An “Acceptable” GMO?

Soybean Field

For many opponents of genetically modified foods, the idea of fiddling with an organism’s genome doesn’t quite sit well in their stomachs. The type of genetic tweaking that renders soybean plants resistant to the herbicide Roundup strikes some not only as unnatural but something that borders on playing God. Similarly, another common objection to genetic engineering is that the transfer of genetic material/DNA genes violates a so-called “species barrier.” Such is the case for Bt corn, which harbors the bacterial gene for Bt toxin, a compound that is poisonous to insect pests. This argument, however, disregards the fact that Nature ignores this barrier all the time. In the wild, DNA is often transferred between species through processes collectively known as horizontal gene transfer. So, not even Nature plays by antiGMO rules.

But what if an already existing gene variant with a desired trait from one organism is genetically engineered into another organism of the same species? Would this make GMOs a little bit more palatable to their detractors?

Soy is one of the most important crops grown in the US and it is nearly ubiquitous in the market. It’s in our food, drinks, biodiesel fuel, even cosmetics. If you rummage through my mom’s kitchen you’ll find soy sauce in the pantry, tofu in the fridge, and edamame in the freezer. Back in the day, she kept soybeans on hand to press her own soy milk.

Soybean cyst nematode and egg SEM
“Low-temperature scanning electron micrograph of soybean cyst nematode and its egg. Magnified 1,000 times.”

Latte drinkers, vegetarians, and us Asians aren’t the only ones who love soy, however. Lurking underground are parasitic worms known as soybean cyst nematodes (SCN), which find the roots of the soybean plant irresistible. These agricultural pests invade the roots of the soy plant where they do a bit of their own agriculturing. These nematodes can create a steady supply of food for themselves by coaxing the root cells that they feed on to divide. Whereas males leave the comforts of their “root homes” in order to find mates, females remain there where they continue to feed and swell in size until eventually their bodies burst through the root. Once mated and having laid her eggs, the female dies and her cuticle hardens, forming characteristic cysts on the roots of the soybean plant. The damage to soy crops comes in at $500 million to $1 billion annually in the US alone.

Segment of soybean root infected with soybean cyst nematode. Signs of infection are brown-white females or cysts with egg masses that are attached to root surfaces.
“Segment of soybean root infected with soybean cyst nematode. Signs of infection are brown-white females or cysts with egg masses that are attached to root surfaces.”

Soybean plants aren’t entirely defenseless, however, as there are soybean plant strains, such as the Forrest cultivar, that are resistant to nematode attack. In this cultivar, the feeding cells that the nematodes “cultivate” in the soybean plant roots die off and the worms starve before they can reproduce. (Conversely, there are also soybean cyst nematodes that are resistant to resistant soybean plants. It just wouldn’t be Nature without the wrinkles, now would it?)

While exactly how the feeding cells in the Forrest cultivar degenerate in response to soybean cyst nematode is unknown, a team of scientists led by Shiming Liu (Southern Illinois University) and Pramod Kandoth (University of Missouri) has recently identifiedmutations in the serine hydroxymethyltransferase (SHMT) gene that are responsible for nematode resistance. Serine hydroxymethyltransferase is an enzyme involved in the shuttling of one-carbon units between molecules–folate in particular–until the carbon is ultimately freed up for the cell to use in important processes such as DNA and protein synthesis. For instance, one of the important functions of serine hydroxymethyltransferase is to convert serine into glycine, both of which are amino acids found in proteins.

One of the reactions that serine hydroxymethyl transferase catalyzes is the conversion of the amino acid serine to glycine.
One of the reactions that serine hydroxymethyl transferase catalyzes is the conversion of the amino acid serine to glycine.

Since the mutations cause changes near the active site of the SHMT protein, or the “business end” where the shuttling of carbons occurs, it’s possible that the mutations affect the activity of the SHMT protein. To test this model, Liu and Kandoth compared the ability of the normal and mutant forms of SHMT to make glycine by expressing these genes in an E. coli bacteria strain that can’t make its own glycine.  This particular strain of bacteria dies when glycine is removed from its diet, but was able to survive when Liu and Kandoth engineered the strain to express the normal form of SHMT. This indicated that expressing the normal SHMT protein restored the bacteria’s ability to make glycine. However, the bacteria didn’t survive as well when the mutant form of SHMT protein was expressed which suggested to the scientists that the mutant protein was less efficient in making glycine.

More importantly, soybean plants that were susceptible to SCN infection became resistant when Liu and Kandoth transferred the mutated Forrest SHMT gene into the susceptible plants. This demonstrated that the mutated Forrest SHMT was responsible for soybean cyst nematode resistance. The scientists speculate that the decreased activity of the mutated SHMT protein in the feeding cells of the soybean plant root reduces either their “nutritiousness” or their ability to divide. As a result the nematodes that infect the Forrest cultivar starve.

So, this brings me back to my original question of what, if anything, would constitute an “acceptable” GMO to opponents of genetic engineering? Would detracters object to a scenario where an already existing mutation* that confers resistance to an agricultural pest is engineered into other soybean plants. Directly transferring the existent Forrest SHMT variant would be more efficient over traditional methods of breeding, since only the Forrest SHMT gene would be introduced into another soybean plant without carrying over any unwanted traits or genes. There are, after all, many different cultivars of soybean plants used for different applications that may benefit from nematode resistance.

*I’ll avoid saying “naturally-occurring” since the Forrest cultivar was developed by a USDA breeding program.

Reference
Liu, S., Kandoth, P., Warren, S., Yeckel, G., Heinz, R., Alden, J., Yang, C., Jamai, A., El-Mellouki, T., Juvale, P., Hill, J., Baum, T., Cianzio, S., Whitham, S., Korkin, D., Mitchum, M., & Meksem, K. (2012). A soybean cyst nematode resistance gene points to a new mechanism of plant resistance to pathogens Nature, 492 (7428), 256-260 DOI: 10.1038/nature11651

Communicating Science in My Native Tongue

Several months ago Drug Monkey asked me this:

@amasianv do you blog in Vietnamese? Could be a cool thing, no?

— Drug Monkey (@drugmonkeyblog) September 9, 2012

Communicating science is tough as it is, never mind doing it in my native tongue. Especially, as I’m embarrassed to admit, when my spoken Vietnamese is atrophying like a disused muscle and my written skills are, well, nothing to write home about.

One of the reasons I started science blogging was a compromise to my father. In the minds of many Vietnamese immigrant parents–this probably extends to other ethnic groups as well–only four career options exist for their children: doctor, lawyer, engineer, or garbage man. No disrespect intended toward my fellow waste collectors, but this is the view of many of our parents. However, my father’s dreams for me went a little against the grain since he wanted me to be a journalist. You can only begin to imagine how perplexing it was for me that my dad was disappointed in my affinity for the sciences. Of course, while blogging was an attempt at finding middle ground with my dad, the central irony in all of this is that my writing isn’t really geared towards him. His English is only a hair better than my Vietnamese. Now, that’s not to say we don’t talk science at all. In fact, many of our conversations range from science news he’s read on Vietnamese-language websites–some of which require elaboration if not outright debunking–to the details of my own thesis project.

Our conversations, however, can be a maddeningly staccato, mish-mash of Vienglish (I know, it lacks that certain yo no sé qué of “Spanglish”), with me attached to either my phone or computer ready to consult Google translate and my dad with his four hardcover Vietnamese-English dictionaries open and ready at his fingertips. But despite this, talking about science is one of the more rewarding experiences I get to share with my dad. For one thing, I practice using simpler analogies and try to find culturally-relevant examples to get around the language barrier. Recently, for instance, while on the topic of fermentation we talked about my dad’s perfected recipe for making dưa chua*, a Vietnamese specialty of pickled mustard greens.

dua-chua-h

Even more rewarding than honing my own communication skills, however, is being able to witness my father’s inquisitive mind at work. We’re talking about someone whose formal education ended somewhere in grade school. His questions and insights from our countless conversations tell me that the limit of one’s curiosity isn’t set by their level of education.

As for my father, I have to believe he enjoys our scientific conversations, as well. Otherwise, he wouldn’t be making cheat sheets like this one:

cheat sheet

*not my dad’s recipe.

Crossposted from Scientopia.

Battle of the Sperms

Inside every Drosophila melanogaster (fruit fly) female is a battleground where sperm can jockey with each other for the honor of fertilizing her eggs. By sequentially mating females with males genetically-engineered to produce sperm that glow either green or red (see video below), scientists have been able to directly observe sperm from two different males competing in what resembles a fruit fly version of Tron. Color coding the sperm in this way allows researchers to distinguish one male’s sperm from another’s and determine who the winners are.

“Sperm from two different males genetically-engineered to express either green or red fluorescent proteins compete within the female reproductive tract of the fruit fly Drosophila melanogaster.”

Surprisingly, it’s not always the fastest sperm that wins.

Continue reading

Drug Resistance in MRSA is Finely-tuned

Cross-posted at PLOS Public Health Perspectives.

In hindsight, shoving my hand into a narrow drinking glass wasn’t such a good idea.  I learned this the hard way a few years ago while vigorously scrubbing the inside of a glass with a sponge. When the glass shattered in my hands, one of the shards cut the base of my index finger–right by the the knuckle–and required a trip to the local urgent care center. After being stitched up, I was sent home with some antibiotic ointment, extra gauze, and instructions to keep the wound clean. And that’s when things got worse.

Several days later, my finger became red, inflamed, and tender to the touch. There was also stomach-turning pus oozing out of the wound. Fearing that it was infected, I went back to the the urgent care center where the doctor took one look at my wound and then stated the obvious, “That looks infected.” A swab sample was taken from my wound to start a bacterial culture, which would be used to identify the nature of the infection. Since it would take a few days for the results to come back from the lab, she preemptively started me on a course of antibiotics. At the end of the week, there was a message left on my voicemail. The culture was positive for methicillin-resistant Staphylococcus aureus (MRSA).

MRSA-infected finger

This was cause for concern because MRSA is a bacterial pathogen that, once it enters the bloodstream, can cause severe to life-threatening infections. MRSA is also notoriously difficult to treat because it is resistant to β-lactams, a class of antibiotics generally prescribed as the first line of defense against normal staph infections. β-lactams, which include drugs like penicillin, oxacillin, and methicillin, kill bacteria by preventing the synthesis of bacterial cell walls–without which bacteria cannot survive. These drugs accomplish this by glomming onto and inactivating penicillin-binding protein (PBP), an enzyme that makes an essential component of bacterial cell walls. MRSA strains, however, are resistant to β-lactam drugs because they carry a gene called mecA. The mecA gene encodes a different form of penicillin-binding protein, PBP2a, which β-lactam drugs cannot inactivate, thus allowing normal cell wall synthesis to occur even in the presence of these drugs.

Methicillin-resistant Staphylococcus aureus (MRSA) Bacteria2
Scanning electron micrograph of methicillin-resistant Staphylococcus aureus bacteria (yellow) killing and escaping from a human white cell.

MRSA infections have long been associated with health care settings such as hospitals and nursing homes. These settings, characterized by a sick general population coupled with high antibiotic usage which selects for drug-resistance, are a perfect environment for MRSA strains to gain a foothold. Given that I had my stitches done at an urgent care center I just assumed that’s where I came into contact with MRSA.

In recent years, however, community-acquired MRSA (CA-MRSA) infections have been on the rise. These are infections contracted from settings like schools, childcare centers, gyms, and prisons. Infections caused by CA-MRSA strains are a particular concern because they are more virulent, spread more rapidly, and can cause more severe infections than its healthcare-acquired MRSA (HA-MRSA) counterparts. What’s worse is the line between the two are blurring as HA-MRSA strains move out into the community and CA-MRSA moves into the hospitals. Because of the increased virulence of CA-MRSA strains there are fears that these strains will eventually replace HA-MRSA strains in healthcare settings–although a recent model published in PLOS Pathogens suggests otherwise[1].

How MRSA developed β-lactam resistance is still unclear. While there are quite a few different strains of MRSA (some of which have also developed resistance to other classes of drugs) they all carry the mecA gene. The mecA gene, in turn, is part of a larger piece of foreign DNA known as the SCCmec element, which is not normally found in S. aureus. Since bacteria are quite adept at exchanging DNA with each other, scientists speculate that the SCCmec element found its way into a normal staph strain from an as-of-yet identified trading partner. This process of swapping and transferring DNA is known as horizontal gene transfer.

Interestingly, MRSA has a finely-tuned, “on-demand system” that turns mecA expression on in the presence of β-lactam drugs, while keeping expression turned off in the absence of these drugs. This regulation is carried out by proteins whose genes are also found on the SCCmec element. In the absence of β-lactams–when the bacteria doesn’t need the drug-resistant PBP2a protein around– the expression of mecA is kept in check by the protein MecI. MecI binds to the DNA promoter region of mecAand prevents gene transcription. However, in the presence of β-lactam drugs the bacteria needs PBP2a around in order to survive. In this case, expression of mecA is turned on through the action of the cell surface protein MecR1 whose job is to keep an eye out for β-lactams. When MecR1 detects the presence of β-lactams, it instructs the bacterial cell to break down the MecI inhibitor. This allows expression of the mecA gene that is essential for the bacteria’s survival to occur.

journal.ppat.1002816.g010460
Figure 10. Model for the mecA induction by MecR1-MecI-MecR2.In the presence of a β-lactam antibiotic, MecR1 is activated and rapidly induces the expression of mecA and mecR1-mecI-mecR2. The anti-repressor activity of MecR2 is essential to sustain the mecA induction since it promotes the inactivation of MecI by proteolytic cleavage. In the absence of β-lactams, MecR1 is not activated and a steady state is established with stable MecI-dimers bound to the mecA promoter and residual copies of MecR1 at the cell membrane [2].

Recently, researchers from Portugal have identified and characterized another gene on the SCC element called mecR2 [2]. As it turns out the MecR2 protein is another component of the finely-tuned, “on-demand system”that regulates mecA expression. When MRSA bacteria encounter β-lactam drugs it starts ramping up the production of MecR2 protein. MecR2, in turn, knocks the MecI inhibitor protein off of the mecA gene promoter, thereby increasing mecA expression. The researchers speculate that the dislodged MecI protein becomes unstable and is then degraded inside the bacterial cell.

Importantly, the researchers demonstrated that in order to get the optimal expression of mecA that would confer resistance to β-lactam drugs, the bacteria needed MecR2 protein around. When they removed the mecR2 gene, the bacteria once again became sensitive to the β-lactam drug oxacillin, which coincided with a decrease in mecA expression. This research not only helps further our understanding of drug resistance in MRSA but also highlights new targets for therapeutics. For instance, drugs could be designed that either short circuit the ability of MecR1 to alert the bacterial cell to the presence of β-lactam drugs or prevent MecR2 from dislodging the MecI inhibitor from the mecA promoter, thereby keeping mecAexpression in check.

As for my finger and me, we made it out of the MRSA scare relatively unscathed–other than a barely noticeable scar at the base of my index finger. Once the lab results came back positive for MRSA, the doctor switched my prescription to Bactrim. Luckily for me, I wasn’t dealing with one of the multi-drug resistant varieties of the bug so the infection cleared in a few days.

Featured image: Scanning electron micrograph of methicillin-resistant Staphylococcus aureus (MRSA, yellow) surrounded by cellular debris. Credit: NIAID

References:

1. Kouyos R, Klein E, & Grenfell B (2013). Hospital-Community Interactions Foster Coexistence between Methicillin-Resistant Strains of Staphylococcus aureus. PLoS Pathogens, 9 (2) PMID: 23468619 doi:10.1371/journal.ppat.1003134

2. Arêde P, Milheiriço C, de Lencastre H, & Oliveira DC (2012). The anti-repressor MecR2 promotes the proteolysis of the mecA repressor and enables optimal expression of β-lactam resistance in MRSA. PLoS Pathogens, 8 (7) PMID: 22911052 doi:10.1371/journal.ppat.1002816

Glaucoma Is not an Equal Opportunity Thief

Wrapping up Glaucoma Awareness Month over at PLOS Public Health Perspectives blog with a post on the ethnic disparities in the risk of developing glaucoma as well as current research in identifying the genetic basis for glaucoma in Asians:

Glaucoma isn’t exactly an equal opportunity thief, either. While it is estimated that over 4 million Americans have glaucoma, the prevalence of glaucoma in African Americans and Latino (particularly Mexican) Americans is significantly greater than in Caucasian Americans. African Americans are also more likely to develop glaucoma at a younger age and suffer blindness from the disease. While roughly 90% of all glaucoma cases in the US are what is known as primary open angle glaucoma (POAG), Asian Americans are at the greatest risk of all ethnicities to develop a different form of glaucoma called primary angle closure glaucoma (PACG)(1). The genetic causes underlying glaucoma remain unclear, but these ethnic disparities in the risk of developing glaucoma suggest a genetic basis that is ethnicity-specific. Read more

Sabotaging the “Warning Beacons” to Prevent Immune Cells from Attacking the Body

Human immune cells are remarkably adaptable. These foot soldiers of the immune system can be harvested from the body, retrained to recognize and fight different diseases, and then redeployed in the body. This process, known as adoptive cell transfer, has incredible potential for treating cancer or chronic infections–particularly in individuals whose immune systems have been weakened by diseases like AIDS. There is, however, a big problem with this technique. Immune cells that have been harvested and engineered to fight specific diseases can often go haywire and turn their weapons on host cells. As a result, healthy cells and tissues in the body that aren’t supposed to be attacked by immune cells get caught up in the crossfire and end up as casualties. As a solution, biologists want to keep these immune cells in line by reprogramming their behavior using the very tools that bacteria employ to slip past our immune system.

All immune cells have a network of proteins that alerts the cell to the presence of pathogenic intruders. For all of you LoTR fans, this network works a lot like the Warning Beacons of Gondor:

On the surface of immune cells are receptor proteins that act like guardians at an outpost. At the first sign of the enemy—usually, bacterial proteins that bind to the receptors—these guardians sound the alarm by “lighting” a beacon. This signals to the other beacons to be lit as well, thereby alerting the immune cell of impending danger.

nrd2289-f1
The “Warning Beacons of Immune Cells” is a communication network of proteins that modify each other in a cascade. The arrows indicate proteins modifying other proteins. Source: K. L. Jeffrey et. al., Nature Reviews Drug Discovery 6, 391-403 (May 2007)

Inside of immune cells, however, this “relay of beacons” is actually made up of proteins that chemically modify other proteins in a cascade. Each time a protein modifies another protein, “word” of the intruder is spread throughout the cell until it finally triggers an immune response. As a result, immune cells release a volley of helpful molecules—some recruit reinforcements, some mark the bacteria as the enemy, while others make immune cells more effective soldiers. Finally, when the alarm reaches the nucleus—the cell’s central command—orders are sent out for the cell to rapidly divide, making even more immune cells to help in the battle.

Shigella flexneri Gram
“Im in ur body, making u p00pz” – Shigella flexneri

Many disease-causing bacteria, however, have evolved a vast array of smoke bombs, stealth cloaks, and other weapons to sabotage our defenses. For instance, when the diarrhea-inducing bacteria Shigella flexneri infects the body it plants a bomb to disrupt the warning beacons. S. flexneri produces a protein called OspF that interacts with the protein MAPK (mitogen activated protein kinase) and prevents MAPK from modifying other proteins. With MAPK unable to “light its beacon,” the alert system is short-circuited leaving the immune cell in the dark and unaware of an attack. While conventional wisdom is to make drugs that target OspF, some researchers see an opportunity to exploit the use of OspF. Since OspF can sabotage the immune response, scientists now want to use this “bomb” as a way to prevent immune cells from attacking other cells in the body during adoptive cell transfer.

In a Letter to Nature, Wendell Lim and colleagues described two ways in which OspF could be used to protect the body’s cells from unwarranted attacks by immune cells. The first way involved reducing the immune cell’s firepower. The scientists genetically-engineered T-cells (a type of immune cell) harvested from the body to produce the bacterial protein OspF. This was accomplished by introducing into the cell DNA that contained not only the OspF gene but also regulatory DNA, which carries instructions for when and where the gene should be expressed. The specific regulatory DNA they used instructs the cell to produce OspF only when the immune response is activated. The scientists then tricked the engineered T-cells into thinking they were under bacterial attack by exposing them to antibodies that bind to the receptor proteins (the outpost guardians) and trigger them to light their beacons. Lim and colleagues observed that the expression of genes turned on by the immune response was reduced in the OspF-producing immune cells compared to normal immune cells. This suggested that OspF weakened the magnitude of the immune response by virtue of its ability to inhibit MAPK. By reducing the firepower of immune cells scientists hope to limit the number of casualties due to “friendly fire.”

Red White Blood cells
Scanning electron micrograph of a T-cell (right), a platelet (center) and a red blood cell (left)

 

Lim and colleagues were also able to institute a “cease fire” in immune cells. The team of scientists genetically-reprogrammed T-cells to produce OspF, but only in the presence of the drug doxycycline. This time, the scientists used regulatory DNA that requires doxycycline to turn on gene expression. These immune cells were also tricked into thinking they were under attack, but doxycycline treatment halted the immune response—the immune cells stopped dividing and stopped releasing immunity-boosting molecules. This means that at the first sign of reprogrammed immune cells attacking other cells in the body, scientists can use doxycycline to order the immune cells to “cease fire.”

Finally, the researchers were able to manipulate OspF to interact with and sabotage different proteins by tinkering with the OspF gene and expressing it in yeast cells. Proteins interact with one another through domains that function like clothing fasteners. Proteins also have different interaction domains just as clothing have different fasteners like Velcro, zippers, and buttons. By swapping the “fastener” domains in OspF, the researchers were able to “stick, zip, or button” OspF to different yeast proteins. Although this experiment was done in yeast, the yeast proteins the researchers targeted for sabotage can also be found in the “warning beacon relay” of immune cells. This opens the door for scientists to specifically target OspF to different proteins in immune cells. Since the alert system triggers different responses in immune cells, this strategy can be used to pinpoint specific beacons in the relay and shut down either the entire immune response or only specific branches.

The work done by Lim and colleagues demonstrate that OspF can be used to reduce the firepower of immune cells and order a ceasefire. These results highlight the potential for using bacterial proteins to reprogram the behavior of immune cells in adoptive cell transfer therapy. Changing the behavior of immune cells, however, is one thing. Effectively mounting a counterattack against pathogens without harming the body remains another. Since these experiments were performed in immune cells outside of the body, the next step in this research is to deploy these reprogrammed foot soldiers back into the body. Then we’ll see how effective they are against actual bacterial invaders while limiting innocent bystander casualties due to friendly fire.

Reference

Wei P, Wong WW, Park JS, Corcoran EE, Peisajovich SG, Onuffer JJ, Weiss A, Lim WA. Bacterial virulence proteins as tools to rewire kinase pathways in yeast and immune cells. Nature. 2012 Aug 16;488(7411):384-8. doi: 10.1038/nature11259. PubMed PMID: 22820255; PubMed Central PMCID: PMC3422413.

Featured image credit:  Lord of the Rings – Return of the King – Blue Ray Edition.

Joining Scientopia!

Hello readers,

An announcement for the New Year. I’m joining a great group of science bloggers over at Scientopia. In addition to writing about science-y topics, I’ll be sharing some of my experiences being a graduate student and an Asian American. I will continue to blog about science here as well. Looking forward to sharing and contributing to the Scientopia community. I hope you will join me there! And please, head over there, poke around, and have a read of some of the other Scientopians.

Here’s the link to my new blog, Wandering Third Instar.

As always, thank you for reading!

Dengue Fever, GMOsquitos, and a “Wolbachian” Invasion

In my recent Public Health Perspectives post for PLOS Blogs, I discussed two ways to control the transmission of dengue fever. The first was through the release of genetically-modified (GM) male mosquitoes that mate with wild females and pass on a gene that is lethal to its offspring–a strategy called Release of Insects carrying a Dominant Lethal (RIDL) (1). If released in sufficient numbers, the GM male mosquitoes will cause a collapse of the mosquito population.

Diagram of the RIDL transgene (image from Oxitec website)
Diagram of the RIDL transgene (image from Oxitec website)

The RIDL transgene (a) that has been engineered into the OX513A strain of mosquitoes carries instructions for the production of a protein called tetracycline transactivator (tTA). tTA , itself, is a product of genetic engineering, created by the fusion of parts of two proteins. One “half” of tTA acts as transcriptional activator–it can turn on and amplify the expression of certain genes. The other “half” can bind to specific DNA sequences called tetO binding sites. By engineering tetO binding sites into the RIDL transgene this allows the tTA protein, itself, to amplify expression of the tTA gene thereby producing even more tTA protein (b). This results in what is known as a positive feedback loop. At high enough levels, the tTA protein interferes with cellular process causing mosquito larvae to die. The expression of the tTA gene can be turned off by tetracycline, however (c). Tetracycline binds to the tTA protein and prevents it from binding to DNA, which short circuits the feedback loop.

“This allows scientists to raise the mosquitoes in the lab by adding tetracycline to the diet of the larvae. Without a source of tetracycline in the wild, however, any mosquito offspring that inherits the gene will live not beyond the larval stage.”

The other strategy I discussed was using Wolbachia infection of mosquitos to prevent dengue transmission. Wolbachia is an symbiotic bacteria that has been shown to protect mosquitos against dengue infection by interfering with the ability of the dengue virus to replicate. Wolbachia can invade and establish itself in insect populations quite rapidly and stably–an ideal characteristic if Wolbachia is to be used in limiting the transmission of dengue. It accomplishes this by employing a cunning strategy called “cytoplasmic incompatibility (2).” In short, when Wolbachia-infected males mate with uninfected females all their offspring die. However, the offspring of Wolbachia-infected females are viable regardless of the infection status of the male. This means that Wolbachia infection confers a reproductive advantage to infected females over uninfected females–infected females are more likely to have offspring because they can mate with both infected and uninfected males. Furthermore, Wolbachia infection is passed on from mother to offspring. It is through this process that Wolbachia “invades” and secures its place in an insect population.

Field studies conducted in Australia showed that when  mosquitoes infected with the wMel Wolbachia strain are released into the wild, within several months stable wMel infection became established in two wild A. aegypti populations (3). The speed at which wMel invaded the natural mosquito populations demonstrated the potential of using Wolbachia infection to control the spread of dengue.

You can read more about this topic here:

Could Wolbachia be an alternative to dengue-fighting GMOsquitos?

References:

1) Phuc HK, Andreasen MH, Burton RS, Vass C, Epton MJ, Pape G, Fu G, Condon KC, Scaife S, Donnelly CA, Coleman PG, White-Cooper H, Alphey L. Late-acting dominant lethal genetic systems and mosquito control. BMC Biol. 2007 Mar 20;5:11. PubMed PMID: 17374148; PubMed Central PMCID: PMC1865532.

2) Walker T, Johnson PH, Moreira LA, Iturbe-Ormaetxe I, Frentiu FD, McMeniman CJ, Leong YS, Dong Y, Axford J, Kriesner P, Lloyd AL, Ritchie SA, O’Neill SL, Hoffmann AA. The wMel Wolbachia strain blocks dengue and invades caged Aedes aegypti populations. Nature. 2011 Aug 24;476(7361):450-3. doi: 10.1038/nature10355. PubMed PMID: 21866159.

3) Hoffmann AA, Montgomery BL, Popovici J, Iturbe-Ormaetxe I, Johnson PH, Muzzi F, Greenfield M, Durkan M, Leong YS, Dong Y, Cook H, Axford J, Callahan AG, Kenny N, Omodei C, McGraw EA, Ryan PA, Ritchie SA, Turelli M, O’Neill SL. Successful establishment of Wolbachia in Aedes populations to suppress dengue transmission. Nature. 2011 Aug 24;476(7361):454-7. doi: 10.1038/nature10356. PubMed PMID: 21866160.

Featured image:
Detail from the original by Emil August Goeldi (1859 – 1917) [Public domain or Public domain], via Wikimedia Commons

by Viet Le

Here’s to an Amasian 2013!

by Viet Le

Just wanted to wish everyone a happy New Year and also to thank all the readers, bloggers, and Tweeps for making my first year of blogging a truly rewarding experience. Y’all have reinvigorated and reinforced my love for science and opened my eyes to something new that I enjoy doing. I know things have been a little bit quiet around these parts (what with me being a late-stage graduate student and all) so my New Year’s resolution is to get back on the blogging ball…that and taking the bus to lab more.

Stay tuned for more Amasian Science…

Rhino horns: From traditional medicine to recreational drug

Rhino horns are a precious commodity. On the black market, they can fetch an absurd price upwards of $60,000/kg. That’s more than the price of gold. Put in a different perspective, drop me a kilo of rhino horn and that pays two years of my graduate stipend…plus a Christmas bonus.* But that price also cost 618 rhinos their lives in 2012. This all-time high continues a rapidly increasing trend dating back to 2008 when poachers killed 83 rhinos–a noticeable uptick from the yearly average of 15 rhinos killed from 2000-2007. The practice is in no way humane, as poachers often cut horns off of tranquilized rhinos and then leave them to die from their wounds. I’ll spare you the grisly photos, but gruesome Internet images abound.

Adapted from Infographic- Understanding the rhino wars
Adapted from Infographic- Understanding the rhino wars

Fueling this demand for rhino horns are East Asian countries like China and Vietnam (I’m shaking my head in disapproval at you, my peoples in Vietnam). There, rhino horns are coveted by practitioners of traditional Chinese medicine who believe its extract can be used for treating fevers as well as other “conditions.” While most news coverage is quick to point out that rhino horns are little more than keratin (the protein found in our hair and nails) and that they lack any curative properties, little discussion is devoted to any actual research on their medicinal value. While published data is scarce–this probably reflects the obstacles in obtaining rhino horns for research–what little that has been published certainly doesn’t support using rhino horn as medicine.

In the early 1990s, Chinese researchers published in the Journal of Ethnopharmacology two studies that tested the ability of rhino horn extract to reduce fever (1,2). In the first study, researchers induced fever in rats by injecting them with turpentine oil, a known fever-causing agent. This was followed by injections of rhino horn extract prepared in either saline or in the herbal concoction traditionally prescribed for fevers. Both preparations of rhino horn extract were able to slightly decrease fevers in rats, but the effect required using rhino horn extract at 20 times the concentration normally prescribed by traditional medicine. Furthermore, the researchers observed that similarly high concentrations of horn extracts from saiga antelope, water buffalo, and cattle, also reduced fever in rats. This result meant that there was nothing special or magical about rhino horns in particular. The researchers concluded that, at least for the purpose of traditional medicine, rhino horns could be swapped out for horns from non-endangered animals.

Image credit: Jim Epler
Rhino horn. Image credit: Jim Epler

Still, the Chinese studies had two other problems. First, they injected the rhino horn extract into the rats, whereas in traditional medicine rhino horn extract is ingested. Second, their study didn’t compare how effective rhino horn extract reduced fever against known anti-fever drugs. These issues were addressed by Laburn and Mitchell, who published their results in the Journal of Basic and Clinical Physiology and Pharmacology (3). In their study, rabbits were injected with bacterial lipopolysaccharide (LPS), a component of bacterial cell walls. Since LPS is foreign to the rabbit’s body, it triggers the rabbit’s immune system and induces fever. To test their fever-reducing abilities, either rhino horn extract, reedbuck (a non-endangered African antelope) horn extract, indomethacin (an anti-fever drug), or water was fed “gavage-style” to the LPS-injected rabbits. This meant that the samples were pumped directly into the rabbit’s stomach through a tube passed through its mouth. To monitor the effect of each agent on fever, rectal temperature was monitored over the course of 250 minutes. The researchers found that neither the rhino nor the reedbuck horn extract did anything to reduce fever in rabbits. More importantly, indomethacin was very effective at reducing the fever. These findings are similar to another report which found that acetaminophen was more effective than rhino horn extract at reducing fever in children.

Rabbits were injected with bacterial lipopolysaccharide (LPS) to induce fever and simultaneously administered rhino horn extract (black circle), reedbuck extract (white square), water (white circle), or the anti-fever drug, indomethacin (black triangle). Rectal temperature was measured to monitor fever over the course of 250 minutes. Only indomethacin (black triangle) was able to reduce LPS-induced fever after about 75 minutes.
Rabbits were injected with bacterial lipopolysaccharide (LPS) to induce fever and simultaneously administered rhino horn extract (black circles), reedbuck extract (white squares), water (white circles), or the anti-fever drug, indomethacin (black triangles). Rectal temperature was measured to monitor fever over the course of 250 minutes. Only indomethacin (black triangles) was able to reduce LPS-induced fever after about 75 minutes (3).

Despite little scientific support for using rhino horns as medicine, the demand for rhino horns in China and Vietnam continues to soar. This week, in response to the growing poaching problem, Vietnam signed a no-poaching agreement with South Africa, where the majority of rhinos have been killed. Whether this will have any appreciable effect on poaching, however, is debatable considering that the demand for rhino horns in Vietnam has overshadowed its own conservation efforts. In 2010, the last of the Javan rhino subspecies native to Vietnam was killed by poachers.

Dehorned rhino
A dehorned rhino just looks so sad. Brent Stirton/National Geographic

Other ways to curb poaching have also been explored, such as routinely shaving off rhino horns. While rhino horns eventually grow back, this practice is unpopular among conservationists since rhinos depend on their horns for defense. It’s also worth noting that many dehorning advocates are also rhino owners whose true financial motives may lie in their support for legalizing the rhino horn trade. Another suggestion that’s been floated around to reduce poaching is to implant GPS devices into rhino horns. This would serve as a sort of RhinoJack that can be used to track down poachers. Others, on the other hand, suggest taking even more drastic actions.

These measures, of course, serve only to make poaching less desirable without dealing directly with demand. What’s troubling is that the demand for rhino horns is now being propped up by new and kookier, unscientific ideas, which extend far beyond its traditional use. Reports from China and Vietnam indicate that con men are peddling rhino horn extract as a miracle cure for whatever malady suits their fancy. As John Platt, of SciAm blogs, reports, “In Vietnam con men recently started marketing rhino horn as a cure for cancer or as a party drug to lessen the effects of alcohol.” (Do I smell a pseudo-cure for Asian Glow as well?) In other cases, rhino horns are being crushed and snorted like cocaine, sprinkled on food, or mixed with alcoholic cocktails as over-the-top displays of wealth popular among Vietnam’s “nouveaux riches.” By linking rhino horns with status symbols, the affluent are only driving up prices. Unfortunately for rhinos, as the price for their horns go up, so does the incentive for poachers. 

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Featured image: 

untitled (Walter Corno) / CC BY-NC-SA 3.0

References:

1. But PP, Lung LC, Tam YK. Ethnopharmacology of rhinoceros horn. I: Antipyretic
effects of rhinoceros horn and other animal horns. J Ethnopharmacol. 1990
Sep;30(2):157-68. PubMed PMID: 2255207.

2. But PP, Tam YK, Lung LC. Ethnopharmacology of rhinoceros horn. II: Antipyretic
effects of prescriptions containing rhinoceros horn or water buffalo horn. J
Ethnopharmacol. 1991 May-Jun;33(1-2):45-50. PubMed PMID: 1943172.

3. Laburn HP, Mitchell D. Extracts of rhinoceros horn are not antipyretic in
rabbits. J Basic Clin Physiol Pharmacol. 1997;8(1-2):1-11. PubMed PMID: 9363565.

 

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