Ph.D., 1992, University of Wisconsin, Madison
Associate
Professor
Center for Agricultural Biotechnology
Plant Sciences Building
University of Maryland
College Park, MD 20742
Phone: (301)-405-7525
E-mail: baehreck@umbi.umd.edu
Research: Steroid regulation of gene expression, differentiation, and programmed cell death during insect development
Steroid hormones regulate diverse metabolic, reproductive, and developmental processes throughout the animal kingdom. The diversity of responses to a hormone may reach its extreme in insects, where the steroid 20-hydroxyecdysone (ecdysone) affects numerous physiological and developmental functions. Our goal is to understand how steroid-mediated changes in gene expression control such extraordinarily diverse biological responses.
We are utilizing the fruit fly, Drosophila melanogaster, as a model system for the study of steroid hormone action in insects. Pulses of ecdysone trigger genetic regulatory hierarchies that mediate the dramatic metamorphosis from a larva to an adult. Insect metamorphosis is broadly composed of two types of tissue responses - histolysis of the larval tissues, and differentiation of adult tissues. We have identified two ecdysone-regulated genes, E93 and who, that appear to be associated with either tissue histolysis or differentiation. The E93 gene encodes a novel nuclear protein that is selectively expressed in cells fated to die during metamorphosis. E93 expression immediately precedes transcription of the programmed cell death gene reaper and histolysis of the salivary gland. Furthermore, E93, reaper, and programmed cell death are inducible by ecdysone under identical conditions in cultured larval salivary glands. In contrast to E93, who is associated with the differentiation of tissues. who is induced by ecdysone at the onset of metamorphosis, when it is expressed in the presumptive adult muscle cells associated with appendages. Animals that possess weak who mutations survive to adulthood but display a wing defect consistent with a role in wing muscle development. Combined, our studies suggest that E93 encodes a regulatory protein that triggers an ecdysone-inducible cell death program, while who is an ecdysone-regulated gene associated with myogenesis.
We are continuing these studies by dissecting the genetic regulatory hierarchies associated with the proper regulation of E93 and who. Our goal is to determine how a single steroid hormone is capable of eliciting biological responses as diverse as histolysis and myogenesis, and how the genetic pathways underlying these biological responses differ. Studying the coordination of Drosophila developmental responses to ecdysone has broad application to other animals, since steroid regulation of processes as diverse as metabolism, reproduction, and development have been conserved throughout eukaryotes. Furthermore, studies of the mechanisms underlying hormonal regulation of insect growth and development may lead to novel methods to manipulate pest insect populations.
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