimpanzees.

(Photo: MIT)

MIT

FRIENDSHIP MAY HELP STEM RISE OF OBESITY IN CHILDREN

0 comentarios

Parents are acutely aware of the influence of friends on their children's behavior -- how they dress, how they wear their hair, whether they drink or smoke. A new laboratory-based study has shown that friends also may influence how much adolescents eat.

"Consider a person who usually comes home alone after school and eats out of boredom," says Sarah-Jeanne Salvy, PhD, assistant professor of pediatrics in the University at Buffalo's Division of Behavioral Medicine and first author on the study.

"But on this day, she has a play date with a friend and socializes instead of eating. In this case, socializing is acting as a substitute for eating. Identifying substitutes provides a potential way to reduce behavior.

"Our findings underscore the importance of considering the child's social network in studying youth's motivation to eat," says Salvy, a member of the Department of Pediatrics in UB's School of Medicine and Biomedical Sciences.

"Previous attempts to find substitutes for food and eating have not been very successful. To our knowledge, no research has studied whether social interactions can be a substitute for food in children."

The study appears online in the current issue of Annals of Behavioral Medicine.

The study involved 54 overweight and non-overweight youth -- 24 boys and 30 girls -- between the ages of 9 and 11. Each was assigned randomly to bring a friend or to be paired with an unfamiliar peer.

Study participants worked on a computer game to earn points exchangeable for food or time to spend with their friend or with an unfamiliar peer.

"The task got increasingly harder and the food and social points became more difficult to earn as a way to measure how hard youth were willing to work for food or for play time with their friend or with an unfamiliar peer," Salvy notes.

In the study, participants matched with an unfamiliar peer showed that when working for food became difficult, they switched to earn time with the unfamiliar peer, and when working for peer activity became harder, they switched to earn food.

However, participants assigned to the friend condition continued to work for time with their friends instead of working for food.

"Peer rejection and ostracism are obvious costs imposed on social interactions," says Salvy. "Even the unavailability of one's peers or friends can limit youth's access to social settings and situations. As a result, children may choose to engage in eating and sedentary activities when social alternatives are unavailable.

"There is emerging evidence that a youth's social network may be uniquely relevant and influential to eating behavior and choice of activities," she continues. "Individuals are influenced by the eating and activity norms set by those around them, and the results of the present study suggest that friendship can provide an alternative to eating.

"These findings, and the work of others, imply that decreasing sedentary behavior and increasing active leisure activities may require meaningful relationships with friends, as friendship may help to promote or 'socialize' active lifestyles."

(Photo: U. Buffalo)

University of Buffalo

Followers

Archive

 

Selected Science News. Copyright 2008 All Rights Reserved Revolution Two Church theme by Brian Gardner Converted into Blogger Template by Bloganol dot com