1,720,959 research outputs found
Karyotype evolution of the family Araneidae
No full textOrb-weavers (Araneidae) are a diversified spider family comprising more than 3,100 species in more than 170 genera. Together with 13 other families, they con- stitute to superfamily Araneoidea. The presented thesis focuses on karyotype evo- lution of Araneidae, including its comparison with a related family Tetragnathidae. The results obtained from 19 araneid and four tetragnathid species confirm previ- ously postulated hypothesis that the ancestral karyotype of Araneoidea (including Araneidae) consists of 24 acrocentric chromosomes in males, including two acro- centric X chromosomes of system X1X20. However, there is a tendency of 2n decrease in some araneids due to centric fusions. In these cases, centric fusions affected most autosomes (and sometimes gonosomes as well); number of chromosome pairs de- creased from 11 to six. Three independent reduction events were detected in this thesis. Furthermore, pattern of nucleolar organizer regions (NORs) was studied in this thesis using fluorescent in situ hybridization, since data on evolution of this marker are scarce in spiders. Striking variability in NORs number was discovered, ranging from one to 13 loci. Remarkably, multiple centric fusions were always ac- companied by considerable increase of NORs number. In araneids and tetragnathids possessing..
Evolution and Organization of Monotreme Sex Chromosomes
Full text linkThe monotreme lineage, including the platypus and echidna, can be described as the oldest surviving mammals. Their evolutionary history and extraordinary biology make them excellent organisms to study key aspects of mammalian evolution. These egg-laying mammals have fascinated scientists and the general public for centuries. One of the most interesting aspects of
monotreme biology is their complex sex chromosomes system. With ten sex chromosomes in
platypus and nine in echidna males, monotremes feature the highest number of sex
chromosomes reported in mammals and one of the highest among vertebrates. Investigation of
this sex chromosome system in the past has been limited due to the lack of molecular tools and
material available for monotremes. Although considerable progress has been made, there are still open questions, such as understanding the processes like chromosome segregation,
interphase organization, mitotic and meiotic behavior, and sex chromosome evolution.
To provide a better understanding of the evolution of genes involved in chromosome segregation in mammals, the investigation of some of the key components of chromosome segregation in monotremes was conducted. In this regard, the chromosome passenger complex
(CPC) is a protein complex essential for chromosome segregation and consists of borealin,
survivin, inner centromere protein and Aurora kinase B or C. This research revealed the absence of Aurora kinase C in monotremes and hence completed the picture of the evolution of this protein family in mammals. It also showed the conservation of other genes associated with
chromosome segregation in monotremes, suggesting their functions have been preserved in
mammals. Lastly, this research identified differences in meiotic behavior of the cohesin between
platypus and echidna, suggesting the evolution of lineage specific cohesin functions in platypus but not echidna.
Evolution of mammalian sex chromosomes is another important aspect and monotremes are a key lineage to investigate this due to its basal evolutionary position. There are two independent evolutionary origins of mammalian sex chromosomes – one that led to the XY sex chromosome system in therian mammals (marsupials and placentals), while monotremes evolved multiple sex
chromosomes (5X and 5Y in platypus males, 5X and 4Y in echidna males) independently. This means that monotreme and therian sex chromosome systems are unrelated, and the therian X shares extensive homology with platypus chromosome 6. This provides an opportunity to
investigate the monotreme autosome that leads to the therian sex chromosome. The meiotic behaviour and segregation pattern of platypus chromosome 6 was analyzed, revealing striking
sex chromosome-like behavior of this chromosome, such as non-random segregation,
association with the sex chromosome complex and presence of an unpaired region. Based on
these results, we propose novel evolutionary scenarios to explain the evolution of mammalian
sex chromosomes.
Monotreme sex chromosomes are also unique for their interphase organization and recent work revealed interphase association of the sex chromosomes which had not been observed in
other species. Given that monotreme sex chromosomes contain X and Y specific copies of the CCCTC-binding factor (CTCF) which facilitates chromosomal interactions, this work
investigated the interphase organization of sex chromosomes and a potential role of the sex
linked CTCF protein in chromatin interactome of males and females. The results suggest the CTCFX and CTCFY proteins bind to individual DNA binding sites, with Y chromosomes containing only Y copy specific binding site, which potentially contributes to male specific functions. Furthermore, a report of novel inter-chromosomal interactions in platypus males that may be mediated by CTCF is reported in this work.
In conclusion, this research has revealed conserved and unique features of regulation of
chromosome segregation in monotremes. Furthermore, this research has shown sex
chromosome-like features of a monotreme autosome, advancing the understanding of how sex
chromosomes can evolve from autosomes. Lastly, this work identified conserved and unique features of monotreme interphase organization of sex chromosomes and CTCF protein, which
suggests sex specific functions of CTCF at interphase, further expanding the knowledge of
regulation of mammalian sex chromosome interactomes.Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 202
Karyotypová evoluce pavouků čeledi Araneidae
Full text linkKrižiakovití (Araneidae) sú početnou čeľaďou pavúkov zahŕňajúcou viac ako 3100 druhov v 170 rodoch. Spolu s 13 ďalšími čeľaďami tvoria nadčeľaď Araneoi- dea. Predložená práca je zameraná na karyotypovú evolúciu čeľade Araneidae, vrá- tane jej porovnania s príbuznou čeľaďou čeľustnatkovití (Tetragnathidae). Vý- sledky získané z 19 druhov križiakov a štyroch druhov čeľustnatiek potvrdzujú pub- likovanú hypotézu, že pôvodný karyotyp nadčeľade Araneoidea (vrátane čeľade Araneidae) pozostáva z 24 akrocentrických chromozómov u samcov, vrátane dvoch akrocentrických chromozómov X systému X1X20. U rady križiakov však dochádza k výraznému zníženiu 2n prostredníctvom centrických fúzií. Centrické fúzie zasiahli väčšinu autozómov (a niekedy aj gonozómy); počet párov klesol z 11 na šesť. V pred- loženej práci boli zistené tri takéto redukčné udalosti. Súčasťou práce bol aj výskum nukleolárnych organizátorov (NOR) s použitím fluorescenčnej hybridizácie in situ, nakoľko dostupné údaje o evolúcii tohto znaku u pavúkov sú obmedzené. Počet NOR bol veľmi variabilný, s rozpätím jeden až 13 lokusov. Mnohonásobné centrické fúzie boli vždy sprevádzané významným zvýšením počtu NOR. Frekvencia chiazmat na chromozóm bola u križiakov a čeľustnatiek s ancestrálnym karyotypom nízka. Na druhej strane u druhov vykazujúcich...Orb-weavers (Araneidae) are a diversified spider family comprising more than 3,100 species in more than 170 genera. Together with 13 other families, they con- stitute to superfamily Araneoidea. The presented thesis focuses on karyotype evo- lution of Araneidae, including its comparison with a related family Tetragnathidae. The results obtained from 19 araneid and four tetragnathid species confirm previ- ously postulated hypothesis that the ancestral karyotype of Araneoidea (including Araneidae) consists of 24 acrocentric chromosomes in males, including two acro- centric X chromosomes of system X1X20. However, there is a tendency of 2n decrease in some araneids due to centric fusions. In these cases, centric fusions affected most autosomes (and sometimes gonosomes as well); number of chromosome pairs de- creased from 11 to six. Three independent reduction events were detected in this thesis. Furthermore, pattern of nucleolar organizer regions (NORs) was studied in this thesis using fluorescent in situ hybridization, since data on evolution of this marker are scarce in spiders. Striking variability in NORs number was discovered, ranging from one to 13 loci. Remarkably, multiple centric fusions were always ac- companied by considerable increase of NORs number. In araneids and tetragnathids possessing...Katedra genetiky a mikrobiologieDepartment of Genetics and MicrobiologyPřírodovědecká fakultaFaculty of Scienc
Molecular composition of constitutive heterochromatin
No full textConstitutive heterochromatin of eukaryotes includes various types of repetitive DNA and transposons characteristic for given region. DNA of centromeric and telomeric re- gions is usually highly methylated and transcribed to RNA transcripts, which participate in formation, functions and spreading of heterochromatin along with histones, their mod- ifications and non-histone proteins. The most typical histone modification in heterochro- matin is methylation, which forms the binding site for protein HP1. This protein (and his paralogues in other eukaryotes except for S. cerevisiae) participates in formation of com- plexes including other proteins like histone methylases SUV39H and their paralogues. Es- sential are also telosome proteins regulating telomeric heterochromatin, Polycomb group proteins and many others, for instance MBD1, Epe1, SUMO and DNA methylases DNMT. Many proteins form complexes, which partake in mechanisms necessary for heterochro- matin maintenance, for example RDRC and RITS complexes in RNA interference, SHREC complex in heterochromatin spreading, and PRC complexes forming heterochromatin in specific situations. Key words: centromere, DNA, histone, HP1, constitutive heterochromatin, methylation, modification, protein, RNA, specific, telomer
Molekulární stavba konstitutivního heterochromatinu
Full text linkKonštitutívny heterochromatín eukaryot obsahuje rôzne typy repetitívnej DNA a transpozóny charakteristické pre danú oblasť. DNA centromerických a telomerických oblastí je obvykle vysoko metylovaná a prepisovaná za vzniku RNA transkriptov, ktoré sa spolu s histónmi, ich modifikáciami a nehistónovými proteínmi podieľajú na tvorbe, funkciách a šírení heterochromatínu. Najtypickejšou modifikáciou histónov v heterochro- matíne je ich metylácia, ktorá tvorí väzbové miesto pre proteín HP1. Tento proteín (a jeho paralógy u ostatných eukaryot okrem S. cerevisiae) sa účastní tvorby komplexov zahŕňa- júcich ďalšie proteíny, z nich významnými sú histónové metylázy SUV39H a ich paralógy. Esenciálne sú aj proteíny telozómu regulujúce telomerický heterochromatín, proteíny zo skupiny "Polycomb" a mnohé ďalšie, ako napr. MBD1, Epe1, SUMO a DNA metylázy DNMT. Mnohé proteíny pracujú spolu v komplexoch, ktoré sa účastnia mechanizmov potrebných pre heterochromatín, napríklad RDRC a RITS komplexy v RNA interferencii, SHREC kom- plex v šírení heterochromatínu či PRC komplexy, ktoré participujú na tvorbe heterochro- matínu v špecifických situáciách. Kľúčové slová: centroméra, DNA, histón, HP1, konštitutívny heterochromatín, metylá- cia, modifikácia, proteín, RNA, špecifický, teloméraConstitutive heterochromatin of eukaryotes includes various types of repetitive DNA and transposons characteristic for given region. DNA of centromeric and telomeric re- gions is usually highly methylated and transcribed to RNA transcripts, which participate in formation, functions and spreading of heterochromatin along with histones, their mod- ifications and non-histone proteins. The most typical histone modification in heterochro- matin is methylation, which forms the binding site for protein HP1. This protein (and his paralogues in other eukaryotes except for S. cerevisiae) participates in formation of com- plexes including other proteins like histone methylases SUV39H and their paralogues. Es- sential are also telosome proteins regulating telomeric heterochromatin, Polycomb group proteins and many others, for instance MBD1, Epe1, SUMO and DNA methylases DNMT. Many proteins form complexes, which partake in mechanisms necessary for heterochro- matin maintenance, for example RDRC and RITS complexes in RNA interference, SHREC complex in heterochromatin spreading, and PRC complexes forming heterochromatin in specific situations. Key words: centromere, DNA, histone, HP1, constitutive heterochromatin, methylation, modification, protein, RNA, specific, telomereDepartment of Genetics and MicrobiologyKatedra genetiky a mikrobiologiePřírodovědecká fakultaFaculty of Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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