Saturday, July 26, 2008

Life's toolkits

Life has a genetic toolkit to build a wide variety of forms from just a few basic, simple and elegant body plans.

Take this into consideration and take a look at how stem cells become specialized.
Many Paths, Few Destinations: How Stem Cells Decide What They'll Become.
How does a stem cell decide what specialized identity to adopt -- or simply to remain a stem cell? A new study suggests that the conventional view, which assumes that cells are "instructed" to progress along prescribed signaling pathways, is too simplistic. Instead, it supports the idea that cells differentiate through the collective behavior of multiple genes in a network that ultimately leads to just a few endpoints -- just as a marble on a hilltop can travel a nearly infinite number of downward paths, only to arrive in the same valley.
The findings, published in the May 22 issue of Nature, give a glimpse into how that collective behavior works, and show that cell populations maintain a built-in variability that nature can harness for change under the right conditions. The findings also help explain why the process of differentiating stem cells into specific lineages in the laboratory has been highly inefficient.
"Nature has created an incredibly elegant and simple way of creating variability, and maintaining it at a steady level, enabling cells to respond to changes in their environment in a systematic, controlled way," adds Chang, first author on the paper.
The landscape analogy and collective "decision-making" are concepts unfamiliar to biologists, who have tended to focus on single genes acting in linear pathways. This made the work initially difficult to publish, notes Huang. "It's hard for biologists to move from thinking about single pathways to thinking about a landscape, which is the mathematical manifestation of the entirety of all the possible pathways," he says. "A single pathway is not a good way to understand a whole process. Our goal has been to understand the driving force behind it."
So stem cells have a built-in toolkit that responds to random changes, enabling then to respond to changes in their environment in a systematic and controlled way, ultimately leading to just a few endpoints. The toolkit harnesses random variation and selection to reach the same destination.
The stem cells are front-loaded (provided with a toolkit) to develop along a certain path while harnessing random variation and selection.

Key Regulator Of DNA Mutations Identified
As a general rule, your DNA is not something you want rearranged. But there are exceptions – especially when it comes to fighting infections. Since the number of microbes in the world far surpasses the amount of human DNA dedicated to combat them, specialized cells in the immune system have adopted an ingenious, if potentially disastrous, strategy for making antibodies. These cells, called B lymphocytes, intentionally mutate their own DNA to ward off invaders they have never seen before.
B lymphocytes have a toolkit that regulates mutations for the purpose of generating antibodies. Thus, here we have another toolkit that harnesses random variation and selection to intentionally generate variety for the purpose of producing novel antibodies.

How many more toolkits that harness quantum randomness and selection to generate controlled variety will we discover?

Genetic toolkits in action:
New Evidence That Ancient Choanoflagellates' Form Evolutionary Link Between Single-celled And Multi-celled Organisms
Evolutionary Origin Of Mammalian Gene Regulation Is Over 150 Million Years Old
Marsupials And Humans Share Same Genetic Imprinting That Evolved 150 Million Years

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