Research Interests

Most animals have two copies of each chromosome, and thus two copies of each gene. Missing or extra copies of whole chromosomes cause such well-known problems as Down syndrome or worse in humans. However, there is usually no effect when individual genes rather than the hundreds to thousands of genes on a single chromosome are duplicated or deleted. The one well-characterized case of a single gene that causes death when it is present in either one or three copies, rather than the normal two, is found in the fruit fly Drosophila melanogaster, and is called Triplo-lethal (Tpl ), and that is the focus of study in my lab.

One focus is the genetic organization of Tpl, which is clearly unusual - it may not code for a protein. This represents a new and growing class of genes whose importance is now being realized. Another focus is on the function of Tpl. We don't know yet why it causes death when the copy number is changed, but we do know something about the process of death. When one copy of Tpl is missing, and there is only one left, the embryos do not hatch, and first the midgut, then the tracheae, then all the other tissues die. When there is a third copy of Tpl present, the same process occurs, but after hatching, in the larval stage. High levels of oxygen seem to at least partially rescue flies with Tpl alterations, for reasons we are attempting to discover.

This research may lead in two possible practical directions. The first is gaining an understanding of how gene copy number alterations such as Down syndrome have deleterious effects in any animal, including humans. The second is in possibly devising strategies of controlling insect pests by altering their Tpl genes.

Recent Publications

• Dorer, D.R. Rudnick, J.A., Moriyama, E.N. and Christensen, A.C., "A Family of Genes Clustered at the Triplo-lethal locus of Drosophila melanogaster has an Unusual Evolutionary History and Significant Synteny with Anopheles gambiae", Genetics, October 2003, in press.
• Smoyer, L.K., Dorer, D.R., Nickerson, K.W. and Christensen, A.C., "Phenotype of the Triplo-lethal locus of Drosophila melanogaster and Its Suppression by Hyperoxia", Genetical Research, in press.
• Abdelnoor, R.V., Yule, R., Elo, A., Christensen, A.C., Meyer-Gauen, G., and Mackenzie, S.A., "Substoichiometric shifting in the plant mitochondrial genome is influenced by a gene homologous to MutS", Proc. Nat. Acad. Sci., 100:5968-5973, 2003.
• Eissenberg, J.C., Ma, J., Gerber, M.A., Christensen, A.C., Kennison, J.A., and Shilatifard, A., "dELL is an essential RNA polymerase II elongation factor with a general role in development", Proc. Nat. Acad. Sci., 99: 9894-9899, 2002.
• Christensen, A.C., "Bacteriophage Lambda-based Expression Vectors", invited review, Molecular Biotechnology, 17: 219-224, 2001.
• Christensen, A.C., "Cats as an aid to teaching genetics", Genetics, 155: 999-1004, 2000.
• Barry, M. K., Triplett, A.A., and Christensen, A.C., "A Peritrophin-like protein expressed in the embryonic tracheae of Drosophila melanogaster", Insect Biochemistry and Molecular Biology, 29: 319-327, 1999.
• Christensen, A.C., "Bacteriophage Lambda-based Expression Vectors", Chapter 4 in Methods in Molecular Biology - Expression and Detection of Recombinant Genes, R. S. Tuan, Editor, J. Walker, Series Editor, Humana Press, 1996.
• Dorer, D.R., Ezekiel, D.H., and Christensen, A.C., "The Triplo-lethal locus of Drosophila melanogaster: Re-examination of mutants, and discovery of a second-site suppressor", Genetics, 141: 1037-1042, 1995.
• Garozzo, M. and Christensen, A.C., "Technical Note: Preparation of DNA from single embryos for PCR", Drosoph. Inf. Serv., 75: 204-205, 1994.
• Dorer, D.R., Cadden, M.A., Gordesky-Gold, B., Harries, G. and Christensen, A.C., "Suppression of a lethal trisomic phenotype by increased dosage of an unlinked locus", Genetics, 134: 243-249, 1993.
• Dorer, D.R., Anane-Firempong, A. and Christensen, A.C., "Ribosomal protein S14 is not responsible for the Minute phenotype associated with the M(1)7C locus in Drosophila melanogaster", Molecular & General Genetics, 230: 8-11, 1991.