Craig Pikaard

Title:	Professor of Biology
Degree:	PHD, Purdue University BS, Pennsylvania State University
Dept:	Biology
Office:	Monsanto Lab Building 505A
Mailbox:	Campus Box 1137 One Brookings Drive St. Louis, MO 63130-4899 Hide Full Mailing Address
Phone:	(314) 935-7569
E-mail:	pikaard@wustl.edu

Courses
Plant Cells and Proteins Laboratory; How Plants Work: Physiology, Growth and Metabolism; Plant Developmental Genetics, Genomics, and Model Systems

Research Interests
In most offspring there are genes that are expressed from the chromosomes inherited from only one parent. Often a maternal or paternal imprint dictates which allele will be active. However, this is not the case for the uniparental expression of ribosomal RNA (rRNA) genes in genetic hybrids. This epigenetic phenomenon, known as nucleolar dominance, occurs both in plants and animals but is best studied in plants because non-sterile hybrids can be generated. The Pikaard lab has shown that rRNA gene silencing involves concerted changes in both DNA methylation and histone modification and we have proposed a model whereby DNA and histone modifications are each upstream of one another in a self-reinforcing, circular pathway. Members of the lab are identifying the chromatin modifying activities involved in this repression cycle, using RNA-interference to knock down the expression of targeted genes. Two histone deacetylases, one DNA methyltransferase and several methylcytosine binding proteins have been identified in the screens thus far. They are making use of a variety of genetic, cytogenetic and biochemical approaches in order to understand the mechanism(s) of action of these chromatin modifying activities and to understand how their actions are intertwined to comprise an epigenetic on-off switch.

A second emphasis in the Pikaard lab is the characterization of nuclear RNA polymerase IV (pol IV), a newly discovered polymerase that is required for the production of small interfering RNAs (siRNAs) that mediate RNA-directed DNA methylation and silencing of genomic repeated sequences, including transposable elements and pericentromeric repeats. Acting in a pathway that includes Dicer-like 3 (DCL3), argonaute 4 (AGO4) and RNA-dependent RNA polymerase 2 (RDR2), pol IV function is required to maintain the normal organization of the chromatin within the nucleus. Consequently, disruption of the pol IV catalytic subunits causes heterochromatin dispersal. However, they don't know precisely how pol IV works. Current priorities include purifying pol IV to homogeneity, determining its complete subunit structure, determining its template requirements (e.g. DNA vs. RNA) and determining its transcripts or enzymatic products.

Selected Publications:

Lawrence RJ, Earley K, Pontes O, Silva M, Chen ZJ, Neves N, Viegas W, Pikaard CS. (2004) A concerted DNA methylation/histone methylation switch regulates rRNA gene dosage control and nucleolar dominance. Molecular Cell 13:599-609.

Onodera, Yasuyuki, Jeremy Haag, Thomas Ream, Pedro Costa Nunes, Olga Pontes and Craig S. Pikaard (2005) Plant Nuclear RNA polymerase IV mediates siRNA and DNA methylation-dependent heterochromatin formation. Cell 120:613-622.

Pontes, Olga, Carey Fei Li, Pedro Costa Nunes, Jeremy Haag, Thomas Ream, Alexa Vitins, Steven E. Jacobsen and Craig S. Pikaard (2006) The Arabidopsis chromatin-modifying nuclear siRNA pathway involves a nucleolar RNA processing center. Cell 126: 79-92.

Li, Carey F., Olga Pontes, Mahmoud El-Shami, Ian R. Henderson, Yana V. Bernatavichute, Simon W.-L. Chan, Thierry Lagrange, Craig S. Pikaard, and Steven E. Jacobsen (2006) An ARGONAUTE-containing nuclear processing center co-localized with Cajal bodies in Arabidopsis thaliana. Cell 126:93-106.

Earley, Keith, Richard J. Lawrence, Olga Pontes, Rachel Reuther, Angel J. Enciso, Manuela Silva, Nuno Neves, Michael Gross, Wanda Viegas, and Craig S. Pikaard (2006) Erasure of histone acetylation by Arabidopsis HDA6 mediates large-scale gene silencing in nucleolar dominance. Genes & Development 20:1283-1293.