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The Role of FBH1 in Maintenance of Genome Stability
Šimandlová, Jitka ; chevelev, Igor (advisor) ; Kratochvíl, Lukáš (referee)
The genome is constantly threatened by various damaging agents and maintaining its integrity is crucial for all organisms. Several repair pathways have been implicated in the removal of different types of lesions from DNA. Among them, homologous recombination (HR) plays a key role in repair of double-strand breaks. HR is a highly important repair mechanism which has to be tightly regulated to prevent excessive HR events. These events could interfere with other DNA repair pathways, generate toxic intermediates, or block the progression of the replication fork. Therefore, it is not surprising that cells have evolved mechanisms that counteract inappropriate HR events. As it has been shown recently, cells possess DNA helicases capable of preventing excessive recombination. A novel human DNA helicase, hFBH1, belonging to the superfamily I has been shown to function as pro- and anti- recombinase. Similar to the two members of RecQ family, BLM and RECQL5, FBH1 disrupts Rad51 from nucleofilament. However, FBH1 might also promote initiation of HR. The FBH1 helicase possesses additional high conserved F-box motif which allows it to act within a Skp1-Cullin-F-box, SCF, complex as ubiquitin ligase and target proteins for degradation.
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Hormonal control of male sexual behaviour in reptiles
Schořálková, Tereza ; Kratochvíl, Lukáš (advisor) ; Landová, Eva (referee)
The most important hormone affecting typical male sexual behavior in reptiles is testosterone, but also other steroid hormones such as dihydrotestosterone, estrogens or progestins may be involved in this regulation. According to the organizational-activational hypothesis testosterone acting during early ontogenic stage has an organizational effect on adult behavior and this behavior is triggered by influence of recent levels of hormones. Moreover, it was formulated the hypothesis on temporary organization of male sexual behvior that could change existing interpretations. Reptile reproductive strategies use to be classified according to gametogenesis and steroidogenesis as associated or dissociated reproductive strategies howerever, this division is rather artificial. This review summarizes existing knowledge of the hormonal influence of sexual behavior in reptiles, and comments the most common methods.
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Molecular cztogenetic analysis of adaptive radiation in the gecko genus Paroedura (Squamata:Gekkota)
Koubová, Martina ; Kratochvíl, Lukáš (advisor) ; Šťáhlavský, František (referee)
Paroedura genus includes 17 described species endemic to Madagascar and the Comoros Islands, where they went through a significant adaptive radiation. The genus Paroedura is monophyletic and well supported hypothesis on phylogenetic relationships among its species was published. Species vary considerably in body size and morphology and in preferences for habitat, some species live in sympatry. The genus Paroedura belongs to cytogenetically poorly studied family Gekkonidae which exhibits high variability in modes of sex determination and in comparison with basal gecko lineages, also considerable variability in the chromosome number and morphology. Karyotypes of only two species of the genus (P. picta, P. sp.) have been published. The aim of my thesis was to describe karyotypes of both sexes in all available species of the genus using conventional and molecular cytogenetic methods, to perform the phylogenetic analysis of karyotype evolution and chromosomal rearrangements in the genus, to assess the role of these rearrangements in the speciation of the genus and to detect sex chromosomes. I acquired karyotypes of both sexes in nine species representing the most of major phylogenetic lineages of the genus. According to the results, species can be divided into three groups according to diploid...
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Effect of food quality on sex ratio in a model passerine bird
Tomiška, Lubomír ; Kratochvíl, Lukáš (advisor) ; Vinkler, Michal (referee)
Sex allocation theory represents one of the key subjects of evolutionary ecology. There are several studies which bring strong evidence for relationship of environment and sex ratio in fish, reptiles, amphibians and some invertebrates. However, we still wait for answering of this question in mammals and birds. One of obstacles is the fact that in this case sex is determined by sex chromosomes. Many authors consider the chromosome segregation distortion (meiotic drive) as the most probable cause of sex ratio manipulation. But according to the traditional Mendelian conception, chromomosome segregation should be a random process. Because of new methods invented in 90's we can determine sex of an individual by molecular techniques and so find out the primary sex ratio. That's why an intensive research has occured at the turn of the century. However, there are many experimental studies we still miss reliable evidence of proximate mechanism and ultimate cause of sex ratio manipulation in birds. According to results of several studies, the sex ratio distortion occurs at primary level but nobody really tested the existence of meiotic drive directly. So we decided to test a possible cause of meiotic drive - centromere methylation. The latest research shows that methylation influences several characteristics...
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Origin, degeneration and detection of sex chromosomes
Jílková, Klára ; Král, Jiří (advisor) ; Kratochvíl, Lukáš (referee)
Sex chromosomes evolved from a pair of autosomes and they are differentiated as a result of supression of recombination. This process leads to a successive degradation of odd sex chromosome (alosome), which is becoming genetically inert finally or even excluded. Fundamental processes taking part in degeneration of alosome are Muller's ratchet, genetic hitchhiking, background selection, accumulation of transposable elements and constitutive heterochromatin. Indeed, these processes take part in either degeneration of both Y or W chromosomes. Remarkably, these alosomes show different rates of degeneration, most probably due to 1) different structure of male and female gonads as well as 2) different course of gametogenesis in both sexes. Furthermore, rate of alosome degeneration is usually lower in plants because they are haploid during the major part of life cycle. Other mechanisms of sex chromosome evolution involve rearrangements between autosomes and gonosomes, nondisjunctions and fissions of original sex chromosomes, transformation of B chromosomes into sex chromosomes or non-random segregation of autosomes with sex chromosomes. Other phenomenon that appears in sex chromosome evolution is transition between XY/XX and ZW/ZZ systems or transition between chromosomal sex determination and epigamy. Actually,...
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Comparative analysis of sexual and agonistic behaviour in eyelid geckos (Eublepharidae)
Rauner, Petr ; Kratochvíl, Lukáš (advisor) ; Frýdlová, Petra (referee)
Sexual selection is one of main selective pressure affecting body size, and subsequently leads to the evolution of sexual size dimorphism (SSD). The eyelid geckoes, family Eublepharidae, are a monophyletic group with considerable variability in SSD, including both male-larger and female-larger species. In general, it was supposed that eyelid geckos are highly variable in presence of male combats and in complexity of male pre-copulatory behaviour, and that this variability in this conspicuous male behaviour may lead to differences in SSD. The aim of this study was to reveal relationships between the direction of SSD and presence/absence of tail vibration during precopulatory phase and male combat behaviour. Using behavioural testing, it was revealed that male combats are present in all tested species, even in species, where the absence of such behaviour was supposed so far. In several species, the strong effect of seasonality to male aggression was observed, which may play a role in the evolution of SSD. The evolutionary changes in the presence/absence of tail vibration during precopulatory phase were independent on changes in the direction of SSD, the presence of tail vibration seems to be ancestral state for these lizards. During the evolution of this group, the tail vibrations disappeared four...
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RTEL1 as a novel suppressor of homologous recombination
Žítek, Ondřej ; chevelev, Igor (advisor) ; Kratochvíl, Lukáš (referee)
Regulator of telomere elongation helicase 1 (RTEL1) is a DNA helicase crucial for regulation of telomere length in mice while its loss has been associated with shortened telomere length, chromosome breaks, and translocations. Moreover, RTEL1 is an important member of the DNA double-strand break-repair (DSBR) pathway. It maintains genome stability directly by suppressing homologous recombination through disassembling D loop recombination intermediates during DNA repair. Antirecombinase properties of RTEL1 make it the key protein required in meiosis and mitosis to execute non-crossover way of DSBR by promoting synthesis-dependent strand annealing (SDSA). Defect in any of these functions might lead to glioma predisposition in human.
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