Human Stem Cell Breakthrough: No Embryos Required

Human Stem Cell Breakthrough: No Embryos Required

Gene cocktails rewire human skin tissue into all-purpose stem cells 

 
MORE THAN SKIN DEEP: Two teams report they have reprogrammed human skin cells such as the above into stem cells capable of differentiating into multiple tissue types, perhaps bypassing the need for human cloning to create embryonic stem cell lines.

The end of the politically explosive, decadelong ethical battle over human embryonic stem cells may finally be in sight. Two groups of researchers report today that washing human skin cells in similar cocktails of four genes enabled them to reprogram the cells to resemble those harvested from embryos. The finding potentially paves the way for scores of labs to generate new stem cell lines without cloned embryos, which had long been considered the only realistic way of making human stem cells in the short run.

"The long run's getting a lot closer," says stem cell biologist James Thomson of the University of Wisconsin School of Medicine and Public Health in Madison, a senior author of one of the studies. "I do believe this is the beginning of a great change."

He is not alone. British newspapers reported this weekend that Ian Wilmut, the University of Edinburgh biologist who led the team that in 1997 cloned Dolly the sheep, is getting out of the cloning business in light of the new findings, which seem to offer researchers a likely new source of stem cell lines for basic research that could one day lead to new treatments and perhaps cures for spinal injuries, diabetes and debilitating disorders such as multiple sclerosis and Parkinson's disease. In the nearer term, reprogrammed cells may improve the screening drug candidates for harmful side effects.

"That's the writing on the wall right now," says biologist Arnold Kriegstein, director of the Institute for Regeneration Medicine at the University of California, San Francisco, who was not involved in the research.

Although both groups' reprogrammed cells were able to differentiate into the three main tissue types when injected into mice, Thomson cautions that they may harbor subtle, yet to be found quirks, and will need considerable tweaking before they could be safely transplanted into humans. Importantly, researchers must still study existing embryonic stem cell lines—the gold standard—to rule out any hidden risks in the lab-made cells, he says. "People want to rush and say, 'we don't need embryonic stem cells anymore,' and over time that might be true, but right now that's premature."

The results help fill in the scientific puzzle kicked off by Dolly's cloning, which proved that mammalian egg cells were capable of dissolving the genetic roadblocks that limit the potential of most adult cells to give rise to only a single type of tissue—that of the organ from which they hail—whereas embryonic stem cells have the potential to become virtually any kind of body tissue.

So researchers began testing genes that were only active in embryonic stem cells to try to pin down those capable of triggering the change. One such group, led by biologist Shinya Yamanaka of Kyoto University in Japan, reported last year that four genes, delivered to mouse cells by a retrovirus, were sufficient to induce pluripotency (the ability to differentiate into a multitude of cell types). The genes—Oct 3/4, Sox2, c-Myc and Klf4—are molecular switches called transcription factors, which activate other genes in series like a power strip.

Yamanaka's group and two others followed up earlier this year with firmer evidence that these induced pluripotent stem (iPS) cells faithfully mimicked the patterns of gene activity and cellular differentiation observed in embryonic stem cells.

Now Yamanaka and his colleagues report in the journal Cell that the same combination of genes induced pluripotency in commercially available human fibroblasts (connective tissue cells that play a crucial role in healing) derived from the facial skin of a 36-year-old woman, the joint tissue of a man, aged 69, and a newborn, respectively.

The researchers report they were able to transform about one in 5,000 cells—enough to get several iPS cells from a single culture dish—and then coax them to become nerve cells or heart tissue on the benchtop. Genetic scans indicated that the cells were more similar to embryonic tissue than to the original fibroblasts.

"What I find remarkable," Kriegstein says, "is essentially the same steps that worked in the mouse were able to work with human cells…. Everybody assumed that it'd be a different story in reprogramming the human cells."

Thomson's team reports producing a similar cellular alchemy using two of the same genes—Oct4 and Sox2—and two different ones—Nanog and Lin28,—making it less likely that the Japanese finding was a fluke.

Thomson, who in 1998 became the first scientist to extract human stem cells from embryos, says his group began seeking these factors four years ago, but chose to work with human cells. As of last spring, he says, his group, led by lab member Junying Yu, had pared an initial list of 100-plus genes to 14.

Then came Yamanaka, who Thomson says beat him to the punch because mouse cells grow much faster than human cells do, allowing more rapid experimentation. "We thought, 'oh no, it's already been done; we've been beaten,'" he recalls.

As many as a dozen major labs, he says, have since tried but failed to make reprogramming work in human cells. His team plugged along, testing gene combinations in four cell types in varying degrees of differentiation, hopeful that this would eventually lead to the correct genetic recipe.

In the online edition of Science, he and his colleagues report that Oct4 and Sox2 were capable of converting neonatal foreskin fibroblasts into cells similar to Yamanaka's, whereas Nanog significantly boosted the frequency of reprogramming and Lin28 upped it by a moderate amount.

Although Oct4 and Sox2 were well-known players in embryonic cells, "we thought this would be such a complicated problem, we never tested those genes up front," Thomson says. "It's kind of remarkably lucky that three or four [genes] are sufficient. I wasn't optimistic it would work."

The new results still leave researchers with the task of double-checking that reprogrammed cells are safe and truly have the same potential as the embryonic variety. They also have to figure out how to circumvent problems with the viral delivery system, which may disrupt important genes, resulting in cancer. Kriegstein notes that the hunt will likely commence for small molecules capable of activating the key genes.

Thomson predicts that companies such as Madison-based Cellular Dynamics International, which he co-founded, that test drug candidates for dangerous heart toxicity, could begin using cells derived from reprogramming in their assays within a year.

Whatever the source of pluripotent cells, Thomson says, researchers face the same scientific challenges—namely, understanding how to convert them into key tissues such as the beta islet cells that are impaired in diabetics, and then how to introduce them safely and effectively into humans.

Opponents of research on human embryos might contend that reprogramming happened because of the federal restrictions on embryonic research, but Thomson believes the stigma on the field made researchers wary and delayed the discovery of reprogramming by several years. "I'm cautiously optimistic" about reprogrammed cells, he says. "The worry is the politics will get involved again and squash caution."

Spared Cyclone’s Worst, Area Still Suffers

Spared Cyclone’s Worst, Area Still Suffers

 

Aid workers measured out rations of rice, lentils and salt to be distributed at the Caritas office in the village of Kanainagar, in southern Bangladesh, after a cyclone last week. 

To the naked eye, this looks like a village that Cyclone Sidr barely grazed. Most of the houses are standing. No one has died. The trees are not even decapitated, as they are in so many hamlets swallowed by the storm.

 
Women hung onto one another as they stood in line for food aid. Millions of Bangladeshis are in dire need of clean water, food and shelter after the cyclone. 

Bangladeshi women waited in line at the Caritas office for their food rations.

But in this part of the world, where life revolves around water, look more closely and see how the storm has fouled so much of everyday life. Rice fields are waterlogged. Shrimp ponds have rotted. Women worry what their children will drink once their pots of rainwater run out. Not enough water, too much water, dirty water. Water bedevils everyone.

Aid began to trickle in across the cyclone zone on Wednesday, nearly a week after the storm. In this village, a long line of supplicants received sacks of rice, lentils and salt, and the country’s neighbors, allies and rivals seemed to fall over themselves to offer charity and succor.

Pakistan, the country’s former ruler, which Bangladesh fought a bitter war of independence against in 1971, announced that it would send two military planes full of medical supplies and blankets. India said that an air force cargo plane would arrive Thursday with 38 tons of aid.

Two United States Navy vessels were en route and expected to arrive with helicopters within days. Saudi Arabia pledged $100 million early this week, the largest amount, until the World Bank offered $250 million on Wednesday. Whether and how soon the pledged support will materialize is a mystery.

Neither the government nor aid agencies had an estimate on how much money was necessary to meet the humanitarian need, but a World Food Program assessment found that $30 million would be required for food just for the next three months. The United Nations resident representative for Bangladesh, Renata Lok Dessalien, said food, water and shelter were the immediate needs, and were all the more acute for cyclone victims who were already poor, likely to be malnourished and vulnerable to disease.

Cyclone Sidr cut a wide and debilitating swath through southern Bangladesh. The government estimates that four million people have been affected, and the full scope of its impact may not be felt for many weeks. By the Bangladeshi Army’s latest count, 3,167 people have died.

In Kanainagar, near Dhaka, the capital, Sunita Mondol, 15, was feeling the cyclone’s toll. She stood at the side of her family’s pond Wednesday morning and found no more than two tiny shrimps clinging to her net. On a normal morning, she would haul in a full basket and take it to the market to sell.

But the storm had spoiled the pond, shaking the leaves and branches from the trees and fouling the water, so much that the shrimps died and floated belly up. On the first morning after the storm, Sunita and her family pulled up more than 13 pounds of dead fish. They threw most away.

Families like hers, who make their living from selling the fish and shrimps they cultivate in their ponds, expect to feel the economic pinch of the cyclone for months. Every family in this village has a small pond, and family after family complained of theirs having been fouled.

Half of the fish in Pinjira Begum’s two big ponds floated belly up, which meant that her daily earnings plummeted by nearly half. The moneylender came to her home last Saturday for his weekly payment. “We told him we didn’t have money to buy rice for the children,” she said. She gave him half of what she owed. He cursed her and left.

Southern Bangladesh is one of the world’s most productive shrimp hubs. Shrimp is one of the country’s largest exports to the United States.

The lucky ones here had rainwater left in their traditional earthen pots. Those whose water had run out, or whose pots had broken, had to drink the pond water, which had turned salty from seawater and had begun to stink from putrefying leaves.

A rickshaw puller down the road wondered aloud how long it would be until dysentery struck. Even without a cyclone, he said, water brings a constant specter of disease.

In the hot months, when the rainwater stores run out and the ponds start drying up, the people of Kanainagar suffer rashes, dysentery and diarrhea. The cyclone made a chronic concern potentially acute.

“Water is our main problem,” said Alamgir Hossain. “People get too sick to work, and still they have to buy medicine.”

Across the Mongla River, Muhammad Nantu Mian worked feverishly to salvage what the water had not wrecked. His rice field was flooded, just two weeks before the harvest was due. The stalks were blown down like scarecrows by the brute wind. He had drained some of the water by cutting channels in his fields. He hired workers to cut what rice stalks had not yet rotted. He figured a third of his crop was gone.

Normally, Mr. Mian said, he sold half of what he produced, saving the rest for his own family and for next year’s seeds. This year, he said, he could reasonably hope to be able to feed his family, and not much more.

Climate Change Pollution Rising—Thanks to Overwhelmed Oceans and Plants

Climate Change Pollution Rising—Thanks to Overwhelmed Oceans and Plants

Carbon dioxide levels in the atmosphere continue to rise thanks to dirtier economies and a weakening in natural systems' ability to remove the greenhouse gas

 

WINDS OF CHANGE: Changed circumpolar winds are interfering with the Southern Ocean's ability to absorb carbon dioxide.

The world may finally acknowledge that global warming is a major environmental hazard. But new research shows that reducing the main greenhouse gas behind it may be even more difficult than previously believed. The reason: the world's oceans and forests, which scientists were counting on to help hold off catastrophic rises in carbon dioxide, are already so full of CO₂ that they are losing their ability to absorb this climate change culprit.

"For every ton of CO₂ emitted [into] the atmosphere, the natural sinks are removing less carbon than before," says biologist Josep "Pep" Canadell, executive director of the Global Carbon Project—an Australia–based research consortium devoted to analyzing the pollution behind global warming. "This trend will continue into the future."

Specifically, oceans and plant growth absorbed only around 540 kilograms per metric ton (1,190 pounds per short ton) of the CO₂ produced in 2006, compared with 600 kilograms per metric ton (1,322 pounds per short ton) in 2000. Coupled with an emissions growth rate of 3.3 percent—triple the growth rate of the 1990s—the atmospheric burden is now rising by nearly two parts per million of CO₂ a year, the fastest growth rate since 1850, the international team of researchers reports in Proceedings of the National Academy of Sciences USA.

"We have yet to make real progress in turning the world toward decreasing CO₂ emissions," says the study's co-author Chris Field, director of the Carnegie Institution of Washington's Department of Global Ecology in Stanford, Calif. "A greater buildup of CO₂ means more warming."

Atmospheric concentrations of the most ubiquitous greenhouse gas reached 381 parts-per-million in 2006 after emissions of CO₂ from burning fossil fuels rose to 8.4 billion metric tons (1.85 x 10¹³ pounds) per year, according to figures from the United Nations, British Petroleum and the U.S. Geological Survey.

All told, human activity released 9.9 billion metric tons (2.18 x 10¹³ pounds) of carbon in 2006, up from just 8.4 billion metric tons (1.85 x 10¹³ pounds) in 2000. At the same time, poleward shifts of westerly winds in the Southern Ocean reduced the region's ability to suck up CO₂ as have mid-latitude droughts, which slowed the growth rate of forests and plants that capture carbon.

New maritime measurements over the past decade also show that the North Atlantic's ability to absorb CO₂ has been cut in half, according to researchers from the University of East Anglia who were not affiliated with the study by Canadell and his colleagues. "Until now, we thought that the decline in the efficiency of natural sinks was going to happen during the 21st century and more strongly during [its] second half," Canadell says. "If we didn't [include in the assumptions] that this was going to happen [so soon], have we underestimated the decline in the efficiency into the future?"

In addition, this research shows that CO₂ emissions over the past decade were higher than those considered in the most dire scenarios for future climate change, which means that even more drastic actions will be needed to stem global warming. "The longer we wait to reduce emissions," Canadell says, "the harder the cuts that will be required to stabilize atmospheric CO₂ emissions."

Even minute levels of lead cause brain damage in children

Even minute levels of lead cause brain damage in children

Even very small amounts of lead in children's blood -- amounts well below the current federal standard -- are associated with reduced IQ scores, finds a new six-year Cornell study.

The study examined the effect of lead exposure on cognitive function in children whose blood-lead levels (BLLs) were below the Centers for Disease Control and Prevention (CDC) standard of 10 micrograms per deciliter (mcg/dl) -- about 100 parts per billion. The researchers compared children whose BLLs were between 0 and 5 mcg/dl with children in the 5-10 mcg/dl range.

"Even after taking into consideration family and environmental factors known to affect a child's cognitive performance, blood lead played a significant role in predicting nonverbal IQ scores," says Richard Canfield, a senior researcher in Cornell's Division of Nutritional Sciences and senior author of the study in the journal Environmental Health Perspectives. "We found that the average IQ scores of children with BLLs of only 5 to 10 mcg/dl were about 5 points lower than the IQ scores of children with BLLs less than 5 mcg/dl. This indicates an adverse effect on children who have a BLL substantially below the CDC standard, suggesting the need for more stringent regulations," he said.

In the United States over the last several months, nearly 50 specific products, including millions of toys for young children, have been recalled due to excessive lead in the paint, plastics and metal. "Our findings emphasize the very real dangers associated with low-level exposures, to which lead in toys can contribute," Canfield said.

U.S. children are exposed to lead primarily from household dust contaminated by deteriorating interior lead-based paint. In addition to toys, other potential sources include contaminated soil, imported food stored in lead-glazed pottery and certain plastic, metallic and painted products.

This most recent finding builds on the same research team's influential 2003 study, published in the New England Journal of Medicine, that reported adverse effects of BLLs below 10 mcg/dl in a group of children followed from infancy to age 5. "Our new findings are based on follow-up testing of the same children at age 6, using a more comprehensive IQ test to assess cognitive function. The results provide compelling evidence that low-level lead exposure has effects into the school-age years," said Todd Jusko '01, a University of Washington Ph.D. candidate in epidemiology and co-author on both reports.

"Children living in poverty disproportionately suffer from elevated BLL," said statistician and co-author Charles Henderson, a Cornell senior researcher in human development. He also noted that "even a small decline in an IQ score is likely to be reflected in aptitude test scores such as the SAT."

According to the CDC, about one out of every 50 children in the United States between ages 1 and 5 has a BLL above 10 mcg/dl and about 10 percent of children have BLLs of 5 mcg/dl or higher; about 25 percent of U.S. homes with children under age 6 have a lead-based paint hazard.

"The bottom line," according to Canfield, "is that lead is a persistent neurotoxin that causes brain damage. The fact that lead has been found in millions of toys, even toys specifically designed for children to put into their mouths, presents an unacceptable risk. Our findings suggest the need to re-evaluate the current federal standards for lead in consumer products and the current definition of an elevated BLL in children." 

Slumber Reruns: As We Sleep, Our Brains Rehash Events of the Day

Slumber Reruns: As We Sleep, Our Brains Rehash Events of the Day

And at six times faster than the normal speed 

WHILE YOU WERE SLEEPING: University of Arizona scientists suggest that while you sleep, your medial prefrontal cortex replays the experiences of the day at six times the speed to aid in memory consolidation.

Your brain doesn't take a rest when you do. While you slept last night, regions of your brain may well have been going over the events of the previous day in a process that could be related to consolidating memories, a team of researchers at the University of Arizona (U.A.) in Tucson says. In fact, the review may be taking place at several times the speed, by whch the experiences took place when you were alert.

The scientists implanted electrodes in the brains of rats, surveying the activity of up to 120 neurons (nerve cells) in the medial prefrontal cortex (a forebrain region responsible for goal-oriented executive functions such as organizing thoughts and actions) while the animals completed a navigational task, scampering between spots in sequence on a circular table top. The research team monitored the rats' brain activity daily for a few weeks as they scurried to complete the 50-minute running session and then napped for 20 minutes to an hour.

Using two different methods—comparing the activity between pairs of cells and surveying patterns over the entire population of monitored neurons—the team noted that neuronal activity sequences that occurred when the rats were running seemed to reappear during sleep.

"We looked at them and it just hit us in the face that there [were] striking similarities," says David Euston, an assistant research scientist at the U.A. College of Medicine's Division of Neural Systems, Memory and Aging.

Not only were the same patterns reactivated while snoozing, but the replay would take place six to seven times faster than when the rats performed the task. "During behavior when we're actually interacting with the world, the brain has to go at the same speed at which the body is going," Euston speculates. "During sleep, maybe the brain can go faster when it's not time-locked to behavior."

This replay phenomenon has previously been shown in the hippocampus, a forebrain structure involved in episodic memory, and in the visual cortex, where sensory information related to sight is processed. Euston believes the process may be related to plasticity, the strengthening and weakening of connections between of nerve cells that is thought to underlie learning.

"One way you could strengthen memories is by playing them multiple times," says Euston, referring to the unique sequence of neuronal activity that accompanies new learning events. By replaying them repeatedly, the brain may be strengthening communication between neurons, thereby consolidating the memories.

Mayank Mehta, an assistant professor of neuroscience at Brown University, says the new findings are interesting, but is skeptical about the assumption that they're based on. "Is this consolidation or erasure?" he asks, questioning whether the phantom activity is really the filing of a memory or whether it is akin to clearing a chalkboard so more learning can take place. "From the point of view of behavior, both [processes] can help," he says.

Euston says the team will now try to determine whether this replay of neuronal activity is associated with learning. If so, he says, the replay patterns should be strongest when the animals have just completed learning-related challenges.