Genetics, Vol. 175, February 2007, Copyright © 2007

ISSUE HIGHLIGHTS

Combining sperm typing and linkage disequilibrium analyses reveals differences in selective pressures or recombination rates across human populations, pp. 795–804

Vanessa J. Clark, Susan E. Ptak, Irene Tiemann, Yudong Qian, Graham Coop, Anne C. Stone, Molly Przeworski, Norman Arnheim and Anna Di Rienzo

This article examines discordance between the estimates of human recombination rate from single sperm typing compared to those from population genetic methods. Polymorphism in CAPN10 identified a segment with localized breakdown of linkage disequilibrium only in African samples, raising the possibility of a recombination hotspot that is restricted to African populations. Estimates of recombination rates from single sperm typing in five non-African men gave results consistent with the linkage disequilibrium (LD) decay in the non-African, but not in the African data. The integrated analysis of sperm-typing data and population genetics data leads to the conclusion that LD patterns across the region are inconsistent with neutral evolution or with a common recombination rate in all populations.

The overexpression of a Saccharomyces cerevisiae centromeric histone H3 variant mutant protein leads to a defect in kinetochore biorientation, pp. 513–525

Kimberly A. Collins, Raymond Camahort, Chris Seidel, Jennifer L. Gerton and Sue Biggins

The centromeric histone H3 (CenH3) variant is localized exclusively to centromeres and replaces canonical H3 in centromeric nucleosomes. The authors report the isolation of mutants in the yeast CenH3 gene (Cse4) that are lethal when overexpressed and show that they fall into three phenotypic classes on the basis of the localization of the endogenous and mutant proteins and whether or not the spindle checkpoint is activated. In doing so, the authors identify the first class of Cse4 mutants that no longer localize to the centromere. In cells overexpressing this class of Cse4 mutant, kinetochores assemble, but they cannot make proper bioriented attachments to microtubules. These results suggest a role for the endogenous Cse4 protein in biorientation in addition to its essential function in assembling the kinetochore.

Onset of the DNA replication checkpoint in the early Drosophila embryo, pp. 567–584

Justin Crest, Nathan Oxnard, Jun-Yuan Ji and Gerold Schubiger

Embryonic development in Drosophila is initiated by cleavage stages that are controlled by maternal gene products. This article provides the first evidence that the DNA replication checkpoint is constitutively active early in development but overridden by the huge amount of Cdk1–CycB. However, reducing the dosage of the dRPA2 gene counteracts the ability of this excess Cdk1–CycB to override checkpoint function. These results suggest an antagonistic interaction between DNA replication checkpoint activation and Cdk1–CycB activity during the transition from preblastoderm to blastoderm cycles.

Drosophila melanogaster male somatic cells feminized solely by TraF can collaborate with female germ cells to make functional eggs, pp. 631–642

Daniel S. Evans and Thomas W. Cline

Cell nonautonomous and autonomous signals together specify Drosophila germ cell sexual identity in contrast to somatic sex determination, which is a cell autonomous process. This article presents the simplifying finding that the somatic sex-switch gene, transformer, can induce all the nonautonomous signals that diplo-X (chromosomally female) germ cells need from the gonadal soma to make functional eggs. Surprisingly, the same experiment shows that haplo-X (chromosomally male) somatic cells in the ovary can successfully execute functions for which their genome is not expected to be dosage compensated and that haplo-X germ cells can successfully compete with diplo-X germ cells in a developing ovary.

Mutation of a ubiquitously expressed mouse transmembrane protein (Tapt1) causes specific skeletal homeotic transformations, pp. 699–707

Gareth R. Howell, Mami Shindo, Stephen Murray, Thomas Gridley, Lawriston A. Wilson and John C. Schimenti

The mouse Tapt1 mutation, identified in a forward genetic mutagenesis screen, causes homeotic-like skeletal transformations similar to knockouts of some Hox genes. However, the mutation is particularly unique in that it does not disrupt the expression of the Hox gene (Hoxc8) whose mutation it phenocopies. Interestingly, Tapt1 is a novel gene, part of which serves as a receptor for human cytomegalovirus.

Development of a near-isogenic line population of Arabidopsis thaliana and comparison of mapping power with a recombinant inbred line population, pp. 891–905

Joost J. B. Keurentjes, Leónie Bentsink, Carlos Alonso-Blanco, Corrie J. Hanhart, Hetty Blankestijn-De Vries, Sigi Effgen, Dick Vreugdenhil and Maarten Koornneef

The development of experimental populations that are structured in such a way to maximize the power and resolution for mapping of quantitative traits is an important challenge. This article presents results from a contrast between two very different designs, recombinant inbred lines (RILs) and near isogenic lines (NILs), using the same pair of Arabidopsis thaliana founders. RILs can be generated by crossing a pair of distinct homozygous lines and inbreeding at the F2 (or later stages) to produce a set of lines with mixed but equal representation of the two founders. Analysis of RILs can be limited because of masking effects of major quantitative trait loci (QTL) and epistatic interactions across multiple QTL. NILs are sets of introgression lines whose genome is predominantly derived from one parent. Results show that the NILs allow discovery of QTL with smaller effects, but the NIL design has lower localization resolution. This analysis will facilitate experimental design for QTL mapping using these two common types of segregating populations.

Importance of the Hsp70 ATPase domain in yeast prion propagation, pp. 621–630

Harriët M. Loovers, Emma Guinan and Gary W. Jones

The Saccharomyces cerevisiae non-Mendelian genetic element [PSI+] is the prion form (infectious protein) of the translation termination factor Sup35p. Chaperones have been implicated as the major cellular factors affecting the propagation of prions. In this article the authors describe the isolation of 26 new mutants of the major yeast cytosolic Hsp70 family that impair propagation of prions in yeast. The vast majority of mutants are located within the ATPase domain. These mutants highlight the importance of Hsp70 interdomain communication and regulation of ATP hydrolysis in the propagation of prions.

An ectopic expression screen reveals the protective and toxic effects of Drosophila seminal fluid proteins, pp. 777–783

Jacob L. Mueller, Jennifer L. Page and Mariana F. Wolfner

Drosophila melanogaster seminal proteins have important effects on mated females, roles that may also have implications for speciation. Some seminal fluid proteins may provide protective functions to mated females, such as antimicrobial activity and/or stimulation of antimicrobial gene expression levels, while others appear to have negative effects on female longevity. By testing ectopic expression of 23 individual seminal proteins, the authors identify three seminal proteins that assist in clearing a bacterial infection, thus potentially exerting protective effects on mated females. Another three are toxic to Drosophila, suggesting negative effects on females. Consistent with this, one of the toxic proteins was previously implicated in the longevity cost of mating. These proteins are candidates for proximate and long-term roles in interaction between the sexes.

An analysis of univalent segregation in meiotic mutants of Arabidopsis thaliana: A possible role for synaptonemal complex, pp. 505–511

Mónica Pradillo, Eva López, Concepción Romero, Eugenio Sánchez-Morán, Nieves Cuñado and Juan L. Santos

As in most other organisms, in Arabidopsis chiasmata play a critical role in ensuring proper meiotic segregation. But what happens when reciprocal recombination is absent? Do the nonexchange homologs segregate at random or is there a backup system (similar to those found in flies and yeast) that can ensure the proper segregation of nonexchange homologs? To address these questions, the authors analyze the chromosome behavior in four meiotic mutants of Arabidopsis thaliana, which shows a high frequency of univalents at diplotene. Nonrandom univalent segregation was observed only in those mutants in which full synapsis was achieved at pachytene. This finding suggests that in Arabidopsis there is a synaptonemal complex-dependent system that promotes the accurate segregation of univalents to opposite poles at anaphase I. These observations provide the first evidence for distributive segregation in a plant.

Mos1 mutagenesis reveals a diversity of mechanisms affecting response of Caenorhabditis elegans to the bacterial pathogen Microbacterium nematophilum, pp. 681–697

Karen Yook and Jonathan Hodgkin

This work demonstrates the utility of Mos1 transposon mutagenesis for rapidly identifying and cloning genes affecting the response to a bacterial pathogen in Caenorhabditis elegans. Four genes were studied in detail: two were previously known from other functions in the biology of the worm, but were found to have new infection-related roles in bacterial response. Two others affect the surface properties of the worm and appear necessary for the initial adhesion of pathogenic bacteria; one encodes a predicted galactosyltransferase and the other encodes a predicted transmembrane protein, which has homologs of unknown function in both eukaryotes and prokaryotes.


Related articles in Genetics:

An Analysis of Univalent Segregation in Meiotic Mutants of Arabidopsis thaliana: A Possible Role for Synaptonemal Complex
Mónica Pradillo, Eva López, Concepción Romero, Eugenio Sánchez-Morán, Nieves Cuñado, and Juan L. Santos
Genetics 2007 175: 505-511. [Abstract] [Full Text]  

The Overexpression of a Saccharomyces cerevisiae Centromeric Histone H3 Variant Mutant Protein Leads to a Defect in Kinetochore Biorientation
Kimberly A. Collins, Raymond Camahort, Chris Seidel, Jennifer L. Gerton, and Sue Biggins
Genetics 2007 175: 513-525. [Abstract] [Full Text]  

Onset of the DNA Replication Checkpoint in the Early Drosophila Embryo
Justin Crest, Nathan Oxnard, Jun-Yuan Ji, and Gerold Schubiger
Genetics 2007 175: 567-584. [Abstract] [Full Text]  

Importance of the Hsp70 ATPase Domain in Yeast Prion Propagation
Harriët M. Loovers, Emma Guinan, and Gary W. Jones
Genetics 2007 175: 621-630. [Abstract] [Full Text]  

Drosophila melanogaster Male Somatic Cells Feminized Solely by TraF Can Collaborate With Female Germ Cells to Make Functional Eggs
Daniel S. Evans and Thomas W. Cline
Genetics 2007 175: 631-642. [Abstract] [Full Text]  

Mos1 Mutagenesis Reveals a Diversity of Mechanisms Affecting Response of Caenorhabditis elegans to the Bacterial Pathogen Microbacterium nematophilum
Karen Yook and Jonathan Hodgkin
Genetics 2007 175: 681-697. [Abstract] [Full Text]  

Mutation of a Ubiquitously Expressed Mouse Transmembrane Protein (Tapt1) Causes Specific Skeletal Homeotic Transformations
Gareth R. Howell, Mami Shindo, Stephen Murray, Thomas Gridley, Lawriston A. Wilson, and John C. Schimenti
Genetics 2007 175: 699-707. [Abstract] [Full Text]  

An Ectopic Expression Screen Reveals the Protective and Toxic Effects of Drosophila Seminal Fluid Proteins
Jacob L. Mueller, Jennifer L. Page, and Mariana F. Wolfner
Genetics 2007 175: 777-783. [Abstract] [Full Text]  

Combining Sperm Typing and Linkage Disequilibrium Analyses Reveals Differences in Selective Pressures or Recombination Rates Across Human Populations
Vanessa J. Clark, Susan E. Ptak, Irene Tiemann, Yudong Qian, Graham Coop, Anne C. Stone, Molly Przeworski, Norman Arnheim, and Anna Di Rienzo
Genetics 2007 175: 795-804. [Abstract] [Full Text]  

Development of a Near-Isogenic Line Population of Arabidopsis thaliana and Comparison of Mapping Power With a Recombinant Inbred Line Population
Joost J. B. Keurentjes, Leónie Bentsink, Carlos Alonso-Blanco, Corrie J. Hanhart, Hetty Blankestijn-De Vries, Sigi Effgen, Dick Vreugdenhil, and Maarten Koornneef
Genetics 2007 175: 891-905. [Abstract] [Full Text]