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Erica G. Bakker, M. Brian Traw, Christopher Toomajian, Martin Kreitman and Joy Bergelson
Plants use defense response genes involved in signaling pathways to counter pathogen and herbivore attack. A collection of 27 defense response genes maintain low levels of protein variation across 96 Arabidopsis strains, with the majority of these genes experiencing purifying selection. This pattern of polymorphism is almost indistinguishable from a large panel of randomly chosen loci spread across the Arabidopsis genome. The high levels of selective constraint experienced by these genes could be attributed to the conserved nature of the end products of these pathways.
Rapid evolution of yeast centromeres in the absence of drive, pp. 2161–2167
Douda Bensasson, Magdalena Zarowiecki, Austin Burt and Vassiliki Koufopanou
Centromeres are the fastest evolving regions of the yeast genome, which is surprising in view of the universally conserved role of centromeres in all eukaryotes. The usual model of a runaway process of meiotic drive cannot
explain this result because the symmetric meioses in yeast preclude meiotic drive. The authors suggest that centromere sequences have elevated mutation rates.
Wispy, the Drosophila homolog of GLD-2, is required during oogenesis and egg activation, pp. 2017–2029
Jun Cui, Katharine L. Sackton, Vanessa L. Horner, Kritika E. Kumar and Mariana F. Wolfner
Development begins with activation for translation of mRNAs stored in the egg. The WISP protein is a member of Drosophila's GLD-2 family of cytoplasmic poly(A) polymerases, which regulate translatability of mRNAs during Caenorhabditis elegans and Xenopus oogenesis. This article describes how WISP in Drosophila extends poly(A) tails of maternal mRNAs like bicoid, whose translation is activation dependent. Wisp is also shown to act during oogenesis to regulate poly(A) addition and to do other things, such as activate MAPK kinases and promote pronuclear migration of post-meiotic nuclei in fertilized eggs.
The Caenorhabditis elegans rsd-2 and rsd-6 genes are required for chromosome functions during exposure to unfavorable environments, pp. 1875–1893
Wang Han, Prema Sundaram, Himanshu Kenjale, James Grantham and Lisa Timmons
RNAi is a conserved and essential gene regulatory process, with big machinery devoted to its function. In Caenorhabditis elegans, well over 100 genes are involved in gene silencing in response to dsRNA. Many of these genes are also required in basic cellular processes such as proper centromere function and chromosome segregation during meiosis and for processes that protect cells against invading viral genomes and transposons. What happens to RNAi-defective individuals when they are treated with dsRNAs? This article describes interesting environmental susceptibilities in two such mutants. Elevated temperature and exposure to dsRNAs elicit phenotypes that include chromosome nondisjunction and transposon mobilization, forces that may drive evolution in less favorable environments.
Quantitative genetic analysis of sleep in Drosophila melanogaster, pp. 2341–2360
Susan T. Harbison and Amita Sehgal
The purpose of sleep remains a biological puzzle, despite decades of intensive study of the problem. Sleep times are negatively correlated with energy reserves in many species, including Drosophila melanogaster, which exhibits many of the characteristics of mammalian sleep. These authors identify novel candidate genes for sleep and three measures of energy stores: protein, glycogen, and triglyceride reserves. Candidate genes for sleep exhibit extensive pleiotropy. The large mutational target observed for sleep suggests that sleep does not have a single purpose.
Pleiotropic patterns of quantitative trait loci for 70 murine skeletal traits, pp. 2275–2288
Jane P. Kenney-Hunt, Bing Wang, Elizabeth A. Norgard, Gloria Fawcett, Doug Falk, L. Susan Pletscher, Joseph P. Jarvis, Charles Roseman Jason Wolf and James M. Cheverud
How complex are complex traits? This article describes 798 single-trait QTL that coalesce to 105 pleiotropic loci affecting 70 morphometric traits relating to the mouse skeleton. Sounds pretty complex to us. Evaluating the pleiotropic relationships of skeletal traits is necessary for sorting out this complexity.
The Rad52 homologs Rad22 and Rti1 of Schizosaccharomyces pombe are not essential for meiotic interhomolog recombination, but are required for meiotic intrachromosomal recombination and mating-type-related DNA repair, pp. 2399–2412
Guillaume Octobre, Alexander Lorenz, Josef Loidl and Jürg Kohli
This article reappraises the meiotic roles of two Rad52 orthologs in fission yeast. Surprisingly, interhomolog recombination is only modestly decreased in a double mutant strain, while intrachromosomal recombination is more severely affected. This result suggests that there is considerable functional diversity of Rad52 enzymes among different species, which is somewhat surprising for such a fundamental process. A novel meiosis-specific, mating-type-related repair function of one of the Rad52 orthologs is also reported.
A Mutator transposon insertion is associated with ectopic expression of a tandemly repeated multicopy Myb gene pericarp color1 of maize, pp. 1859–1874
Michael L. Robbins, Rajandeep S. Sekhon, Robert Meeley and Surinder Chopra
In Mu-based suppression, continued transposase activity is required for the persistence of the mutant phenotype. However, the authors report an unusual mutant, caused by a Mu insertion in the six-copy tandemrepeated pericarp color1 gene, which results in the ectopic expression from uninterrupted copies of the pericarp color1 gene. Interestingly, this ectopic expression does not depend on continued transposase activity. Instead, the transposon insertion in the 5'-UTR of one of the repeated genes altered the epigenetic suppression of uninserted genes that is imposed by the multicopy gene complex. To explain this data, the authors propose that the Mu1 insertion interferes with the DNA methylation and related chromatin packaging of the pericarp color1 gene, thereby inducing expression from genes that are otherwise suppressed.
Genetic analysis of the Caenorhabditis elegans GLH family of P-granule proteins, pp. 1973–1987
Caroline Spike, Nicole Meyer, Erica Racen, April Orsborn, Jay Kirchner, Kathleen Kuznicki, Christopher Yee, Karen Bennett and Susan Strome
Germ cells of many species have distinctive cytoplasmic "granules" whose function is mysterious. This article investigates a family of four germline helicase (GLH) proteins related to Drosophila Vasa that associate with germ granules in Caenorhabditis elegans. The authors demonstrate that GLH-1 is the most important, GLH-4 serves as a back up, and GLH-2 and GLH-3 are dispensable. Loss of both GLH-1 and GLH-4 causes germ granules to lose some of their protein components and makes worms sterile.
The Saccharomyces cerevisiae actin cytoskeletal component Bsp1p has an auxiliary role in actomyosin ring function and in the maintenance of bud-neck structure, pp. 1903–1914
Daniel J. Wright, Ewen Munro, Mark Corbett, Adam J. Bentley, Nigel J. Fullwood, Stephen Murray and Clive Price
As we converge on a complete catalog of gene function, proteins that have resisted functional assignment come under increasingly intense scrutiny. Bsp1p is one such protein. It is a component of the budding yeast cytoskeleton that is associated with actin structures involved in the cell cycle, endocytosis, exocytosis, and cytokinesis. The authors report that Bsp1p plays a role in actin recruitment to the bud neck through an interaction with a GTPase-activating protein called IQGAP, and it also functions in the maintenance of bud-neck structure. This brings us closer to the completion of the yeast protein functional catalog.
Multiple rescue factors within a Wolbachia strain, pp. 2145–2160
Sofia Zabalou, Angeliki Apostolaki, Savvas Pattas, Zoe Veneti, Charalampos Paraskevopoulos, Ioannis Livadaras, George Markakis, Terry Brissac, Hervé Merçot and Kostas Bourtzis
Wolbachia are intracellular bacteria commonly associated with the induction of cytoplasmic incompatibility in numerous arthropods. The cytoplasmic incompatibility of different Wolbachia variants are usually explained assuming a single pair of modification and rescue factors specific to each variant. A single Wolbachia strain can possess multiple rescue determinants belonging to different cytoplasmic incompatibility systems. This article describes a "suicide" Wolbachia strain, unravels unique cytoplasmic incompatibility properties of bacterial strains present in Drosophila species, and provides the framework for a deeper understanding of the diversity and the evolution of new types of cytoplasmic incompatibility.
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