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(Bio) Cell Mobility and Cellular Antennae (Cilia)

 
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adedios
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PostPosted: Mon May 08, 2006 7:29 am    Post subject: (Bio) Cell Mobility and Cellular Antennae (Cilia) Reply with quote






Source: UT Southwestern Medical Center

Posted: May 7, 2006

'Cellular Antennae' On Algae Give Clues To How Human Cells Receive Signals

By studying microscopic hairs called cilia on algae, researchers at UT Southwestern Medical Center have found that an internal structure that helps build cilia is also responsible for a cell's response to external signals.

Cilia perform many functions on human cells; they propel egg and sperm cells to make fertilization possible, line the nose to pick up odors, and purify the blood, among other tasks.

With such a range of abilities, cilia serve as both motors and "cellular antennae," said Dr. William Snell, a professor of cell biology at UT Southwestern and senior author of new research on cilia published in the May 5 issue of Cell.

Genetic defects in cilia can cause people to develop debilitating kidney disease or to be born with learning disabilities, extra fingers or toes, or the inability to smell.

But no one really knows how cilia work, or, in some parts of the body, what their function is.

"There are cilia all over within our brain, and we don't have a clue about what they're doing," Dr. Snell said.

He and his team use the microscopic green alga, Chlamydomonas reinhardtii, which has two individual cilia. This alga allows researchers to manipulate genes and study the resulting effects on cilia in a way that would be impossible in animals such as mice.

"Chlamy is one of the few model organisms in which it's possible to do these kinds of studies," Dr. Snell said.
Normally, cilia -- also called flagella -- are built and maintained by an internal bidirectional, escalator-like system that ferries molecules to and from the tips by a process called intraflagellar transport, or IFT.

The UT Southwestern researchers used a mutant temperature-sensitive strain of the alga that behaved normally at lower temperatures. At higher temperatures, however, the IFT process stopped, and its components disappeared from the cilia. The cilia themselves were still able to beat, or move back and forth, for about 40 minutes before they began to shorten.

The team focused on fertilization of the alga, a process that requires a cilium to bind to a molecule on a cilium from a cell of the opposite mating type. They found that when the external molecule binds to a cilium, it activates an enzyme that signals the start of a chain of chemical reactions.

Although the cilia could move without IFT and bind to the molecules of the cilia of the opposite type, those cells were unable to respond to the signaling molecules. The failure to activate the chain of chemical reactions indicated that IFT was necessary for this function.

Analysis showed that the cilia signaling process was similar to that found in human cells, such as those in the nose involved in the sense of smell and those in the developing nervous system that sculpt our brains.

Uncovering this series of reactions will make it possible to test, for instance, drugs that can affect cilia, in the hope of finding substances that would also be effective in higher animals, Dr. Snell said.

"This is another example of how basic science research can have big results," he said. "Studies on Chlamydomonas will help us understand the unique qualities of cilia that have led to their use in chemosensory pathways in humans."

Other UT Southwestern researchers involved in the study were Dr. Qian Wang, lead author and postdoctoral researcher in cell biology, and Dr. Junmin Pan, assistant professor of cell biology.

The work was supported by the National Institutes of Health.

*************************************************************

Questions to explore further this topic:

Cells Alive: Animations

http://www.cellsalive.com/toc.htm

Cell Biology Animation

http://www.johnkyrk.com/

An introduction to cell structure

http://www.wiley.com/legacy/co.....ucture.htm
http://www.emc.maricopa.edu/fa.....CELL2.html
http://users.rcn.com/jkimball......Cells.html

Cell structure details

http://www.tvdsb.on.ca/westmin...../cells.htm
http://ebiomedia.com/gall/cell/cellmain.html

What is the cytoskeleton?

http://www.biology.arizona.edu...../main.html
http://web.mit.edu/esgbio/www/cb/cytoskeleton.html

Cell Mobility: A powerpoint presentation

http://anatomy.med.unsw.edu.au.....sld001.htm

What are actin and myosin?

http://www.wiley.com/college/p.....index.html
http://nessie.bch.ed.ac.uk/PAUL/ACTIN/

What are actomyosin and kinesin?

http://www.scripps.edu/cb/milligan/projects

What are flagella and cilia?

http://www.cytochemistry.net/C...../cilia.htm
http://programs.northlandcolle.....ellum.html

What are microtubules?

http://www.cytochemistry.net/C.....crotub.htm
http://www.biologie.uni-hambur.....25/25b.htm

Animations of flagella

http://microscope.mbl.edu/bayp.....39614.htm#

What are ciliates?

http://ebiomedia.com/gall/ciliates/index.html

What are rotifers?

http://ebiomedia.com/gall/roti.....rmain.html

*************************************************************

Science Lesson: The Sense of Smell

http://www.paete.org/forums/viewtopic.php?t=934

How does the brain detect odors?

http://www.sciencedaily.com/re.....040220.htm
http://www.sciencedaily.com/re.....123857.htm
http://www.sciencedaily.com/re.....104056.htm

GAMES

http://www.zerobio.com/target_....._cells.htm
http://www.wisc-online.com/obj.....id=AP11403


Last edited by adedios on Sat Jan 27, 2007 3:36 pm; edited 2 times in total
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PostPosted: Mon May 29, 2006 9:33 am    Post subject: Algae's Protein 'Tails' Create Motion ... And Aid Munching Reply with quote

Source: Brown University

Posted: May 29, 2006


Algae's Protein 'Tails' Create Motion ... And Aid Munching

When single-celled organisms such as sperm crack their whip-like appendages called flagella, the beating sets them in motion. But in certain colonies of green algae, flagella also boost nutrient uptake, according to surprising new research.

In the early online edition of the Proceedings of the National Academy of Sciences, researchers from the University of Arizona and Brown University explain how flagella allow these algae to get the energy they need to multiply and create colonies – the critical secret that allowed them to evolve into multicellular organisms.

“This is the first evidence that flagella not only help organisms move, but can help them feed at a rate that allowed them to evolve to a larger size,” said Thomas Powers, an assistant professor of engineering at Brown who studies microorganisms in motion. “This is a critical piece of information, since understanding how one-celled life forms evolve into many-celled ones is a fundamental question in biology.”

The team studied a group of green algae known as the volvocines, organisms so common they can be found in puddles of rain. Biologists study the group, which runs the gamut from single-celled organisms to teeming colonies, to understand how cells differentiate and multiply. But how did the volvocines jump from solo cells to Volvox, a colony of as many as 50,000 cells?

It’s a puzzler of a question, given the size of a Volvox colony and the laws of physics. Bigger organisms need more energy – a lot more energy – to survive. And Volvox is the largest colony that the volvocines make, a giant ball of flagella-waving body guards protecting a small cluster of reproductive cells. When the radius of the spherical colony increases by a factor of two, the area of the sphere increases by a factor of four. So it follows that the energy demands for Volvox would quadruple, too, as it grows.

Yet microscopic organisms such as volvocines get nutrients through diffusion, a process by which bits of food bump into the cell and pass through the cell membrane. Doubling the radius of the colony doubles – not quadruples – the colony’s food intake rate. So a large organism such as a Volvox colony shouldn’t survive because it would demand more energy than passive feeding could supply, a conundrum that researchers refer to as the “bottleneck problem.”

The research team had a hunch that flagella somehow played a role in bringing in nutrients needed for Volvox to grow and survive. Raymond Goldstein, a professor of physics and applied mathematics at the University of Arizona, gathered together a group of scientists with expertise in physics, mathematics, engineering and biology to work on the problem.

The team created a mathematical model that allowed them to calculate how the flagella created a flow of water around the colony and verified this prediction with experimental measurements. Then they used the model to show that the coordinated beating of the flagella concentrated the nutrients just ahead of the moving colony. The colony plows into this nutrient-rich region and leaves a plume of waste in its wake.

So a Volvox colony doesn’t just passively feed, it actively increases the concentration of nutrients around it using its flagella. Put another way, these tiny protein whips not only acts as legs, but also as arms, gathering in food the colony needs to grow and thrive.

Powers, brought in to help with biomechanical theory, said the surprise in the finding is that the nutrient current created by Volvox was proportional to the surface area of the colony. In other words, Volvox met its rapidly increasing demand for nutrients through flagellar beating, allowing the organism to make the multicellular leap.

“Previous models would have predicted that the nutrient demands of Volvox would outstrip the supply,” Powers said. “But we showed that metabolic supply can, in fact, keep up with metabolic demand. The colony beat the bottleneck problem. Its increasing size is actually an advantage, allowing it to create a faster flow of nutrients.”

The National Science Foundation funded the work.
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PostPosted: Fri May 11, 2007 6:47 am    Post subject: Scientists equip bacteria with custom chemo-navigational sys Reply with quote

Emory University
11 May 2007

Scientists equip bacteria with custom chemo-navigational system

Using an innovative method to control the movement of Escherichia coli in a chemical environment, Emory University scientists have opened the door to powerful new opportunities in drug delivery, environmental cleanup and synthetic biology. Their findings are published online in the Journal of the American Chemical Society and will be published in a future print issue.

Justin Gallivan, PhD, assistant professor of chemistry, and graduate student Shana Topp successfully reprogrammed E. coli's chemo-navigational system to detect, follow and precisely localize to specific chemical signals. In doing so, the scientists exploited E. coli's natural chemotaxis, a microbe's ability to move toward specific chemicals in its environment.

"Equipping bacteria with a way to degrade pollutants, synthesize and release therapeutics, or transport chemicals with an ability to localize to a specific chemical signal would open new frontiers in environmental cleanup, drug delivery and synthetic biology," says Dr. Gallivan.

The researchers equipped E. coli with a "riboswitch," a segment of RNA that changes shape when bound to certain small target molecules, which can then turn genes on or off. Dr. Gallivan and Topp believe that the riboswitch can be used to equip other types of self-propelled bacteria with "chemo-navigation" systems to move them toward desired targets.

Chemotactic bacteria navigate chemical environments by coupling their information-processing capabilities to powerful, tiny molecular motors that propel the cells forward.

Researchers have long envisioned reprogramming bacteria so that microbes capable of synthesizing an anti-cancer drug, for instance, can be used to target diseased cells while sparing healthy cells of side effects. Likewise, scientists are researching ways to use bacteria to clean up oil spills or remove other pollutants from soil, water and wastewater.

"This new ability to equip motile bacteria with a precise and tunable chemo-navigation system will greatly enhance the impressive arsenal of natural and engineered cell behaviors," says Dr. Gallivan.


###
The study was supported by the Arnold and Mabel Beckman Foundation and the National Institutes of Health.
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PostPosted: Mon Jul 23, 2007 9:34 am    Post subject: Toward giving artificial cells the ability to move Reply with quote

Toward giving artificial cells the ability to move
Journal of the American Chemical Society
23 July 2007

Got legs" Chemists in Japan and Italy are reporting development of self-propelled oil droplets that could provide a basis for giving artificial cells the ability to move. Their collaborative study from the University of Tokyo and Protolife in Venice is scheduled for the August 8 issue of the Journal of the American Chemical Society (JACS), a weekly publication.

Tadashi Sugawara and colleagues note that efforts to make artificial cells have focused partly on genetics and enabling such cells — which could become biofuel factories and other technological advances — to reproduce. Sugawara’s group previously reported a self-reproducing lipid capsule in JACS. Scientists in the United States recently announced successful transplantation of a bacterial genome, an achievement described as a major step toward creating synthetic forms of life.

The new study focuses on “another essential and perhaps more fundamental characteristic of cells, the ability to move.” In laboratory experiments, the researchers showed that an oil droplet, used to represent an artificial cell, underwent sustained movement through a chemical solution for several minutes until finally coming to a stop. In doing so, the researchers say, the droplet demonstrated a “primitive form of chemotaxis,” one of the most basic cellular responses in which the cell directs its movement toward the presence of certain chemicals in its environment. The study could provide a blueprint for designing future locomotion systems for artificial cells, the scientists suggest.

ARTICLE #1 FOR IMMEDIATE RELEASE
“Fatty Acid Chemistry at the Oil-Water Interface: Self-Propelled Oil Droplets”


DOWNLOAD PDF
http://pubs.acs.org/cgi-bin/sa.....706955.pdf

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http://pubs.acs.org/cgi-bin/sa.....06955.html
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PostPosted: Wed Oct 03, 2007 1:52 pm    Post subject: Cilia: small organelles, big decisions Reply with quote

Johns Hopkins Medical Institutions
3 October 2007

Cilia: small organelles, big decisions

Johns Hopkins researchers say they have figured out how human and all animal cells tune in to a key signal, one that literally transmits the instructions that shape their final bodies. It turns out the cells assemble their own little radio antenna on their surfaces to help them relay the proper signal to the developmental proteins “listening” on the inside of the cell.

The transmitters are primary cilia, relatively rigid, hairlike “tails” that respond to specialized signals from a host of proteins, including a key family of proteins known as Wnts. The Wnts in turn trigger a cascade of shape-making decisions that guide cells to take specific shapes, like curved eyelid cells or vibrating hair cells in the ear, and even make sure that arms and legs emerge at the right spots.

“Our experiments go to the heart of the development and maintenance of our body tissue,” says Johns Hopkins geneticist Nicholas Katsanis, Ph.D., associate professor at the McKusick-Nathans Institute for Genetic Medicine. “Any miscues with the Wnt signaling pathway,” says Katsanis, “and you’re looking at major childhood diseases and defects.”

In a report published on September 30 in Nature Genetics, Katsanis and his team used a small transparent fish, zebrafish, to literally watch what happened if they chemically blocked the production of three proteins that are required for primary cilia function during the period when a fish egg develops into a grown up, fully-finned fish.

The more they blocked, the more developmental errors - for example, the growing fish would not properly extend their tails - they were able to track to defective Wnt signaling.

Katsanis notes that once inside a cell, the Wnt pathway splits into two branches that need to be balanced depending on the needs of each cell: the so-called canonical branch, which typically drives cells to multiply, and the non-canonical branch, which controls messages to refine cell shape and growth. The errors seen in the fish pointed to an imbalance where canonical signaling predominated.

A series of biochemical studies revealed that cilia normally help a cell keep the right balance by selectively destroying proteins in the canonical branch to prevent excess growth. Defective ciliary function therefore leads to defective destruction of key proteins, which then causes problems in interpreting the Wnt signal.

“We thought that the key to the balancing act occurred inside the cell, but it now seems clear that the cilia are the main relay stations,” Katsanis says. “We’ve just reset a huge volume of literature under a new light.”


###
The research was funded by the National Institute of Child Health and Development, the National Institute of Diabetes, Digestive and Kidney Disorders, the National Institute for Arthritis and Musculoskeletal Disorders, the German Academic Exchange Service, and the Medical Research Council.

Authors on the paper are Philip Beachy of Stanford School of Medicine; Philip Beales of University College London; George DeMartino from UT Southwestern; and Jantje M. Gerdes, Norann Zaghloul, Carmen Leitch, Shaneka S. Lawson, Masaki Kato, Shannon Fisher and Katsanis of Johns Hopkins.

On the Web:
http://katsanis.igm.jhmi.edu/
http://www.nature.com/ng
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