bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transposon Mutagenesis of the Mouse Germline
Authors: Carlson Corey M , Dupuy Adam J , Fritz Sabine , Roberg-Perez Kevin J , Fletcher Colin F , Largaespada David A 
Published: April 2021

Abstract
Sleeping Beauty is a synthetic “cut-and-paste” transposon of the Tc1/mariner class. The Sleeping Beauty transposase (SB) was constructed on the basis of a consensus sequence obtained from an alignment of 12 remnant elements cloned from the genomes of eight different fish species. Transposition of Sleeping Beauty elements has been observed in cultured cells, hepatocytes of adult mice, one-cell mouse embryos, and the germline of mice. SB has potential as a random germline insertional mutagen useful for in vivo gene trapping in mice. Previous work in our lab has demonstrated transposition in the male germline of mice and transmission of novel inserted transposons in offspring. To determine sequence preferences and mutagenicity of SB-mediated transposition, we cloned and analyzed 44 gene-trap transposon insertion sites from a panel of 30 mice. The distribution and sequence content flanking these cloned insertion sites was compared to 44 mock insertion sites randomly selected from the genome. We find that germline SB transposon insertion sites are AT-rich and the sequence ANNTANNT is favored compared to other TA dinucleotides. Local transposition occurs with insertions closely linked to the donor site roughly one-third of the time. We find that ∼27% of the transposon insertions are in transcription units. Finally, we characterize an embryonic lethal mutation caused by endogenous splicing disruption in mice carrying a particular intron-inserted gene-trap transposon.
The Extent of Linkage Disequilibrium and Haplotype Sharing Around a Polymorphic Site
Authors: Innan Hideki , Nordborg Magnus 
Published: April 2021

Abstract
Various expressions related to the length of a conserved haplotype around a polymorphism of known frequency are derived. We obtain exact expressions for the probability that no recombination has occurred in a sample or subsample. We obtain an approximation for the probability that no recombination that could give rise to a detectable recombination event (through the four-gamete test) has occurred. The probabilities can be used to obtain approximate distributions for the length of variously defined haplotypes around a polymorphic site. The implications of our results for data analysis, and in particular for detecting selection, are discussed.
Limitations of Allotopic Expression of Mitochondrial Genes in Mammalian Cells
Authors: Oca-Cossio Jose , Kenyon Lesley , Hao Huiling , Moraes Carlos T 
Published: April 2021

Abstract
The possibility of expressing mitochondrial DNA-coded genes in the nuclear-cytoplasmic compartment provides an attractive system for genetic treatment of mitochondrial disorders associated with mitochondrial DNA mutations. In theory, by recoding mitochondrial genes to adapt them to the universal genetic code and by adding a DNA sequence coding for a mitochondrial-targeting sequence, one could achieve correct localization of the gene product. Such transfer has occurred in nature, and certain species of algae and plants express a number of polypeptides that are commonly coded by mtDNA in the nuclear-cytoplasmic compartment. In the present study, allotopic expression of three different mtDNA-coded polypeptides (ATPase8, apocytochrome b, and ND4) into COS-7 and HeLa cells was analyzed. Among these, only ATPase8 was correctly expressed and localized to mitochondria. The full-length, as well as truncated forms, of apocytochrome b and ND4 decorated the periphery of mitochondria, but also aggregated in fiber-like structures containing tubulin and in some cases also vimentin. The addition of a hydrophilic tail (EGFP) to the C terminus of these polypeptides did not change their localization. Overexpression of molecular chaperones also did not have a significant effect in preventing aggregations. Allotopic expression of apocytochrome b and ND4 induced a loss of mitochondrial membrane potential in transfected cells, which can lead to cell death. Our observations suggest that only a subset of mitochondrial genes can be replaced allotopically. Analyses of the hydrophobic patterns of different polypeptides suggest that hydrophobicity of the N-terminal segment is the main determinant for the importability of peptides into mammalian mitochondria.
A General Statistical Framework for Mapping Quantitative Trait Loci in Nonmodel Systems: Issue for Characterizing Linkage Phases
Authors: Lin Min , Lou Xiang-Yang , Chang Myron , Wu Rongling 
Published: April 2021

AbstractBecause of uncertainty about linkage phases of founders, linkage mapping in nonmodel, outcrossing systems using molecular markers presents one of the major statistical challenges in genetic research. In this article, we devise a statistical method for mapping QTL affecting a complex trait by incorporating all possible QTL-marker linkage phases within a mapping framework. The advantage of this model is the simultaneous estimation of linkage phases and QTL location and effect parameters. These estimates are obtained through maximum-likelihood methods implemented with the EM algorithm. Extensive simulation studies are performed to investigate the statistical properties of our model. In a case study from a forest tree, this model has successfully identified a significant QTL affecting wood density. Also, the probability of the linkage phase between this QTL and its flanking markers is estimated. The implications of our model and its extension to more general circumstances are discussed.
The Divergent Orphan Nuclear Receptor ODR-7 Regulates Olfactory Neuron Gene Expression via Multiple Mechanisms in Caenorhabditis elegans
Authors: Colosimo Marc E , Tran Susan , Sengupta Piali 
Published: April 2021

Abstract
Nuclear receptors regulate numerous critical biological processes. The C. elegans genome is predicted to encode ∼270 nuclear receptors of which &gt;250 are unique to nematodes. ODR-7 is the only member of this large divergent family whose functions have been defined genetically. ODR-7 is expressed in the AWA olfactory neurons and specifies AWA sensory identity by promoting the expression of AWA-specific signaling genes and repressing the expression of an AWC-specific olfactory receptor gene. To elucidate the molecular mechanisms of action of a divergent nuclear receptor, we have identified residues and domains required for different aspects of ODR-7 function in vivo. ODR-7 utilizes an unexpected diversity of mechanisms to regulate the expression of different sets of target genes. Moreover, these mechanisms are distinct in normal and heterologous cellular contexts. The odr-7 ortholog in the closely related nematode C. briggsae can fully substitute for all ODR-7-mediated functions, indicating conservation of function across 25–120 million years of divergence.
Evolution of the HumanASPMGene, a Major Determinant of Brain Size
Authors: Zhang Jianzhi 
Published: April 2021

AbstractThe size of human brain tripled over a period of ∼2 million years (MY) that ended 0.2–0.4 MY ago. This evolutionary expansion is believed to be important to the emergence of human language and other high-order cognitive functions, yet its genetic basis remains unknown. An evolutionary analysis of genes controlling brain development may shed light on it. ASPM (abnormal spindle-like microcephaly associated) is one of such genes, as nonsense mutations lead to primary microcephaly, a human disease characterized by a 70% reduction in brain size. Here I provide evidence suggesting that human ASPM went through an episode of accelerated sequence evolution by positive Darwinian selection after the split of humans and chimpanzees but before the separation of modern non-Africans from Africans. Because positive selection acts on a gene only when the gene function is altered and the organismal fitness is increased, my results suggest that adaptive functional modifications occurred in human ASPM and that it may be a major genetic component underlying the evolution of the human brain.
Fission Yeast Mus81·Eme1 Holliday Junction Resolvase Is Required for Meiotic Crossing Over but Not for Gene Conversion
Authors: Smith Gerald R , Boddy Michael N , Shanahan Paul , Russell Paul 
Published: April 2021

Abstract
Most models of homologous recombination invoke cleavage of Holliday junctions to explain crossing over. The Mus81·Eme1 endonuclease from fission yeast and humans cleaves Holliday junctions and other branched DNA structures, leaving its physiological substrate uncertain. We report here that Schizosaccharomyces pombe mus81 mutants have normal or elevated frequencies of gene conversion but 20- to 100-fold reduced frequencies of crossing over. Thus, gene conversion and crossing over can be genetically separated, and Mus81 is required for crossing over, supporting the hypothesis that the fission yeast Mus81·Eme1 protein complex resolves Holliday junctions in meiotic cells.
Distinguishing the Hitchhiking and Background Selection Models
Authors: Innan Hideki , Stephan Wolfgang 
Published: April 2021

Abstract
A simple method to distinguish hitchhiking and background selection is proposed. It is based on the observation that these models make different predictions about the average level of nucleotide diversity in regions of low recombination. The method is applied to data from Drosophila melanogaster and two highly selfing tomato species.
Derivation of a Bayes Factor to Distinguish Between Linked or Pleiotropic Quantitative Trait Loci
Authors: Varona L , Gómez-Raya L , Rauw W M , Clop A , Ovilo C , Noguera J L 
Published: April 2021

AbstractA simple procedure to calculate the Bayes factor between linked and pleiotropic QTL models is presented. The Bayes factor is calculated from the marginal prior and posterior densities of the locations of the QTL under a linkage and a pleiotropy model. The procedure is computed with a Gibbs sampler, and it can be easily applied to any model including the location of the QTL as a variable. The procedure was compared with a multivariate least-squares method. The proposed procedure showed better results in terms of power of detection of linkage when low information is available. As information increases, the performance of both procedures becomes similar. An example using data provided by an Iberian by Landrace pig intercross is presented. The results showed that three different QTL segregate in SSC6: a pleiotropic QTL affects myristic, palmitic, and eicosadienoic fatty acids; another pleiotropic QTL affects palmitoleic, stearic, and vaccenic fatty acids; and a third QTL affects the percentage of linoleic acid. In the example, the Bayes factor approach was more powerful than the multivariate least-squares approach.
Influence of Spatial and Temporal Heterogeneities on the Estimation of Demographic Parameters in a Continuous Population Using Individual Microsatellite Data
Authors: Leblois Raphael , Rousset François , Estoup Arnaud 
Published: April 2021

Abstract
Drift and migration disequilibrium are very common in animal and plant populations. Yet their impact on methods of estimation of demographic parameters was rarely evaluated especially in complex realistic population models. The effect of such disequilibria on the estimation of demographic parameters depends on the population model, the statistics, and the genetic markers used. Here we considered the estimation of the product Dσ2 from individual microsatellite data, where D is the density of adults and σ2 the average squared axial parent-offspring distance in a continuous population evolving under isolation by distance. A coalescence-based simulation algorithm was used to study the effect on Dσ2 estimation of temporal and spatial fluctuations of demographic parameters. Estimation of present-time Dσ2 values was found to be robust to temporal changes in dispersal, to density reduction, and to spatial expansions with constant density, even for relatively recent changes (i.e., a few tens of generations ago). By contrast, density increase in the recent past gave Dσ2 estimations biased largely toward past demographic parameters values. The method was also robust to spatial heterogeneity in density and estimated local demographic parameters when the density is homogenous around the sampling area (e.g., on a surface that equals four times the sampling area). Hence, in the limit of the situations studied in this article, and with the exception of the case of density increase, temporal and spatial fluctuations of demographic parameters appear to have a limited influence on the estimation of local and present-time demographic parameters with the method studied.
Homology Modeling and Mutational Analysis of Ho Endonuclease of Yeast
Authors: Bakhrat Anya , Jurica Melissa S , Stoddard Barry L , Raveh Dina 
Published: April 2021

Abstract
Ho endonuclease is a LAGLIDADG homing endonuclease that initiates mating-type interconversion in yeast. Ho is encoded by a free-standing gene but shows 50% primary sequence similarity to the intein (protein-intron encoded) PI-SceI. Ho is unique among LAGLIDADG endonucleases in having a 120-residue C-terminal putative zinc finger domain. The crystal structure of PI-SceI revealed a bipartite enzyme with a protein-splicing domain (Hint) and intervening endonuclease domain. We made a homology model for Ho on the basis of the PI-SceI structure and performed mutational analysis of putative critical residues, using a mating-type switch as a bioassay for activity and GFP-fusion proteins to detect nuclear localization. We found that residues of the N-terminal sequence of the Hint domain are important for Ho activity, in particular the DNA recognition region. C-terminal residues of the Hint domain are dispensable for Ho activity; however, the C-terminal putative zinc finger domain is essential. Mutational analysis indicated that residues in Ho that are conserved relative to catalytic, active-site residues in PI-SceI and other related homing endonucleases are essential for Ho activity. Our results indicate that in addition to the conserved catalytic residues, Hint domain residues and the zinc finger domain have evolved a critical role in Ho activity.
Genetic and Bioinformatic Analysis of 41C and the 2R Heterochromatin ofDrosophila melanogaster: A Window on the Heterochromatin-Euchromatin Junction
Authors: Myster Steven H , Wang Fei , Cavallo Robert , Christian Whitney , Bhotika Seema , Anderson Charles T , Peifer Mark 
Published: April 2021

AbstractGenomic sequences provide powerful new tools in genetic analysis, making it possible to combine classical genetics with genomics to characterize the genes in a particular chromosome region. These approaches have been applied successfully to the euchromatin, but analysis of the heterochromatin has lagged somewhat behind. We describe a combined genetic and bioinformatics approach to the base of the right arm of the Drosophila melanogaster second chromosome, at the boundary between pericentric heterochromatin and euchromatin. We used resources provided by the genome project to derive a physical map of the region, examine gene density, and estimate the number of potential genes. We also carried out a large-scale genetic screen for lethal mutations in the region. We identified new alleles of the known essential genes and also identified mutations in 21 novel loci. Fourteen complementation groups map proximal to the assembled sequence. We used PCR to map the endpoints of several deficiencies and used the same set of deficiencies to order the essential genes, correlating the genetic and physical map. This allowed us to assign two of the complementation groups to particular “computed/curated genes” (CGs), one of which is Nipped-A, which our evidence suggests encodes Drosophila Tra1/TRRAP.
EXO1 Contributes to Telomere Maintenance in Both Telomerase-Proficient and Telomerase-Deficient Saccharomyces cerevisiae
Authors: Bertuch Alison A , Lundblad Victoria 
Published: April 2021

Abstract
Previous work in budding yeast has indicated that telomeres are protected, at least in part, from the action of Exo1, which degrades the C-rich strand of partially uncapped telomeres. To explore this further, we examined the consequences of Exo1-mediated activity in strains that lacked Ku, telomerase, or both. Loss of Exo1 partially rescued the telomere length defect in a yku80Δ strain, demonstrating that exonuclease action can directly contribute to telomere shortening. The rapid loss of inviability displayed by a yku80Δ est2Δ strain was also partially alleviated by an exo1Δ mutation, further supporting the proposal that Exo1 is one target of the activities that normally protect wild-type telomeres. Conversely, however, Exo1 activity was also capable of enhancing telomere function and consequently cell proliferation, by contributing to a telomerase-independent pathway for telomere maintenance. The recovery of recombination-dependent survivors that arose in a yku80Δ est2Δ strain was partially dependent on Exo1 activity. Furthermore, the types of recombination events that facilitate telomerase-independent survival were influenced by Exo1 activity, in both est2Δ and yku80Δ est2Δ strains. These data demonstrate that Exo1 can make either positive or negative contributions to telomere function and cell viability, depending on whether telomerase or recombination is utilized to maintain telomere function.
Construction of Transgenic Drosophila by Using the Site-Specific Integrase From Phage φC31
Authors: Groth Amy C , Fish Matthew , Nusse Roel , Calos Michele P 
Published: April 2021

Abstract
The φC31 integrase functions efficiently in vitro and in Escherichia coli, yeast, and mammalian cells, mediating unidirectional site-specific recombination between its attB and attP recognition sites. Here we show that this site-specific integration system also functions efficiently in Drosophila melanogaster in cultured cells and in embryos. Intramolecular recombination in S2 cells on transfected plasmid DNA carrying the attB and attP recognition sites occurred at a frequency of 47%. In addition, several endogenous pseudo attP sites were identified in the fly genome that were recognized by the integrase and used as substrates for integration in S2 cells. Two lines of Drosophila were created by integrating an attP site into the genome with a P element. φC31 integrase injected into embryos as mRNA functioned to promote integration of an attB-containing plasmid into the attP site, resulting in up to 55% of fertile adults producing transgenic offspring. A total of 100% of these progeny carried a precise integration event at the genomic attP site. These experiments demonstrate the potential for precise genetic engineering of the Drosophila genome with the φC31 integrase system and will likely benefit research in Drosophila and other insects.
Mitochondrial Cytochrome b DNA Variation in the High-Fecundity Atlantic Cod: Trans-Atlantic Clines and Shallow Gene Genealogy
Authors: Árnason Einar 
Published: April 2021

Abstract
An analysis of sequence variation of 250 bp of the mitochondrial cytochrome b gene of 1278 Atlantic cod Gadus morhua ranging from Newfoundland to the Baltic shows four high-frequency (&gt;8%) haplotypes and a number of rare and singleton haplotypes. Variation is primarily synonymous mutations. Natural selection acting directly on these variants is either absent or very weak. Common haplotypes show regular trans-Atlantic clines in frequencies and each of them reaches its highest frequency in a particular country. A shallow multifurcating constellation gene genealogy implies young age and recent turnover of polymorphism. Haplotypes characterizing populations at opposite ends of the geographic distribution in Newfoundland and the Baltic are mutationally closest together. The haplotypes are young and have risen rapidly in frequency. Observed differentiation among countries is due primarily to clinal variation. Hypotheses of historical isolation and polymorphisms balanced by local selection and gene flow are unlikely. Instead the results are explained by demic selection of mitochondria carried by highly fit females winning reproductive sweepstakes. By inference the Atlantic cod, a very high-fecundity vertebrate, is characterized by a high variance of offspring number and strong natural selection that leads to very low effective to actual population sizes.
Dynamic Changes in the Distribution of a Satellite Homologous to Intergenic 26-18S rDNA Spacer in the Evolution of Nicotiana
Authors: Lim K Y , Skalicka K , Koukalova B , Volkov R A , Matyasek R , Hemleben V , Leitch A R , Kovarik A 
Published: April 2021

Abstract
An ∼135-bp sequence called the A1/A2 repeat was isolated from the transcribed region of the 26-18S rDNA intergenic spacer (IGS) of Nicotiana tomentosiformis. Fluorescence in situ hybridization (FISH) and Southern blot analysis revealed its occurrence as an independent satellite (termed an A1/A2 satellite) outside of rDNA loci in species of Nicotiana section Tomentosae. The chromosomal location, patterns of genomic dispersion, and copy numbers of its tandemly arranged units varied between the species. In more distantly related Nicotiana species the A1/A2 repeats were found only at the nucleolar organizer regions (NOR). There was a trend toward the elimination of the A1/A2 satellite in N. tabacum (tobacco), an allotetraploid with parents closely related to the diploids N. sylvestris and N. tomentosiformis. This process may have already commenced in an S3 generation of synthetic tobacco. Cytosine residues in the IGS were significantly hypomethylated compared with the A1/A2 satellite. There was no clear separation between the IGS and satellite fractions in sequence analysis of individual clones and we found no evidence for CG suppression. Taken together the data indicate a dynamic nature of the A1/A2 repeats in Nicotiana genomes, with evidence for recurrent integration, copy number expansions, and contractions.
Mapping Quantitative Trait Loci in F2 Incorporating Phenotypes of F3 Progeny
Authors: Zhang Yuan-Ming , Xu Shizhong 
Published: April 2021

AbstractIn plants and laboratory animals, QTL mapping is commonly performed using F2 or BC individuals derived from the cross of two inbred lines. Typical QTL mapping statistics assume that each F2 individual is genotyped for the markers and phenotyped for the trait. For plant traits with low heritability, it has been suggested to use the average phenotypic values of F3 progeny derived from selfing F2 plants in place of the F2 phenotype itself. All F3 progeny derived from the same F2 plant belong to the same F2:3 family, denoted by F2:3. If the size of each F2:3 family (the number of F3 progeny) is sufficiently large, the average value of the family will represent the genotypic value of the F2 plant, and thus the power of QTL mapping may be significantly increased. The strategy of using F2 marker genotypes and F3 average phenotypes for QTL mapping in plants is quite similar to the daughter design of QTL mapping in dairy cattle. We study the fundamental principle of the plant version of the daughter design and develop a new statistical method to map QTL under this F2:3 strategy. We also propose to combine both the F2 phenotypes and the F2:3 average phenotypes to further increase the power of QTL mapping. The statistical method developed in this study differs from published ones in that the new method fully takes advantage of the mixture distribution for F2:3 families of heterozygous F2 plants. Incorporation of this new information has significantly increased the statistical power of QTL detection relative to the classical F2 design, even if only a single F3 progeny is collected from each F2:3 family. The mixture model is developed on the basis of a single-QTL model and implemented via the EM algorithm. Substantial computer simulation was conducted to demonstrate the improved efficiency of the mixture model. Extension of the mixture model to multiple QTL analysis is developed using a Bayesian approach. The computer program performing the Bayesian analysis of the simulated data is available to users for real data analysis.