genes biology 88.
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When do genes behave like enterprising daredevils and when are they careful and conservative? Prof. Naama Barkai of the molecular genetics department at the Weizmann Institute, who has investigated this subject, has just received the Rehovot institute's Helen and Martin Kimmel Award for Innovative Investigation, accompanied by a research grant of $1 million over five years.
Taking a chance - experimenting - is one of the impulses that drive evolution. Living cells are, in this context, great subjects for experimentation: Changes in one molecule can have all sorts of interesting consequences for others in a cell. Such experiments on genes and proteins have led all of life on a long and fascinating evolutionary journey.
Barkai took a look at gene expression - the process by which encoded instructions are translated into proteins - and the evolution of cell mechanisms for controlling that expression. Changes in genes, and thus in protein structure, can give cells new advantages for survival, but can also spell disease or death.
Not all genes evolve at the same rate. Indeed, some have been conserved through long stretches of evolution. Similar versions of some genes can be found in yeast, plants, worms, flies and humans. When do cells hold onto specific gene sequences, and when do they allow evolution to experiment? Clearly, highly conserved genes fulfill some basic function; changes in their sequences have drastic consequences, such as death or sterility. How does evolution "decide" which genes need to be conserved, and which it can change? What keeps some genes safe from the experimentation that's carried out on other genes?
Barkai and her team discovered a sort of "risk distribution law" for evolution. They found that a genetic "phrase" that regularly shows up in the promoter region of genes (the bit responsible for activating a gene) contains a key to gene conservation; the level of risk appears to be written into the gene code in a way that's similar to financial risk analysis. When the cost of error is high, an investor's willingness to take a chance is low, but if the cost of a mistake is negligible, the possibility of gain may make the risk worthwhile.
Evolution, it seems, discovered this principle millions of years before Wall Street.
'IT' EASES YOUR BRAIN
Pronouns - noun substitutes such as I, you, he, she, this, it, who and what - may play a far greater role than simply replacing a proper name in a sentence. A University of South Carolina study suggests that pronouns help keep the brain's circuitry and limited memory system from being overloaded. Using fMRI (functional magnetic resonance imaging), researcher Dr. Amit Almor and colleagues studied the brain activity of 21 adults aged 19 to 34 who were asked to read sequences of sentences to compare the brain's response to pronouns versus proper names. Almor's findings were recently published in the NeuroReport.
"The brain lit up with activity when proper names were used, including areas not associated with language," Almor said. "We saw considerable activity in areas of the parietal lobe that involve spatial processing that was absent when pronouns were used."
Almor is the first researcher to use brain imaging to explore the neurological underpinnings of humans' preference for pronouns. The brain responds to proper names by drawing from various parts of its memory to assemble complex information associated with that person. Every time a name is repeated, the brain responds by creating a new representation of the person. The integration of these multiple representations requires effort that can disrupt a brain's ongoing processing of what it hears.
Pronouns, while potentially ambiguous, don't cause the same disruptions when used in the right context. In fact, they allow a brain to move easily from one thought or sentence to another. This allows a person to digest more fully the meaning of a thought being conveyed, said Almor. "We are at the mercy of our memory system, which is limited," Almor said. "The more items or representations we hold, the more effort we need to spend so as not to lose information. Pronouns let us avoid that juggle. I expected to find activity in classic language areas of the brain. I was surprised to see activity in the spatial areas, but it makes perfect sense."
Almor says American Sign Language uses a similar system. In ASL, a person will sign a proper name on first reference and then point to a specific location in the air, as if "placing" that name on an invisible desktop. Instead of re-signing the name, the signer will point to where he or she had "placed" it.
"Language has evolved to meet our brain's needs, and sign language is no different," said Almor. "In fact, although sign languages are often studied through comparison to spoken languages, in this case sign language may show the internal working of the brain's language ability more transparently than any spoken language. Our study suggests that, just like signers, English speakers place people that were previously mentioned in a 'virtual' brain space." The research may help those who study topics that range from language acquisition and brain injury/recovery to Alzheimer's disease and autism.
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