Program Schedule

The Program Schedule is available for download (104k PDF).

Friday Morning Keynote Lecture

RNA silencing is a generic term describing related gene silencing pathways controlled by 21- to 30-nucleotide small RNAs such as siRNAs and miRNAs. Discovery of the first viral suppressors of RNA silencing in 1998 has played a major role in establishing the first biological function of RNA silencing as an antiviral immunity in plants. My lab has since identified similar RNA silencing suppressors encoded by a variety of plant, insect and mammalian viruses. Functional and mechanistic analyses of these viral suppressors show that the siRNA pathway is also antiviral in fruit fly and mosquito cells as has been found in plants. A possible role for the miRNA pathway in viral pathogenesis in both plants and animals will be discussed.

Friday Evening Keynote Lecture

Recent efforts from many laboratories have resulted in the identification of mammalian genes with the potential to block retrovirus replication. These genes, acting at many different steps in the viral life cycle, raise the possibility that therapeutic strategies that exploit their activities could be devised. To help identify such genes, we have devised genetic selections for cells that are refractory to transduction by murine retroviral vectors. We have characterized two such clones arising after chemical mutagenesis in detail. The lines are resistant to both MuLV and HIV pseudotypes, and arrest infection at different points early in infection. One shows altered cytoskeletal morphology. A highly expressed gene that acts as an effector of the resistance in one line has been isolated. We have also selected cDNAs which suppress the blocks in these mutant lines and reestablish virus susceptibility; a normal cytoskeleton is coordinately restored by these cDNAs, suggesting a ca! usal link between these phenotypes.

We have also screened mammalian cDNA libraries for new dominant-acting genes that prevent infection. Virus-resistant cells were selected from pools of transduced clones as before, and an active antiviral cDNA was recovered from one such line. Expression of the gene caused a profound and specific loss of viral mRNAs from the cytoplasm without affecting the levels of nuclear mRNAs. The gene, designated ZAP, encodes a CCCH-type zinc finger antiviral protein. ZAP contained four predicted zinc finger motifs near the amino terminus, and a protein destabilization motif near the carboxyterminus. Mutational analyses showed that cysteine residues in the second and fourth of the zinc finger motifs of ZAP were critical for the antiviral activity. A region near the 3’ end of the Moloney MuLV RNA was identified as necessary and sufficient to provide sensitivity to ZAP and to target mRNAs for loss.

ZAP was tested for its ability to inhibit viruses from other families and was shown to potently inhibit the replication of multiple members of the alphavirus genus, including Sindbis, Semliki Forest, Ross River, and Venezuelan equine encephalitis viruses. However, expression of ZAP did not induce a universal antiviral state: some viruses, including HIV-1, vesicular stomatitis virus, poliovirus, and herpes simplex virus type 1 replicated to normal levels in ZAP-expressing cells. As for retroviruses, the major block to Sindbis could be localized to a small portion of the genome.