Contributed by Guest Blogger: C. Romero ’14
Recent research has shown that microRNA miR-275 in the Aedes aegypti mosquito is necessary for blood digestion and egg development. A. aegypti is the most common vector of arboviruses, or ARthropod-BOrne viruses, which include the dengue fever and yellow fever viruses that infect millions and kill thousands each year. Mosquitoes require vertebrate blood to produce eggs, making them good vectors for human diseases. Blood feeding and egg maturation occur in cycles, where blood feeding is required to trigger a step in the process of egg production. In A. aegypti, researchers from University of California, Riverside led by Alexander Raikhel found that miR-275 plays a critical role in this regulatory system.
MicroRNA is a relatively recent discovery, having been first identified in 1993. It appears as if their primary function is post-transcriptional regulation, in which microRNA sequences bind to complementary mRNA. The outcome has come to be known as translational repression or gene silencing, where mRNA is kept from reaching ribosomes and producing proteins, thus interrupting gene expression.
The researchers developed a RNA inhibitor specific to the microRNA molecule, known as an antagomir, to bind to miR-275 before it could silence its corresponding mRNA. By injecting female A. aegypti with this antagomir, blood digestion, fluid excretory function and egg production were all severely inhibited.
This discovery opens new doors to control of the spread of arboviruses, where removal of a single tiny molecule can limit the mosquito’s function at a fundamental level.
Many new questions arise from this research, some of which are already pending investigation by Raikhel’s UC Riverside team. The researchers plan on looking into the particular mRNA that miR-275 targets, and thus find the genes that regulate the blood-meal-mediated egg maturation cycle and see what role they play. Raikhel also plans on looking into the mechanism that underlies the activation of miR-275.
Further off, however, are considerations of how to bring this finding into the real world with a new mosquito control method. New innovations in microRNA research will surely bring us closer to harnessing its power, much as the scientific community has done in DNA genetics.
Contributed by Guest Blogger: L. Herrera-Torres ’14
Like in several other landforms in tropical regions, Puerto Rico is victim to seasonal increases in the Dengue fever and West Nile Virus, which are transmitted via the mosquitoes Aedes aegypti and Culex quiquefasciatus respectively. In order to test whether or not active septic tanks with raw sewage provide an adequate environment for the development of mosquitoes (particularly Aedes aegypti) and therefore aid in the spread of these diseases, a test was conducted in a southern municipality of Puerto Rico, called Salinas. In the community of Playa-Playita 89 septic tanks with varying structural integrity and water quality were sampled for the presence and abundance of mosquito larvae using floating funnel traps and 93 septic tanks were tested for the presence and abundance of adult mosquitoes using screened, plastic emergence traps.
Predictably, Culex quinquefasciatus, the vector of West Nile virus, which has been proven to thrive in polluted waters, was found in 74% of the septic tanks in larval form and in 97% in adult form. However, the results of vector for Dengue fever (the main focus of the experiment) were more surprising.
Previously Ae. Aegypti was known to be well adapted to urban areas and were often found in artificial containers, but it was still generally accepted that these larvae developed in clean water. However in 18% of the septic tanks sampled revealed that Ae. Aegypti was present in this water despite its contamination and had a positive association with the cracking of septic tank walls, uncapped tanks, and larger tank surface area. Similar results were found for Ae. Aegypti adults. 49% of the tanks showed both their presence and abundance as well as their positive correlation with cracking, uncapping, and septic water pH. The correlation between the amount of larvae collected from the septic tanks and the amount of adult mosquitoes recorded strongly insinuates that this environment is conducive to mosquito reproduction and development and is not just a resting place as others have suggested.
These findings led the researchers to believe that Ae. Aegypti can develop in sewage water and that septic tanks provide ideal conditions for mosquito productivity and can serve as potential to maintain dengue transmission during the dry season.