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First Video of DNA Organization Settles Scientific Debate

A condensin protein complex creates a loop in DNA. (Credit: Cees Dekker Lab TU Delft/Scixel)

For all its precise helical structure, the DNA inside our cells is a mess.

When a cell isn’t preparing for the process of splitting itself in two, our DNA lies in a massive tangle inside the cell nucleus; a strand more than six feet in length jumbled like an earbud cord. But when it comes time to undergo cellular division, this disorderly strand must be packaged neatly into chromosomes to be passed onto daughter cells — stuffed into a space much tighter than before.

Around and Around

To accomplish the task, a protein complex known as condensin grabs onto a strand of DNA and passes it through a ring-like structure to coil it into orderly loops perfect for packaging — a process that researchers have caught on camera for the first time. A team of researchers from Germany and the Netherlands was able to stain the proteins responsible so they could be viewed in action under a microscope and fix the DNA in place in order to watch the process happen in real time. The feat settles a debate about how condensin works and could provide insights into hereditable diseases and some forms of cancer.

That condensin is responsible for looping DNA has been suggested for years now — the idea, in fact, seems to have come to one researcher as he handled ropes and climbing equipment during a mountaineering expedition — but researchers weren’t quite sure if that theory or another was accurate. Either condensin looped DNA, or it relied on hook-like structures to tie it together. The video, part of research published Thursday in Science, makes clear that the former mechanism is the right one.

After staining the condensin with a fluorescent protein and pinning down a strand of DNA in the lab, the researchers introduced a slight current that would stretch any resulting loops out clearly. After that, all they had to do was bring it into focus with a microscope. The resulting footage shows condensin drawing in a strand of DNA and spooling it out in a clear loop.

And the protein complex is good at its job, too. Opponents of the looping theory had suggested that such a mechanism would suck up too much energy, in the form of ATP, for it to work. The researchers newest work indicates that condensin is actually quite efficient, likely because it reels DNA in many base pairs at a time, as opposed to one by one. It’s fast, too, operating at a relatively high rate of around 1,500 base pairs per second. Intriguingly, they also observed that condensin only pulls on one of the two sides of the loop it is gathered, something they still can’t explain.

The findings aren’t only visual evidence of a crucial cellular process, they could also help elucidate the causes of certain genetic diseases related to the protein family condensin belongs to, called SMC. Arranging chromosomes during cell division, something that condensin also helps with, can lead to cancer if done incorrectly. The new insights into how it operates could provide further avenues for research in that direction as well.

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A Functioning Fake Womb

In a potential breakthrough for human babies born prematurely, scientists announced this year they’d successfully removed lamb fetuses from their mother’s wombs and raised them into healthy sheep. Their survival comes thanks to an artificial placenta — called a BioBag — created by researchers at the Children’s Hospital of Philadelphia.

The fake womb consists of a clear plastic bag filled with electrolytes. The lamb’s umbilical cord pulls in nutrients, and its heart pumps blood through an external oxygenator. The success caps a decades-long effort toward a working artificial placenta.

The BioBag could improve human infant mortality rates and lower the chances of a premature baby developing lung problems or cognitive disorders. But there are still challenges to scaling the device for human babies, which are much smaller than lambs. The scientists are also refining the electrolyte mix and studying how to connect human umbilical cords. They expect human trials in three to five years.

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Are Airplanes Really a Microbial Playground?

(credit: Matej Kastelic/Shutterstock)

Crying babies, chronic snorers — they’re the usual targets of our displeasure when we fly. But, the real villains of the sky might be germs.

Flyers are packed into a cramped metal tube for hours on end where movement is limited. It seems like a microbe’s playground. But research on the topic is a bit inconclusive, despite worrying cases involving SARS and an aggressive type of influenza. Studies suggest that caution is warranted, but researchers have so far had trouble saying exactly how air travel affects disease transmission. At the moment, public health guidelines state that anyone within two rows of an infected individual could be at risk, although other studies suggest otherwise.

Fly the Germy Skies?

Most recently, a team of researchers from Emory University and the Georgia Institute of Technology—funded by Boeing—conducted their own boots-on-the-plane study of infectious disease transmission aboard commercial aircraft. On 10 flights from Atlanta to the West Coast and back, they took swabbed samples of various surfaces and recorded how often passengers and crew members moved around. Pairing the data with models of air movement and microbe dispersion gave them an idea of just how far a potential pathogen might travel.

Their findings, published Monday in the Proceedings of the National Academy of Sciences, indicate that a sick neighbor is certainly something to worry about when flying. Those within a row of a sick person and within two seats to either side had an 80 percent chance of getting sick in their model, which used a fairly high assumed rate of transmission. The risk of infection drops off sharply after that, though. Those more than a few seats away had little to worry about. That’s even closer than the two row-minimum suggested by public health agencies.

A sick crew member, however, posed a little more danger. They move around the cabin more and have more contact with passengers, so the risk of transmission increases. Just one sick flight attendant infected almost five people on average in the researcher’s model. That’s a big number, but it does make some assumptions, the biggest of which is that sick crew members even come in to work. It’s more likely that they would just stay home.

Back Down to Earth

There are difficulties in modeling disease transmission rates on such a small scale like this, and this particular study wasn’t very big. They looked at just ten flights and the longest was only a bit over five hours. International flights can go for fifteen hours or longer, and involve much more movement on the part of passengers, something that could increase the risk of infection.

Their model also only looked at microbes that could be carried by droplets, which don’t travel very far. Viruses spread by smaller aerosol particles could circulate much longer and farther. This includes diseases like tuberculosis and measles. Air travel also involves extended periods of contact with other passengers at boarding gates, security checkpoints and elsewhere, and this could affect rates of transmission as well.

It’s also worth pointing out that we encounter similarly confined, crowded spaces during the course of our daily lives. Buses, movie theaters, workplaces and more pose the same sort of risks, though the authors don’t provide any measure of comparison here. Airplanes, do, however, travel long distances very quickly, something that can turn a local epidemic into a pandemic within days. That hasn’t happened yet, though scattered cases involving SARS and Ebola, among other diseases, have stoked worry.

Ultimately, a review of the scientific literature on the topic found moderate evidence that airplane cabins helped to spread influenza. This latest study doesn’t really change that, though it does reveal the danger that an infected crew member poses.

So, for flight attendants — and for all of us, really — if you’re sick, just stay home.

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This Optical Illusion Could Help to Diagnose Autism

(Credit: Turi et al., eLife, 7:e32399, 2018)

You probably see a cylinder when you look at the illusion above. But how our brains translate two intersecting sheets of moving dots into a 3D image reveals telling differences in visual perception that could perhaps help diagnose autism spectrum disorder.

It’s been shown that people with autism are better at picking out the details of complex images, at the cost of understanding what all those details mean when put together. This can mean seeing the trees, but not the forest, or the strokes of a paintbrush but not the subject of a painting. It’s a trait that’s supported by years of research, but it can be difficult to assess exactly how an individual perceives an image just by asking them questions. The cylinder illusion, applied here by a group of researchers from Italy and Australia, offers a more reliable way of telling what a subject is seeing.

Grow and Shrink

It comes down to the pupils. Our pupils are responsive to light, but they also widen and constrict in response to the notion of brightness or darkness, even if light levels remains the same. Here, the white dots are perceived as brighter, and the black dots as darker, and our pupils respond accordingly. It’s a way for the researchers to tell what parts of the illusion study participants are focusing on. They published their findings in March in the journal eLife.

The illusion itself relies on our brain’s assumptions of how a rotating cylinder behaves. The dots cross over each other just as marks on a transparent cylinder would, they even slow down at the edges to give the impression of curvature. The two colors give imply depth, though a closer look reveals that neither actually seems to be in front — some white dots cross over black dots, and some black over white. It allows us to reverse the cylinder’s apparent direction by focusing on one color over the other. Importantly for the researchers, the illusion is composed of both discrete details in the form of the dots, and a holistic image, in the form of the cylinder. Having both allows them to see which component their study participants favor.

They asked 50 adults, none of whom had autism, to watch the illusion, and while they were doing so, the researchers were watching them — their pupils at least. They wanted to see whether their pupils changed size rapidly throughout the experiment or stayed the same. If they changed size, it indicated that the participants were switching focus back and forth between the white and the black dots — i.e. they were focused on the details of the images. If their pupils stayed about the same, they were likely focused on both at once, meaning they saw the image as a whole. Crucially, both methods of perception produce the same cylinder illusion. But how they do so differs.


Before taking the test, the subjects all took the autism spectrum quotient, a self-reported questionnaire that measures various behaviors associated with autism. Higher scores indicate more correlation with autistic traits. When they paired scores on the test with measurements of pupil dilation and contraction, they saw that they were clearly related. Those whose pupils changed with greater frequency also reported more autistic traits. It was another validation of the theory that those with autism tend to focus on specific details as opposed to entire images.

Remember, none of the subjects had been formally diagnosed with autism, and none of their scores on the test indicated that they should be. In fact, the mean value of the test scores was about average. But, autism is a spectrum, and we all lie on it somewhere. Even in nominally average individuals, a tendency toward autistic traits was associated with a propensity to focus on details over holistic images. It adds further evidence that autism alters how we process visual information, and hints that it extends beyond those diagnosed with the disorder. The researchers say measuring changes in pupil size could potentially serve as another means of diagnosing autism.

The results are still a bit preliminary, so it’s too soon to draw definite conclusions based on their work. The surveys were all self-reported, for one thing, which can skew results a bit. And the study involved participants without autism, meaning that we’d need to see similar work in those with autism spectrum disorder to back up their findings.

But, with more research, the authors think their research could be used to perform assessments of those with autism who are non-verbal, which can happen in children. It would give doctors and teachers a way to get information from those who may not be able to communicate it themselves.

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