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R. Bergero, A. Forrest and D. Charlesworth
Y chromosomes, because they do not recombine with the X chromosome, degenerate over evolutionary time, with gene loss and pseudogenization, and the accumulation of repetitive sequences, including transposable elements. This article found a surprisingly high frequency of active MITE elements on Y chromosomes sampled from natural populations of Silene latifolia (white campion), but low frequencies elsewhere in the genome. The results suggest that insertions are deleterious and selection against insertions on the Y chromosome is less effective than it is elsewhere in the genome.
Lethal accumulation of guanylic nucleotides in Saccharomyces cerevisiae HPT1-deregulated mutants, pp. 815–824
Annick Breton, Benoît Pinson, Fanny Coulpier, Marie-France Giraud, Alain Dautant and Bertrand Daignan-Fornier
Feedback regulation of enzymes in biosynthetic pathways is a major means for matching the level of a pathway's product to the cell's needs. This article shows it can also be essential for survival. The authors apply genetic approaches to break the double regulatory lock that normally restrains guanylic nucleotide synthesis. Overexpression of a feedback-resistant HGPRT enzyme results in massive accumulation of guanylic nucleotides, which quickly arrests cell growth and causes massive cell death. Thus, overdose of essential cellular building blocks can be as detrimental as starvation for them.
Neuropathology in Drosophila mutants with increased seizure susceptibility, pp. 947–956
Tim Fergestad, Lisa Olson, Khelan P. Patel, Rosie Miller, Michael J. Palladino and Barry Ganetzky
Seizure-prone mutants of Drosophila have proven to be an important experimental model of epilepsy. This article describes the use of these mutants to investigate how genetic predisposition to seizures affects the long-term viability of neurons. They found that seizureprone mutants have shortened life spans and premature neurodegeneration, indicating that the affected proteins play a neuroprotective role. They also show that proper cellular metabolism is required to maintain normal neuronal activity and viability.
Multiple pathways influence mitochondrial inheritance in budding yeast, pp. 825–837
Rebecca L. Frederick, Koji Okamoto and Janet M. Shaw
Mitochondrial inheritance is tightly coupled with yeast bud emergence, ensuring that mothers pass their mitochondria on to their daughters. These authors describe multiple, independent pathways that facilitate organelle distribution during yeast budding. Despite the tight physical association of mitochondria and endoplasmic reticulum (ER), coordinated inheritance of these two organelles is not required to ensure each bud receives both mitochondria and ER.
DAF-16-dependent suppression of immunity during reproduction in Caenorhabditis elegans, pp. 903–918
Sachiko Miyata, Jakob Begun, Emily R. Troemel and Frederick M. Ausubel
How do animals balance the demands of different energy-intensive activities, such as pathogen defense and reproduction? These authors address this intriguing question by demonstrating that sterile mutants of the nematode Caenorhabditis elegans have increased resistance to pathogens, dependent on the evolutionarily conserved DAF-16 FOXO transcription factor. Because the timing of DAF-16 activation in sterile animals coincides with embryonic development in wild-type animals, the authors propose that a reproduction-dependent signal from developing embryos normally turns down DAF-16 activity, thus trading immunity for reproduction.
Functioning of the Drosophila Wilms'-tumor-1-associated protein homolog, Fl(2)d, in sex-lethal-dependent alternative splicing, pp. 737–748
Jill K. M. Penn, Patricia Graham, Girish Deshpande, Gretchen Calhoun, Ahmad Sami Chaouki, Helen K. Salz and Paul Schedl
The Drosophila homolog of Wilms'-tumor-1-associated protein (WTAP) regulates the alternative splicing of Sex-lethal (Sxl), a gene that plays a critical role in sex determination. Although WTAP has been found in human spliceosomes, what it contributes to the splicing process remains unknown. The authors show that the fly WTAP is associated with Sxl splicing complexes in vivo and that it binds to Sxl protein in vitro. Other results presented in this article indicate that these two proteins function at an early step of splicing.
Population biology of cytoplasmic incompatibility: Maintenance and spread of Cardinium symbionts in a parasitic wasp, pp. 1003–1011
Steve J. Perlman, Suzanne E. Kelly and Martha S. Hunter
A common cause of incompatibility in insects occurs when uninfected females mate with Wolbachia-infected males, resulting in death of all or most of their offspring. The authors study how the recently discovered incompatibility microbe Cardinium spreads through infected wasp populations. They find that virtually all hosts in a population are infected and the infection is faithfully transmitted from mothers to their offspring. The low fecundity of infected females still poses a mystery: How does the infection initially spread in the population?
Templated mutagenesis in bacteriophage T4 involving imperfect direct or indirect sequence repeats, pp. 661–673
Gary E. Schultz, Jr., and John W. Drake
Clustered mutations arise in imperfect sequence repeats when an extending DNA strand melts, reanneals with an ectopic template, extends briefly, and then returns to the correct template. This process resembles replication repair, in which extension is blocked by template damage and the daughter strand serves as the ectopic template. Mutations that impair replication repair can enhance templated mutagenesis, whose intensity can be exquisitely sensitive to local sequence. The donor and recipient arms of the repeat can exchange roles, and double mutants carrying two alleles, each affecting both templated mutagenesis and replication repair, can have unexpected phenotypes.
Caenorhabditis elegans ABCRNAi transporters interact genetically with rde-2 and mut-7, pp. 801–814
Prema Sundaram, Wang Han, Nancy Cohen, Benjamin Echalier, John Albin and Lisa Timmons
This article adds a surprising twist to a bewildering story emerging from transposon-related studies of Argonaute proteins, repeat-associated RNAs, and RNAi. These authors previously surprised us with their observation that some mutants of Caenorhabditis elegans with nonfunctional ABC transporters are defective in RNAi. Here they report another surprise—in addition to influencing RNAi, these same ABC transporter genes are required for silencing of parasitic mobile elements. Could it be that ABC transporters add an environmental factor to this story, or do they protect chromosomes from environmental assault? Stay tuned.
Microarray analysis of replicate populations selected against a wing-shape correlation in Drosophila melanogaster, pp. 1093–1108
Kenneth E. Weber, Ralph J. Greenspan, David R. Chicoine, Katia Fiorentino, Mary H. Thomas and Theresa L. Knight
How complex are complex traits? These authors address this question by profiling gene expression in wings of flies subjected to bidirectional selection on the phenotypic correlation between two wing dimensions. Replicated experiments on one population identified 29 loci with consistent, significant association with the trait. Additional experiments with a geographically distant population identified almost completely different loci associated with the trait, confirming recent evidence that a surprisingly large number of genes can affect wing shape.
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