Location: HHSC 611
RNA interference (RNAi) was discovered as a gene-silencing phenomenon initiated by double stranded RNA (dsRNA). While RNAi is widely used as a tool for downregulation of gene expression, we are interested in the endogenous RNAi processes in the nematode C. elegans. The key components of various RNAi-related pathways are short RNAs produced from dsRNA precursors and the ancient Argonaute family proteins that interact with these short interfering RNAs (siRNAs). The focus of our research is on RNAi pathways that lead to transcriptional repression and its accompanying changes in chromatin organization. We are interested in both the mechanisms of RNAi-induced transcriptional silencing and its role in regulation of gene expression during development.
1) Molecular function of ZFP-1. Our results suggest that Zinc Finger Protein 1 (ZFP-1) and endogenous siRNAs antisense to protein coding genes cooperate in repressing their targets. We found that ZFP-1 interacts with histones and would like to understand how it functions to regulate the expression of genes targeted by endogenous siRNAs.
2) RNAi in stress response and longevity. Using whole genome expression array analysis we found that endogenous RNAi processes contribute to the regulation of downstream target genes of the insulin signaling pathway and also repress genes encoding translation initiation factors and ribosomal proteins. Both insulin signaling and translation factors are involved in the regulation of stress response and longevity. We are investigating the role of RNAi in longevity pathways.
3) Cooperation of RNAi and Rb. The C. elegans Retinoblastoma protein LIN-35 is responsible for the repression of germ cell-specific fate in somatic tissues of the worm. We found that a number of germ cell-specific transcripts inappropriately expressed in somatic cells of lin-35 (Rb) mutants are also targeted by endogenous siRNAs. Cyclin E belongs to this category of germline-enriched genes repressed in the soma and may represent one of the markers of stem cells. Enhanced expression of cyclin E in the intestine of Rb and Argonaute double mutant worms causes an increase in the number of cell divisions in this tissue (image). We are studying how Rb and RNAi cooperate in repressing the cyclin E gene and other genes specifying stem cell fates.
Grishok, A., Hoersch, S., and Sharp, P.A. RNAi and Retinoblastoma Related Genes are Required for Repression of Endogenous siRNA Target Genes in C. elegans. PNAS (in press).
Grishok, A., and Sharp, P.A. Negative regulation of nuclear divisions in Caenorhabditis elegans by retinoblastoma and RNA interference-related genes. PNAS 102, 17360-17365 (2005).
Grishok, A., Sinskey, J.L. and Sharp, P.A. Transcriptional silencing of a transgene by RNAi in the soma of C. elegans. Genes & Dev 19, 683-696 (2005).
Grishok, A., Pasquinelli, A.E., Conte, D., Li, N., Parrish, S., Ha, I., Baillie, D.L., Fire, A., Ruvkun, G. and Mello, C.C. Genes and Mechanisms Related to RNA Interference Regulate Expression of the Small Temporal RNAs that Control C. elegans Developmental Timing. Cell 106, 23-34 (2001).
Grishok, A., Tabara, H. and Mello, C.C. Genetic Requirements for Inheritance of RNAi in C. elegans. Science 287, 2494-2497 (2000).