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MIB
B.V. VIP - Contributor
Joined: Oct 02, 2001
Posts: 42279
Location: Innsmouth
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 Posted: Sat Jun 22, 2002 8:49 pm Post subject: Squishy Skeletons in our Cells Feel the Effects of Gravity |
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June 21, 2002 8:30 CDT
Kenneth Snelson is a sculptor with a vision. His creation-called \"Needle Tower\" -- at first seems to defy gravity.
Appearing deceptively fragile at first, it stubbornly soars upwards 20 meters before topping out.
It continues to mock its own appearance, withstanding winds (it merely bends in acknowledgement) and being completely unfazed when it is shoved from below. In fact, the structure seems to almost.
His sculpture bears an almost uncanny similarity to the skeletons of cells. That\'s right-cells have a skeleton. Okay, they\'re not made up of calcium like the bones we usually hear about, but they provide an inner structure just the same. Biologists call them cytoskeletons. They\'re made up of protein molecules that are arranged into chains. Cytoskeletons give cells their shape, help cells move, and hold the nucleus in place.
Snelson\'s sculptures also share another thing in common with cytoskeletons. They both have tensegrity, which is short for tensional integrity. They balance compression with tension, and yield to forces without breaking. In the Needle Tower, the wires carry tension and the rods bear compression. In a cytoskeleton, protein chains--some thin, some thick and some hollow--take the place of wires and rods. Linked together they form a stable, but flexible, structure.
NASA is intrigued by cytoskeletons, specifically the way they respond to gravity. Weight can provide both tension and compression. But what happens (during space travel, for example) when weight vanishes? Do cells behave differently when their cytoskeletons relax?
[img]http://www3.cosmiverse.com/newsimages/cells_endothelial_cytoskeleton1.jpg[/img]
It\'s a question Don Ingber and a team of researchers has been working hard to find the answer to. Speaking to NASA, Ingber reported what they\'ve learned so far by explaining, \"The cytoskeleton perceives gravity -- or any force -- through special proteins known as integrins, which poke through the cell\'s surface membrane.\" Inside the cell, they\'re hooked to the cytoskeleton. Outside, they latch onto a framework known as the extracellular matrix -- fibrous scaffolding to which cells are anchored in our bodies.
When the integrins move, the cytoskeleton stiffens in response. They learned this by coating small magnetic beads (approx 1 to 10 microns in size) with special molecules that bind to the integrins. They attached the beads to the integrins and then applied a magnetic field.
\"The beads turned and tried to align with the field, just like a compass needle would want to align with the earth\'s magnetic field,\" explains Ingber. The beads twisted the integrins and, in turn, tweaked the cytoskeleton. As more stress was applied, the cytoskeleton became stiffer and stiffer. In fact, it become so stiff that the beads couldn\'t be turned much past a few degrees!
[img]http://www3.cosmiverse.com/newsimages/cells_red_blood1.jpg[/img]
In addition to causing the integrins to stiffen, it also activated certain genes. According to Ingber, \"Activating a gene,\" means coaxing a gene to generate RNA and proteins. That\'s important because proteins are little messages that signal the cell to take action. Tickling the cytoskeleton, it seems, can make cells switch between different genetic programs.
Ingber\'s team had already uncovered a link between the shape of the cell and the cell\'s behavior. In one experiment they forced living cells to take on different shapes -- spherical or flattened, square or round--by placing them on tiny adhesive islands of extracellular matrix.
Cells that were flat and stretched tended to divide. Cells that were round and cramped tended to die. Says Ingber: \"Mechanical restructuring of the cell and cytoskeleton apparently tells the cell what to do.\"
Very flat cells with taut cytoskeletons somehow sense that more cells are needed--to cover a cut, for example. Rounder, cramped cells might sense an overpopulation problem and decide it\'s time to die and make room for others. In either case, they are responding to a control system in which the shape-shifting cytoskeleton serves as a switching mechanism.
This discovery has already been instrumental to creative a prospective cancer treatment based on changes in cell shape. It opens up new possibilities for the treatment of osteoporosis, cardiac disease, lung problems and developmental abnormalities. Every tissue in the body, says Ingber, has some disease that results from cells responding abnormally to mechanical forces. The pursuit of solving how cells respond to gravity has opened up entirely new aspects of cell regulation.
Ingber believes that tensegrity is a core organizing principle of the entire physical world. Self-stabilizing structures form spontaneously at every scale -- cytoskeletons are merely one example. Another would be spherical carbon molecules called \"BuckyBalls\" that look like atomic soccer balls.
Clay molecules also arrange themselves into tensegrity patterns that some researchers think harbored the first microscopic life forms on Earth. Even the universe itself, with its black holes (compression) and gravitationally linked galaxies (tension), may be a tensegrity structure.
\"I gave a talk once at NASA on evolutionary biology,\" he recalls. \"The last slide of my talk was a picture of the universe: super clusters of galaxies. Next to it was a one of capillary cells in a dish, formed into networks. The two pictures looked identical.\"
http://www3.cosmiverse.com/news/science/science06210201.html |
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