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- Volume 46, 2012
Annual Review of Genetics - Volume 46, 2012
Volume 46, 2012
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Mutations Arising During Repair of Chromosome Breaks
Vol. 46 (2012), pp. 455–473More LessMutations stimulate evolutionary change and lead to birth defects and cancer in humans as well as to antibiotic resistance in bacteria. According to the classic view, most mutations arise in dividing cells and result from uncorrected errors of S-phase DNA replication, which is highly accurate because of the involvement of selective DNA polymerases and efficient error-correcting mechanisms. In contrast, studies in bacteria and yeast reveal that DNA synthesis associated with repair of double-strand chromosomal breaks (DSBs) by homologous recombination is highly inaccurate, thus making DSBs and their repair an important source of mutations. Different error-prone mechanisms appear to operate in different repair scenarios. In the filling in of single-stranded DNA regions, error-prone translesion DNA polymerases appear to produce most errors. In contrast, in gene conversion gap repair and in break-induced replication, errors are independent of translesion polymerases, and many mutations have the signatures of template switching during DNA repair synthesis. DNA repair also appears to create complex copy-number variants. Overall, homologous recombination, which is traditionally considered a safe pathway of DSB repair, is an important source of mutagenesis that may contribute to human disease and evolution.
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Recessively Inherited Forms of Osteogenesis Imperfecta
Vol. 46 (2012), pp. 475–497More LessMore than 90% of people who have osteogenesis imperfecta (OI) have heterozygous mutations in one of the two type I collagen genes, COL1A1 and COL1A2. The effects of these changes range from death in the perinatal period to barely increased fracture frequency and reflect different types of mutations. Introduction of bisphosphonates during the past 20 years has targeted bone fragility by decreased resorption. The recent recognition of biallelic mutations in genes that affect either collagen assembly and processing or the regulation of osteoblast development has raised hopes for therapies that would be specific for single-gene disorders and identify cellular targets in individuals with the dominant forms of OI. These hopes are yet to be met, but the study of the recessively inherited forms of OI has illuminated the details of the collagen processing pathways.
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Neural Regeneration in Caenorhabditis elegans
Vol. 46 (2012), pp. 499–513More LessAxon regeneration is a medically relevant process that can repair damaged neurons. This review describes current progress in understanding axon regeneration in the model organism Caenorhabditis elegans. Factors that regulate axon regeneration in C. elegans have broadly similar roles in vertebrate neurons. This means that using C. elegans as a tool to leverage discovery is a legitimate strategy for identifying conserved mechanisms of axon regeneration.
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Genetics of Borrelia burgdorferi
Vol. 46 (2012), pp. 515–536More LessThe spirochetes in the Borrelia burgdorferi sensu lato genospecies group cycle in nature between tick vectors and vertebrate hosts. The current assemblage of B. burgdorferi sensu lato, of which three species cause Lyme disease in humans, originated from a rapid species radiation that occurred near the origin of the clade. All of these species share a unique genome structure that is highly segmented and predominantly composed of linear replicons. One of the circular plasmids is a prophage that exists as several isoforms in each cell and can be transduced to other cells, likely contributing to an otherwise relatively anemic level of horizontal gene transfer, which nevertheless appears to be adequate to permit strong natural selection and adaptation in populations of B. burgdorferi. Although the molecular genetic toolbox is meager, several antibiotic-resistant mutants have been isolated, and the resistance alleles, as well as some exogenous genes, have been fashioned into markers to dissect gene function. Genetic studies have probed the role of the outer membrane lipoprotein OspC, which is maintained in nature by multiple niche polymorphisms and negative frequency-dependent selection. One of the most intriguing genetic systems in B. burgdorferi is vls recombination, which generates antigenic variation during infection of mammalian hosts.
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Dosage Compensation of the Sex Chromosomes
Vol. 46 (2012), pp. 537–560More LessDifferentiated sex chromosomes evolved because of suppressed recombination once sex became genetically controlled. In XX/XY and ZZ/ZW systems, the heterogametic sex became partially aneuploid after degeneration of the Y or W. Often, aneuploidy causes abnormal levels of gene expression throughout the entire genome. Dosage compensation mechanisms evolved to restore balanced expression of the genome. These mechanisms include upregulation of the heterogametic chromosome as well as repression in the homogametic sex. Remarkably, strategies for dosage compensation differ between species. In organisms where more is known about molecular mechanisms of dosage compensation, specific protein complexes containing noncoding RNAs are targeted to the X chromosome. In addition, the dosage-regulated chromosome often occupies a specific nuclear compartment. Some genes escape dosage compensation, potentially resulting in sex-specific differences in gene expression. This review focuses on dosage compensation in mammals, with comparisons to fruit flies, nematodes, and birds.
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Memories from the Polycomb Group Proteins
Vol. 46 (2012), pp. 561–589More LessThe first genes composing the Polycomb group (PcG) were identified 50 years ago in Drosophila melanogaster as essential developmental functions that regulate the correct segmental expression of homeotic selector genes. In the past two decades, what was initially described as a large family of chromatin-associated proteins involved in the maintenance of transcriptional repression to maintain cellular memory of homeotic genes turned out to be a highly conserved and sophisticated network of epigenetic regulators that play key roles in multiple aspects of cell physiology and identity, including regulation of all developmental genes, cell differentiation, stem and somatic cell reprogramming and response to environmental stimuli. These myriad phenotypes further spread interest for the contribution that PcG proteins revealed in the pathogenesis and progression of cancer and other complex diseases. Recent novel insights have increasingly clarified the molecular regulatory mechanisms at the basis of PcG-mediated epigenetic silencing and opened new visions about PcG functions in cells. In this review, we focus on the multiple modes of action of the PcG complexes and describe their biological roles.
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Understanding the Relationship Between Brain Gene Expression and Social Behavior: Lessons from the Honey Bee
Vol. 46 (2012), pp. 591–615More LessBehavior is a complex phenotype that is plastic and evolutionarily labile. The advent of genomics has revolutionized the field of behavioral genetics by providing tools to quantify the dynamic nature of brain gene expression in relation to behavioral output. The honey bee Apis mellifera provides an excellent platform for investigating the relationship between brain gene expression and behavior given both the remarkable behavioral repertoire expressed by members of its intricate society and the degree to which behavior is influenced by heredity and the social environment. Here, we review a linked series of studies that assayed changes in honey bee brain transcriptomes associated with natural and experimentally induced changes in behavioral state. These experiments demonstrate that brain gene expression is closely linked with behavior, that changes in brain gene expression mediate changes in behavior, and that the association between specific genes and behavior exists over multiple timescales, from physiological to evolutionary.
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Identity by Descent Between Distant Relatives: Detection and Applications
Vol. 46 (2012), pp. 617–633More LessShort segments of identity by descent (IBD) between individuals with no known relationship can be detected using genome-wide single nucleotide polymorphism data and recently developed statistical methodology. Emerging applications for the detected IBD segments include IBD mapping, haplotype phase inference, genotype imputation, and inference of population structure. In this review, we explain the principles behind methods for IBD segment detection, describe recently developed methods, discuss approaches to comparing methods, and give an overview of applications.
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Paleopopulation Genetics
Vol. 46 (2012), pp. 635–649More LessPaleopopulation genetics is a new field that focuses on the population genetics of extinct groups and ancestral populations (i.e., populations ancestral to extant groups). With recent advances in DNA sequencing technologies, we now have unprecedented ability to directly assay genetic variation from fossils. This allows us to address issues, such as past population structure, changes in population size, and evolutionary relationships between taxa, at a much greater resolution than can traditional population genetics studies. In this review, we discuss recent developments in this emerging field as well as prospects for the future.
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Active Transposition in Genomes
Vol. 46 (2012), pp. 651–675More LessTransposons are DNA sequences capable of moving in genomes. Early evidence showed their accumulation in many species and suggested their continued activity in at least isolated organisms. In the past decade, with the development of various genomic technologies, it has become abundantly clear that ongoing activity is the rule rather than the exception. Active transposons of various classes are observed throughout plants and animals, including humans. They continue to create new insertions, have an enormous variety of structural and functional impact on genes and genomes, and play important roles in genome evolution. Transposon activities have been identified and measured by employing various strategies. Here, we summarize evidence of current transposon activity in various plant and animal genomes.
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Rules of Engagement: Molecular Insights from Host-Virus Arms Races
Vol. 46 (2012), pp. 677–700More LessMammalian genes and genomes have been shaped by ancient and ongoing challenges from viruses. These genetic imprints can be identified via evolutionary analyses to reveal fundamental details about when (how old), where (which protein domains), and how (what are the functional consequences of adaptive changes) host-virus arms races alter the proteins involved. Just as extreme amino acid conservation can serve to identify key immutable residues in enzymes, positively selected residues point to molecular recognition interfaces between host and viral proteins that have adapted and counter-adapted in a long series of classical Red Queen conflicts. Common rules for the strategies employed by both hosts and viruses have emerged from case studies of innate immunity genes in primates. We are now poised to use these rules to transition from a retrospective view of host-virus arms races to specific predictions about which host genes face pathogen antagonism and how those genetic conflicts transform host and virus evolution.
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Brassinosteroid Signaling Network and Regulation of Photomorphogenesis
Vol. 46 (2012), pp. 701–724More LessIn plants, the steroidal hormone brassinosteroid (BR) regulates numerous developmental processes, including photomorphogenesis. Genetic, proteomic, and genomic studies in Arabidopsis have illustrated a fully connected BR signal transduction pathway from the cell surface receptor kinase BRI1 to the BZR1 family of transcription factors. Genome-wide analyses of protein-DNA interactions have identified thousands of BZR1 target genes that link BR signaling to various cellular, metabolic, and developmental processes, as well as other signaling pathways. In controlling photomorphogenesis, BR signaling is highly integrated with the light, gibberellin, and auxin pathways through both direct interactions between signaling proteins and transcriptional regulation of key components of these pathways. BR signaling also cross talks with other receptor kinase pathways to modulate stomata development and innate immunity. The molecular connections in the BR signaling network demonstrate a robust steroid signaling system that has evolved in plants to orchestrate signal transduction, genome expression, metabolism, defense, and development.
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Previous Volumes
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Volume 58 (2024)
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Volume 57 (2023)
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Volume 56 (2022)
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Volume 55 (2021)
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Volume 54 (2020)
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Volume 53 (2019)
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Volume 52 (2018)
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Volume 51 (2017)
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Volume 50 (2016)
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Volume 49 (2015)
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Volume 48 (2014)
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Volume 47 (2013)
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Volume 46 (2012)
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Volume 45 (2011)
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Volume 44 (2010)
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Volume 43 (2009)
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Volume 42 (2008)
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Volume 41 (2007)
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Volume 40 (2006)
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Volume 39 (2005)
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Volume 38 (2004)
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Volume 37 (2003)
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Volume 36 (2002)
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Volume 35 (2001)
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Volume 34 (2000)
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Volume 33 (1999)
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Volume 32 (1998)
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Volume 31 (1997)
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Volume 30 (1996)
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Volume 29 (1995)
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Volume 28 (1994)
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Volume 27 (1993)
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Volume 26 (1992)
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Volume 25 (1991)
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Volume 24 (1990)
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Volume 23 (1989)
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Volume 22 (1988)
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Volume 21 (1987)
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Volume 20 (1986)
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Volume 19 (1985)
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Volume 18 (1984)
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Volume 17 (1983)
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Volume 16 (1982)
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Volume 15 (1981)
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Volume 14 (1980)
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Volume 13 (1979)
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Volume 12 (1978)
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Volume 11 (1977)
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Volume 10 (1976)
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Volume 9 (1975)
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Volume 8 (1974)
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Volume 7 (1973)
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Volume 6 (1972)
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Volume 5 (1971)
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Volume 4 (1970)
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Volume 3 (1969)
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Volume 2 (1968)
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Volume 1 (1967)
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Volume 0 (1932)