We study the ways genes are activated and repressed, using techniques of genetics, biochemistry and molecular biology. Our current research projects are focused on the roles that chromatin proteins and small interfering RNAs (siRNAs) play in epigenetic phenomena. Our favorite epigenetic phenomenon is nucleolar dominance, which occurs in genetic hybrids and describes the transcription (by RNA polymerase I) of ribosomal RNA genes inherited from only one of the progenitors due to the selective silencing of the other parental set of rRNA genes. Nucleolar dominance operates on a scale of millions of basepairs of chromosomal DNA and in its scope is second only to the inactivation of one X-chromosome in the somatic cells of female mammals. However, unlike X-inactivation, the choice of which set of rRNA genes to silence is not random, nor is it dictated by a maternal or paternal imprint.

Another focus of the lab concerns RNA polymerase IV and its role in the RNA-directed DNA methylation pathway. RNA polymerase IV is a plant-specific class of polymerase that we have shown to be localized in the nucleus. In Arabidopsis, we know of two known forms of Pol IV, Pol IVa and Pol IVb, both of which are structurally related to DNA-dependent RNA polymerases I,II and III. Pol IVa is required for the production of 24 nt siRNAs that direct the silencing of repeated sequences in the genome via DNA methylation, with Pol IVb acting late in the pathway. Our studies of this pathway led us to the discovery of an siRNA processing center that is located in the nucleolus.

Where we are located: The Pikaard laboratory is in the Biology Department at Washington University in St. Louis, Missouri. Ph.D. students doing thesis projects or research rotations in the lab have been members of numerous graduate programs, including the Plant Biology Program, Biochemistry Program, Molecular Genetics and Genomics Program, Developmental Biology Program and Molecular Cell Biology Program.

Our Funding: Our work is supported by grants from the National Institutes of Health, National Science Foundation and the Monsanto Company. Any materials or opinions expressed at this site are those of the author(s) and do not necessaily reflect the views of our sponsors.