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Descent of Man In this lecture, beginners can familiarize themselves with basic information and terms used to describe the evolution of humanity beginning with the origin of primates through the comings and goings of Genus Homo. |
Difference Between Humans And Primates
Posted: Wednesday, February 25, 2004
Source: University Of Pennsylvania Medical Center
First Protein Difference Between Humans And Primates That Correlates To Anatomical Changes In Early Hominid Fossil Record
(Philadelphia, PA) – In an effort to find the remaining genes that govern myosin--the major contractile protein that makes up muscle tissue--researchers at the University of Pennsylvania School of Medicine have made a discovery that may be central to answering key questions about human evolution.
Published in the March 25 issue of Nature, Penn researchers have found one small mutation that undermines an entire myosin gene. Their estimated dating for the appearance of this mutation places it at about 2.5 million years ago, just prior to a period of major evolutionary changes in the hominid fossil record. These include the beginning of larger brain size, so important in making us human. While the characterization of this mutation may better help understand such genetic diseases as muscular dystrophy, this finding has potentially wider implications for re-interpreting long-held notions about the appearance and early evolution of the genus Homo.
Anthropologists have long debated how humans evolved from ancestors with larger jaw muscles and smaller brains. This newly discovered mutation seems responsible for the development of smaller jaw muscles in humans as compared to non-human primates. These converging lines of evidence suggest the question: Did this genetic mutation lift an evolutionary constraint on brain growth in early humans?
In a classic case of scientific sleuthing, Hansell Stedman, M.D., Associate Professor of Surgery, Nancy Minugh-Purvis, Ph.D., Director of Advanced Gross Anatomy, Department of Cell and Developmental Biology, and colleagues took their discovery of a mutation that prevents the expression of a variety of myosin -- designated MYH16 on chromosome 7 -- to its ultimate context: what makes humans different from other primates.
"Around the lab, we jokingly call this the 'room for thought' mutation, since we had to involve scientists from several disciplines to make sense of the possible domino effects," says Stedman. "In other words, we had to do a lot of experiments to connect the dots from DNA to RNA to protein to muscle fiber to whole muscle to boney attachment sites. Then in looking at the modern and fossil skulls it dawned on us that we just might have to look 'outside of the box' to appreciate the real significance of the initial findings."
The study began with the discovery of an unexpected similarity between an "anonymous" piece of the human genome sequence and some previously studied genes known to power muscle contraction. The surprise came when a small, inactivating deletion was found in this sequence, perhaps explaining why the computer programs had previously passed by the area without recognizing it as a gene.
To determine whether the mutation was a rare form of an active gene and not a mistake introduced by the technical nature of the investigation, the team tested DNA samples from geographically disparate human populations. They found the gene-inactivating mutation in all modern humans sampled--natives of Africa, South America, Western Europe, Iceland, Japan, and Russia. However, the mutation was not present in the DNA of seven species of non-human primates, including chimpanzees.
Additional studies showed that versions of this gene in non-human primates bear the imprint of a critically important function for the animal, which implies that the mutation afflicts all humans, in one sense of the word, with the same inherited muscle "disease." The intriguing questions became, what is the "disease" and why is it so common?
To find out in which tissue the MYH16 gene is normally activated, the investigators examined a wide range of muscle types in the readily available macaque monkey and humans. In macaques, they found the MYH16 protein was only made in a group of related muscles in the head, those involved principally with chewing and biting. In humans, they found that messenger RNA, which translates the genetic code into workaday proteins, was still active in these muscles, but no protein was being made by virtue of the mutation.
But how does this relate to the anatomical differences seen in modern humans versus non-human primates? First, the jaw muscles and their bony attachments in apes and monkeys are much larger and more powerful than in humans. At the tissue level, the researchers found that macaque chewing and biting muscles are nearly ten times as large as in humans, which correlates with the fact that MYH16 protein is made in macaques and not in humans. So maybe the "disease" is a weaker bite, raising a question as to why this mutated version of the gene could have become so widespread among modern humans.
By comparing a portion of the MYH16 gene sequence in humans to that in five other animals--quantifying the so-called molecular clock--the researchers calculated that the inactivating mutation appeared in a hominid ancestor about 2.4 million years ago, after the lineages leading to humans and chimpanzees diverged. Shortly thereafter, roughly 2.0 million years ago, the less muscled, larger brained skulls of the earliest known members of the genus Homo start to appear in the fossil record.
From this the investigators postulated that the first early hominids born with two copies of the mutated MYH16 gene would show many effects from this single mutation--most notably a reduction in size and contractile force of the jaw-closing muscles, some of which exert tremendous stress across and/or cause deposition of additional bone atop growth zones of the braincase. "The coincidence in time of the gene-inactivating mutation and the advent of a larger braincase in some early Homo populations may mean that the decrease in jaw-muscle size and force eliminated stress on the skull, which 'released' an evolutionary constraint on brain growth," says Minugh-Purvis. Indeed, aspects of the evolutionary trend of shrinking jaws and teeth, resulting in the lighter, more delicate structure found in humans today, roughly coincided with the increase in brain size characterizing the evolution of Homo over the past two million years.
Dr. Stedman is also a member of the Pennsylvania Muscle Institute at Penn. Dr. Minugh-Purvis is also adjunct assistant professor in Cell Biology and Anatomy at the University of Pennsylvania School of Dental Medicine; growth specialist in the Facial Reconstruction Center, Division of Plastic Surgery, Children's Hospital of Philadelphia; and a research associate at Penn's University Museum of Archaeology and Anthropology. Other Penn researchers collaborating on this work are Benjamin W. Kozyak, Anthony Nelson, Danielle M. Thesier, Leonard T. Su, David W. Low, Charles R. Bridges, Joseph B. Shrager, and Marilyn A. Mitchell.
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The research was supported in part by grants from the National Institutes of Health, Muscular Dystrophy Association, Association Française contre les Myopathies, Veterans Administration, and Genzyme Corporation. The authors have no competing financial interest in this work.
PENN Medicine is a $2.2 billion enterprise dedicated to the related missions of medical education, biomedical research, and high-quality patient care. PENN Medicine consists of the University of Pennsylvania School of Medicine (founded in 1765 as the nation's first medical school) and the University of Pennsylvania Health System (created in 1993 as the nation's first integrated academic health system).
Penn's School of Medicine is ranked #2 in the nation for receipt of NIH research funds; and ranked #4 in the nation in U.S. News & World Report's most recent ranking of top research-oriented medical schools. Supporting 1,400 fulltime faculty and 700 students, the School of Medicine is recognized worldwide for its superior education and training of the next generation of physician-scientists and leaders of academic medicine.
Penn Health System consists of four hospitals (including its flagship Hospital of the University of Pennsylvania, consistently rated one of the nation's "Honor Roll" hospitals by U.S. News & World Report), a faculty practice plan, a primary-care provider network, three multispecialty satellite facilities, and home health care and hospice.
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Posted: Friday, February 20, 2004
Source: Arizona State University
A century ago, when biologists used to talk about the primordial soup from which all life on Earth came, they probably never imagined from how far away the ingredients may have come. Recent findings have the origins of life reaching far out from what was once considered "the home planet." Evolution on the early Earth may have been influenced by some pretty far-out stuff.
In a paper published this week in the journal Science, Arizona State University Chemistry Professor Sandra Pizzarello claims that materials from as far away as the interstellar media could possibly have played an active role in establishing the chemistry involved in the origin of life on this planet.
In the paper, Pizarello and her co-author Arthur L. Weber of the SETI Institute show that the exclusive chirality of the proteins and sugars of life on Earth - their tendency to be left- or right-handed, could in fact be due to the chemical contribution of the countless meteorites that struck the planet during its early history. This paper provides a plausible explanation for how, with a little help from outside, the chemistry of non-life - characterized by randomness and complexity - becomes the ordered and specific chemistry of life.
Pizzarello studies meteorites and the chemicals housed within them. A particular type of meteorite - carbonaceous chondrites - holds particular interest. Carbonaceous chondrites are very primitive, stony meteorites that contain organic carbon. These meteorites are rare, but also very exciting for chemists interested in the origins of life on Earth and in the solar system. They contain amino acids - the molecules that make up proteins, and an essential part of the chemistry of life.
According to Pizzarello, it has been known for the last century that there are large amounts of carbon, hydrogen and nitrogen - the so-called biogenic elements - in the cosmos. And that it is reasonable to assume that these elements might have undergone some amount of chemical evolution before life even began.
According to Pizzarello, who studies meteorites from the collection at ASU (which has the largest university-owned collection in the world) the meteorites are the only evidence of chemical evolution scientists have in hand today. New techniques of meteorite analysis are leading to great breakthroughs in understanding where these meteorites came from and how they were formed. Even more exciting, work Pizzarello and her colleagues have recently published in Science explores what sort of contribution the chemical evolution represented by meteorites might have had on the early Earth.
The paper addresses what has been a basic difficulty in relating the chemical evolution represented by meteorites and the origin of terrestrial life on Earth. According to Pizzarello, this problem is that chemical evolution - what we see in meteorites - is characterized by randomness, while terrestrial life relies on specificity and selection. For example, the meteorites contain over 70 amino acids. A mere 20 amino acids make up life's proteins. "There is a fundamental difficulty in trying to figure out how you go from confusion and randomness to functionality and specificity," said Pizzarello.
So far, only one trait has been found to be similar, to some extent, between amino acids in meteorites and biopolymers, that of L-"handedness" (chirality). Because organic molecules can be asymmetric if they have different groups attached to a carbon atom, they can arrange spatially in two ways, like the two hands, and be either left or right handed. All proteins involved in life on Earth are made up of L-amino acids, while sugars involved in life have a D structure. Scientists call this "homochirality."
An overabundance (excess) of the L-form (the chemical name is enantiomer), has also been found in some amino acids in meteorites. Pizzarello and Weber devised an experiment to find whether or not the amino acids found with L-enantiomeric excess in meteorites could have transferred their asymmetry during organic syntheses on the early Earth . If so, the meteorites could have provided a constant influx of materials with this excess - especially during a period early in the solar system's history in which the Earth and other planets were pummeled heavily by meteorites.
Pizzarello and Weber report in Science that in fact their experiment succeeded in proving this possibility. In the laboratory, when performing sugar syntheses in water, using reactions that modeled what may have existed on the early Earth, the asymmetry in the amino acids led to a similar asymmetry in the sugars. Pizzarello and Weber thus were able to conclude that the delivery of material from outer space via meteorites - despite the seeming randomness and complexity of these materials - could in fact have "pushed" chemical evolution on Earth toward homochirality.
Pizzarello points out that these findings do not imply that life did not evolve on Earth, or that the meteorites were the only early source of enantiomeric excess - only that the steady contribution of these meteorites might have provided a nudge in the "right" (or, more accurately, "left") direction.
The original news release:
www.asu.edu/asunews/research/ordersfromspace_022004.htm
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Giant Black Hole Rips Apart Unlucky Star Posted: Thursday, February 19, 2004
Source: Chandra X-ray Observatory Center
Thanks to two orbiting X-ray observatories, astronomers have the first strong evidence of a supermassive black hole ripping apart a star and consuming a portion of it.The event, captured by NASA's Chandra and ESA's XMM-Newton X-ray Observatories, had long been predicted by theory, but never confirmed.
Astronomers believe a doomed star came too close to a giant black hole after being thrown off course by a close encounter with another star. As it neared the enormous gravity of the black hole, the star was stretched by tidal forces until it was torn apart. This discovery provides crucial information about how these black holes grow and affect surrounding stars and gas.
"Stars can survive being stretched a small amount, as they are in binary star systems, but this star was stretched beyond its breaking point," said Stefanie Komossa of the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany, leader of the international team of researchers. "This unlucky star just wandered into the wrong neighborhood."
While other observations have hinted stars are destroyed by black holes (events known as "stellar tidal disruptions"), these new results are the first strong evidence. Evidence already exists for supermassive black holes in many galaxies, but looking for tidal disruptions represents a completely independent way to search for black holes. Observations like these are urgently needed to determine how quickly black holes can grow by swallowing neighboring stars.
Observations with Chandra and XMM-Newton, combined with earlier images from the German Roentgen satellite, detected a powerful X-ray outburst from the center of the galaxy RXJ1242-11. This outburst, one of the most extreme ever detected in a galaxy, was caused by gas, heated to millions of degrees Celsius, from the destroyed star being swallowed by the black hole. The energy liberated in the process was equivalent to a supernova.
"Now, with all the data in hand, we have the smoking gun proof that this spectacular event has occurred," said coauthor Guenther Hasinger, also of MPE.
The black hole in the center of RXJ1242-11 is estimated to have a mass of about 100 million times Earth's sun. By contrast, the destroyed star probably had a mass about equal to the sun, making it a lopsided battle of gravity. "This is the ultimate David versus Goliath battle, but here David loses," said Hasinger.
The astronomers estimated about one percent of the star's mass was ultimately consumed, or accreted, by the black hole. This small amount is consistent with predictions the momentum and energy of the accretion process will cause most of the destroyed star's gas to be flung away from the black hole.
The force that disrupted the star in RXJ1242-11 is an extreme example of the tidal force caused by differences in gravity acting on the front and back of an object. The tidal force from the moon causes tides in Earth's oceans. A tidal force from Jupiter pulled Comet Shoemaker-Levy apart, before it plunged into the giant planet.
The odds stellar tidal disruption will happen in a typical galaxy are low, about one in 10,000 annually. If it happened at the center of the Milky Way Galaxy, 25,000 light-years from Earth, the resulting X-ray outburst would be about 50,000 times brighter than the brightest X-ray source in our galaxy, beside the sun, but it would not pose a threat to Earth.
Other dramatic flares have been seen from galaxies, but this is the first studied with the high-spatial resolution of Chandra and the high-spectral resolution of XMM-Newton. Both instruments made a critical advance. Chandra showed the RXJ1242-11 event occurred in the center of a galaxy, where the black hole lurks. The XMM-Newton spectrum revealed the fingerprints expected for the surroundings of a black hole, ruling out other possible astronomical explanations.
Information and images about the event are available on the Internet at: http://chandra.harvard.edu and http://chandra.nasa.gov
chandra.harvard.edu/press/04_releases/press_021804.html
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Diamond Star Thrills Astronomers Posted: Tuesday, February 17, 2004
By Dr David Whitehouse
Science Editor
BBC News Online 2-15-4
Twinkling in the sky is a diamond star of 10 billion trillion trillion carats, astronomers have discovered.
The cosmic diamond is a chunk of crystallised carbon, 1,500 km across, some 50 light-years from the Earth in the constellation Centaurus.
It's the compressed heart of an old star that was once bright like our Sun but has since faded and shrunk.
Astronomers have decided to call the star "Lucy," after the Beatles song, "Lucy in the Sky with Diamonds."
Lucy in the sky
"You would need a jeweller's loupe the size of the Sun to grade this diamond!" says astronomer Travis Metcalfe of the Harvard-Smithsonian Center for Astrophysics, who led the team of researchers that discovered it.
The diamond star completely outclasses the largest diamond on Earth, the 530-carat Star of Africa which resides in the Crown Jewels of England. The Star of Africa was cut from the largest diamond ever found on Earth, a measly 3,100-carat gem.
The huge cosmic diamond - technically known as BPM 37093 - is actually a crystallised white dwarf. A white dwarf is the hot core of a star, left over after the star uses up its nuclear fuel and dies. It is made mostly of carbon.
For more than four decades, astronomers have thought that the interiors of white dwarfs crystallised, but obtaining direct evidence became possible only recently.
The white dwarf is not only radiant but also rings like a gigantic gong, undergoing constant pulsations.
"By measuring those pulsations, we were able to study the hidden interior of the white dwarf, just like seismograph measurements of earthquakes allow geologists to study the interior of the Earth.
We figured out that the carbon interior of this white dwarf has solidified to form the galaxy's largest diamond," says Metcalfe.
Astronomers expect our Sun will become a white dwarf when it dies 5 billion years from now. Some two billion years after that, the Sun's ember core will crystallise as well, leaving a giant diamond in the centre of our Solar System.
"Our Sun will become a diamond that truly is forever," says Metcalfe.
© BBC MMIV
news.bbc.co.uk/2/hi/science/nature/3492919.stm
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Hubble And Keck Find Farthest Known Galaxy In The Universe Posted: Monday, February 16, 2004
Source: European Space Agency
An international team of astronomers may have set a new record in discovering what is the most distant known galaxy in the Universe. Located an estimated 13 billion light-years away, the object is being viewed at a time only 750 million years after the big bang, when the Universe was barely 5 percent of its current age. The primeval galaxy was identified by combining the power of the NASA/ESA Hubble Space Telescope and CARA's W. M. Keck Telescopes on Mauna Kea in Hawaii. These great observatories got a boost from the added magnification of a natural ‘cosmic gravitational lens’ in space that further amplifies the brightness of the distant object. The newly discovered galaxy is likely to be a young galaxy shining during the end of the so-called "Dark Ages" - the period in cosmic history which ended with the first galaxies and quasars transforming opaque, molecular hydrogen into the transparent, ionized Universe we see today.
The new galaxy was detected in a long exposure of the nearby cluster of galaxies Abell 2218, taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. This cluster is so massive that the light of distant objects passing through the cluster actually bends and is amplified, much as a magnifying glass bends and magnifies objects seen through it. Such natural gravitational ‘telescopes’ allow astronomers to see extremely distant and faint objects that could otherwise not be seen. The extremely faint galaxy is so far away its visible light has been stretched into infrared wavelengths, making the observations particularly difficult. "As we were searching for distant galaxies magnified by Abell 2218, we detected a pair of strikingly similar images whose arrangement and colour indicate a very distant object," said astronomer Jean-Paul Kneib (Observatoire Midi-Pyrénées and California Institute of Technology), who is lead author reporting the discovery in a forthcoming article in the Astrophysical Journal. Analysis of a sequence of Hubble images indicate the object lies between a redshift of 6.6 and 7.1, making it the most distant source currently known. However, long exposures in the optical and infrared taken with spectrographs on the 10-meter Keck telescopes suggests that the object has a redshift towards the upper end of this range, around redshift 7.
Redshift is a measure of how much the wavelengths of light are shifted to longer wavelengths. The greater the shift in wavelength toward the redder regions of the spectrum, the more distant the object is.
"The galaxy we have discovered is extremely faint, and verifying its distance has been an extraordinarily challenging adventure," said Dr. Kneib. "Without the 25 x magnification afforded by the foreground cluster, this early object could simply not have been identified or studied in any detail at all with the present telescopes available. Even with aid of the cosmic lens, the discovery has only been possible by pushing our current observatories to the limits of their capabilities!"
Using the combination of the high resolution of Hubble and the large magnification of the cosmic lens, the astronomers estimate that this object, although very small - only 2,000 light-years across - is forming stars extremely actively. However, two intriguing properties of the new source are the apparent lack of the typically bright hydrogen emission line and its intense ultraviolet light which is much stronger than that seen in star-forming galaxies closer by.
"The properties of this distant source are very exciting because, if verified by further study, they could represent the hallmark of a truly young stellar system that ended the Dark Ages" added Dr. Richard Ellis, Steele Professor of Astronomy at Caltech, and a co-author in the article.
The team is encouraged by the success of their technique and plans to continue the search for more examples by looking through other cosmic lenses in the sky. Hubble's exceptional resolution makes it ideally suited for such searches.
"Estimating the abundance and characteristic properties of sources at early times is particularly important in understanding how the Universe reionized itself, thus ending the Dark Ages," said Mike Santos, a former Caltech graduate student, now a postdoctoral researcher at the Institute of Astronomy, Cambridge, UK. "The cosmic lens has given us a first glimpse into this important epoch. We are now eager to learn more by finding further examples, although it will no doubt be challenging."
"We are looking at the first evidence of our ancestors on the evolutionary tree of the entire Universe," said Dr. Frederic Chaffee, director of the W. M. Keck Observatory, home to the twin 10-meter Keck telescopes that confirmed the discovery. "Telescopes are virtual time machines, allowing our astronomers to look back to the early history of the cosmos, and these marvellous observations are of the earliest time yet." Notes for editors The team reporting on the discovery consists of Drs. Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA), Richard S. Ellis (Caltech, USA), Michael R. Santos (Caltech/Institute of Astronomy, UK) and Johan Richard (Observatoire Midi-Pyrénées, France/Caltech, USA).
Animations of the discovery and general Hubble Space Telescope background footage are available from http://www.spacetelescope.org/bin/videos.pl?type=news&string=heic0404
Image credits: European Space Agency, NASA, J.-P. Kneib (Observatoire Midi-Pyrénées) and R. Ellis (Caltech)
http://www.esa.int/export/esaCP/SEM6DJ1PGQD_index_0.html
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Genomic Changes Reveal Evolution Of SARS Virus Posted: Sunday, February 1, 2004
Source: University Of Chicago Medical Center
Careful study of changes in the genetic make-up of the SARS virus through the recent epidemic has allowed researchers from China and the University of Chicago to bolster the evidence for the animal origins of SARS and to chart three phases of the virus's molecular evolution as it gradually adapted to human hosts, becoming more infectious over time.
The earliest phase involved cases that appeared to be independent and featured viral genomes identical to those found in animal hosts, the researchers report in Science Express, the online version of the journal Science. The second phase, marked by clusters of human-to-human transmission, reveals how the virus quickly adapted to its human hosts. The third phase involved selection and stabilization, as the virus gravitated toward one common genotype that predominated through the end of the epidemic.
"What we see is the virus fine-tuning itself to enhance its access to a new host: humans," said study co-author Chung-I Wu, Ph.D., professor and chairman of ecology and evolution at the University of Chicago. "This is a disturbing process to watch, as the virus improves itself under selective pressure, learning to spread from person to person, then sticking with the version that is most effective."
In the early cases, infection rates were low, with only about three percent of those in direct contact with infected patients coming down with the disease. Within a few months that rate increased to nearly 70 percent of direct contacts.
This study, which combines a precise epidemiologic narrative of the emergence of the virus with rigorous analysis of the virus's genetic adaptations, confirms the importance of containing any new outbreaks quickly, the researchers said, before the virus becomes more difficult to control. It also points to potential targets for a vaccine aimed at the "spike" protein, involved in viral-host receptor recognition and internalization.
(Although Hua Tang, a Ph.D. student in Wu's lab, made significant contributions to the data analysis and interpretation, Tang and Wu emphasize that the bulk of the experimental and bioinformatic work was performed by their Chinese colleagues.)
The researchers looked at the genetic sequences of 63 SARS viruses, collected from the early, middle and late phases of the 2002-2003 epidemic.
The early phase, beginning mid-November 2002, involved 11 seemingly independent cases from different locations in the Pearl River Delta area of Guangdong Province, China. In this region, they note, rapid economic development has led to "culinary habits involving exotic animals." Six of the 11 early cases had documented contact with wild animals.
The middle phase begins with the first "super-spreader event," the major SARS outbreak in a hospital in Guangzhou beginning January 31, 2002. This outbreak produced 130 cases, including 106 acquired in the hospital. A doctor from this hospital carried the virus to Metropole Hotel in Hong Kong on February 21. Other hotel guests became infected and carried the virus away with them.
Cases following the hotel cluster fall into the late phase.
Although most of the known genomes of the SARS virus have come from the late phase of the epidemic, this study focused on 29 genomic sequences obtained from 22 patients from Guangdong Province with disease onset in all three phases of the epidemic, plus two patients from the late phase in Hong Kong.
Two genotypes dominated the early phase of the epidemic. Both differed from later viral samples in a region known as Orf8. Five early isolates contained a short sequence, 29 nucleotides long, that is missing from most of the previously known virus sequences. Four other early isolates showed a previously unreported 82-nucleotide deletion.
"It is interesting to note," write the authors, that both sequences of the early phases were also identified from other mammalian hosts." The early sequence with the extra 29 nucleotides matches viruses isolated from animals in a market in Shenzen. The sequence with the 82-nucleotide deletion is identical to viruses obtained from farmed civets in Hubei Province.
By the middle phase, the version with the 29-nucleotide deletion had become dominant.
Besides the large deletions, the researchers found 299 smaller variations, changing just a single piece of the virus's genetic code. Because SARS, like HIV, uses RNA instead of DNA to store its genetic information, it has a high mutation rate.
The researchers discovered a series of genetic motifs, like molecular fingerprints, that enabled them to distinguish between different lineages. Viruses from the early phase have a characteristic motif that is shared by the viruses isolated from animals.
The middle-phase viruses show a slightly different fingerprint, with two variations, one tied to the majority of the cases in the hospital outbreak and a different version associated with Hong Kong.
From the hotel cluster to the end of the epidemic in August, viruses with a different motif dominate. "Surprisingly few genotypes predominated in the late phase," note the authors.
The researchers tentatively trace this late-phase virus back to one patient infected with an unusual variation in the hospital in February. She began having symptoms on February 7, and subsequently had contact with the physician who carried the virus to Hong Kong on February 21.
The researchers also looked closely at the history of mutations in one gene, the spike protein, thought to be involved in the process the virus uses to enter cells. This gene underwent rapid mutation in the earliest stages of the epidemic, but that rate slowed in the later stages after it had learned to infect humans rather than other animals.
"The genetic fingerprints add a whole new layer to our understanding of the course of events in this epidemic," said Wu, "but this work could not have been done without a remarkable effort by our Chinese colleagues in the field and in the lab to unravel the precise history of hundreds of patients affected by this epidemic."
Wu, one of the 51 authors of the paper, served with Guoping Zhao of the Chinese National Human Genome Center, as co-leader of the data-analysis group. Zhao is the corresponding author for the entire paper. Wu and Tang were the only non-Chinese members of the research team.
This work was supported by the Chinese High Technology Development Program, the National Key Program for Basic Research and the People's Government of Guangdong Province.
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Counting Atoms That Aren't There Posted: Sunday, February 1, 2004
Source: Argonne National Laboratory
Counting Atoms That Aren't There, In Stars That No Longer Exist
Researchers at the U.S. Department of Energy's Argonne National
Argonne scientists, in collaboration with colleagues at the University of Chicago, Washington University and the Universita di Torino in Italy, examined stardust from a meteorite and found remnants of now-extinct technetium atoms made in stars long ago.
The stardust grains are tiny bits of stars that lived and died before the solar system formed. Each grain is many times smaller than the width of a human hair, and carries a chemical record of nuclear reactions in its parent star.
Famed scientist P.W. Merrill fifty years ago observed the signature of live technetium - an element that has no stable isotopes - in the starlight from certain types of stars, thereby proving the then-controversial theory that stars make atoms via a process called nucleosynthesis. The researchers' discovery that their stardust grains once harbored live technetium brings the science of nucleosynthesis full circle.
"Finding traces of technetium decay products in stardust provides a very precise confirmation of the theories of how atoms are made inside stars," said Michael Savina, Argonne scientist and the lead author on the research, which is published today in Science. "The fact that we can both predict and measure very tiny effects in the chemistry of these grains gives us a lot of confidence in our models of how stars work."
Authors on the report, in addition to Savina, are Michael Pellin and C. Emil Tripa of Argonne, Andrew M. Davis and Roy S. Lewis of the University of Chicago, Sachiko Amari of Washington University in St. Louis, and Roberto Gallino of Universita di Torino in Italy. Funding was provided by the U.S. Department of Energy Office of Science, the University of Chicago, NASA, and the Italian FIRB Progetto Origine Astrofisica degli Elementi Pesanti Oltre il Ferro.
The work was made possible by a specialized instrument at Argonne called CHARISMA, the only instrument of its type in the world. "CHARISMA is designed to analyze very tiny samples – the kind where you can't afford to waste atoms, because there are so few of them to work with," Savina said.
CHARISMA is presently being upgraded, with funding from the Department of Energy Office of Science and from NASA, in anticipation of samples from the Genesis mission to collect samples of the solar wind – single atoms and electrically charged particles from the sun – which scientists believe hasn't changed since the sun was born.
The research group at Argonne will be among the scientists to analyze the samples in an effort to better understand how the planets formed. Current measurements of the sun's composition are not precise enough to answer key questions about events in the early solar system. The researchers are also preparing to analyze samples from the Stardust mission, which recently captured dust grains from a comet's tail and will bring them back to Earth in 2006.
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The nation's first national laboratory, Argonne National Laboratory conducts basic and applied scientific research across a wide spectrum of disciplines, ranging from high-energy physics to climatology and biotechnology. Argonne has worked with more than 600 companies and numerous federal agencies and other organizations to help advance America's scientific leadership and prepare the nation for the future. The University of Chicago operates Argonne as part of the U.S. Department of Energy's national laboratory system.
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