Elevated Rates of Sister Chromatid Exchange at Chromosome Ends

Chromosome ends are known hotspots of meiotic recombination and double-strand breaks. We monitored mitotic sister chromatid exchange (SCE) in telomeres and subtelomeres and found that 17% of all SCE occurs in the terminal 0.1% of the chromosome. Telomeres and subtelomeres are significantly enriched for SCEs, exhibiting rates of SCE per basepair that are at least 1,600 and 160 times greater, respectively, than elsewhere in the genome

Human Subtelomeric WASH Genes Encode a New Subclass of the WASP Family

Subtelomeres are duplication-rich, structurally variable regions of the human genome situated just proximal of telomeres. We report here that the most terminally located human subtelomeric genes encode a previously unrecognized third subclass of the Wiskott-Aldrich Syndrome Protein family, whose known members reorganize the actin cytoskeleton in response to extracellular stimuli. This new subclass, which we call WASH, is evolutionarily conserved in species as diverged as Entamoeba. We demonstrate that WASH is essential in Drosophila. WASH is widely expressed in human tissues, and human WASH protein colocalizes with actin in filopodia and lamellipodia. The VCA domain of human WASH promotes actin polymerization by the Arp2/3 complex in vitro. WASH duplicated to multiple chromosomal ends during primate evolution, with highest copy number reached in humans, whose WASH repertoires vary. Thus, human subtelomeres are not genetic junkyards, and WASH's location in these dynamic regions could have advantageous as well as pathologic consequences

A sequence-based survey of the complex structural organization of tumor genomes

Tumors and cancer cell lines were surveyed with end-sequencing profiling, yielding the largest available collection of sequence-ready tumor genome breakpoints and providing evidence that some rearrangements may be recurrent

Formins in development: Orchestrating body plan origami.

Formins, proteins defined by the presence of an FH2 domain and their ability to nucleate linear F-actin de novo, play a key role in the regulation of the cytoskeleton. Initially thought to primarily regulate actin, recent studies have highlighted a role for formins in the regulation of microtubule dynamics, and most recently have uncovered the ability of some formins to coordinate the organization of both the microtubule and actin cytoskeletons. While biochemical analyses of this family of proteins have yielded many insights into how formins regulate diverse cytoskeletal reorganizations, we are only beginning to appreciate how and when these functional properties are relevant to biological processes in a developmental or organismal context. Developmental genetic studies in fungi, Dictyostelium, vertebrates, plants and other model organisms have revealed conserved roles for formins in cell polarity, actin cable assembly and cytokinesis. However, roles have also been discovered for formins that are specific to particular organisms. Thus, formins perform both global and specific functions, with some of these roles concurring with previous biochemical data and others exposing new properties of formins. While not all family members have been examined across all organisms, the analyses to date highlight the significance of the flexibility within the formin family to regulate a broad spectrum of diverse cytoskeletal processes during development

Wash functions downstream of Rho and links linear and branched actin nucleation factors

Wiskott-Aldrich Syndrome (WAS) family proteins are Arp2/3 activators that mediate the branched-actin network formation required for cytoskeletal remodeling, intracellular transport and cell locomotion. Wasp and Scar/WAVE, the two founding members of the family, are regulated by the GTPases Cdc42 and Rac, respectively. By contrast, linear actin nucleators, such as Spire and formins, are regulated by the GTPase Rho. We recently identified a third WAS family member, called Wash, with Arp2/3-mediated actin nucleation activity. We show that Drosophila Wash interacts genetically with Arp2/3, and also functions downstream of Rho1 with Spire and the formin Cappuccino to control actin and microtubule dynamics during Drosophila oogenesis. Wash bundles and crosslinks F-actin and microtubules, is regulated by Rho1, Spire and Arp2/3, and is essential for actin cytoskeleton organization in the egg chamber. Our results establish Wash and Rho as regulators of both linear- and branched-actin networks, and suggest an Arp2/3-mediated mechanism for how cells might coordinately regulate these structures

CO-FISH Probe Map and Frequency of SCE

<p>(A) Single-stranded CO-FISH probes X, Y, and Z, shown as green ovals, hybridize 10 Mb, 110 kb, and 10 kb from the end of chromosomes, respectively. Y and Z probes hybridize to duplicated subtelomeric sequences, shown as grey rectangles. The orange probe indicated by the circle hybridizes to the telomere-repeat sequence (TTAGGG)_n at the ends of all chromosomes. The amount of SCE occurring between the orange telomeric signal and each green probe signal was measured in separate experiments. The scale bar indicates 20 kb. (B) In each experiment, four different CO-FISH configurations are possible in fully processed and hybridized chromosomes, shown as examples and diagrams as in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0030032#pgen-0030032-g001" target="_blank">Figure 1</a>. The number of chromosomes (and relative frequency) observed in each configuration is shown below. SCE events within the telomere that split the telomere probe signal between two chromatids at the same end were counted separately and not included in our estimates of terminal SCE rates (<a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0030032#pgen-0030032-sd001" target="_blank">Text S1</a>). GM08729 is a normal lymphoblastoid cell line, and GM16375 is a lymphoblastoid cell line derived from a patient with Bloom syndrome.</p