In Drosophila, molting and metamorphosis are initiated by pulses of a single steroid hormone, 20-hydroxyecdysone (20E). Although hormone exposure at the cellular level is global, the response of individual cells to the steroid signal can be considerably different and diverse. Understanding how these tissue-specific responses are manifested at the molecular level is of particular interest to our lab.
We are using the larval salivary gland as an assay system to investigate how changes in gene expression directly induced by the hormone, are manifested into a temporal- and spatial-specific response within the tissue. Our lab is especially interested in elucidating the underlying mechanisms of the massive secretion of packaged glue proteins induced by a 20E signal. This knowledge will provide us with a model for steroid-regulated exocytosis in vertebrates. We are approaching this problem by observing live animals or live dissected tissues (expressing RED cargo proteins and GREEN target proteins) after they have been experimentally manipulated. Thus, we have been able to test candidate genes using traditional whole-animal mutants, tissue-specific gene targeting, conventional pharmacological treatments, and tissue-specific gene silencing with double-stranded interfering RNA (RNAi). The results of this multidisciplinary approach have allowed us to piece together a pathway that involves steroid exposure; induction of DNA-binding proteins; changes in intracellular calcium levels; and changes in the activity of calcium-binding proteins, myosin motors, and cytoskeletal structures. We are complementing this directed approach with open-ended loss-of-function and targeted overexpression genetic screens that should allow us to identify molecules that are functionally required for steroid-regulated secretion.
Notch (N) is an important signaling protein that is known to be critical for embryonic development in most animals. Part of its essential role is to influence cell-fate decisions and to establish the proper number of progenitor neurons in the developing nervous systems of flies and humans. Our lab became fascinated with Notch after intriguing twin discoveries: (1) Notch is processed by a gamma-secretase complex containing Presenilin (Psn) into a signaling molecule that can enter the nucleus, and (2) mutations in human Psn correlate with the absolute development of some familial forms of Alzheimer's disease.
We have tested the requirement of Notch in adult flies with a fully differentiated nervous system. This is possible because of the powerful molecular and genetic tools to compromise the Notch protein after development is complete using conditional alleles, inducible dominant-negative transgenes, or inducible RNAi molecules. We have shown that adult flies without functional Notch have a dramatically reduced lifespan, show impairments in locomotion with age, and display defects in long-term memory. The last phenotype is notably compelling because Notch-compromised adult flies display short-term memories that are indistinguishable from controls. Currently we are using these Notch phenotypes to genetically map the regions of the fly brain necessary for long-term memory by selectively silencing Notch in defined subregions of the central nervous system. We hope to use this information to model aspects of human memory acquisition and dysfunction.
Andres, A. J. (2004). Flying through the genome: A comprehensive study of functional genomics using RNAi in Drosophila. TRENDS in Endocrinol and Metab, 15: 243-247.
Presente, A., Boyles, R. S., Serway, C. N., deBelle, S. J., and Andres, A. J. (2004). Notch is necessary for long-term memory in Drosophila. Proc. Natl. Acad. Sci. UAS 101:1764-1768.
Presente, A., Shaw, S., Nye, J. S., and Andres, A. J. (2002). Transgene-mediated RNA interference defines a novel role for Notch in chemosensory startle behavior. Genesis 34: 165-169.
Bentley, A. M., Williams, B. C., Goldberg, M. L., and Andres, A. J. (2002). Phenotypic characterization of Drosophila ida mutants: Defining the role of APC5 in cell cycle progression. J. Cell Sci. 115: 949-961.
Presente, A., Andres, A., and Nye, J. S. (2001). Requirement of Notch in adulthood for neurological function and longevity. Neuroreport, 12: 3321-3325.
Biyasheva, A., Do, T.-V., Lu, Y., Vaskova, M., and A. J. Andres (2001). Glue secretion in the Drosophila salivary gland: A model for steroid-regulated exocytosis. Dev. Biol. 231: 234-251.
Vaskova, M., Bentley, A. M., Marshall, S., Reid, P., Thummel, C. S., and A. J. Andres (2000). Genetic analysis of the Drosophila 63F early puff: Characterization of mutations in E63-1 and maggie, a putative Tom22. Genetics 156: 229-244.
Andres, A. J. and C. S. Thummel (1995). The Drosophila 63F early puff contains E63-1, an ecdysone-inducible gene that encodes a novel Ca2+-binding protein. Development 121: 2667-2679.
Andres, A. J., Fletcher, J. C., Karim, F. D., Thummel, C. S. (1993). Molecular analysis of the initiation of insect metamorphosis: A comparative study of Drosophila ecdysteroid-regulated transcription. Dev Biol 160: 388-404.
SEB Program Group: Integrative Physiology
SEB Lab Location: 3154/3155
Additional Info: SEB Lab Phone Number: 702-895-1553