Member Institutions:

• Bowling Green State U.
• Cleveland State U.
• Kent State U.
• Medical College of Ohio
• Miami U.
• The Ohio State U.
• Ohio U.
• University of Cincinnati
• University of Toledo
• Wright State U.
• Youngstown State U.

Harry van Keulen Department of Biological, Geological and Environmental Sciences Cleveland State Univerisity Cleveland, Ohio 44115 Phone (216) 687-4562 FAX (216) 687-5443 email h.vankeulen@popmail.csuohio.edu

Research Interests

Giardia, an intestinal parasite, undergoes a unique form ofcell differentiation, from an organism with two nuclei, the trophozoite, usually found attached to the epithelial cells in the upper small intestines, to an environmentally resistant cyst that contains four nuclei and is surrounded by a unique structure, the cyst wall. This is a layer composed of filaments and a double membrane. The filamentous layer consists of a polymer made up of acetylgalactosamine (GalNac) residues. Cyst formation can be induced in vitro by adding bile to a culture of trophozoites. During encystment five enzymes of an enzymic pathway are induced leading to formation of UDP-GalNac, the direct precursor to the cyst wall filaments. The gene for the first enzyme of this pathway, isomerase, has been cloned and studied in detail at the molecular level. This enzyme. glucosamine 6-phosphate isomerase, Nag1, converts fructose 6-phosphate plus ammonia to glucosamine 6-phosphate (GluN-P). The gene was cloned and sequenced and subsequently used to study gene expression. The nagl gene appears to be activated at the level of transcription, and is turned on as early as 6 h after induction with bile. Of the remaining enzymes in this pathway, two are of particular interest, the third, UDP-N-acetylglucosamine pyrophosporylase, which converts N-acetylglucosamine 1-phosphate plus UTP in UDP-GlucNac and is under allosteric control by the end product of Nagl, GlucN-P and UDP-N-acetylglucosamine- 4'-epimerase, which converts its substrate (UDP-GlucNac) in UDP-GalNac. This enzyme is the fifth of the inducible enzymes and is induced dramatically after bile is added. Cloning and sequence analysis of the genes for these enzymes is in progress and, when finished, will make an in depth study on the regulation of cyst wall synthesis possible.

Future plans related to plant biotechnology

A possible use of this research on Giardia applied to plant biotechnology is using Giardia genes to replace the homologous genes in key plant metabolic pathways to change their control, or to alter products. The advantage of using Giardia genes are several: some of the enzymes that are tightly regulated in higher eukaryotes are not, or differently, controlled in Giardia. In addition, Giardia genes are intronless, and, therefore, simple in nature. Giardia is considered to be an ancient or primitive organism, and in that manner a source of gene material that could be seen as "embryonic" in nature. Finally, all known genes in Giardia show a high degree of identity with plant genes, suggesting a common ancestry. These features might be of use and attempts will be made to construct chimeric plants using Giardia genes, to test these ideas.

Recent references:

• van Keulen, H., Homan, W.L., Erlandsen, S.L. and Jarroll, E.L. 1995. A Three Nucleotide Signature Sequence in Small Subunit rRNA Divides Human Giardia in Two Different Genotypes. J. Euk. Microbiol. 42, 392-394.
• van Keulen, H., Feely, D.E., Macechko, P.T., Jarroll, E L., and Erlandsen, S.L. 1998. The Sequence of Giardia Small Subunit rRNA shows that voles and muskrats are parasitized by a unique species G. microti. J. of Parasitol. 84, 294-300
• van Keulen, H., Steimle, P.A., Bulik, D.A., Borowiak, R.K., and Jarroll, E.L. 1998. Cloning of two Giardia glucosamine 6-phosphate isomerase genes only one of which is transcriptionally activated during encystment. J. Euk. Microbiol. 45, 637-642.

Cleveland State Department of Biological, Geological and Environmental Sciences
Cleveland State University homepage
Back to Scientists