Dr. Ron Dzikowski, Ph.D.

Head of malaria gene expression laboratory

Education

1999-2003 Ph. D. in Parasitology at the Faculty of Agriculture, Food and Environmental Quality Sciences, the Hebrew University of      Jerusalem.

1996-99     M. Sc. MAGNA CUM LAUDE  in Animal Science at the Faculty of Agriculture, Food and Environmental Quality Sciences, the Hebrew University of Jerusalem.

1993-96    B. Sc. in Animal Science at the Faculty of Agriculture, Food and Environmental Quality Sciences the Hebrew University of Jerusalem.


Experience

2008          Senior lecturer, Department of Microbiology & Molecular Genetics, The Kuvin Center for Study of Infectious and Tropical Diseases, The Institute for Medical Research Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.

2007          Lecturer, Department of Parasitology, The Kuvin Center for Study of Infectious and Tropical Diseases, The Hebrew University-Hadassah Medical School, Jerusalem, Israel.

2003-2007  NIH postdoctoral fellow, Department of Microbiology and Immunology, Weill Medical College of Cornell University. New York, USA

2001          International scholar, Department of Microbiology, Pathology & Parasitology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC USA.



Ongoing research

The deadliest form of human malaria is caused by the protozoan parasite Plasmodium falciparum that annually affects millions worldwide. The virulence of P. falciparum is attributed to its ability to evade the human immune system, by modifying the host red blood cell surface to adhere to the vascular endothelium and to undergo antigenic variation. The main antigenic ligands responsible for both cytoadherence and antigenic variation are members of the P. falciparum Erythrocyte Membrane Protein-1 (PfEMP1) family. These polymorphic proteins are encoded by a multi-copy gene family called var. Each individual parasite expresses a single var gene at a time, whereas the remaining ~60 var genes found in its genome are maintained in a transcriptionally silent state. As the antibody response against the single PfEMP1 expressed develops, small sub-populations of parasites, which have switched expression to alternative forms of PfEMP1, avoid the antibody response and re-establish infection. The regulation of var gene expression is therefore responsible for both immune evasion and the pathogenicity of the disease.

Immune evasion through antigenic variation in malaria depends on the ability of the parasite to exclusively express only a single var gene at a time, and then to switch expression to another gene that will also be expressed in mutually exclusive manner. Recently, my research focused on the elucidation of the molecular mechanisms that control antigenic switching and mutually exclusive expression. Using genetic manipulation of cultured parasites, we have succeeded in interfering with this genetic pathway, creating parasites in which we can control expression of the virulence genes, effectively knocking out the entire gene family in a reversible way. Thus, for the first time creating transgenic parasite lines that do not express the main virulence factor of the disease. These experiments demonstrated that the expression of the antigen is not required to keep the rest of the var family in transcriptionally silent state, and that mutually exclusive expression in malaria is not mediated through a negative feedback as demonstrated in other eukaryotic systems.

These transgenic parasites enabled us for the first time to control the switches that turn the expression of individual var genes on and off at their chromosome locations. This was used to study var gene switching in order to identify if transcriptional switches favor the expression of particular subgroups of var genes and if var gene activation within a clonal population of parasites follows a pre-determined order. We showed that transcription of var genes located in the central regions of chromosomes is remarkably stable and without selection these genes rarely undergo transcriptional switches. In contrast subtelomericaly located var genes exhibit a more dynamic switching pattern with clonal parasite populations readily switching to alternative var loci. We also demonstarted that after selection for activation of either subtelomeric or central var loci, populations of parasites with completely different var gene expression profiles develop over time, thus providing an explanation for how a parasite population can exhibit heterogenous patterns of var gene activation despite the uniform bias towards expression of var genes with low off rates.  

In addition, we showed that cooperative interactions between two promoters found in each gene are required for both silencing and mutually exclusive expression, and disruption of these interactions results in simultaneous expression of multiple var genes within the same parasite, thus definitively demonstrating the necessity for cooperative regulatory elements for var gene regulation. Further, heterologous promoters can serve in place of var intron promoter elements for cooperative regulation, shedding light on the silencing mechanism through promoter-promoter interaction.

These findings led us to explore the hypothesis that a nuclear expression site is involved in var genes regulation and mutually exclusive expression. we used transgenic parasite lines in which var gene expression can be manipulated using drug selection, and in which specific var loci have been tagged for visualization by fluorescent in situ hybridization (FISH). Simultaneously active var genes co-localize within the nucleus, providing the first strong evidence for a postulated subnuclear var-specific expression site, but also suggesting that it can accommodate multiple transcriptionally active var promoters.

Recently we provided evidence for a tritratable, var-specific factor that is necessary for var gene activation. By manipulating the copy number of var promoter-containing episomes, it was possible to compete for this limiting factor and repress transcription of all chromosomal var genes. When the competing episomes were removed, the parasites did not return to their previous var gene expression pattern, but rather displayed random var gene activation, demonstrating that the epigenetic marks that control var gene expression had been completely erased and thus linking active transcription to the maintenance of cellular memory. We also reported that the cellular memory that is involved in the control of var gene expression is associated with methylation of histone H3 at lysine K9 as an epigenetic chromatin mark.


List of Publications

21. Dzikowski, R.  & Deitsch, K.  2009. Genetics of antigenic variation in Plasmodium falciparum. Curr Genet (in press).

20.  Pasternak, D. N.  & Dzikowski, R.  2009. PfEMP1: An antigen that plays a key role in the pathogenicity and immune evasion of the malaria parasite Plasmodium falciparum. Int J Biochem Cell B (in press).

19. Dzikowski, R. & Deitsch, K. 2008. Active transcription is required for maintenance of epigenetic memory in the malaria parasite Plasmodium falciparum. J Mol Biol 382: 288-297.

18. Dzikowski, R., Li, F., Amulic, B., Eisberg, A., Frank, M., Patel, S., Wellems, T. E. & Deitsch, K. 2007. Mechanisms underlying mutually exclusive expression of virulence genes in malaria parasites. EMBO Rep 8(10): 959-965.

17.  Functional Genomics Workshop Group, The Broad Institute of Harvard and MIT. 2007. Mechanism of gene regulation in Plasmodium. Am J Trop Med Hyg 77(2): 201-208.

16. Frank, M.*, Dzikowski, R.*, Amulic, B. & Deitsch, K. 2007. Variable switching rates of malaria virulence genes are associated with chromosomal position. Mol Microbiol 64(6): 1486-1498.
* Equal authorship contribution

15. Chookajorn, T., Dzikowski, R., Frank, M., Li, F., Jiwani, A. Z., Hartl, D. L. & Deitsch, K. 2007. Epigenetic memory at malaria virulence genes. Proc Natl Acad Sci USA104(3): 899-902.

14. Dzikowski, R., Templeton, T. J. & Deitsch K. W. 2006. Variant antigen gene expression in malaria. Cell Microbiol 8(9): 1371-1381

12. Frank, M., Dzikowski, R., Costantini, D., Amulic, B., Berdougo, E. & Deitsch, K. W. 2006. Strict pairing of var promoters and introns is required for var gene silencing in the malaria parasite Plasmodium falciparum. J Biol Chem 281(15): 9942-995.


11. Dzikowski, R., Frank, M. & Deitsch, K. W. 2006. Mutually exclusive expression of virulence genes by malaria parasites is regulated independently of antigen production. PLoS Pathog 2(3): e22.


10. Dzikowski, R. & Deitsch, K. W. 2006. Antigenic variation by protozoan parasites: insights from Babesia bovis. Mol  Microbiol  59(2): 364-366.


9. Dzikowski, R., Hulata, G., Harpaz, S. & Karplus, I. 2004. Inducible reproductive plasticity of the guppy Poecilia reticulata in response to predation cues. J Exp Zool 301A: 776-782.

8. Dzikowski R., Levy M.G., Poore M.F., Flowers J.R. & Paperna I. 2004. Clinostomum complanatum and Clinostomum marginatum (Rudolphi, 1819) (Digenea: Clinostomatidae) are separate species based on differences in rDNA. J Parasitol 90: 413-414.

7. Dzikowski R., Levy M.G., Poore M.F., Flowers J.R. & Paperna I. 2004. Use of rDNA polymorphism for identification of Heterophyidae infecting freshwater fishes. Dis Aquat Organ 59: 35-41. 

6. Dzikowski R., Levy M.G., Poore M.F., Flowers J.R. & Paperna I. 2003. Genetic and morphologic differentiation of Bolbophorus confusus and B. levantinus (Digenea: Diplostomatidae), based on rDNA SSU polymorphism and SEM. Dis Aquat Organ 57: 231-235.

5. Dzikowski, R., Diamant, A. & Paperna, I. 2003. Trematode metacercariae of fish as sentinels for a changing limnological environment. Dis Aquat Organ 55: 145-150.

4. Dzikowski, R., Diamant, A. & Paperna, I. 2003. Multi-annual changes in parasite communities of the rabbitfish Siganus rivulatus (Siganidae) in the Gulf of Aqaba, Red Sea. Helgol Mar Res 57: 228-225.

3. Dzikowski, R., Diamant, A. & Paperna, I. 2003. Use of fish parasitological species richness indices in analyzing anthropogenically – impacted coastal marine ecosystems. Helgol Mar Res 57: 220-227.
 
2. Levy, M.G., Flowers, J.R., Poore, M.F., Khoo, L., Pote, L.M., Mullen, J.E., Paperna, I., Dzikowski, R. & Litaker, R.W. 2002. Morphologic, pathologic, and genetic investigations of Bolbophorus spp. (Diplostomatida, Trematoda) affecting cultured Ictalurus punctatus in the Mississippi delta. J Aquat Anim Health 14: 235-246.

1. Dzikowski, R., Hulata, G., Karplus, I. & Harpaz, S. 2001. Effect of temperature and dietary L-carnitine supplementation on reproductive performance of female guppy (Poecilia reticulata). Aquaculture 199: 323-332.

Research Support

2008-2001 The United States – Israel Binational Science Foundation grant no. 2007350 “The nuclear envelope of the malaria parasite Plasmodium falciparum”. In collaboration with Dr. Kirk Deitsch, Cornell University.

2008-2011 The Marie Curie International Reintegration Grant (IRG) grant no. 203675  “The role of a nuclear expression site in the regulation of virulence genes in malaria parasites”

2008          The German Israeli Foundation (GIF) young scientist grant no. 2163-1725.11/2006 “Interaction between malaria parasite surface antigens and host immune system”

2008          The Lejwa Fund For Biochemistry. "Gene activation in malaria parasites"