photo credit: James D. Gathany/CDC
Over 200 million people are infected by malaria each year, and the majority of the 627,000 deaths per year are children younger than five. The disease is carried by mosquitos who act as vectors for the parasite. It’s only transmitted to humans by female mosquitoes, as they’re the only ones who bite. A team of researchers led by Andrea Crisanti of the Imperial College London managed to genetically modify mosquitos to produce 95% male offspring, eliminating mosquito populations along with the risk of malaria. The results of the study were published in Nature Communications.
In most species of mosquito, the females need a blood meal in order to acquire the nutrients to create viable eggs. When she does, she can lay about 200 eggs at a time in water, and up to 3,000 eggs over the course of her lifetime. About half of those offspring will be daughters, many of whom will live long enough to produce that amount of offspring also. For humans living near mosquitos carrying the parasite that causes malaria, those numbers of female mosquitos present a very real threat.
But what if the numbers could be skewed so that the sex ratio favors males, who are harmless to humans? This is exactly what Crisanti’s team set out to do with Anopheles gambiae, a species of mosquito endemic to sub-Saharan Africa, where 95% of malaria deaths occur. The researchers modified the males with the enzyme I-Ppol, which excises the X chromosome during spermatogenesis. This renders sperm that would produce daughters to be non-functional, while the sperm that will create male offspring are unaffected. As a result, about 95% of the resulting offspring are male.
Next, modified males were introduced to five caged wild-type populations. As the males mated with the females, they passed along the same mutation until it dominated the population. For four of the five populations, it took only six generations for the mosquitos to die out due to a lack of females.
“What is most promising about our results is that they are self-sustaining,” co-author Nikolai Windbichler said in a press release. “Once modified mosquitoes are introduced, males will start to produce mainly sons, and their sons will do the same, so essentially the mosquitoes carry out the work for us.”
This study was the first to successfully manipulate mosquito sex ratios, and it was done in a big way. The researchers hope that this information will be used to develop genetic mutations to be used in the wild, bringing large populations of mosquitos to their knees.
“The research is still in its early days, but I am really hopeful that this new approach could ultimately lead to a cheap and effective way to eliminate malaria from entire regions,” added lead author Roberto Galizi. “Our goal is to enable people to live freely without the threat of this deadly disease.”
Of course, while eradicating the mosquitos would be fantastic for eliminating the threat of malaria, what other affects would it have? Wouldn’t there be harsh consequences for the ecosystem? After all, mosquitos have been on the planet for about 100 million years and represent 3,500 species. As it turns out, mosquitos wouldn’t really be missed if they were to disappear. While mosquitos can act as pollinators as well as a food source for other animals, their absence would be merely a temporary setback before another species filled the niche. Of course, there is a gamble in assuming the replacement organism would be harmless.
“Malaria is debilitating and often fatal and we need to find new ways of tackling it. We think our innovative approach is a huge step forward. For the very first time, we have been able to inhibit the production of female offspring in the laboratory and this provides a new means to eliminate the disease,” Crisanti explained.
Each year, sub-Saharan Africa loses about $12 billion in economic productivity due to malarial infections. Considering developed areas in these countries have per capita incomes of about US$1500, this would have very real implications for the quality of life for people in those areas. Eliminating that disease would also allow doctors and hospitals to address other health concerns, and the environment would likely benefit from not having to use insecticides.
Galizi, R. et al. 2014. ‘A synthetic sex ratio distortion system for the control of the human malaria mosquito’. Nature Communications, 10 June 2014.
How Deadly Marburg Virus Silences Immune System: Breakthrough Findings Point to Targets for Drugs and Vaccines
Scientists at The Scripps Research Institute have determined the structure of a critical protein from the Marburg virus, a close cousin of Ebola virus. These viruses cause similar diseases and are some of the deadliest pathogens on the planet, each killing up to 90 percent of those infected.
The Marburg virus VP35 protein (beige) surrounds the virus’s double-stranded RNA (blue), masking it from immune system detection. (Credit: Image by Christina Corbaci, The Scripps Research Institute) (up)
Described in the Sept. 13, 2012 publication of the journal PLoS Pathogens, the new research reveals how a key protein component of the Marburg virus, called VP35, blocks the human immune system, allowing the virus to grow unchecked. The structure provides a major step forward in understanding how the deadly virus works, and may be useful in the development of potential treatments for those infected.
“The immune system is designed to recognize certain hallmarks of virus infection,” said Erica Ollmann Saphire, the Scripps Research scientist who led the effort. “When these are sensed, an immediate antiviral defense is launched. However, the Marburg and Ebola viruses mask the evidence of their own infection. By doing so, the viruses are able to replicate rapidly and overwhelm the patient’s ability to launch an effective defense.”
Ebola virus outbreaks have occurred in the last month in both Uganda and the Democratic Republic of the Congo, while Marburg virus broke out in Angola in 2005 to 2006 and again in Uganda in 2007. The Angolan Marburg virus outbreak began in a pediatric ward and killed 88 percent of those it infected. The virus has since been imported into the United States (Colorado) and the Netherlands by tourists who had visited Africa.
There is currently no cure for Marburg hemorrhagic fever. The virus is spread when people come into contact with the bodily fluids of a person or animal who is already infected. The best treatment consists of administering fluids and taking protective measures to ensure containment, like isolating the patient and washing sheets with bleach.
Most people, however, die within two weeks of exposure from a combination of dehydration, massive bleeding, and shock. A smaller number of people have stronger and immediate immune responses against the virus and survive.
A New Roadmap for Defense
The breakthrough described in the PLoS Pathogens article explains a key reason why the viruses are so deadly and provides the necessary templates to develop drugs to treat the infection.
The study’s lead author, Research Associate Shridhar Bale, explains that a key signature of Marburg virus infection is the double-stranded RNA that results from its replication inside cells. When human immune system proteins detect this virus-specific RNA, they sound an alarm to signal the rest of the immune system to respond. The new research describes how the VP35 protein of the Marburg virus binds to the viral double-stranded RNA and hides it to prevent the alarm from being sounded.
The new research also revealed a surprise. Images from the Marburg virus reveal the VP35 protein spirals around the double-stranded RNA, enveloping it completely. This is in contrast to previous images of the similar VP35 protein from Ebola virus that showed it only capping the ends of the RNA, leaving the center of the RNA helix exposed for possible recognition.
In addition to Ollmann Saphire and Bale, the article, “Marburg virus VP35 can both fully coat the backbone and cap the ends of dsRNA for interferon antagonism,” was authored by Jean-Philippe Julien, Zachary A. Bornholdt, Michelle A. Zandonatti, Gerard J.A. Kroon, Christopher R. Kimberlin, Ian J. MacRae, and Ian A. Wilson of The Scripps Research Institute, and Peter Halfmann, John Kunert, and Yoshihiro Kawaoka of the University of Wisconsin.
Support for the research was provided by grants from the Burroughs Wellcome Fund and The Skaggs Institute for Chemical Biology at Scripps Research.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Bale S, Julien J-P, Bornholdt ZA, Kimberlin CR, Halfmann P, et al. Marburg Virus VP35 Can Both Fully Coat the Backbone and Cap the Ends of dsRNA for Interferon Antagonism. PLoS Pathog. PLoS Pathogens, 2012; 8(9): e1002916 DOI: 10.1371/journal.ppat.1002916
Between 50 million and 100 million dengue infections occur each year, according to the World Health Organization.
VIRUS CARRIER: This picture shows the presence of the dengue virus in the mosquitoes’ chemosensory (antennae and palp) and feeding organs (proboscis). (Photo: Johns Hopkins Bloomberg School of Public Health)
Mosquitoes are already blood-sucking machines, but new research indicates that the dengue virus, which the mosquitoes transmit to humans, makes them even thirstier for blood.
The virus specifically turns on mosquito genes that make them hungrier for a blood meal; the activated genes also enhance mosquitoes’ sense of smell, something that likely improves their feeding skills. The result is a mosquito better able to serve the virus by carrying it more efficiently to human hosts.
“The virus may, therefore, facilitate the mosquito’s host-seeking ability, and could — at least theoretically — increase transmission efficiency, although we don’t fully understand the relationships between feeding efficiency and virus transmission,” study researcher George Dimopoulus, of the Johns Hopkins Bloomberg School of Public Health, said in a statement. “In other words, a hungrier mosquito with a better ability to sense food is more likely to spread dengue virus.”
The virus doesn’t hurt the mosquitoes that carry it, a specific species called Aedes aegypti, but it lives in them. When the mosquito bites a human, it spreads the deadly disease through its saliva. More than 2.5 billion people live in areas where dengue fever-infected mosquitoes live. The World Health Organization estimates that between 50 million and 100 million dengue infections occur each year.
The researchers analyzed the mosquito genes before and after being infected with the virus, finding changes in 147 genes. These post-infection genes make proteins that are involved in processes that include virus transmission, immunity, blood feeding and host seeking, they found.
“Our study shows that the dengue virus infects mosquito organs, the salivary glands and antennae that are essential for finding and feeding on a human host,” Dimopoulus said. “This infection induces odorant-binding protein genes, which enable the mosquito to sense odors.”
“We have, for the first time, shown that a human pathogen can modulate feeding-related genes and behavior of its vector mosquito, and the impact of this on transmission of disease could be significant,” Dimopoulos said.
This is just one of many recent examples of a parasite taking control of an animal for its own benefit. Other examples include a fungus that turns ants into zombiesand a virus that causes caterpillars to dissolve and then rain virus particles down on other potential hosts.
The study was published on March 29 in the journal PLoS Pathogens.
http://www.mnn.com/earth-matters/animals/stories/dengue-virus-increases-mosquitos-lust-for-blood by Jennifer Welsh, LiveScience
Sim S, Ramirez JL, Dimopoulos G (2012) Dengue Virus Infection of the Aedes aegypti Salivary Gland and Chemosensory Apparatus Induces Genes that Modulate Infection and Blood-Feeding Behavior. PLoS Pathog 8(3): e1002631. doi:10.1371/journal.ppat.1002631
(left) Drosophila Orb2 plays an important role in the persistence of memory. Upon stimulation, Orb2 (shown in yellow) forms amyloid-like oligomers (shown in red), which are an essential ingredient for the formation of long-term memory. Credit: Illustration: Nicolle Rager Fuller, Sayo-Art
Memories in our brains are maintained by connections between neurons called “synapses”. But how do these synapses stay strong and keep memories alive for decades? Neuroscientists at the Stowers Institute for Medical Research have discovered a major clue from a study in fruit flies: Hardy, self-copying clusters or oligomers of a synapse protein are an essential ingredient for the formation of long-term memory.
The finding supports a surprising new theory about memory, and may have a profound impact on explaining other oligomer-linked functions and diseases in the brain, including Alzheimer’s disease and prion diseases.
“Self-sustaining populations of oligomers located at synapses may be the key to the long-term synaptic changes that underlie memory; in fact, our finding hints that oligomers play a wider role in the brain than has been thought,” says Kausik Si, Ph.D., an associate investigator at the Stowers Institute, and senior author of the new study, which is published in the January 27, 2012 online issue of the journal Cell.
Si’s investigations in this area began nearly a decade ago during his doctoral research in the Columbia University laboratory of Nobel-winning neuroscientist Eric Kandel. He found that in the sea slug Aplysia californica, which has long been favored by neuroscientists for memory experiments because of its large, easily-studied neurons, a synapse-maintenance protein known as CPEB (Cytoplasmic Polyadenylation Element Binding protein) has an unexpected property.
A portion of the structure is self-complementary and—much like empty egg cartons—can easily stack up with other copies of itself. CPEB thus exists in neurons partly in the form of oligomers, which increase in number when neuronal synapses strengthen. These oligomers have a hardy resistance to ordinary solvents, and within neurons may be much more stable than single-copy “monomers” of CPEB. They also seem to actively sustain their population by serving as templates for the formation of new oligomers from free monomers in the vicinity.
CPEB-like proteins exist in all animals, and in brain cells they play a key role in maintaining the production of other synapse-strengthening proteins. Studies by Si and others in the past few years have hinted that CPEB’s tendency to oligomerize is not merely incidental, but is indeed essential to its ability to stabilize longer-term memory. “What we’ve lacked till now are experiments showing this conclusively,” Si says.
In the new study, Si and his colleagues examined a Drosophila fruit fly CPEB protein known as Orb2. Like its counterpart in Aplysia, it forms oligomers within neurons. “We found that these Orb2 oligomers become more numerous in neurons whose synapses are stimulated, and that this increase in oligomers happens near synapses,” says lead author Amitabha Majumdar, Ph.D., a postdoctoral researcher in Si’s lab.
The key was to show that the disruption of Orb2 oligomerization on its own impairs Orb2’s function in stabilizing memory. Majumdar was able to do this by generating an Orb2 mutant that lacks the normal ability to oligomerize yet maintains a near-normal concentration in neurons. Fruit flies carrying this mutant form of Orb2 lost their ability to form long-term memories. “For the first 24 hours after a memory-forming stimulus, the memory was there, but by 48 hours it was gone, whereas in flies with normal Orb2 the memory persisted,” Majumdar says.
Si and his team are now following up with experiments to determine for how long Orb2 oligomers are needed to keep a memory alive. “We suspect that they need to be continuously present, because they are self-sustaining in a way that Orb2 monomers are not,” says Si.
The team’s research also suggests some intriguing possibilities for other areas of neuroscience. This study revealed that Orb2 proteins in the Drosophila nervous system come in a rare, highly oligomerization-prone form (Orb2A) and a much more common, much less oligomerization-prone form (Orb2B). “The rare form seems to be the one that is regulated, and it seems to act like a seed for the initial oligomerization, which pulls in copies of the more abundant form,” Si says. “This may turn out to be a basic pattern for functional oligomers.”
The findings may help scientists understand disease-causing oligomers too. Alzheimer’s, Parkinson’s and Huntington’s disease, as well as prion diseases such as Creutzfeldt-Jakob disease, all involve the spread in the brain of apparently toxic oligomers of various proteins. One such protein, strongly implicated in Alzheimer’s disease, is amyloid beta; like Orb2 it comes in two forms, the highly oligomerizing amyloid-beta-42 and the relatively inert amyloid-beta-40. Si’s work hints at the possibility that oligomer-linked diseases are relatively common in the brain because the brain evolved to be relatively hospitable to CPEB proteins and other functional oligomers, and thus has fewer mechanisms for keeping rogue oligomers under control.
The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Stowers Institute for Medical Research press release
Original Research: Abstract for “Critical Role of Amyloid-like Oligomers of Drosophila Orb2 in the Persistence of Memory” by Amitabha Majumdar, Wanda Colón Cesario, Erica White-Grindley, Huoqing Jiang, Fengzhen Ren, Mohammed “Repon” Khan, Liying Li, Edward Man-Lik Choi, Kasthuri Kannan, Fengli Guo, Jay Unruh, Brian Slaughter, and Kausik Si in Cell
Science is bringing some understanding of the heritability, prevalence, and inner workings of one of the most devastating diseases.(left) A PET scan’s bright areas reveal the concentration of amyloid beta, a protein that forms a plaque in Alzheimer’s patients. The scan compares the brains of a healthy patient (left) and a patient suffering from Alzheimer’s (right). Image: Alzheimer’s Disease Education and Referral Center, NIH
This has been a big week in Alzheimer’s news as scientists put together a clearer picture than ever before of how the disease affects the brain. Three recently published studies have detected the disease with new technologies, hinted at its prevalence, and described at last how it makes its lethal progress through the brain.
The existence of two forms of Alzheimer’s—early- and late-onset—has long baffled scientists. Of the estimated five million Americans who suffer from Alzheimer’s, only a few thousand are diagnosed with an early-onset form of the affliction, which affects people before the age of 65. This rare early-onset form is thought to be hereditary and scientists have associated multiple genetic mutations contributing to its occurrence. Late-onset Alzheimer’s, although more common, has been the bigger mystery. One variant of the APOE gene-—sometimes known as the Alzheimer’s gene—is linked to the late-onset disease. But the APOE gene, unlike dominant early-onset genes, does not determine whether a person will ultimately have dementia.
Now there’s evidence that late-onset Alzheimer’s has a genetic basis similar to that of early-onset Alzheimer’s. By sequencing select genes associated with the latter, along with frontotemporal dementia, researchers at Washington University in Saint Louis and other institutions found that patients with late-onset Alzheimer’s carry some of the same genetic mutations as those with the early-onset form. The evidence, published on Wednesday in PLoS ONE, bolsters the argument that the forms of Alzheimer’s that appear at different life stages should be classified as the same disease. As to why the disease appears earlier in some cases, the scientists speculated that those patients diagnosed relatively early in life carry more genetic risk factors for the disease.
This study’s use of rapid genetic sequencing, the authors noted, may provide a model for more precise identification of dementias. Within the study, the researchers identified patients who may have been misdiagnosed as having Alzheimer’s; the genes of these patients suggested that they had another type of dementia. Given the heritable component, patients with a family history could be screened to detect and diagnose Alzheimer’s early.
Other genetic research unveiled in the past week or so has shed light on the biological processes that underlie how Alzheimer’s affects the brain. Certain mutations may lead to an increased production of a protein called amyloid beta in the region of the brain that creates memory. This excess amyloid beta, naturally secreted by brain cells, then becomes a complex called an oligomer. These oligomers may interrupt the signals transmitted between neurons. As in other neurodegenerative diseases like Parkinson’s or Huntington’s, the spread of oligomers appears to be driving the disease process.
Oligomer-linked diseases are relatively common, in part because oligomers can also play an essential biological role in the brain. A recent investigation using fruit flies reveals that the presence of a specific oligomer is actually required for the flies to form long-term memories.
In an early stage of Alzheimer’s, the naturally secreted amyloid beta protein builds up as oligomers in the brain, which then go on to form larger aggregates called plaques. Later in the disease, another aberrant form of a protein called tau starts to build up, in the entorhinal cortex. Normally, tau helps provide structure crucial to neuron functioning. The buildup of tau, however, causes the protein to tangle and eventually kill brain cells. What was unknown until recently, however, was how the tau protein spreads through different brain regions.
Two studies—one to be published in Neuron and the other published in PLoS ONE on Wednesday—have answered this question using brain samples from mice genetically engineered to express tau as it occurs in the human brain. Using a staining technique to highlight tau’s distribution in the brain, they compared samples from mice of different ages to analyze how tau moved through brain cells over time. They found the protein spread from neuron to neighboring neuron, traveling along synapses.
Understanding how this protein moves may allow scientists to stop tau in its tracks. “This opens up a whole new world of biology,” says Columbia University’s Karen Duff, an author on the study published in PLoS ONE. Tau is implicated in 30 different forms of dementia. In addition, the movement of tau may be similar to the spread of oligomers associated with Parkinson’s and Huntington’s. Nonetheless, we are still a long way from a therapeutic solution and stopping tau, which comes at a relatively late stage of Alzheimer’s, might be a very limited therapy.
As the world’s population continues to age, Alzheimer’s becomes a threat to more of us with every passing day. Although we may not yet have new treatments from this work, the take-away on these findings is clear: If we really are going to win the war, or even a battle, against Alzheimer’s, we need basic research that can delve into the complex biology that contorts proteins and kills brain cells to find treatments for this disease.