This laboratory focuses on the endocrinology of one of the two families of hormones controlling insect metamorphosis: the juvenile hormones (JH), which maintain both the growth and development of the larval stages and reproduction in adults, through temporally precise changes in their hemolymph titers at critical developmental stages. Changes in the JH titer are precisely controlled by various processes (sythesis, transport, degradation, excretion), and of these, mechanisms which regulate JH synthesis are the main interests of the laboratory.

JH synthesis by paired endocrine glands known as the corpora allata (CA) is known to be controlled via the axons of cerebral neurons that innervate these glands. Past studies have defined two neuropeptides that affect JH synthesis: an amidated tridecapeptide that stimulates the CA, known as an allatotropin (Mas-AT), and an allatostatin (Mas-AS) which inhibits JH biosynthesis. We have shown that cytosolic free Ca2+ is involved in the regulation of larval CA activity, and recently have demonstrated that the neurotransmitter dopamine either stimulates or inhibits JH synthesis during larval-pupal metamorphosis, depending on the stage. These results indicate the existence in the CA of D1- like and D2- like dopamine receptors. Pharmacological studies with agonists and antagonists of these receptor sub-types have shown that while these receptors share some characteristics of vertebrate D1 and D2 receptors, they have unique features which place them in separate sub-type categories. We are currently involved in cloning these dopamine receptors, as well as examining the interaction of the allatotropin and allatostatin with each other and with dopamine, in modulating levels of JH synthesis.

Pseudocolored ratio images of corpus allatum cells from the fifth larval stadium and early pupal period loaded with Fura-2 and incubated in Grace's medium containing 0.1 mmol-1 Ca2+. (A) day 0, fifth stadium: (B) day 1; (C) day 2; (D) day 4; (E) day 6; (F) day 0 pupa. The color spectrum in (A) corresponds to the concentration range (mmol-1 of Ca2+. Scale bars, 10 µm.

Finally, we have known for some time that the other family of hormones involved in the control of insect metamorphosis, the ecdysteroids (which elicit molting), can stimulate or inhibit the synthesis of JH via short-term, cerebral feedback loops. Treatment of larvae with exogenous ecdyteroids over 24 hr can change the response of the CA to dopamine in subsequent incubations in vitro, suggesting that perhaps ecdysteroids can also affect JH synthesis at the level of the gland. We are currently examining the ecdysteroid receptor in the CA and have found developmental changes in the isoforms of one of the two proteins that comprise the ecdysteroid receptor, Ultraspiracle, that are coordinate with increases in the ecdysteroid titer in vivo. Comparable changes appear to be elicited by incubating CA with ecdysteroids in vitro.

The ultimate objective of these lines of research is to find novel ways to control the growth and development of insect vectors of disease and food plant pests.

Goodman, W.G., Orth, A., Toong, Y.C., Ebersohl, R., Hiruma, K. and Granger, N. 1995. Recent advances in radioimmunoassay technology for the juvenile hormones. Arch. Insect Biochem. Physiol .30:295-306.

Granger, N.A., Sturgis, S.L., Ebersohl, R., Geng, C., and Sparks, T.C. 1996 Dopaminergic control of corpora allata activity in the larval tobacco hornworm, Manduca sexta. Arch. Insect Biochem. Physiol. 32:449-466.

deKort, C.A.D. and Granger, N.A. 1996. Regulation of JH titers: The relevance of degradative enzymes and binding proteins. Arch.Insect Biochem. Physiol. 33:1-26.

Sparks, T.C., Geng, C., Gajewski, R.P., Skomp, J.R., Granger, N.A. and Fescemeyer, H.W. 1997. The application of n-EC-HPLC to the analysis of insect biogenic amines. In: Progress in HPLC (I.N. Acworth et al., eds.), vol. 6, pp. 145-168.

Granger, N.A., Ebersohl, R., and Sparks, T.C. 2000. Pharmacological characterization of D1- and D2-like receptors in the corpora allata of larval Manduca sexta. Insect Biochem. Mol. Biol. 30:755-66.

Gilbert, L.I., Granger, N.A, and Roe, R.M. 2000. The insect juvenile hormones: Historical perspectives and prospects for future research. Insect Biochem. Mol. Biol. 30: 616-644.