M BoC | ASCB ANNUAL MEETING HIGHLIGHT

Kristine Willis (Georgetown University) spoke about the rela- Chromatin and chromosomes tionship between gene activation and positioning within the Saccharomyces cerevisiae nucleus. By tracking both the position David M. Gilberta and Lori L. Wallrathb and the protein product of an inducible reporter gene, she finds aDepartment of Biological Science, Florida State University, Tallahassee, that the reporter gene requires movement to the nuclear periph- b FL 32306; Department of , University of Iowa, Iowa City, ery before activation. In a subset of the cells, the activated gene IA 52242 remains at the periphery, while in other cells the gene moves to the interior and remains active. Interestingly, mutations in chro- matin-remodeling factors caused defects in retention at the pe- riphery, suggesting a requirement for a remodeled chromatin Recent advances in our understanding of chromosome behavior state at the periphery. have been made possible by the development of cutting-edge Using S. cerevisiae as a model to study chromosome segrega- cytological and molecular techniques. Presentations in this Minisym- tion, Min-Hao Kuo (Michigan State University) discovered that his- posium applied these techniques to a diverse set of topics. tone H3 monitors mitotic tension between sister chromatids at peri- Sarah Elgin (Washington University) described her lab’s studies centromeres. Mutation of several amino acids within the H3 on the 1360 transposable element in melanogaster. Pre- “tension-sensing motif” caused the loss of Shugoshin (Sgo1) from viously, they showed that transgenes possessing this element pro- pericentromeres and chromosome segregation defects. GCN5, a moted formation when inserted at ectopic sites in histone acetyltransferase, suppressed the Sgo1 recruitment and the genome. Now, using site-specific integration technology, they segregation defects. A model was proposed whereby GCN5 acts as performed structure/function analyses and mapped the region re- a negative regulator of Sgo1 spreading, limiting localization to the sponsible for silencing to the transposon’s transcription start sites. pericentric region. She also discussed her continued studies on the connection be- Carl Schildkraut (Albert Einstein College of Medicine) used tween heterochromatin proteins and RNA interference machinery. single-molecule analysis of replicated DNA to examine replica- Knockdown of Piwi, an Argonaute/Piwi family member that binds tion forks and origins. Studies of replication forks stalled by hy- Piwi-interacting RNAs and Heterochromatin Protein 1a (HP1a), in droxyurea revealed that phosphorylation of replication protein A the female germline caused loss of HP1a and H3K9me2/3. This re- reduced single-stranded DNA and stimulated DNA synthesis to sulted in increased expression of the telomeric element HeT-A, maintain replication fork integrity. When applied to studies of demonstrating a role for Piwi in gene silencing in the female mouse telomeres, this technique revealed that chromosome germline. ends replicate bidirectionally from sites surrounding and within Yasushi Hiraoka (Osaka University) identified the telomeric repeats. Schizosaccharomyces pombe Sme2 locus as a chromosome-pair- Deborah Lannigan (University of Virginia) identified a function ing site during meiosis. A genomic fragment of Sme2 containing for the extracellular signal–regulated kinase 8 (ERK8) in DNA rep- the TATA box and transcription start site is both necessary for lication. ERK8 shares sequence identity with mitogen-stimulated pairing at the endogenous location and sufficient to induce pair- kinases and was hypothesized to have self-phosphorylating activ- ing at ectopic genomic sites. Sme2 encodes a noncoding RNA ity, yet its role in cell biology was unknown. Knockdown of ERK8 that remains associated with the locus, possibly serving as a scaf- reduced levels of proliferating cell nuclear antigen (PCNA), result- fold for proteins involved in pairing. ing in increased DNA breaks. Adding back excess PCNA rescued this defect. Substitutions within the phosphatidylinositol phos- DOI: 10.1091/mbc.E10-12-0990 phate (PIP) domain of ERK8 recapitulated the ERK8 knockdown Molecular Biology of the Cell Volume 22 Page 717 , suggesting this domain as a site of interaction. Knock- MBoC is pleased to publish this summary of the Minisymposium “Chromatin and down of HDM2, an E3 ligase with a PIP domain, increased the Chromosomes“ held at the American Society for Cell Biology 2010 Annual Meet- ing, Philadelphia, PA, December 12, 2010. levels of PCNA and rescued ERK8 knockdown defects, suggest- Address correspondence to: Lori L. Wallrath ([email protected]). ing that recruitment of ERK8 to chromatin protects PCNA at © 2011 Gilbert and Wallrath. This article is distributed by The American Society for the replication fork. Cell Biology under license from the author(s). Two months after publication it is avail- Collectively, these presentations introduced American Society able to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0). for Cell Biology Annual Meeting attendees to the latest technolo- “ASCB®,“ “The American Society for Cell Biology®,” and “Molecular Biology of gies used to reveal fundamental principles that govern chromo- the Cell®” are registered trademarks of The American Society of Cell Biology. some biology.

Volume 22 March 15, 2011 717