PRESS RELEASE

SPANISH PARTICIPATION IN THE SEQUENCING OF THE MOSQUITO (Culex quinquefasciatus) GENOME

• Researchers from the Centre for Genomic Regulation (CRG), along with other Spanish groups, have participated in an international sequencing project for one species of mosquito from the genus Culex.
  
  
• The work, published in the journal Science, collected the sequence of Culex quinquefasciatus, one of the most widespread mosquitoes in tropical and temperate regions, which acts as a vector for several diseases.
  
  
• The sequencing of the genus Culex establishes a platform for the comparative study of the genomes of those mosquitoes which transmit the most diseases. Previously the genus Anopheles (which transmits malaria) and Aedes (which transmits dengue fever) had been sequenced.

Mosquitoes are the main vectors of human diseases, especially in temperate and tropical regions. They are responsible for the transmission of diseases such as malaria (Anopheles), dengue and yellow fever (Aedes), several kinds of encephalitis and lymphatic filariasis (Culex, Aedes, Anopheles), among others.

Previously, one species of mosquito from the genus Anopheles and one from Aedes had been sequenced. With the sequencing of Culex quinquefasciatus, the reference genomes for the three most important disease-transmitting mosquitoes on the planet have been completed. Specifically, Culex is the most diverse of the mosquito genera (it is comprised of more than 1200 described species) and the most geographically widespread. Mosquitoes of the genus Culex act as vectors for various diseases, particularly West Nile encephalitis and lymphatic filariasis.

Roderic Guigó, head of the Bioinformatics and Genome group of the Centre for Genomic Regulation (CRG) asserts that “the sequence of Culex provides us with a very good library of genes for the comparative study of mosquito genomes”. “We hope that the study of these genomes will give us the key to an in-depth understanding of mosquito biology and allow us to decrease their activity as the vectors of so many diseases”, concludes Guigó.

The work, which is published in Science, reveals that the genome of C. quinquefasciatus is composed of 18,883 genes which code for proteins and is 22% bigger than that of Aedes aegypti and up to 52% bigger than that of Anopheles gambiae. The researchers observed that the increase in the Culex genome, compared with the other two genera sequenced, corresponds to the expansion of certain gene families. Specifically, the work indicates that these families with greater representation are related to taste and olfactory receptors, genes related to the immune system and genes with possible detoxification functions.

What does the Culex quinquefasciatus genome have that the others lack?

The accurate analysis of the expanded gene families could explain some of the evolutionary advantages of this mosquito such as its widespread distribution.

The gene families related to detoxification could indicate better adaptation of the larvae of this mosquito to pollution and even resistance to insecticides.

In relation to a sense of smell, C. quinquefasciatus has the largest number of olfactory receptors of any dipteran species studied to date. This makes this mosquito capable of detecting possible prey on which to feed. At the same time, the great variety of taste receptors means that it is able to feed from diverse prey (birds, livestock and humans).

Finally, C. quinquefasciatus also has a wide range of proteins which may be linked to the capacity of the mosquito to suck blood without the host noticing and to reduce the coagulating activity of the blood.

The Culex quinquefasciatus genome sequencing project was led by investigators from the University of California and included participation from the Bioinformatics and Genome group from the Centre for Genomic Regulation (CRG) in Barcelona, directed by Roderic Guigó. This group worked on the prediction of the genes in the Culex genome. Other Spanish researchers, from the University Hospital Complex in Santiago, the Institute of Biomedical Investigation in Bellvitge (IDIBELL), the Gallician Public Foundation for Genomic Medicine and the University of A Coruña, also participated in the study. José Tubío, responsible for the project in Galicia and who now works at the Centre for Genomic Regulation (CRG), explains that “the Gallician group conducted the annotation of repetitive sequences called transposable elements, which was crucial for the correct later identification of the genes in the genome of this mosquito”. Tubío also participated in the sequencing of Aedes and has focused his work over the last few years on the study of various disease-transmitting insects.

Reference work: Arensburger, P et al. (2010). “Sequencing of Culex quinquefasciatus Establishes a Platform for Mosquito Comparative Genomics”. Science. DOI: 10.1126/science.1191864.

For more information: Laia Cendrós, Dept. Comunicació i RRPP. Centre de Regulació Genòmica (CRG), Dr. Aiguader, 88 – Edif. PRBB, 08003 Barcelona. Tel. +34 93 316 02 37.