Video: A cell’s first steps: Building a model to explain how cells grow

Friday, May 18, 2012

A collaboration between Lehigh University physicists and University of Miami biologists addresses an important fundamental question in basic cell biology: How do living cells figure out when and where to grow?

The teams of Assistant Professor Dimitrios Vavylonis and Associate Professor Fulvia Verde discovered that protein Cdc42 oscillates throughout yeast cells, precipitating a ballet of proteins that change its polarity. By changing polarity, Cdc42 regulates shape, structure and function in yeast cells, starting the growth process by clustering in an area of the cellular membrane. The oscillatory mechanism they found may be a general strategy among all self-organizing biological systems, not just simple yeast.

“The research is fundamental because it provides science with an important answer to how a living cell controls its growth process,” said Vavylonis. “Knowing how this particular protein controls growth could in the long run affect the search for drugs to control cell growth for tissue regeneration, organ development, and explain how neurons extend in different directions.”

This work indicates how Cdc42 activates bipolar growth only once a minimal cell length has been achieved. At that point, Cdc42 begins to oscillate back and forth through the cell, as the two tips compete for it. Using fluorescent markers to tag each of the many proteins involved, researchers observed the Cdc42 protein oscillate from side to side within a cell, switching sides about every five minutes. The fluctuations provide an adaptable mechanism for cells to control their size and structure in the fast-changing environment within.

The study, Oscillatory Dynamics of Cdc42 GTPase In The Control of Polarized Growth, appears today in the journal Science.

The findings demonstrate just part of the complex process of cell growth and differentiation, but mark how advanced the science of biophysics has become. Only recently has the clear imaging and monitoring of protein activity become possible at the minute sizes and shortened time scales of individual cell maturation.

“Up until now, no one has ever seen the way this protein oscillates back and forth throughout the cell,” said Tyler Drake, a Lehigh graduate student and co-author of the paper. “Looking at a simple system like yeast may allow us to understand the principles behind growth in other cells.”

This video shows active Cdc42 oscillating through yeast cells.Credit: University of Miami Miller School of Medicine

The Lehigh team developed the mathematical model of this phenomenon by analyzing cell data collected by Maitreyi Das and Fulvia Verde at the University of Miami. Drake and Vavylonis used a Lehigh Class of 1968 Junior Faculty Fellowship and a Sigma Xi grant to visit the University, where they began to test their mathematical theory. According to the model, changes in abundance or activity of Cdc42, or of its regulators, can shift the system to more asymmetric or symmetric states. The model’s conclusions were supported by biological observations of the Miami team, who genetically manipulated regulators of the protein and realized they could change cell shape and growth symmetry by adjusting Cdc42.

Vavylonis’s research has for years explored the way the cellular cytoskeleton organizes and functions. In collaboration with biologists and computer scientists, his team uses physics to study, analyze, and model the physical properties of these adaptive biological materials.

###

Lehigh University: http://www.lehigh.edu

Thanks to Lehigh University for this article.

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Sunday, May 20th, 2012 courage No Comments

G-8 summit protesters predict peaceful demonstrations in Maryland town near Camp David

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Sunday, May 20th, 2012 courage No Comments

Day 279: The long distance relationship [update] | And thus, it begins

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Sunday, May 20th, 2012 courage No Comments

Positive Affirmation #24294 – bmindful – the positive affirmation and …

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Saturday, May 19th, 2012 courage No Comments

Bubba Watson wins Hickok Belt Award for April (Rochester Democrat and Chronicle)

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Saturday, May 19th, 2012 courage No Comments

Video: PFT Live: Shanahan raves about draft pick RGIII

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Friday, May 18th, 2012 courage No Comments

No cause in death of football player

No cause in death of football player

TOLEDO — A semipro football player took a hit to the chest from an opponent’s helmet and died during a charity game while his brother, a teammate, watched from the sideline.

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Friday, May 18th, 2012 courage No Comments

Iran’s tough nuclear stance masks struggles at top

Iran’s Ambassador to the International Atomic Energy Agency, IAEA, Ali Asghar Soltanieh talks to journalists as he arrives for talks with the IAEA, at the permanent mission of Iran in Vienna, Austria, Tuesday, May 15, 2012. The U.N. nuclear agency has started new talks with Iran Monday, aimed at getting access to what it suspects was the site of secret tests to make nuclear arms. (AP Photo/Ronald Zak)

Iran’s Ambassador to the International Atomic Energy Agency, IAEA, Ali Asghar Soltanieh talks to journalists as he arrives for talks with the IAEA, at the permanent mission of Iran in Vienna, Austria, Tuesday, May 15, 2012. The U.N. nuclear agency has started new talks with Iran Monday, aimed at getting access to what it suspects was the site of secret tests to make nuclear arms. (AP Photo/Ronald Zak)

The Iranian flag waves at the permanent mission of Iran in Vienna, Austria, Tuesday, May 15, 2012, where the U.N. nuclear agency has started new talks with Iran Monday, aimed at getting access to what it suspects was the site of secret tests to make nuclear arms. (AP Photo/Ronald Zak)

(AP) ? The negotiating stance from Iranian officials never varies: The Islamic Republic will not give up its capabilities to make nuclear fuel. But embedded in the messages are meanings that reach beyond Tehran’s talks with world powers.

It points to the struggles within Iran’s ruling system as it readies for the next round of talks scheduled to begin next week in Baghdad.

Iran’s Islamic leadership ? which crushed an opposition groundswell nearly three years ago and later swatted back a power grab by President Mahmoud Ahmadinejad ? has now staked its political credibility on its ability to resist Western sanctions and hold firm to its rights under U.N. treaties to enrich uranium.

Any concessions ? either too great or too fast ? could risk internal rifts within Iran’s power structure. And that could draw powerful forces into the mix, including the Revolutionary Guard that acts as defender of the theocracy and overseer of the nuclear program. As talks deepen, so do the political considerations for an Islamic establishment that cannot afford to appear to come away empty handed.

“Insisting on a halt to enrichment is a deal breaker,” said Tehran-based political analyst Behrooz Shojaei. “It is Iran’s red line.”

This means smaller targets are likely necessary to keep dialogue alive after the Baghdad session next Wednesday between Iran and the six-nation group comprising the permanent U.N. Security Council members plus Germany.

A possible steppingstone goal for the U.S. and allies is to seek to halt Iran’s production of uranium enriched to 20 percent levels, the highest-grade material acknowledged by Tehran. The enrichment level is far above what’s needed for Iran’s lone energy-producing reactor, but it is appropriate for use in medical research. It also could be boosted to weapons-grade strength in a matter of months.

Iran insists it has no interest in developing atomic weapons, but it sees its uranium labs as a mainstay of its technological advances that include long-range missiles and an aerospace program that has promised another satellite launch this month. There still could be some room, however, for bargaining.

Iran has signaled it could consider ending the 20 percent enrichment. In return, though, it wants Washington and Europe to ease some of the most painful new sanctions, including those hitting Iran’s oil exports and its access to international banking networks.

Such demands would directly test the West’s flexibility.

Previously, Washington and European allies have insisted that Iran must take the first step and suspend all uranium enrichment as required by several U.N. Security Council resolutions. They also are under pressure from Israel to avoid protracted give-and-take negotiations.

Last week, the European Union’s foreign policy chief Catherine Ashton met with Israeli officials, including Prime Minister Benjamin Netanyahu, to discuss the upcoming talks. Later, Ashton said she hoped for “concrete” results in Baghdad.

But the semiofficial Fars news agency quoted Gen. Yadollah Javani, a Revolutionary Guard adviser, as saying it’s too early to be optimistic.

“Iran does not trust the West,” he said. “The West should build the trust in the long run.”

Netanyahu derided the opening round of talks last month in Istanbul, mocking them as a “freebie” that gave Iran international cover to continue enriching uranium. Iran, in turn, has accused Israel of trying to destroy the negotiations as pretext to a possible military strike.

“All the sides are moving with extreme caution,” said Mustafa Alani, a regional affairs analyst at the Gulf Research Center based in Geneva. “It seems no one wants to give too much or say too much at this stage. But also no one wants to be portrayed as the side that killed the talks.”

This is the tricky ground being navigated by Iran.

Its leaders are desperate to avoid any impression of caving under the Western economic squeeze. Any serious rollbacks ? without Western concessions in return ? could open room for hard-liners to take pot shots at the ruling clerics. It also could put the Revolutionary Guard in the awkward position of defending the Islamic system against ultra-nationalists who normally side with the Guard.

The timing, too, brings added concerns for Iran.

Ahmadinejad is moving into his last year in office and the ruling theocracy is closely watching for any signs of an opposition resurgence before next year’s elections. It took months for the Revolutionary Guard to snuff out unprecedented street protests after Ahmadinejad’s disputed re-election in June 2009. Then the ruling system turned against Ahmadinejad last year after he tried to challenge the authority of Supreme Leader Ayatollah Ali Khamenei.

“Too much political capital has been invested in the nuclear program for … Khamenei to simply slink away and retreat,” wrote Iranian affairs analyst Afshin Molavi in Tuesday’s edition of The National newspaper in Abu Dhabi.

Even after the feuds with Khamenei, Ahmadinejad has been a loyal advocate to Iran’s negotiating positions at the talks.

“If the Westerners change their attitudes and pay respect to the Iranian nation, they will be treated respectfully by Iranians, in return,” Ahmadinejad said Monday during a tour of eastern Iran.

He added: “They should know that Iranian nation will not take a single step back from their basic rights” ? a clear reference to uranium enrichment.

In Vienna, envoys from Iran and the U.N. nuclear agency held a second day of talks over suspicions that Tehran might have tested atomic arms technology at a military site. Iran denies the claims.

The International Atomic Energy Agency has sought access to the Parchin base for more than four years. It also wants to interview scientists and review documents.

The IAEA believes Iran in 2003 ran explosive tests needed to set off a nuclear charge. The suspected blasts took place inside a pressure chamber, the agency said.

A senior diplomat familiar with the IAEA probe says Iran has never said whether the chamber existed. A computer-generated drawing provided to The Associated Press by a nation critical of Iran’s nuclear program shows such a structure. The official who shared it said the drawing was based on information from someone who saw the chamber.

Iranian envoy Ali Asghar Soltanieh told reporters in Vienna “everything is on the right track.” He described the atmosphere as “very constructive.”

___

Murphy reported from Dubai, United Arab Emirates. Associated Press writer George Jahn in Vienna contributed to this report.

Associated Press

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Friday, May 18th, 2012 courage No Comments

Obama keeps up with Kardashians, Avengers, more

(AP) ? President Barack Obama can hold his own when it comes to pop culture: He’s up on “The Avengers” superheroes, has a handle on the Kardashians and says he catches up with TV hits during long flights on Air Force One. But the president punted to wife Michelle when he was asked about the erotic fiction book “Fifty Shades of Grey.”

Obama, who took a quick pop culture quiz during an appearance Tuesday on ABC’s “The View,” drew a blank when asked to name “the controversial sex book that’s on millions of women’s bedside tables.”

“I’ll ask Michelle when I get home,” he promised, to hoots of laughter from the audience.

Obama did better with TV and celebrity trivia.

He knew which Kardashian was married for just 72 days.

“That would be Kim,” he answered, saying he only knew because she was married to pro basketball player Kris Humphries.

He’s seen “The Avengers,” and was able to name three superheroes: Hulk, Captain America and Ironman.

And he knew that View participant Sherri Shepard had been on “Dancing with the Stars.”

He didn’t know whether Jessica Simpson had had her baby. (She had a girl earlier this month.)

Obama said he catches up with TV shows like “Mad Men” and “Homeland” on long flights such as trips to Afghanistan, when there’s time to study his briefing books and still have hours left over.

And he said his daughters, at a private 50th birthday roast for their dad, gave him credit for being embarrassing, but “not too embarrassing.”

Associated Press

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Thursday, May 17th, 2012 courage No Comments

California Workers Compensation : Best Way to Invest | Honest …


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Thursday, May 17th, 2012 courage No Comments
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