Greg L. Harris Laboratory

San Diego State University

Research Program

Molecular Genetics of Sphingolipid Metabolism in Drosophila 

 

                 During the past several years my laboratory has become focused on the analysis of sphingolipid metabolism in flies. Sphingolipids are a complex and ubiquitous class of membrane lipids found in most eukaryotic cells. The bio-active sphingolipid polar metabolites: ceramide, sphingosine and sphingosine-1-phosphate have gained wide recognition for their involvement in signaling pathways that regulate diverse cellular activities such as proliferation, migration, apoptosis, calcium mobilization, growth arrest and differentiation - all of which are critical for the proper development and function of an organism. We have identified eight key enzymes in flies that regulate the synthesis of these bioactive metabolites. Each of these enzymes have highly homologous counterparts in humans. We are characterizing mutations in genes that encode these enzymes and have created transgenic flies that mis-express them. By using this molecular genetic approach to systematically perturb the accumulation of the sphingolipid metabolites in vivo, we are gaining novel insights into the physiological functions and mechanisms of action of these enigmatic lipids.  

 

The Roles of Sphingolipids in Drosophila Development and Physiology 

 

                 Most of our analyses of sphingolipid function have been focused on various aspects of Drosophila development. In collaboration with the laboratory of Dr. Julie Saba at the Children’s Hospital Oakland Research Institute, we discovered that mutations in the gene encoding sphingosine-1-phosphate lyase, a key degradative enzyme in the sphingolipid metabolic pathway causes a profound accumulation of both phosphorylated and unphosphorylated sphingolipid metabolites. The dramatic rise in accumulated sphingolipids occurs early in development and leads to: 1) abnormalities in the numbers, morphology, function and integrity of skeletal muscles; 2) reproductive defects affecting both the ovaries and testes leading to diminished fecundity; 3) disruption of fatty acid metabolism; and, 4) markedly reduced viability and lifespan. Since that initial study we have analyzed mutations affecting sphingosine kinase, serine palmitoyltransferase and sphingosine desaturase. Each mutation causes unique sets of phenotypes that affect muscle, reproductive and nervous system function and alter global lipid homeostasis. The central hypothesis of our work is that tight regulation of sphingolipid metabolism is critical for normal development and the subsequent function of adult tissue. We are currently analyzing developmental defects in muscle, gonads, adipose tissue and the nervous system associated with mutations of in each of the key metabolic enzymes that have been identified. For these studies, we use a series of genetic, behavioral, physiological, biochemical, molecular and morphometric-based analytical approaches. It is anticipated that this work will form a firm and novel foundation for understanding the roles that specific sphingolipid molecules play in the development and physiology of complex animals. 
 

Molecular Genetic Analysis of Obesity 

 

                 Obesity is a multi-factorial metabolic disorder that results in excessive accumulation of body fat and is associated with related pathologies including diabetes, coronary heart disease and cancer. A variety of genetic lesions that tip the balance between food intake and energy expenditure can lead to phenotypes that lie along a broad spectrum ranging between obesity and starvation. In our work using Drosophila as a model organism for the molecular genetic dissection of sphingolipid metabolism we have discovered that disruption of the sphingolipid metabolic pathway can lead to the development of obesity as assessed by increased body weight, elevated triglycerides and excess deposition of fat. To our knowledge, this is the first time that sphingolipid metabolism has been linked to obesity and given the global derangement of lipids that occurs in sphingolipid metabolic mutant flies, it seems likely that the proposed work will shed light on the molecular mechanisms that regulate the flow of lipids through the various compartments and metabolic pathways within an organism. 

 Recent Related Publications:  (see Publications link)

 

Deron R. Herr and Greg L. Harris (2004). Close head-to-head juxtaposition of genes favors their coordinate regulation in Drosophila melanogaster. FEBS Letters, 572:147-153.

 

Deron R. Herr, Henrik Fyrst, Michael Creason, Van Phan, Julie D. Saba & Greg L. Harris (2004). Characterization of the Drosophila sphingosine kinases and requirement for SK2 in normal reproductive function. J. Biol Chem. 279(13):12685-12694.

 

Henrik Fyrst, Deron R. Herr, Greg L. Harris and Julie D. Saba (2004). Characterization of Endogenous C₁₄ and C₁₆ Sphingoid Bases in Drosophila. J. Lipid Res. 45-54-62.

 

Deron R. Herr, Henrik Fyrst, Van Phan, Karie Heinecke, Rana Georges, Greg L. Harris & Julie D. Saba. (2003). Sply regulation of sphingolipid signaling molecules is essential for Drosophila development. Development. 130(11):2443-53.

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