Creatures as large as elephants are unusual; it takes a long time to evolve such size.
How long does it take for a mammal as small as a mouse to evolve into something as large as an elephant? A really, really long time, a recent study has found: about 24 million generations, at minimum.
To get that number, researchers looked at the evolution of body mass over the last 70 million years, after the dinosaurs went extinct and surviving animals expanded into the ecological niches they left behind. That estimate is far longer than earlier estimates, which, extrapolating from bursts of super-fast evolution in mice, range from just 200,000 to 2 million generations. Such speedy evolution, in actuality, is probably not sustainable over the long term—hence the lengthy new estimate.
What’s the News: While mice are a major tool for biomedical research, they’re not always useful for testing the toxicity of pharmaceutical drugs because their livers don’t react to drugs the same way that human livers do. But in a new study, published in the journal PNAS, scientists at MIT have gotten around this issue by implanting mice with miniature, humanized livers. Researchers may be able to use the artificial organs to help create drugs for diseases like hepatitis C, which mice don’t normally contract, and improve the development of other drugs. “In the near term, we envision using these mice alongside existing toxicology models to help make the drug development pipeline safer and more efficient,” said MIT biomedical engineer Alice Chen (via LiveScience).
What’s the News: In the animal kingdom, prey species must follow one rule above all others: keep away from predators. To do this, some animals take chemical cues from the urine they stumble upon. Now, new research published in the Proceedings of the National Academy of Science has identified a single molecule in the urine of many mammalian carnivores that causes rodents to scurry in fear. This chemical could eventually help scientists understand instinctual behavior in animals.
What’s the News: The bacterium that causes ulcers and some stomach cancers, Helicobacter pylori, could at least contribute to Parkinson’s disease, according to a new study in mice presented at a microbiology conference yesterday. Mice infected with H. pylori have shown Parkinson’s-like symptoms, building on earlier work that has suggested a link between the bacteria and Parkonson’s disease.
Even with 15 percent of their hearts removed, newborn mice possess the extraordinary ability to mend themselves, researchers report today in the journal Science. It’s the first time that mammals outside of the womb have shown the regenerative ability to repair the heart.
Only newborn mice could regenerate part of their hearts, and they lost this ability after about a week after birth. Still, the results were quite impressive: Olson’s team removed 15 percent of the heart one day after birth, and when the researchers checked up three weeks later, the whole heart was repaired in 99 percent of the mice. Until now, scientists had seen fish and amphibians regenerate heart tissue as adults, but only embryonic mammals had been spotted doing the same.
“When a person has a heart attack and heart muscle cells are lost, the heart loses pump function, causing heart failure and eventual death,” said Eric Olson, a molecular biologist at Southwestern Medical Centre in Dallas, Texas. “Now that we know that the mammalian heart indeed possesses the potential to regenerate, at least early in life, we can begin to search for drugs or genes or other things that might reawaken this potential in the adult heart of mice and eventually of humans.” [The Guardian]
First they have to understand what the newborn rodent’s bodies are up to. Initially, Olson and colleagues weren’t sure how the mice were mending themselves—with stem cells, or cells that had already become muscle cells. But the appearance of the cells gave them away, says Dr. Stephen Badylak, who wasn’t involved in the study.
The burgeoning field of optogenetics—using shot of light on neurons to control behavior—has already produced some intruiging and peculiar results. Now add one more: Scientists can use it to make mice angry and aggressive.
With a pulse of light, Dayu Lin from New York University can turn docile mice into violent fighters – it’s Dr Jekyll’s potion, delivered via fibre optic cable. The light activates a group of neurons in the mouse’s brain that are involved in aggressive behaviour. As a result, the mouse attacks other males, females, and even inanimate objects.
Lin focused on a primitive part of the brain called the hypothalamus that keeps our basic bodily functions ticking over. It lords over body temperature, hunger, thirst, sleep and more. In particular, Lin found that a small part of this area – the ventrolateral ventromedial hypothalamus (VMHvl) – acts as a hub for both sex and violence.
This week in bizarre new forms of mammal reproduction: mice who have genetic material from two fathers but nary a mother, the next step in a progression of scientific efforts to get more creative with sex and reproduction.
“It has been a weird project, but we wanted to see if it could be done” in mice, says Richard Behringer, lead author of the study and a developmental geneticist at M.D. Anderson in Houston. [Wall Street Journal]
Weird, and also complex: The process requires several generations and some creative genetic trickery. To make it happen, Behringer’s team started with a single male mouse. Let’s call him Fred. Scientists took cells from Fred and transformed them into a line of induced pluripotent stem cells, which can grow into any kind of cell in the body. Normally, of course, a male’s sex chromosomes are X and Y. But when the researchers created these stem cells, some of them—about 1 percent—lost the Y chromosome through ordinary mistakes that happen in cell division.
Thus, the scientists had a batch of Fred-derived stem cells that had no Y, and thus were labeled XO cells. The next step was to take ordinary mice blastocysts—early stage embryos that had been conceived in the traditional fashion—and inject the XO cells into them. When this XO-injected embryo was implanted into a normal female mouse, she gave birth to offspring called chimera—what we call animals with two or more genetically distinct populations of cells. In this case the mouse possessed, in addition to the normal cells from its mother and father, some XO cells derived from Fred.
According to a new study out in Science Translational Medicine, treating depressed mice with gene therapy in the brain to bolster a protein connected to the neurotransmitter serotonin can make those depressive symptoms dissipate.
Here’s the gist: The gene in question creates a protein called p11 that help carry serotonin receptors up to the surface of a brain cell where they can receive signals from other brain cells. Poor serotonin signaling may be one of the major drivers behind depression, and a dearth of p11 could worsen the problem, according to study author Michael Kaplitt.
“In the absence of p11, a neuron can produce all the serotonin receptors it needs, but they will not be transported to the cell surface,” said Kaplitt. [AFP]
A little stress can do a mouse good, a new cancer study suggests.
Matthew During wanted to see whether stressing out mice by messing with their environment would affect the rate of tumor growth. So, for a study that now appears in Cell, he and his team divided up their mice into two groups. Some mice lived quiet, peaceful lives in cages shared between five mouse roommates, while the other group lived in a stressful cluttered cacophony, where the cages held 18 to 20 animals plus numerous distractions and challenges like toys, mazes, and wheels.
Mice were then injected with tumor cells, which led to malignancies in all of the control animals within 15 days… The rate of tumor formation in animals living in the enriched environment was significantly delayed, and 15 percent had not developed tumors after nearly three weeks; when tumors were visible, they were 43 percent smaller than the lesions on control animals [Scientific American].
Because the “enriched environment” gave those mice so much more to do, an obvious conclusion would be that it’s the uptick in physical activity—not the effect of added stress—that kept tumors at bay. So During’s team tested the mice to see if just giving them more time on the running wheel, independent of the other factors, was enough to see the effect. It wasn’t.
It feels good to win. And it feels even better to win at home.
For a new study in the Proceedings of the National Academy of Sciences, Matthew Fuxjager and his colleagues investigated the winner effect, wherein animals (and perhaps humans) build up testosterone in advance of a confrontation, and the fight’s winner maintains that elevated level. By studying male mice fighting one another, Fuxjager was able to see what happens in the brains of winners. Not only did victorious mice experience the “winner effect,” but those who won at home—in their own cages—saw the most activity, and wanted to keep on fighting.
To get these results, Fuxjager’s team essentially created a tournament of mouse fights.
It’s the essence of instinct: If you take a lab mouse who has never caught a glimpse of a cat and waft a little eau de feline towards it, the mouse will freeze in fear, and will then back away from the source of the odor. Now researchers have pinned down the chemical signals the mice are reacting to–and have shown in the process a fascinating new form of inter-species communication.
Mice have a specialized organ in their noses that picks up chemical signals, called the vomeronasal organ, which helps them detect pheromones emitted by other mice. These mice pheromones have a direct effect on behavior–most obviously in the realms of mating and fighting. In this new study, published in the journal Cell, neurobiologist Lisa Stowers decided to investigate whether the vomeronasal organ was capable of picking up signals from other species as well.
Last spring, researchers confirmed that brown fat—the kind that burns energy rather than storing it and is especially prevalent in newborns—can be found in small pockets in adults, too, and slimmer adults have more of it. This spring, a team says it might have found one of the first steps in activating that fat-burning fat in adults. Their study comes out in Science this week.
Brown fat is packed with energy-producing mitochondria, and babies have a lot of it because it helps them keep warm. Once humans begin to regulate their own body temperature they don’t need as much brown fat anymore, so it gets replaced by energy-storing white fat, which helps store energy but leads to expanded waistlines in this age of affluence.
Testing on mice, the team led by Stephan Herzig upped the use of an enzyme called cyclooxygenase-2 (COX-2). While the enzyme plays a role in many physiological functions, the researchers found that pushing it in mice could induce their white fat to act more like energy-burning brown fat, and their weight dropped by around 20 percent.
“There has been a lot of excitement around brown fat, but … there wasn’t any clear indication that turning up brown fat would make animals lose weight,” says Chad Cowan, a professor in the Department of Stem Cell and Regenerative Biology at Harvard Medical School who studies fat cell development. “What this paper does is make a good link to something that might be clinically beneficial [TIME].
The notion that stress can cause hair to turn gray isn’t entirely a myth: at least when it comes to genetic stress applied to laboratory mice. That’s what researchers found when they damaged mice’s DNA with ionizing radiation, according to a study published in the journal Cell.
Scientists already knew that cells known as melanocyte stem cells were responsible for youthful hair color. Each of these cells divides into two cells: One that replaces itself and another that differentiates into a pigment-producing daughter cell called a melanocyte, which imbues hair with its browns, reds and blacks. Earlier research has suggested that the depletion of these stem cells was to blame for grayness. But how exactly these stem cells disappeared was mysterious. With no more stem cells around to produce melanocytes, hair turns gray [Science News].
When the Vikings set sail for the British Isles they had small, furry stowaways aboard their ships, and researchers say that the descendants of those mice can offer clues about the voyages taken by Viking seafarers. A new study examined the DNA of house mice throughout the British Isles and found that mice from areas where the Vikings are thought to have settled are genetically distinct from mice in other regions.
Says study coauthor Cath Jones: “We have found that most of the mice in the north of Scotland – from Orkney, Shetland and Caithness – are all of one very similar type that we have named the Orkney lineage and they are very similar to Norwegian mice. And the only explanation for that is that when the Vikings came raping and pillaging to Scotland they took their house mice with them” [Scotsman].
80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles on the day's most compelling topics.
80beats is written by Veronique Greenwood and Valerie Ross. This team darts through each day's science news faster than the ruby-throated hummingbird that beats its wings 80 times per second. Send ideas, tips, suggestions, and complaints to [azeeberg at discovermagazine dot com].
What’s the News: The bacterium that causes ulcers and some stomach cancers, 
This week in bizarre new forms of mammal reproduction: mice who have genetic material from two fathers but nary a mother, the next step in a progression of scientific efforts to 
According to a new 
A little 
It feels good to win. And it feels even better to win at home.
It’s the essence of instinct: If you take a lab mouse who has never caught a glimpse of a cat and waft a little eau de feline towards it, the mouse will freeze in fear, and will then back away from the source of the odor. Now researchers have pinned down the chemical signals the mice are reacting to–and have shown in the process a fascinating new form of inter-species communication.
Last spring, researchers 
The notion that stress can cause hair to turn gray isn’t entirely a myth: at least when it comes to genetic stress applied to laboratory mice. That’s what researchers found when they damaged mice’s DNA with ionizing radiation, according to a 
When the 
