Science-- there's something for everyone

Saturday, March 31, 2012

Does it mean what you think it does?


When we hear someone speak, we infer far more information than is actually present in the words.  It isn’t a surprise that this occurs, but I found myself a bit surprised at the degree to which it occurs. For example, suppose you hear someone say, “I broke a finger yesterday.” Did you notice that you had only assumed that the person broke her own finger and not someone else’s?  That wasn’t stated.

Ryan Doran, Gregory Ward and Meredith Larson from Northwestern University were interested in whether people are aware of how much extra information they tend to infer from statements.  They gave 74 participants a series of short written conversations and asked them to evaluate the truth of the declarations. They found that people can distinguish between what is implicitly stated and what is inferred, but they do a better job if they are directed to focus on the truth of each statement.  That is, if they were keyed to interpret meanings literally, they were less likely to add implied meanings in their heads.

I’m not sure how useful this information is, other than in designing riddles to trick your friends.  But it is interesting how readily we tend to add extra meaning to what we hear or read.

Friday, March 30, 2012

Bacteria have programmed cell death


Programmed cell death (PCD), also called apoptosis, is a necessary part of life for multicellular creatures such as ourselves.  Superfluous, sickly or harmful cells must do the right thing and kill themselves before they cause problems for the entire organism.  PCD is essential not only for keeping us healthy as adults (think of avoiding cancer), but for our very development from embryos.  For example, it’s PCD that removes the webbing in between our fingers at around eight weeks gestation.

It’s harder to see why single-celled prokaryotes would have PCD, but they do.  In conditions of extreme stress (lack of nutrients, attack by viruses), greatly reducing the population may allow a few individuals to carry on.  Since members of a population of bacteria are likely to be clonally related, this sacrifice actually increases the chances that the microbes’ gene pool will persist, which is after all the ultimate goal of all organisms.

One of the ways prokaryotes control when to off themselves is via ‘toxin-antitoxin’ (TA) systems.  The bacteria produce both a toxin and the corresponding antitoxin.  However, the antitoxin degrades more quickly than the toxin.  Thus, if a microbe sustains damage to its DNA or protein assembly machinery such that it can’t make more antitoxin, the lingering toxin will kill it.  Although this seems like a crazy idea, it does ensure that only properly functioning bacteria survive.

Ariel Erental, Idith Sharon and Hanna Engelberg-Kulka from the Hebrew University-Hadassah Medical School have identified a second method of PCD that more closely mimics the system used in eukaryotes.  This system is triggered solely by DNA damage and may have originated as part of the DNA repair system.

Taken together, these two pathways of cell death weed out excess or damaged individuals from a cluster of bacteria.  

Thursday, March 29, 2012

The dark side of organ donation


Monir Moniruzzaman of Michigan State University studied the horrific organ donation practices in Bangladesh, where poor people are coerced into selling their organs to rich recipients. He managed to collect this appalling data by going undercover in some of the poorest areas.

Selling body parts is actually illegal, even in Bangladesh and other parts of the world in which it occurs.  This doesn’t stop organ buyers from advertising in local newspapers.  If questioned by authorities, it’s easy enough to pretend that the organ seller is a relative and deny that he is being compensated. 

A typical scenario goes as follows.  A desperately poor Bangladeshi sees an ad requesting a kidney.  He meets with a broker who promises a huge payment, by the standards of that impoverished community, and often a visa and job in another country. The seller is often misled throughout the proceedings about the function of the kidney, what the removal will entail, and what the recovery will be like.

If the organ seller and buyer are a match, the broker arranges for a fake passport or visa so that the seller can travel to the donation site, which is often in India. Once there, the seller’s passport is confiscated and he’s held captive with other sellers, none of whom are allowed to change their minds about donation.  The sellers receive minimal post-operative care and most cannot afford proper follow-ups.

Most of the sellers end up in far worse shape than they started.  They sold their organs to pave the way for a better life for themselves and their families, but ended up with little to show for it but a giant scar. 27 out of 33 kidney sellers did not receive the payment they’d been promised, let alone the chance for a job in another country.  Many could no longer work at all due to pain and deteriorating health.  Because of the stigma of having sold an organ, many were ashamed to let anyone see their scars, which made them unmarriageable.

To be clear, these abhorrent practices should in no way be compared to legitimately conducted living organ donations.  If properly cared for both during and after surgery, kidney donors go on to enjoy normal healthy lives.  They perform a selfless generous act with little danger to themselves.  That’s not the situation that Moniruzzaman has been describing.

What can be done?  Unfortunately, the situation is grim.  Rich people with the means to buy an essential body part for themselves or their loved ones will try to do so, poor people will do whatever they can to help their families, and unethical brokers will bring those two groups together.  

Wednesday, March 28, 2012

Just for fun: Drew Berry's molecular animations



Drew Berry of the Walter and Eliza Hall Institute of Medical Research makes the most amazing molecular animations.  But don't take my word for it.  By the way, in case you were wondering, the animations are scientifically accurate for both scale and speed. It’s like a racetrack in our cells! 








You can also watch Berry's TED Talk here.

Tuesday, March 27, 2012

Oldest hard-bodied creature


Erica Clites and Mary Droser from the University of California, Riverside and James Gehling from South Australian Museum describe a particularly interesting specimen from the Ediacaran Period (635 to 542 million years ago). It’s the oldest creature yet found with a hard body structure.

The very earliest multicellular organisms had soft bodies that fossilized only under the most fortuitous circumstances.  They did sometimes leave other traces of their presence, such as tracks or imprints, but these too are uncommon.  It wasn’t until the advent of hard body parts that the fossil record became as rich as it is. Those hard-bodied fossils first appeared during the Cambrian Period (from 542 to 488 million years ago).

That makes the discovery of Coronacollina acula, a small cone-shaped creature with hard radiating spindles, of great significance.  C. acula lived during the Ediacaran Period, but unlike its contemporaries, it had hard skeleton supports.  Not only that, but the creature shows similarities to Cambrian Period sponges.

Why does this matter?  Living creatures can trace their ancestry back to an organism that lived during the Cambrian Period. However, if you go further back in time to the Ediacaran Period, many of the trails disappear. So how did traits like hard skeletons arise? C. acula represents a long sought bridge between the Ediacara and Cambrian periods.

 

Caption: This is a reconstruction of how Coronacollina would have appeared in life. Coronacollina remained in place on the sea floor, and may have used its spicules as support struts. Coronacollina resembles the Cambrian fossil sponge, Choia. The three raised points on the rim are evident, with a central hollow and four spicules extending from the cone rim.
Credit: Daniel Garson for Droser lab, UC Riverside



Monday, March 26, 2012

Nanoparticles affect iron absorption…maybe


Nanoparticles are almost ubiquitous in medicines and cosmetics.  I recently posted a diagram detailing their myriad uses.  But are they safe?  This is a question that Michael Shuler from Cornell University, Gretchen Mahler from Binghamton University and their colleagues set out to answer.  They found that nanoparticles do affect iron absorption, but that the body can probably compensate for this.

Nanoparticles are simply teeny tiny particles.  They vary in size and construction, depending on what they’re being used for.  For this study, the researchers added both 50 nanometer (nm) in diameter and 200 nm particles of different types and dosages to intestinal epithelial cell cultures.  They also fed 50 nm particles to live chickens. In each case, the number of nanoparticles was calculated to yield a dosage similar to what a person would ingest with a pill, which would be over a trillion.

The test tube studies showed that the addition of nanoparticles did affect how readily intestinal cells could take up iron and how easily they could pass it on (which would be to the bloodstream in a living animal). However, different types and concentrations of nanoparticles affected iron absorption in different ways, sometimes increasing absorption and sometimes decreasing it.


This figure shows 50 nm carboxylated polystyrene nanoparticles (green) interacting with a cell culture model of the intestinal epithelium (red). Oral exposure to these particles was shown to affect iron transport.
Credit: Nature Nanotechnology

Tests were also done with two groups of chickens.  The chronic exposure group was fed 50 nm particles every day for two weeks.  The acute exposure group was only fed the nanoparticles on sampling day.  When analyzed, the acute group had far less iron absorption than controls, but the chronic group had far more iron adsorption. Further examination showed that the chronically exposed chickens actually had many more villi in their intestines. 

So what does all this mean?  Clearly nanoparticles are having an effect on chickens, and by extension, almost certainly on humans as well.  It’s interesting that the body seems able to compensate for exposure to the nanoparticles.  You’d almost wonder if doctors should administer nanoparticles as a cure for anemia or malnutrition, if it will increase the number of villi in our intestines. 

Sunday, March 25, 2012

Light-sensitive stinging cells


David Plachetzki of the University of California, Davis and Caitlin Fong and Todd Oakley from the University of California, Santa Barbara have found that Hydra magnipapillata, a creature similar to a jellyfish, has light sensitive neurons.  This might not be so interesting if it weren't for the fact that hydras have no eyes.  They use light to regulate their stinging cells rather than for vision.

Hydra are tiny freshwater polyps in the phylum Cnidaria.  Like other members of this group, they have stinging cells called cnidocytes.  These cells contain harpoon-like structures that can fire in less than a microsecond when activated (see left).  As the barb hits the Cnidarian’s prey, a toxin is injected.  This is what makes contact with a jellyfish’s tentacles so painful. Although this system is highly effective, it does have one drawback: each harpoon can only be used once.  Thus, it’s in the animal’s best interest not to waste a discharge.

Plachetzki and his colleagues have found that H. magnipapillata’s cnidocytes are connected to light-sensitive neurons that use the same components as the light-sensitive neurons in our eyes. And in fact, experiments show that the hydra’s stinging cells fire much less under bright than under dim lights.

How could information about ambient light conditions help an eyeless predator?  The authors have a few ideas.  For one thing, the amount of light in the environment might naturally coincide with the abundance of prey.  Perhaps prey is scarce during the day so it’s not worth the creature’s while to bother wasting its stingers. Alternatively, the light-sensitive cells might be able to detect the shadow of a prey item, helping to align the stinging cells for maximal effect.

Below, you can watch a tough little hydra (though a different species) taking on tiny planktonic crustaceans called Daphnia.





Saturday, March 24, 2012

Introducing the SpeechJammer


Ever wish you could get someone to shut up? Kazutaka Kurihara at the National Institute of Advanced Industrial Science and Technology and Koji Tsukada at Ochanomizu University may have just the thing for you.  They’ve been testing a device that effectively silences speakers. Their ‘SpeechJammer’ relies on the fact that people find it impossible to speak when their words are replayed to them a fraction of a second later.

The idea of repeating back a person’s own words on a short delay is not a new one.  In fact, devices that rely on delayed auditory feedback have been used to improve stuttering.  The artificial delay between speaking a word and hearing that word affects most people’s ability to speak, for better or worse.  Stutterers are helped, but unimpaired people are muted by the confusion this causes.

The researchers made use of this phenomenon by remotely recording and playing back people’s speech.  They built a couple of prototypes that use lasers to aim direction-sensitive microphones and speakers at tiresome talkers. In preliminary tests, the devices worked pretty well at preventing people from reading aloud, but were less effective at stopping spontaneous speech.

The authors see many uses for their product, as illustrated in the following video.


Hat tip: Not Exactly Rocket Science.

Friday, March 23, 2012

The emergence of organelles

Over a billion years ago, one group of single-celled organisms engulfed a second group and gained a partner rather than a meal. Thus, the endosymbionts called mitochondria and chloroplasts were formed.  


Originally, these organelles were individual cells with their own complete genomes.  Today, mitochondria and chloroplasts still contain their own genes (a huge benefit for genealogical and evolutionary studies), but not a complete genome.  Many of the genes required to build the organelles are found not within the organelles themselves, but in the nuclei of the host cells.  At some point, genes were transferred from the proto-organelles to the host genome.  After that time, proteins critical for making organelles were assembled in the cytoplasm and delivered to those organelles, making the organelles completely dependent upon their hosts. 

It can be difficult to reconstruct processes that occurred over a billion years ago. Luckily, an organism with a more recent foray into endosymbiosis has been discovered. The amoeba Paulinella chromatophora has chromatophores that resemble chloroplasts (they too originated as cyanobacteria, are separated from the host cell by a double membrane and have transferred most of their original genes to the host nucleus) but were incorporated into the amoebae only about 60 million years ago. By studying this amoeba, Eva Nowack and Arthur Grossman of Stanford University have been able to see how proteins encoded in the host genome are transported to the chromatophores.

Interestingly, most of the genes required for photosynthesis, the very raison d'ĂȘtre for chloroplasts or chromatophores, are encoded within the nuclear genome. This gives the host complete control of the organelles’ activities. Because the process of transferring organelle genes to the host nucleus had already occurred in P. chromatophora, it may be an early process in the conversion from two individual cells to a single cell.



Thursday, March 22, 2012

First meat, now soft drinks



This time, Frank Hu and his colleagues from Harvard followed over 40,000 men for twenty years to see how drinking sugary drinks would affect their hearts. As I’m sure you’ve guessed, the news was not good.

The men were sent a questionnaire every four years asking them how many sugar-sweetened beverages they typically consumed.  Drinks included colas and other soft drinks as well as fruit drinks like lemonade and fruit punch. A subset of the men also provided blood samples. Living participants were asked to provide information as to whether they’d ever had any cardiovascular disease, and the records of diseased individuals were checked for cardiac events.

As with the red meat study, the more sugary drinks a person consumed the more likely he was to smoke, eat poorly and not exercise. That said, there was a clear association between sugared beverages and heart attacks.  Adding one serving per day increased a man’s risk of having a heart attack by about 20%. I’m not sure you could get a result like that if you injected lard directly into your veins.

Although this study only looked at men, a similar study of women also showed a huge increase in risk (15%). One possibility is that the increased sugar caused a compensatory increase in inflammatory factors, which in turn leads to more cardiovascular disease. Higher consumption of sugary drinks was in fact associated with increases in inflammatory blood factors.

Whatever the mechanism, it seems clear that sugared drinks are not good for you.  Sorry to be a downer.  I suggest you take another look at yesterday’s baby tortoise until you feel better.    


Wednesday, March 21, 2012

Just for fun: Baby tortoise



We have a baby tortoise.  Someone once asked me if it ate insects.  My response was, "Insects?  It can't even catch lettuce!"


You can see why in this clip of a baby sulcata tortoise attempting to eat a bit of tomato.




Tuesday, March 20, 2012

Powering your pacemaker with heartbeats

Millions of people live long productive lives thanks to the pacemakers within their chests.  Unfortunately, those pacemakers are currently battery-powered, and the batteries last no more than ten years.  Consequently, patients with pacemakers have to have new batteries surgically installed on a regular basis.  That may be changing, thanks to the efforts of Amin Karami and Daniel Inman of the University of Michigan.  They’re working on a way to use the vibrational energy of the heartbeats themselves to power pacemakers.

Thus far, the researchers have been optimizing the structures and materials necessary for such a device.  They’ve been able to develop a model that delivers more than enough power to maintain a pacemaker at heartbeats ranging from 7 to 700 beats per minute.  In other words, if a person’s heart is beating at all, the pacemaker will work.  Since it’s the job of the pacemaker to see that the heart continues to beat, once the system is running it should be just as good as a conventional battery. 

To be clear, the engineers are only at the mathematical model stage of testing their idea.  The next step would be to build a prototype, and then try it in an animal model.  Not until then will we know whether the system might be beneficial for humans. I'm sure many cardiac patients share my hope that it will be.

Image: Pacemaker and electrode
Photo by Steven Fruitsmaak, 10/13/2007.

Monday, March 19, 2012

It’s OK to be obese…after you hit 85


Obesity shortens lifespans for every demographic, with one possible exception.  According to Jiska Cohen-Mansfield and Rotem Perach of Tel Aviv University, excess weight is protective for people age 85 and older.  I have my doubts.

First, let’s explain the study. From 1989 to 1992, the researchers enrolled 1369 people who were then between 75 and 94 years old.  At that time, interviewers measured participants’ height and weight and calculated their body mass indices (BMI).  People with a BMI of less than 22 were considered to be underweight, those with a BMI of 22 to 30 were considered to be of normal weight and people with a BMI above 30 were considered to be obese.  Over the next 20 years, the researchers recorded who lived and who died.

The association between mortality and obesity broke into two groups.  For those who had been 75 to 84 at the time their information was collected, obesity increased the risk of death compared to normal weight people.  For those who had been 85 to 94, obesity very slightly decreased the mortality risk. Underweight people of all ages had higher mortality rates than normal weight people.

So why am I skeptical?  My biggest concern is that the study includes only a single data point for each participant, taken on the day that person was enrolled in the study.  In other words, we have no idea whether people had been obese all their lives or had gained weight late in life.  We don’t even know whether people who had been obese or underweight at the start of the study stayed in that same category for the rest of their lives. It’s hard to imagine that this information would not play a critical role in evaluating mortality risk.  Someone who maintains a normal weight until age 83 and then becomes obese is probably not going to have the same health risks as someone who has been obese from childhood.

That said, I suppose it could be true that obesity prolongs your life once you reach the age of 85.  Unfortunately, that same excess weight will most likely prevent you from making it to that age in the first place.  My conclusion is that if you are approaching your 85th birthday, by all means have that extra piece of pie.

Sunday, March 18, 2012

Carnivores can't detect sweetness

In order to be a successful carnivore, you need weapons to catch and devour your prey and a digestive system that can metabolize meat.  What you don’t need is a discriminating sense of taste.  Peihua Jiang and his colleagues at the Monell Chemical Senses Center sequenced the taste receptor genes of 12 carnivores and got some surprising results.

Mammals use specific receptors to detect different tastes.  We have at least five kinds of taste receptors for sweet, salt, bitter, sour and umami (meatiness or savoriness).  There is also now evidence of a sixth type of receptor that detects fat.  All mammals have remnants of the genes for these different receptors, but those genes aren’t necessarily functional. In particular, the obligate carnivores that were tested (animals such as cats that rely exclusively on a meat diet) had lost their sense of sweet taste. In contrast, the more omnivorous creatures (dogs and bears) retained their sense of sweetness.  This was tested both by looking for intact receptor genes and by offering the animals a choice between sweetened and unsweetened bowls of water. Interestingly, the different species tested had different errors in their receptor genes, indicating that they had independently lost the ability to taste sweetness.

This does make a certain amount of evolutionary sense.  An animal whose diet consists of living prey that can’t spoil or ripen has a limited need to detect how sweet its food is. On the other hand, animals that also eat plants can benefit from fully tasting their food.

This brings up an intriguing question.  If dogs have a better sense of taste than cats, then why are cats so picky while my dog will eat anything that hits the floor?

For more information on this study, check out Not Exactly Rocket Science.

A fossa, an obligate carnivore from Madagascar.    

Saturday, March 17, 2012

Just for fun: St. Patrick's Day song


Here's an offering from Cadamole, the singing biologist.  OK, it's a year old, but still good.





Friday, March 16, 2012

Good news for the boys—the Y chromosome is not disintegrating

Carried only by males, Y chromosomes are by far the smallest of all the human chromosomes.  In fact, they carry fewer than 200 genes.  In contrast, the X chromosome, which is carried by both sexes, encodes about 2000 genes.  And it’s not even the largest chromosome.  That honor is held by human chromosome 1, thought to encode over 4200 genes.

The Y chromosome wasn’t always so diminutive. 300 million years ago, the X and Y were a matched pair containing the exact same genes, just like all the other autosomes (non-sex chromosomes). In the case of the autosomes, that identicalness is maintained by exchanging genetic material (crossing over) between the pairs. 300 million years ago, a section of the Y stopped crossing over with the X. That unpaired section of the Y no longer had any evolutionary constraints on it, and many genes were lost from that region.  In the intervening years, four more sections of the Y stopped matching up with the X, most recently 30 million years ago, with each event resulting in the loss of genes. Many scientists believed that the Y was still shedding genes and that in the far future, human males would no longer have a Y chromosome at all.

Not so, according to a new study led by Jennifer Hughes and David Page of MIT.  They sequenced the Y chromosomes of both humans and rhesus macaque monkeys, a creature with which we share a common ancestor 25 million years ago.  Since that divergence point, rhesus Y chromosomes have not lost a single gene, and human Y chromosomes have lost only one gene.  More significantly, the lost gene was from the most recent region of the Y to have stopped crossing over with the X.  In other words, the parts of the Y that haven’t matched up with the X for hundreds of millions of years were completely stable.

This strongly suggests that the Y is here to stay, which is good news for men and genealogists. 


Thursday, March 15, 2012

Red meat can kill you



Frank Hu and his colleagues from Harvard followed over 120,000 people (about 30% men and 70% women) for almost three decades, looking at their health and diet habits.  It wasn’t good news for red meat eaters.  If you eat a daily serving of red meat, you could be increasing your risk of dying from cardiovascular disease or cancer by up to 20%.

A few caveats about this study.  First, the dietary information came strictly from questionnaires.  In other words, the researchers relied on participants to tell them exactly what they ate.  People are notoriously poor at this, both due to faulty memory and the desire to make themselves look good.  How often have you eaten ground beef in the past two years?  Unless you’re a vegetarian, you probably have no idea.

Second, frequent red meat eaters tended to be a surprisingly unhealthy bunch.  As a group, they were inactive, overweight smokers who didn't eat their fruits and vegetable. Who knew red meat would be associated with such bad health habits? To be fair, the authors did their best to account for known confounders such as smoking, body mass index or family history of diabetes, cancer or heart disease.

Even accounting for these potential problems, the news for red meat eaters was pretty grim. People may not have remembered exactly how much meat they ate, but they probably did know whether to put themselves in the ‘rarely’ or ‘daily’ categories.  Therefore, the broad generalizations of this study probably hold true, if not the exact risk assessments.

So, will red meat kill you?  I wouldn’t panic if you’re having dinner out and hamburgers are all that’s on offer.  But unless further studies refute these results, it seems clear that you don’t want to eat red meat too often.  Substituting other protein sources (beans, fish, poultry, nuts, etc) as much as possible is an excellent idea.

Now if you’ll excuse me, I have to go and convince myself that I really enjoy veggi-dogs.  So far, it’s not going well. 

Wednesday, March 14, 2012

Saving patients from acetaminophen overdose


Acetaminophen (brand names include Tylenol and Paracetamol) is a safe and effective drug if taken in the proper amounts.  Unfortunately, taking 50% more than the recommended daily maximum (four grams for adults) can damage your liver, and taking five times as much can kill you.  If you consider the fact that many medicines (such as cold remedies) contain acetaminophen, I think you can see why acetaminophen is the leading cause of acute liver injury in the U.S.  It’s just too darn easy to reach those dangerous levels.

There is a treatment for acetaminophen damage.  If a patient is given N-Acetylcysteine (N-Ac) within the first twelve hours after overdosing, liver damage can be averted.  If a patient doesn’t receive N-Ac during this critical time, it may be too late to save the liver.  In that case, the patient’s only chance to live rests with receiving a liver transplant.  The problem is that emergency care workers often don’t know whether a patient is or is not within that twelve-hour window.  If he is, he should receive N-Ac.  If not, giving the patient N-Ac just wastes everyone’s time and may delay putting him on the liver transplant list until it’s too late.

Researchers from the University of Utah decided to see if they could develop a rubric for determining which patients should immediately be placed on the liver transplant list and which should be treated with N-Ac.  They used the fact that acetaminophen-caused liver damage follows a known progression.  The injured liver releases certain enzymes that peak at a certain number of hours after exposure.  The scientists used this data to plot the time and extent of the overdose and to predict which patients would require a liver transplant.  Thus far, it appears to be more useful than previous models.

The authors are aware that many confounding factors (other drugs or alcohol, the general health of the patient) will probably affect the efficacy of their model.  All the same, it’s a valuable tool for health care providers dealing with an acetaminophen crisis.  

Tuesday, March 13, 2012

The virus that infects the bacteria that infects the aphid that saves it from the wasp... some of the time


Or, Evolution marches on. 

There’s a species of parasitic wasp (Aphidius ervi) that lays its eggs in pea aphids (Acyrthosiphon pisum).  This is very unfortunate for the aphids, which get consumed alive by the wasp larva inside them.  However, some aphids have a defense.  Those pea aphids that are infected with a particular bacteria (Hamiltonella defensa) that are in turn infected with a specific bacterial virus (Acyrthosiphon pisum secondary endosymbiont, or APSE) are largely protected from the wasp eggs within them.  This is because both H. defensa and APSE make toxins that in concert can kill a wasp larva.

So, to recap, pea aphids that are infected with APSE-infected bacteria are protected from parasitic wasps.

 

The parasitic wasp, Aphidius ervi, attacks the pea aphid, Acyrthosiphon pisum
Credit: Alex Wild.

At this point, you may be wondering if the wasps have found a way around this problem of the fortified aphid.  Why, yes, they have.  According to research by Kerry Oliver from the University of Georgia and her colleagues from Akita Prefectural University and the University of Arizona, wasps can compensate for the toxins by laying two or more eggs in infected aphids.  Interestingly, a single wasp emerges from each aphid, regardless of the number of eggs deposited. More eggs seem dilute the toxins so that a single larva can survive.

You won’t be surprised to learn that female wasps preferentially lay more than one egg in infected aphids, but only one in uninfected aphids.  How can they tell the difference?  Aphids secrete alarm pheromones, and after all, what’s more alarming than the prospect having your innards digested by a foreign invader?  Other aphids, upon detecting the pheromone, try to flee the area.  There is some evidence that aphids infected with H. defensa secrete less of the alarm pheromone, and that wasps can detect the difference. 

You can read more about this fascinating story here and here.

Monday, March 12, 2012

What’s your blood type?

You may know whether you’re A, B, O or AB, and even whether you’re Rhesus (Rh) positive or negative.  But do you know where you fall amongst the other 30 categories of blood types?  Hold on, make that 32.  An international team of scientists, led by Lionel Arnaud of the National Institute of Blood Transfusion and Bryan Ballif of the University of Vermont, has added two new proteins to the rolls of molecules that determine blood type compatibility.

Our red blood cells (RBCs) can have any of a wide variety of different molecules on their surfaces.  For example, if you have type A blood, you have type A antigen on your RBCs.  People with type B blood have B antigens, people with AB blood have both, and people with type O blood have neither.  Why is this important?  Under normal circumstances, it isn’t.  One blood type is just as good as another for serving all the purposes that RBCs have, namely carrying around oxygen and nutrients.  It only becomes an issue when someone else’s RBCs get deposited into your body.  There are two main ways in which this can occur, by transfusion and during pregnancy.

If a person receives a blood transfusion of RBCs with the same or fewer antigens (O or A blood going into a person with AB blood), there’s no problem.  If, however, a person receives blood containing alien antigens (A blood going into a person with O or B blood), the recipient’s immune system will attack the new blood, leading to a devastating cascade of symptoms and possibly even death. Pregnant women may not be able to carry babies to term if those babies inherit incompatible blood groups from their fathers.


Diagram showing blood group compatibility for transfusion purposes.

As you can see, the more tightly doctors can type blood groups, the less chance of rejection for transfusion patients.  Thanks to the efforts of researchers like Arnaud and Ballif, we now have thirty-two separate antigen groups to screen for.  Interestingly, the new ones, Langereis (Lan) and Junior (Jr), also happen to be associated with resistance to anti-cancer drugs.

Both Lan and Jr are molecular transporters, responsible for moving specific molecules across membranes.  They are encoded by ABCB6 and ABCG2, respectively.  The ABCG2 protein is also known as the Breast Cancer Resistance Protein because it actively transports many anticancer drugs out of cells.  Getting rid of toxins would normally be a good thing, but not when you’re trying to kill tumor cells. Until recently, it had not been known that Lan and Jr were also blood type systems.  The significance of this is that there are perfectly healthy people (particularly many Japanese in the case of Jr) who are negative for these transporter proteins.  If the genes can be knocked out in cancer patients, that might make treatment easier.

If you like, you can peruse the list of blood types here.  

Helias, V., Saison, C., Ballif, B., Peyrard, T., Takahashi, J., Takahashi, H., Tanaka, M., Deybach, J., Puy, H., Le Gall, M., Sureau, C., Pham, B., Le Pennec, P., Tani, Y., Cartron, J., & Arnaud, L. (2012). ABCB6 is dispensable for erythropoiesis and specifies the new blood group system Langereis Nature Genetics, 44 (2), 170-173 DOI: 10.1038/ng.1069.

Saison, C., Helias, V., Ballif, B., Peyrard, T., Puy, H., Miyazaki, T., Perrot, S., Vayssier-Taussat, M., Waldner, M., Le Pennec, P., Cartron, J., & Arnaud, L. (2012). Null alleles of ABCG2 encoding the breast cancer resistance protein define the new blood group system Junior Nature Genetics, 44 (2), 174-177 DOI: 10.1038/ng.1070.


Sunday, March 11, 2012

Inject your way to a healthy heart


Karen Christman and her colleagues from the University of California, San Diego have developed a way to treat heart problems via injection, rather than surgery.  They were able to repair rat hearts that had suffered from myocardial infarction (MI) by injecting a gel made from ventricular extracellular matrix (ECM). 

Here’s the recipe:

First, get some heart tissue.  You’ll most likely be using porcine tissue.  It’s similar to human heart tissue and you can get as much as you need.  Next, strip away the cells leaving behind the ECM proteins.  Freeze dry those proteins, grind them into powder and then use enzymes to liquefy that powder.  You now have an ECM hydrogel that’s liquid when sitting on the lab bench but a gel at body temperature.  When injected into an ailing heart, this gel forms a new scaffold upon which an animal’s own heart cells can assemble.


Tissue spins in a beaker at the end of the cleansing process that removes all of the cells. The process retains the tissue's structural proteins, a key component of the hydrogel.
UC San Diego Jacobs School of Engineering

To be clear, we’re talking about repairing injured hearts simply by injecting a gel directly into the damaged area.  When this procedure was done on rats it preserved cardiac function after an MI.  In pigs, the hydrogel did not stray throughout the rest of the body but stayed at the heart site after injection. These are both promising results, though more animal experiments must be done before this procedure can be tested on humans. 

You can watch the preparation of the gel here.  You may want let the film clip fully load before starting it though.  When I tried to watch it too quickly, it kept restarting. 

Saturday, March 10, 2012

Calorie listings could be much better


Since 2010, restaurants with more than 20 locations have been required to include calorie data on their menus.  While this is a good idea in principle, just how useful is that information?   According to research by Elizabeth Gross Cohn from the Columbia University School of Nursing and her colleagues, not very useful at all.

The researchers asked volunteers to document what kind of calorie information fast food restaurants throughout Harlem, New York were posting on their menu boards. Many of the restaurants presented a range of calories, depending on how the item was prepared and how many people it was meant to serve.  Unfortunately, in most cases, that range was not particularly informative.  For example, the menu board at one chicken restaurant stated that their six-piece meal had 1200 to 4250 calories.  I assume the higher number is if you ate the entire meal yourself, but how much can you eat to hit the bottom number?  1.7 pieces?  By the same token, calorie ranges given for items with a choice of toppings or side dishes usually didn’t specify which calorie count matched which menu choice, so there was no way to know how many calories a finished item would actually have.

In addition, none of the restaurants offered any information about suggested daily caloric intake.  In other words, although customers can get information about calorie counts for food items, that information is not put into any meaningful context.

The authors suggest that more effort be made to let consumers know how much their choice of toppings and preparation will affect the final calorie count of their selection. The FDA is also looking for ways to improve nutritional reporting.  

Friday, March 9, 2012

Circadian rhythms save plants


Rice University researchers have shown that Arabidopsis plants use their circadian clocks to ensure that their peak toxicity coincides with the feeding behavior of their insect nemesis, Trichoplusia ni, a.k.a the cabbage looper. 

Circadian clocks control the internal rhythms that living things use to organize their day.  If you always get drowsy at 2 pm and hungry at 6 pm, you can thank your circadian clock.  Other creatures also exhibit different behaviors at different times of day. For example, cabbage loopers feed most actively in the late afternoon.  Arabidopsis secretes plant hormones that regulate the production of toxic chemicals so that they peak at exactly that time.

The researchers grew Arabidopsis under varying conditions.  In some cases, the plants were subjected to the same twelve hour light/dark cycles as the caterpillars.  In other cases, the plants were twelve hours out of phase with the herbivores. The plants that were on the same cycle as the insects showed significantly less predation than those that thought it was day when the insects thought it was night.  When this same set of experiments was done with plants that had defective circadian clocks, there was no difference between in phase and out of phase samples.

You can watch an explanation below.  As an aside, I was particularly impressed by the camouflage of these caterpillars.





Thursday, March 8, 2012

Steamy waterworld exoplanet


I know, another exoplanet.  But just because hundreds of these non-solar planets have been found doesn’t mean we’re not learning interesting things about them. Take the planet GJ1214b, which was discovered in 2009 by the MEarth project.  Data from the new Wide Field Camera 3 on the Hubble telescope has now confirmed that the planet is mostly water.

At about seven times the mass of the Earth, GJ121b is classed as a ‘super-Earth’.  It was discovered by the transit method. That is, astronomers caught it passing in front of its star as it whips around its red dwarf host every 38 hours.  More importantly, the position of the transit and the energy output of the star make it possible to detect the planet’s atmosphere as it obscures the light coming from the star behind it.

Although a few models could have been consistent with the data, the most likely scenario is that GJ121b contains an atmosphere that is at least 50% water vapor. The planet also likely has a rock and ice core surrounded by a thick envelope of hydrogen, helium and water. So, GJ121b is watery world with a steamy atmosphere. Another first in the assembly of exoplanets.

 

GJ1214b, shown in this artist's conception, is a super-Earth orbiting a red dwarf star 40 light-years from Earth. New observations from NASA's Hubble Space Telescope show that it is a waterworld enshrouded by a thick, steamy atmosphere. GJ1214b therefore represents a new type of world, like nothing seen in our solar system or any other planetary system currently known.
Credit: David A. Aguilar (CfA)