Endocrinology of Mosquito Reproduction
Endocrinology of Mosquito Reproduction
Knowledge of chemical messengers and their actions in female mosquitoes will point to mechanisms that can be targeted for the development and application of novel genetic or chemical controls.
Several million people around the world are infected with nematodes, malaria, and viruses that are carried by mosquitoes, and hundreds of thousands, especially children, die each year from the effects of such parasites. These parasites develop and divide only in female mosquitoes, which require a blood meal for egg maturation, and the inoculum of infection for mosquitoes and humans is the blood meal.
My research program focuses on the hormonal regulation of reproduction in female mosquitoes and contributes to a fundamental understanding of the interaction between mosquitoes and their parasites. Our objectives are to determine the structure and function of neuropeptides and other hormones and their action through receptors and signal transduction pathways. Knowledge of chemical messengers and their actions in female mosquitoes will point to mechanisms that can be targeted for the development and application of novel genetic or chemical controls.
Below is a summary of our progress this year.
1. Two types of neuropeptides, ovary ecdysteroidogenic hormone and insulin-like peptides (ILPs), are known to stimulate egg development after blood ingestion by females of the yellow fever mosquito (Aedes aegypti), but their roles in Anopheles mosquitoes that transmit malaria have not been resolved. Genes encoding such peptide hormones exist in Anopheles species, but the bioactive peptide form and function had not been established. We extracted and characterized the structure of one ILP from the heads of Anopheles stephensi adults. The peptide was synthesized in a form predicted to be bioactive, and it along with the isolated native form stimulated ecdysteroid production by ovaries from this and a related species, as well as Aedes and Culex species. Ecdysteroid hormones are required for egg development in mosquitoes. These results are the first to establish that the function of the ILP is conserved across the major mosquito genera that transmit different pathogens to humans and animals. This work was published this year.
Nuss, A. B. and Brown, M. R. 2017 Isolation of an insulin-like peptide from the Asian malaria mosquito, Anopheles stephensi, that acts as a steroidogenic gonadotropin across diverse mosquito taxa. General and Comparative Endocrinology available online at https://doi.org/10.1016/j.ygcen.2017.05.007.
2. There is a great need for a reliable and inexpensive assay of ecdysteroid hormone levels in insects, especially in regard to our research. We produced antisera that recognize the predominant forms and developed a protocol for their use in enzyme linked immunoassays. To validate the immunoassays, we extracted ecdysteroids from mosquitoes following established protocols, but the amounts measured in different numbers of individuals failed to scale. A variety of solvents and extraction steps were tested to overcome this problem, and one method was settled upon that enhances recovery efficiency and quantification in the immunoassays. This work was recently published (see below), and two companies that market antibodies and immunoassays have obtained licenses from the UGA Research Foundation to market the antisera we produced. We expect the antisera and extraction protocol will be of great use to the community of insect and arthropod endocrinologists.
McKinney, D. A., Strand, M. R., and Brown, M. R. 2017 Evaluation of ecdysteroid antisera for a competitive enzyme immunoassay and extraction procedures for the measurement of mosquito ecdysteroids. General and Comparative Endocrinology 253:60-69.
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