A team of international scientists has put together the first draft of the complete genome (DNA map) of the Aedes aegypti mosquito, which transmits dengue and yellow fever and other serious tropical diseases, and is second only to the malaria-carrying Anopholes mosquito in terms of worlwide infection rates.
The results of their study is published in the early online edition of Science Express.
The hope is that by knowing more about the DNA of the Aedes aegypti mosquito, further research can now proceed to develop better insecticides or even create genetically modified versions that can’t carry dengue, yellow fever and other harmful viruses.
The study was led by Vishvanath Nene at The Institute for Genomic Research (TIGR) in Rockville, Maryland, and David Severson at the University of Notre Dame, Indiana, both in the United States.
Nene and Severson were joined by a team of researchers from 24 worldwide universities and institutions in countries like Brazil, France, Germany, Ireland, Spain, Switzerland and the UK, as well as other US research centres.
The Aedes aegypti genome is five times the size of the malaria mosquito genome and also more complex to unravel.
One of the challenging tasks the team faced in “cracking the code” involved annotating transposable elements of the Aedes aegypti mosquito’s genome.
Transposable elements are important bits of genetic material (nucleic acid) that move around the genome and also control its structure and size.
To illustrate the complexity of this project, one of the transposable elements, called Feilai, has more than 50,000 copies of it interspersed in the Aedes aegypti genome and altogether, the scientists uncovered and described more than 1,000 transposable elements.
50 per cent of the genome of Aedes aegypti is made up of transposable elements compared with only 25 per cent of the malaria-carrying Anopheles.
Transposable elements, also called TEs, could be developed as genetic tools to examine the way mosquitoes and pathogens interact, and this could help scientists develop ways to control transmisssion of disease, said Zhijian (Jake) Tu, associate professor in the Department of Biochemistry at Virginia Tech in the US.
“By introducing TEs in a more or less random way to see what happens to the laboratory mosquitoes, the TEs become a tool to study the genetic mechanism of mosquito-virus interaction, to help us understand mosquito biology and reveal new ways to interfere with disease transmission,” explained Tu.
Another key task was validating the 15,000 or so protein coding genes in the mosquito’s genome. Jinsong Zhu, assistant professor of biochemistry at Virginia Tech who worked on this part of the project explained:
“An important part of this project is gene annotation which predicts numbers and locations of mosquito genes in the genome. In parallel to sequencing DNA in chromosomes, scientists have also sequenced large amounts of messenger RNAs collected from different mosquito tissues at distinct developmental stages. Matching a messenger RNA to a predicted gene will validate authenticity of this gene.”
Dengue fever and dengue hemorrhagic fever (DHF) are acute diseases accompanied by fever that occur in the tropics in the same regions as malaria. The virus spreads through Aedes aegypt mosquitoes that bite at sunrise and just before sunset. There are many variants of the virus which are sufficiently different as to offer a person who has had it once no immunity to the next infection.
Although in 2005 there were just over 230,000 reported cases of dengue fever worldwide and 1,600 deaths, the World Health Organization (WHO) suggests the actual infection rate is more likely to be around 50 million cases a year. This would make it the most prevalent mosquito-borne disease after malaria. It is the leading cause of death among children in several South East Asian countries.
Yellow fever, also called yellow jack or black vomit, is a virus that also causes hemorrhagic illness in Africa, South and Central America, and the Caribbean. The yellow refers to the fact the illness makes the skin appear jaundiced. It has a complicated route to epidemic, remaining deceptively dormant for some years before erupting in a human population. For instance, in South American rain forests it infects treetop monkeys via another type of mosquito called Haemagogus and when the trees are cut down woodcutters become infected via Haemagogus and then the Aedes mosquito passes it on from them to the rest of the population.
“Genome Sequence of Aedes aegypti, a Major Arbovirus Vector.”
Vishvanath Nene, Jennifer R Wortman, Daniel Lawson, et al.
Published Online in Science Express, May 17, 2007.
Science DOI: 10.1126/science.1138878
Written by: Catharine Paddock
Writer: Medical News Today