Frank M. Horodyski, Ph.D.

     Neuropeptides are a diverse class of molecules that regulate the physiology, development and behavior of an organism. We are using the lepidopteran insect, Manduca sexta, as a model to understand the synthesis, secretion and action of these compounds. The endocrinology and physiology of Manduca is among the best understood of all the insects based on decades of research in many laboratories. Our research focuses on the analysis of a specific neuropeptide, allatotropin, and encompasses the cellular and developmental regulation of its expression, mode of action in the target cell, and its effects on the physiology of the insect.

     The juvenile hormones (JH) are sesquiterpenoids that regulate molting and metamorphosis in larval insects and reproductive processes in the adult. The regulation of JH levels is in part due to the control of its synthesis by the corpora allata (the source of JH). Allatotropin stimulates JH synthesis by the CA, but this effect in Manduca has only been demonstrated during the adult stage. A modification of the bioassay for CA activity may be necessary to demonstrate an effect in the larva.

     Like many neuropeptides, allatotropin has multiple actions. In a collaborative study with Mary Chamberlin, we have shown that allatotropin rapidly inhibits active ion transport across the larval midgut epithelium. Since active ion transport is critical for providing the energy necessary for nutrient absorption, allatotropin may play an important role in the utilization of dietary nutrients.

     In our studies on the regulation of allatotropin gene expression, we showed that the allatotropin gene is expressed as three alternatively spliced mRNAs whose synthesis is controlled in a stage- and tissue-specific manner. The precursor proteins encoded by two of these mRNAs are predicted to encode peptides that are structurally related to allatotropin, and we have shown that these peptides have overlapping biological activities. Strikingly, starvation and other manipulations that cause the cessation of feeding increase the level of one of these mRNAs. Therefore, alternative splicing can provide a mechanism to regulate the identity of peptides expressed from a single gene. We are trying to understand if the biological role of this regulated change is to increase JH synthesis or modify gut physiology.

     Currently, our efforts are directed toward identifying the receptor that mediates allatotropin action on the target cells. We hope to understand the biochemical changes that occur in these cells and how they relate to the overall physiology of the insect. We are also investigating the how these peptides reach their cellular targets, whether they act as hormones or locally upon release from the cell.

     Our long-term goals are both basic and applied. The characterization of insect neuropeptides provides a simple model with which to understand the synthesis, processing and secretion of peptides in a defined cell type. The biochemical mode of action of these peptides can be characterized in the target cell and integrated with the physiological and behavioral effects that take place in the organism. The applied component of this work is the potential to develop safe, specific, and novel mechanisms to control insect pests. Manipulation of JH levels is already used as a biorational pesticide and an alternative to chemical insecticides that have numerous deleterious effects on nontarget species and the environment.

Selected References:

• Lee, K.-Y., and F.M. Horodyski (2001). Restriction of nutrient intake results in the increase of a specific Manduca sexta allatotropin (Manse-AT) mRNA in the nerve cord. Peptides, in press.

• Horodyski, F.M., S.R. Bhatt, and K.-Y. Lee (2001). Alternative splicing of transcripts expressed by the Manduca sexta allatotropin (Mas-AT) gene is regulated in a tissue-specific manner. Peptides 22, 263-269.

• Bhatt, T.R., and F.M. Horodyski (1999). Expression of the Manduca sexta allatotropin gene in cells of the central and enteric nervous systems. J.Comp.Neurol. 403, 407-420.

• Lee, K.-Y., F.M. Horodyski, and M.E. Chamberlin (1998). Inhibition of midgut ion transport by allatotropin (Mas-AT) and Manduca FLRFamides in the tobacco hornworm, Manduca sexta. J.Exp.Biol. 201, 3067-3074.

• Bhatt, T.R, P.A. Taylor III., and F.M. Horodyski (1997). Combined fluorescence in situ hybridization (FISH) and immunocytochemistry double-labeling in whole mount Manduca sexta tissue. BioTechniques 23, 1000-1006.

• Taylor, P.A.,III, T.R. Bhatt, and F.M. Horodyski (1996). Molecular characterization and expression analysis of Manduca sexta allatotropin. Eur.J.Biochem. 239, 588-596.

• Horodyski, F.M. (1996). Neuroendocrine control of insect ecdysis by eclosion hormone. J.Insect Physiol. 42, 917-924.