Entomology: Personnel
Entomology Faculty
Mark R. BrownProfessor of Entomology Contact InformationAddress: Department of Entomology Phone: (706) 542-2317 |
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Courses Taught
ENTO 8250 Insect Physiology (syllabus)
ENTO 8570 Molecular Entomology (syllabus)
ENTO 8080 Topics in Insect Physiology and Biochemistry
Research Program
Funding
National Institutes of Health
United States Department of Agriculture
Lab Personnel
| Name | Position |
| Dan Fendley | Technician |
| Erin Baker | Technician |
Please contact Dr. Brown if you are interested in mosquito endocrinology and seek a position as a postdoctoral associate or graduate student. Funding for such positions may be available in the future.
Overview
Reproduction in female insects encompasses a highly regulated sequence of behavioral, metabolic, and synthetic processes that result in the production of eggs. As in all other animals, peptide hormones bind to cell receptors that activate signal transduction pathways to provide precise and short-term regulation of physiological processes, including the synthesis of steroid or juvenile hormones that also modulate reproduction. Mosquitoes are exceptional model systems for this research because each successive cycle of egg maturation begins with a blood meal and ends with egg deposition two to three days later. Blood provides females with nutrients for egg maturation and metabolic storage, thus enabling survival to initiate another cycle. Understanding the regulation of reproduction in mosquitoes will give us insight into how pathogens, such as malaria and arboviruses that are ingested in a blood meal from an infected host, can multiply in the female’s body during a reproductive cycle. Then, with another meal, the pathogens are transmitted to a different host, resulting in further dissemination.
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The primary objective of my research program is to characterize the structure and function of peptide hormones and their receptors that activate key reproductive processes in two mosquito species: the yellow fever mosquito, Aedes aegypti, and the African malaria mosquito, Anopheles gambiae. The development of genome databases for both species has greatly aided the identification of genes and cDNAs encoding such proteins. Tissue and hemolymph expression profiles during development and oogenesis in females are being defined for the peptides and receptors of interest. As well, the receptors have been expressed for ligand binding studies. Conservation of peptide signaling and function in both species is being evaluated with bioassays.
Riehle, M. A., S. F. Garczynski, J. W. Crim, C. A. Hill, and M. R. Brown. 2002. Neuropeptides and Peptide Hormones in Anopheles gambiae. Science 298: 172-175.
Aedes aegypti Head Peptide I (Aea-HP-I)
This is the first neuropeptide to be isolated from mosquitoes, and it is a member of the extensive "RFamide" family of animal neuropeptides. This peptide inhibits the host-seeking behavior of female Ae. aegypti, but its receptor has yet to be identified. The Aea-HP gene and its expression during development and a reproductive cycle have been characterized.
Brown, M. R., M. J. Klowden, J. W. Crim, L. Young, L. Shrouder, and A. O. Lea. 1994. Endogenous regulation of mosquito host-seeking behavior by a neuropeptide. J. Insect Physiol. 40: 399-406.
Stracker, T. H., S. Thompson, G. L. Grossman, M. A. Riehle, and M. R. Brown. 2002. Characterization of the AeaHP gene and its expression in the mosquito, Aedes aegypti (Diptera: Culicidae). J. Medical Entomology 39(2): 331-342. PDF file
Ovary Ecdysteroidogenic Hormone (OEH)
As the only steroidogenic gonadotropin identified in invertebrates to date, it is the functional equivalent of follicle-stimulating hormone and luteinizing hormone in vertebrates. Neurosecretory cells in the brain and abdominal ganglion secrete OEH into the hemolymph for several hours after a blood meal, and during this time, ovaries of female mosquitoes begin secreting ecdysteroid hormones in response to OEH. The rising titer of ecdysteroids stimulates the fat body to synthesize yolk proteins, which are stored in mature eggs and used during embryonic development. Because this peptide is present in larvae and males, it likely has other functions.
Brown, M. R., R. Graf, K. M. Swiderek, D. Fendley, T. H. Stracker, D. E. Champagne, and A. O. Lea. 1998. Identification of a steroidogenic neurohormone in female mosquitoes. J. Biol. Chem. 273: 3967-3971.
Brown, M. R. and C. Cao. Distribution of ovary ecdysteroidogenic hormone I in the nervous system and gut of mosquitoes. 13 pp. J. Insect Science 1.3—Online journal. PDF file
A new effort is underway to identify the proteins and enzymes involved in the biosynthesis of ecdysteroid hormones in the mosquito ovary, and as these elements are known, the regulation of their expression or activation by OEH is evaluated.
Sieglaff, D. H, K. A. Duncan, and M. R. Brown. 2005. Expression of genes encoding proteins involved in ecdysteroidogenesis in the female mosquito, Aedes aegypti. Insect Biochemistry and Molecular Biology 35: 369-514. PDF file
Insulin-Related Peptides (ILP's)
In vertebrates, insulins are important growth factors and multifunctional regulators of metabolism. For a few insect species, including the two mosquitoes of interest, sequences for ILPs are known, but their function is uncertain. Studies have shown that the development of malaria in mosquitoes was stimulated by the ingestion of vertebrate insulin. With immunocytochemistry, we have identified brain neurosecretory cells and midgut endocrine cells in larvae and adults that secrete ILPs. Now that nucleotide and amino acid sequences are known for ILPs in mosquitoes, we are investigating their regulatory roles.
In collaboration with Dr. Rolf Graf (University of Zurich, Switzerland), we showed that vertebrate insulins stimulate steroidogenesis and protein synthesis in mosquito ovaries and identified an insulin receptor in ovaries. This activation of steroidogenesis in ovaries is through a conserved insulin signaling pathway. Expression of the insulin receptor and a serine/threonine kinase, Akt—an intracellular regulatory nexus, have been described during development and egg maturation in female Aedes aegypti.
Graf, R., S. Neuenschwander, M. R. Brown, and U. Ackermann. 1997. Insulin mediated secretion of ecdysteroids from mosquito ovaries and molecular cloning of the insulin receptor homologue (MIR) from ovaries of bloodfed Aedes aegypti. Insect Molec. Biol. 6: 151-163.
Riehle, M. A. and Brown, M. R. 1999. Insulin stimulates ecdysteroid production through a conserved signaling cascade in the mosquito Aedes aegypti. Insect Biochem. Molec. Biol. 29: 855-860. PDF file
Cao, C. and M. R. Brown. 2001. Localization of an insulin-like peptide in brains of two flies. Cell and Tissue Research 304: 317-321. PDF file
Riehle, M. A. and M. R. Brown. 2002. Insulin receptor expression during development and a reproductive cycle in the ovary of the mosquito Aedes aegypti. Cell and Tissue Research 308(3): 409-420. PDF file
Riehle, M. A. and Brown, M. R. 2003. Molecular analysis of the serine/threonine kinase Akt and its expression in the mosquito, Aedes aegypti. Insect Molecular Biology 12(3): 225-232. PDF file
Krieger, M. B. J., Jahan, N., Riehle, M. A., Cao, C., and Brown, M. R. 2004. Molecular characterization of insulin-like peptide genes and their expression in the African malaria mosquito, Anopheles gambiae. Insect Molecular Biology 13: 305-315. PDF file
Wu, Q. and M. R. Brown. 2006. Signaling and function of insulin-like peptides in insects. Annual Review of Entomology, Vol. 51, 1-24. PDF file
Riehle, M. A., Y. Fan, C. Cao, and M. R. Brown. 2006. Molecular characterization and developmental expression of insulin-like peptides in the yellow fever mosquito, Aedes aegypti. Peptides in press. PDF file
Neuropeptide F
The midgut endocrine system of insects is an important source of peptide hormones, which are presumed to regulate appetite and digestion in the same ways as gut peptides in vertebrates. A second objective of my research program is to identify specific peptides originating from this system in insects and to define their regulatory roles. Progress in this area is the result of a long standing collaboration with Dr. Joe Crim (Cellular Biology, University of Georgia).
This work began with a description of the midgut endocrine system in the corn earworm, Helicoverpa zea. Subsequently, a short peptide was isolated from larval midguts that has tantalizing similarity to the neuropeptide Y (NPY) family in vertebrates. With an immunoassay specific for this H. zea peptide, we obtained a peptide from an extract of Drosophila melanogaster that is an authentic member of the aforementioned family, which also includes the neuropeptide Fs (NPF) identified in other invertebrates. The Drosophila peptide was the first NPF to be identified in arthropods. As with the NPY family in vertebrates, NPF is expressed in specific cells in the brain and gut of all Drosophila life stages. Information obtained from our Drosophila studies led to the identification of related NPFs in Aedes aegypti and Anopheles gambiae. The expression of the mosquito NPFs has been reported, along with the identification of their G-protein coupled receptors. Future studies seek to discover specific functions for NPF signaling in mosquitoes.
Brown, M. R. and A. O. Lea. 1990. Neuroendocrine and midgut endocrine systems in the adult mosquito. In Advances in Disease Vector Research, Vol. 6, Ed. K. F. Harris, p. 29-58.
Huang, Y-Q, M. R. Brown, T. D. Lee, and J. W. Crim. 1998. RF-amide peptides isolated from the midgut of the corn earworm, Helicoverpa zea, resemble pancreatic polypeptides. Insect Biochem. Molec. Biol. 28: 345-356.
Brown, M. R., Crim, J. W., Arata, R. C., Cai, H. N., Chun, C., and Shen, P. 1999. Identification of a Drosophila Brain-Gut Peptide Related to the Neuropeptide Y Family. Peptides 20, 1035-1042.
Garczynski, S. F., M. R. Brown, P. Shen, T. F. Murray, and J. W. Crim. 2002. Characterization of a functional neuropeptide F receptor from Drosophila melanogaster. Peptides 23: 773-780. PDF file
Stanek, D. M., J. Pohl, J. W. Crim, and M. R. Brown. 2002. Neuropeptide F and its expression in the yellow fever mosquito, Aedes aegypti. Peptides 23: 1367-1378. PDF file
Brown, M. R. 2003. Insect gut as an endocrine organ. In: Encyclopedia of Hormones (Henry, H. L. and Norman, A. W., Eds.), pp. 328-333. Academic Press.
Garczynski, S. F., J. W. Crim, and M. R. Brown. 2005. Characterization of neuropeptide F and its receptor from the African malaria mosquito, Anopheles gambiae. Peptides 26: 99-107. PDF file
New projects and relevant publications
Short neuropeptide F (sNPF): Genes encoding sNPFs are expressed in the nervous system of Drosophila and both mosquitoes. The 4 or 5 peptides processed from the sNPF propeptide have limited sequence similarity to the Aedes head peptides and FMRFamide peptides. The expression of the sNPFs and their receptors in Drosophila and mosquitoes have been characterized, and now their function is being explored.
Garczynski, S. F., M. R. Brown, and J. W. Crim. 2005. Structural studies of Drosophila short neuropeptide F: occurrence and receptor binding activity. Peptides 27: 575-582. PDF file
Garczynski, S. F., J. W. Crim, and M. R. Brown. 2006 Characterization and expression of the short neuropeptide F receptor in the African malaria mosquito, Anopheles gambiae. Peptides in press.
Adipokinetic hormone (AKH): These peptides mobilize carbohydrate and lipid reserves in insects, and Christian Kaufmann, a visiting graduate student, is investigating the expression of AKHs and their function in female An. gambiae.
Kaufmann, C. and M. R. Brown. 2006. Adipokinetic hormones in the African malaria mosquito, Anopheles gambiae: Identification and expression of genes for two peptides and a putative receptor. Insect Biochemistry and Molecular Biology 36: 466-481. PDF file
Regulation of mosquito development and response to food manipulations: A collaborative project with Dr. Aparna Telang (Department of Biology, University of Richmond, Richmond,VA) is in progress to further our understanding of mosquito development and its hormonal regulation. Results from this work may provide insights into better ways to control mosquito populations in the field.
Telang, A., L. Yiping, F. G. Noriega, and M. R. Brown. 2006. Effects of larval nutrition on the endocrinology of mosquito egg development. Journal of Experimental Biology 209: 645-655. PDF file
Summary
Progress in this research contributes to two concepts shared by insect and vertebrate endocrinology. First, peptide hormones, as chemical messengers, are conserved to a high degree both in structure and function across the phyla of multicellular animals. Second, the nervous and digestive systems of animals use these messengers to coordinate metabolism and homeostasis, so that development and reproduction can occur. The elucidation of key regulatory pathways in mosquitoes can lead to stable and functional peptide mimics or to genetic transformation that may offer a new way to control their development or block pathogen transmission.