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Molecular composition and ultrastructure of holokinetic chromosomes
Šejgunovová, Nikola ; Král, Jiří (advisor) ; Dalíková, Martina (referee)
Holokinetic chromosomes are a specific type of chromosomes which differentiate from standard (monocentric) chromosomes especially by a diffuse form of domain which binds microtubules (holocentromere). It is related to changes on an ultrastructural and molecular level. These changes are shown in modifications in mitotic and meiotic division and in evolution of karyotypes. Holokinetic chromosomes don't have a primary constriction with a localized centromere and therefore neither an inner centromere domain which would connect sister chromatids. Kinetochore structure of holokinetic chromosomes seems to be simpler than kinetochore structure of monocentric chromosomes. Kinetochore covers most of the surface of mitotic chromosomes. There have been described several variants of meiosis of holokinetic chromosomes which differentiate by position of kinetochore on chromosomes. On a molecular level holokinetic chromosomes differentiate from monocentric chromosomes by a distribution of proteins of a centromere-kinetochore complex, which cover most of the surfaces of mitotic and meiotic chromosomes. This applies, for example, to centromeric histone H3 (CENH3), whose amount and distribution changes during interphase and nuclear division, which is unique in comparison to monocentric chromosomes. The distribution...
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Karyotype evolution of the family Araneidae
Pajpach, Filip ; Král, Jiří (advisor) ; Sember, Alexandr (referee)
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...
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Analysis of dosage effect of speciation gene Prdm9 on fertility of mouse hybrids
Flachs, Petr ; Trachtulec, Zdeněk (advisor) ; Stopka, Pavel (referee) ; Král, Jiří (referee)
(eng) The phenomenon of hybrid sterility represents one of the evolutionary mechanisms that enables speciation. Only a few speciation genes have been uncovered. The only one found in mammals is Prdm9 (PR-domain 9). Data in the literature on the involvement of Prdm9 in decreased fertility of various semifertile hybrid males of house mouse subspecies were scarce before the results of this thesis were completed, despite that such males are much more frequent in nature than the fully sterile ones. Utilizing a panel of genetic tools and a battery of phenotyping tests, this thesis shows a central role of Prdm9 in fecundity of hybrids, including many fertility disorders and age dependency. Both increasing and reducing the Prdm9 gene dosage significantly elevated fertility parameters. Surprisingly, even the allele that in one copy causes full hybrid sterility increased F1 hybrid fertility when present in multiple copies. The PRDM9 protein also plays a role in identifying the sites of meiotic recombination. This study also points out the principles of allelic competition in determination of the sites of preferred recombination (hotspots), which suggests a possible link between both previously described Prdm9 roles. This thesis summarizes a set of three logically interconnected publications with the ambition...
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Genetic interactions of the Prdm9 gene
Šebestová, Lenka ; Trachtulec, Zdeněk (advisor) ; Král, Jiří (referee)
The Prdm9 gene (PR domain containing 9, Meisetz, Hybrid sterility 1) encodes enzyme that trimethylates histone 3 on lysines 4 and 36. These methylation marks determine the positions of DNA double-strand breaks that are repaired by meiotic homologous recombination. In this study, we assayed genetic interactions of Prdm9 with two genes important for spermatogenesis - Mili (Piwil2) involved in piRNA biogenesis and Mybl1 encoding transcription factor that regulates many genes important for prophase I, including piRNA precursors. We crossed laboratory mice carrying mutation in Prdm9 with heterozygotes for mutation in Mybl1 or Mili, and created compound heterozygotes and, in case of Mybl1, also double homozygotes. We assessed body weight and male fertility parameters (weight of testes, sperm count, malformed sperm, percentage of tubules containing spermatocytes and of abnormal nuclei of pachytene spermatocytes) of these mice and compared them to controls. We also investigated the effect of Mybl1 and Mili mutations on fecundity of F1 intersubspecific hybrids. Our results revealed possible interactions of Prdm9 and Mybl1 in the laboratory mouse. Decreased gene dosage of Mybl1 reduced fertility of intersubspecific F1 hybrids. Interaction between Prdm9 and Mili in both laboratory mouse and F1 hybrids remain...
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