Tetrahymena
http://www.lifesci.u...me/Tetrahymena/
Tetrahymena is a small pear-shaped ciliate ranging in size from 40-150 microns long.
Tetrahymena can be obtained from science supply companies, they reproduce quickly and are easy to maintain. They are cultured and used as a food source for baby fish.
The following is from WSU's 'Ask Dr. Universe' as an answer to the question 'why do we die?'
You probably know that your cells must divide and multiply so that your body can grow and repair itself. Well, a scientist named Leonard Hayflick discovered that there is a LIMIT to how many times they can divide. That number, which is now called the "Hayflick Limit," is around 50.
Since Professor Hayflick made this discovery, other scientists have done the same experiment with cells from other species. What they've found out is that, generally, the more times an animal's cells divide, the longer its lifespan.
Makes sense, doesn't it? But I didn't know anything about this until Ray Reeves, a scientist here at Washington State University, explained it to me the other day. Professor Reeves studies the structure of "chromatin" and how it affects the way genes work. Chromatin is the actual stuff that your chromosomes are made of.
And chromosomes, you'll recall, are the packages of genes in all your cells that tell your body how to grow and operate.
Anyway, Professor Reeves says that the Hayflick Limit is like a clock ticking inside us--although (of course!) it's not quite that simple.
Naturally, scientists weren't satisfied with just finding out that cells will divide only a certain number of times. They wanted to know WHY.
Some friends of Professor Reeves came up with a clue. Elizabeth Blackburn and Carol Greider discovered how the ends of chromosomes are repaired in a one-cell organism called a Tetrahymena. Now get this. As far as anyone can tell, the Tetrahymena LIVES FOREVER. (Unless it's eaten, squashed, starved, or whatever.)
Of course, the single cell doesn't live forever. Remember, cells reproduce by dividing. The result of each division is identical to the parent cell. Regardless of HOW it lives forever, though, an immortal cell gets aging scientists pretty excited.
At about the same time, James Watson and A.M. Olovnikov found that there's a basic problem that occurs when DNA copies itself so that a cell can divide. In order for the strands of DNA to separate, they require a PRIMER, something to get them started. This primer is another molecule called RNA.
When the RNA primer finishes its job and disappears, it leaves a GAP in the DNA strand. What this means is that each time the DNA copies itself so that the cell can divide, the chromosome gets shorter.
AHA! THIS MUST BE THE AGING CLOCK!
This clock, the end of the chromosome, is called a "telomere." Telomeres are made up of the same DNA message pattern repeated over and over and over. So when a little disappears, it's okay, the message is still there. But there is a limit to how much can get clipped off--the Hayflick Limit! AHA!
But now, back to our one-celled friend, the Tetrahymena. When the Tetrahymenae divide, their chromosomes stay about the same length. So Professors Blackburn and Greider figured there must be something that fills in the gaps at the chromosome ends. Sure enough, they found an enzyme called "telomerase."
The telomerase sees the shortened DNA strand, gloms on, and fills it in. It's telomerase that repairs and maintains the length of its chromosomes and makes the Tetrahymena immortal!
But that's not all. YOUR cells contain telomerase! At least some of them, such as your "stem" cells, which help create new cells for your immune system. And your other cells CAN contain telomerase--IF their genes EXPRESS it.
So WHY don't they just express telomerase so you can live forever?
Well, says Professor Reeves, immortality takes a lot more than keeping the ends of your chromosomes the right length. You and your cells age in a lot of ways, from exposure to the ultraviolet light in sunlight, from the free radicals we talked about in the last column, and so on.
And another thing. You know what other cells have learned to turn on their telomerase genes so they can live forever? Cancer cells.
Cancer cells are basically cells that don't stop dividing when they're supposed to. Get the drift? In a sense, says Professor Reeves, we die so we won't get cancer.
Maybe you heard that earlier this year scientists actually figured out how to get human cells they grew in the laboratory to break past the Hayflick Limit. In other words, they figured out how to get the cells to turn on the genes that express telomerase!
This is really amazing. And it will probably help scientists treat different diseases. But it does NOT mean we can live forever. Why?
There's a lot more to aging than telomerase, says Professor Reeves again.
Even if we could figure out all the complications and just keep pumping out the telomerase without our cells turning into cancer tumors, even then--you still wouldn't be immortal. At some point you'd get hit with a meteorite or something. Sure, suppose you could live thousands of years. At some point, ACCIDENTS HAPPEN. That's what EVOLUTION has to do with how long we live! I'll get to this in the next column.
http://www.wsu.edu/D...rse/death2.html
