Where does the gene activity of youth go? New findings may hold the key
New evidence may explain why it is that we lose not only our youthful looks, but also our youthful pattern of gene activity with age. A report in the November 26th issue of the journal Cell, a Cell Press publication, reveals that a protein perhaps best known for its role in the life-extending benefits of a low-calorie diet also maintains the stability of the mammalian genome—the complete set of genetic instructions "written" in DNA.
The researchers found in studies of mammalian stem cells that the protein SIRT1 controls the packaging of DNA into chromatin, thereby setting the youthful pattern of gene activity by keeping select genes switched off. In response to DNA damage, those SIRT1 proteins leave their posts to go off and assist in the necessary repairs. That change in SIRT1's job description leads to shifts in gene activity that parallel those seen in the aging mouse brain, they show. They suspect similar changes would also be found in other body tissues as well.
" The critical protein controls both which genes are off and on as well as DNA repair; it's used for both processes, and that's the catch," said David Sinclair of Harvard Medical School. "As cells accumulate DNA damage, the protein can't do both jobs sufficiently." Once SIRT1 loses control, gene activity goes haywire, a state of affairs that leads to symptoms associated with aging.
Sinclair's team also found what they consider to be good evidence that the aging process can be slowed. Mice with an excess of SIRT1 had an improved ability to repair DNA and prevent those unwanted changes in gene expression. The hope is that those improvements could be reproduced with a drug that stimulates SIRT1, they said.
Indeed, the famous red wine ingredient known as resveratrol offers benefits through its effects on SIRT1, as do several more targeted drugs at some stage of development or testing. The new findings offer an explanation for how those life-promoting chemicals may be working. The ultimate test, Sinclair said, will be whether such drugs can indeed maintain a youthful gene profile.
While scientists had long known that gene activity changes with age, the driving force behind those changes remained mysterious, Sinclair said. Many had also proposed a connection between DNA damage and aging. After all, it's common knowledge that UV damage to the skin leaves it looking older. But again, he said, no one had really put their finger on just what the relationship is, or at least they hadn't in mammals.
In fact, scientists had discovered some years ago that Sir2, the yeast equivalent of SIRT1, stabilizes the genome. With age or in response to a DNA break, however, the Sir2 complex takes off for the damaged sites, activating genes that leave the yeast sterile, a characteristic associated with aging.
The new results show that the yeast aging process may be remarkably relevant to mammals. "If you step back and think, it's pretty striking," Sinclair said. "Something as simple as yeast can tell us about the mechanism of aging in mammals."
"'I'll make old vases for you if you want them—will make them just as I made these.' He had visions of a room full of golden brown beard. It was the most appalling thing he had ever witnessed, and there was no trickery about it. The beard had actually grown before his eyes, and it had now reached to the second button of the Clockwork man's waistcoat. And, at any moment, Mrs. Masters might return! "Worth stealing," a Society journalist lounging by remarked. "I could write a novel, only I can never think of a plot. Your old housekeeper is asleep long ago. Where do you carry your latchkey?" "Never lose your temper," he said. "It leads to apoplexy. Ah, my fine madam, you thought to pinch me, but I have pinched you instead." How does that strike you, Mr. Smith? Fancy Jerusha Abbott, (individually) ever pat me on the head, Daddy? I don't believe so-- The confusion was partly inherited from Aristotle. When discussing the psychology of that philosopher, we showed that his active Nous is no other than the idea of which we are at any moment actually conscious. Our own reason is the passive Nous, whose identity is lost in the multiplicity of objects with which it becomes identified in turn. But Aristotle was careful not to let the personality of God, or the supreme Nous, be endangered by resolving it into the totality of substantial forms which constitute Nature. God is self-conscious in the strictest sense. He thinks nothing but himself. Again, the subjective starting-point of305 Plotinus may have affected his conception of the universal Nous. A single individual may isolate himself from his fellows in so far as he is a sentient being; he cannot do so in so far as he is a rational being. His reason always addresses itself to the reason of some one else—a fact nowhere brought out so clearly as in the dialectic philosophy of Socrates and Plato. Then, when an agreement has been established, their minds, before so sharply divided, seem to be, after all, only different personifications of the same universal spirit. Hence reason, no less than its objects, comes to be conceived as both many and one. And this synthesis of contradictories meets us in modern German as well as in ancient Greek philosophy. 216 "I shall be mighty glad when we git this outfit to Chattanoogy," sighed Si. "I'm gittin' older every minute that I have 'em on my hands." "What was his name?" inquired Monty Scruggs. "Wot's worth while?" "Rose, Rose—my dear, my liddle dear—you d?an't mean——" "I'm out of practice, or I shouldn't have skinned myself like this—ah, here's Coalbran's trap. Perhaps he'll give you a lift, ma'am, into Peasmarsh." Chapter 18 "The Fair-pl?ace." "Yes," replied Black Jack, "here they are," drawing a parchment from his pocket. "This is the handwriting of a retainer called Oakley." HoME大桥未久AV手机在线观看
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