CULICOIDES GENE DISCOVERY PROJECT REVEALS PUTATIVE PHARMACOLOGICAL FACTORS IN MIDGE SALIVA

Authors: Campbell, Corey; VANDYKE, KIRK - UNIVERSITY OF WYOMING; Letchworth, Geoffrey; Drolet, Barbara; Wilson, William - Bill

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/1/2004
Publication Date: 11/1/2004
Citation: Campbell, C.L., Vandyke, K., Letchworth, G., Drolet, B.S., Wilson, W.C. 2004. Culicoides gene discovery project reveals putative pharmacological factors in midge saliva [abstract]. Entomological Society of America.

Interpretive Summary: Culicoides sonorensis is a biting midge that transmits virus (bluetongue and epizootic hemorrhagic disease virus) diseases to animals, such as cows and deer. The only time that these viruses are transmitted to animals is through an insect bite. Thus the insects are referred to as disease vectors. The insects pick up the virus by biting an infected host animal. Before the virus can be transferred to a new host animal, the virus must first successfully infect the vector insect and move from the initial infection site, the gut, to the salivary glands for a subsequent bite. For this reason, we are especially interested in learning how the virus infects the insect gut. Some scientists postulate that variations in the insect's ability to be infected with a virus and then transmit it to another animal host may be caused by either differences in the environment or genetic differences between individual insects. It is also possible that a combination of these two factors play a part in whether an individual insect can successfully transmit the virus. Increased knowledge about the insect gut and how the virus invades and grows in it will make it possible to devise ways to prevent virus spread to the salivary glands. For these reasons, we have chosen to sequence and catalog expressed genes (cDNAs) from salivary tissues of this biting midge. This sequence information will provide us with new tools that will be useful for a variety of purposes, from evolutionary comparisons with other disease vector insects to functional studies to determine the roles played by genes enabling the spread of viruses. We chose to generate a high volume, low quality sequence collection. These are known as expressed sequence tags or ESTs. Conceptual translation of this expressed sequence tag collection revealed many putative pharmacologically-relevant proteins. Possible functional groups include allergens and factors that affect the host immune response. One such group is a novel class of short D7-related proteins, a diverse class of proteins of unknown function belonging to the odorant/pheromone binding family. Another group comprises a new class of putative coagulation inhibitors bearing the Kunitz_BPTI protease inhibitor domain. The potential significance of this cDNA collection to future studies of virus/vector/host interactions will be described.

Technical Abstract: Culicoides biting midges are economically-important vectors of livestock viruses (arboviruses) and medically-important vectors of human filarial or virus pathogens. In North America, Culicoides spp. transmit bluetongue and epizootic hemorrhagic disease viruses to domestic and wild ruminants. Studies of other arthropods suggest that vector saliva potentiates establishment of arbovirus infection in mammalian hosts, even in the absence of viremia. In addition to transmitting pathogens, midge biting activity may also cause other animal health problems. For example, Culicoides salivary allergens cause type I hypersensitivity in horses, known as sweet itch, and may cause similar responses in other animals, as well. In order to generate tools for future elucidation of these conditions, we generated a cDNA library from adult female salivary glands and performed single pass DNA sequencing. Conceptual translation of this expressed sequence tag collection revealed many putative pharmacologically-relevant proteins. Possible functional groups include allergens and immunomodulatory factors. One such group is a novel class of short D7-related proteins, a diverse class of proteins of unknown function belonging to the odorant/pheromone binding family. Another group comprises a new class of putative coagulation inhibitors bearing the Kunitz_BPTI protease inhibitor domain. The potential significance of this cDNA collection to future studies of virus/vector/host interactions will be described.