Meiosis is a specialized cell division that produces haploid cells (gametes) from diploid progenitors. During meiosis parental chromosomes (homologs) need to pair, synapse and eventually segregate. Faithful chromosome segregation depends on chromosome recombination. In the beginning of prophase I programmed double strand breaks (DSBs) are introduced in meiotic cells by SPO11 enzyme. DSBs are positioned at hotspot sites that are specified by that action of DNA-binding histone methyltransferase PRDM9. Specific enzymes act at the site of breaks to create 5’ single stranded DNA ends. With the assistance of the strand exchange proteins DMC1 and RAD51 these ends invade homologous DNA sequence and DSB repair is initiated. DSB repair can be completed either as a crossover (reciprocal exchange of DNA) or as a non-crossover. Crossover events lead to the formation of chiasmata between homologs and ensure proper segregation during the first meiotic division. An interesting feature in male meiosis is the XY chromosomes. The shared region between sex chromosomes is short and is called pseudoautosomal region (PAR). Due to their large non synapsed region, XY chromosomes need to be transcriptionally silenced. Thus they are covered with the phosphorylated histone variant H2AX (γH2AX) forming the so called sex body. PAR region has higher density of DSBs than autosomes and it had been shown that sex chromosomes undergo delayed homologous pairing. Nevertheless little is known how meiotic recombination is regulated in PAR region of sex chromosomes. In close proximity with sex body it has been found a structure named dense body (DB). There are few reports suggesting that DB contains RNAs/proteins but no DNA. Its role in meiosis was unclear because no structural component had been described. In the present thesis the role of two meiotic expressed genes is described. In our group after performing RNA screens we identified several genes that are highly expressed during meiotic prophase I. Based on the expression profile we selected polycomb-related sex comb on midleg like 1 (Scml1) gene and the ankyrin repeat domain 31 (Ankrd31) to study their role in mammalian meiosis.:List of figures i List of abbreviations ii 1. Introduction 1 1.1 Gametogenesis 1 1.2 Meiotic prophase I 2 1.2.1 Meiotic recombination 4 1.2.2 Regulation of meiotic recombination 7 1.2.2.1 Meiotic recombination hotspots and PRDM9 activity 7 1.2.2.2 Meiotic surveillance mechanisms 8 1.3 Unique properties of XY recombination 9 1.4 Sex chromatin associated structure: The dense body 10 1.5 Aim of the thesis 11 2. Publications 12 3. Discussion 92 4. Summary 98 5. References 102 Acknowledgements 108 Declarations 109

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...

- ABSTRACT - Among vertebrates, reptiles represent the ideal group for the study of sex determination. Reptiles include lineages with environmental sex determination (ESD) as seen in crocodiles and tuatara, lineages with genotypic sex determination (GSD), like e.g. iguanas, chameleons, skinks, lacertid lizards and birds, and few groups which possess variability in sex determination mechanisms, i.e. geckos, dragon lizards and turtles. This thesis is focused on the evolution of sex chromosomes and sex determination in turtles. The majority of turtle species exhibit ESD, which is considered the ancestral sex determination system of this group, while GSD either as male or female heterogamety evolved independently at least five times. We investigated the presence of sex chromosomes in representative species of turtles by cytogenetic analyses. The analyses included the reconstruction of karyotypes, distribution of constitutive heterochromatin (C-banding, methylation analysis) and repetitive elements (fluorescence in situ hybridization) and comparative genome hybridization (CGH), which often characterize the degenerated Y or W and can be helpful in the identification of "cryptic" sex chromosomes. We described XX/XY sex chromosomes in seven previously unstudied Australasian chelids (Pleurodira) from the genera...

- ABSTRACT - Snakes (Serpentes) are a group of squamate reptiles (Squamata) that represents more than one third of the total reptile species diversity. Snake karyotype is generally conserved with the most common chromosome number of 36 (16 macro- and 20 microchromosomes) in diploid state. It is believed that this karyotype was also present in the common ancestor of all snakes. The majority of snake species belong to the group Caenophidia and share homologous ZW sex chromosomes. Snakes from the groups "Scolecophidia" and "Henophidia" have mostly poorly differentiated, homomorphic sex chromosomes, which made them impossible to distinguish from the autosomes in the past. These snakes were for many years assumed to have ZW sex chromosomes as well. However, recent studies demonstrated not only ZW but also two non- homologous XY sex chromosome systems in non-caenophidian snakes and thus the sex determination systems in snakes are much more variable than previously thought. In this thesis, eight species of henophidian snakes (representatives from the genera Eryx, Cylidrophis, Python and Tropidophis) and one caenophidian species (Ophiophagus hannah) were examined using conventional and molecular cytogenetic methods. However, sex chromosomes were not detected in the henophidian species, only in Ophiophagus hannah,...

Durant ces dernières décennies, la fertilité masculine est en constante diminution à l’échelle mondiale. Même si les facteurs environnementaux ont une part de responsabilité indéniable, il n’en reste pas moins que les altérations génétiques mais également épigénétiques semblent aussi largement impliquées. La compréhension des mécanismes épigénétiques qui régulent la fertilité masculine est récente mais essentielle pour le développement de nouvelles approches thérapeutiques. Dans ce contexte, l’objectif de mes travaux de thèse s’est focalisé sur l’étude du rôle du variant d’histone H3.3 dans la spermatogenèse. H3.3 possède la capacité de remplacer l’histone canonique H3 dans la chromatine modifiant ainsi les propriétés épigénétiques de cette dernière. H3.3 est nécessaire à la spermatogenèse mais son rôle reste à élucider. Grace à plusieurs modèles murins, mes travaux de thèse ont montré que la forme H3.3B est essentielle à la reproduction masculine notamment pour la transition méiose/post-méiose. Lors de cette transition, on observe une forte régulation des piARN, des rétrotransposons et des chromosomes sexuels. Nos expériences révèlent pour la première fois que la perte de H3.3B provoque une chute de l’expression des piARN. À l’inverse, l’absence de H3.3B est aussi associée à une augmentation de l’expression de l’ensemble des gènes des chromosomes sexuels comme des rétrotransposons RLTR10B et RLTR10B2. Ces changements d’expression se traduisent par une spermatogenèse altérée et une infertilité. Par des expériences de ChIP-seq, nous avons observé que H3.3 est fortement enrichie sur les piRNA, les rétrotransposons RLTR10B et RLTR10B2 et l'ensemble des chromosomes sexuels. Toutes ces expériences ont permis de mieux caractériser la fonction régulatrice de l’histone H3.3B au cours de la spermatogenèse. En particulier, elles démontrent que H3.3B, en fonction de sa localisation sur la chromatine, intervient dans la régulation positive ou négative de l'expression de régions chromatiniennes définies. Ces résultats montrent l’importance des contrôles épigénétiques au cours de la spermatogenèse et ouvrent de nouvelles pistes dans la compréhension des causes d’infertilité masculine. / In last decades, male fertility has been steadily declining worldwide. Even if environmental factors have an undeniable responsibility, the fact remains that both genetic and epigenetic alterations also seem to be widely implicated. The understanding of the epigenetic mechanisms that regulate male fertility is recent but essential to develop a new therapeutic approaches. In this context, the objective of my thesis work focused on the study of the role of histone variant H3.3 in spermatogenesis. H3.3 has the ability to replace the H3 canonical histone in chromatin thus modifying the epigenetic properties of chromatin. H3.3 is necessary for spermatogenesis but its role remains unclear. Used to several mouse models, my thesis work has shown that the H3.3B form is essential for male reproduction and especially for the meiosis/post-meiosis transition. During this transition, there is a strong regulation of piRNAs, retrotransposons and sex chromosomes. Our experiments reveal at the first time that the loss of H3.3B resulted in down-regulation of the expression of piRNA. In contrast, the absence of H3.3B is also associated with increased expression of all sex chromosom genes as well as of both RLTR10B and RLTR10B2 retrotransposons. These expression changes result in altered spermatogenesis and infertility. By ChIP-seq experiments, we observed that H3.3 is markedly enriched on the piRNA clusters, RLTR10B and RLTR10B2 retrotransposons and the whole sexual chromosomes. All these experiments allowed bettering characterizing the regulatory function of histone H3.3B during spermatogenesis. In particular, he demonstrates that H3.3B, depending on its chromatin localization, is involved in either up-regulation or down-regulation of expression of defined chromatin regions. These results show the importance of epigenetic controls during spermatogenesis and open new tracks for understanding the causes of male infertility.

Giardia intestinalis is a protozoan causing diarrhea worldwide. Beside its medical importance, it is evolutionary distant protist with two nuclei within a cell adapted for parasitic life in the environment poor of oxygen. Its genome is small and compact in term of gene content and size. It is therefore an attractive model organism for studies of minimal requirements for cellular processes. Present work brings new partial information on different levels of chromosome integrity maintenance of this parasite. Our study presents characteristics of chromosome termini and their protection. We localized telomeres during all stages of the trophozoite cell cycle and determined the length of Giardia telomeres ranging from 0.5 to 2.5 kb, we proved an existence of an active telomerase enzyme synthesizing telomeric repeats in in this parasite, despite the fact that giardial telomerase is structurally divergent. Present data support the view that the chromosomal termini in Giardia are maintained in a conservative manner that is common to other eukaryotes. We described effects of commonly used drug for treatment of anaerobic infections, metronidazole, on DNA and cell cycle progression in susceptible and resistant cell lines. Incubation of cells with this drug causes phosphorylation of histone H2A in cell nuclei...

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...

Indiana University-Purdue University Indianapolis (IUPUI) / External apical root resorption (EARR) is a common sequela of orthodontic treatment, although it may also occur without orthodontic treatment. Despite rigorous investigation, no single factor or group of factors that directly causes root resorption has been identified. Experiment 1. A sample of 83 pairs of full siblings who had undergone orthodontic treatment was studied. Measurements were made of the longest maxillary central incisor, mandibular central incisor and mesial and distal roots of the mandibular first molars. Heritability estimates were generated by generalized liner models. Our results showed that the heritability estimate of the EARR was 64% on average. It was concluded that there was sufficient heritability for EARR to pursue genetic analysis. Experiment 2. Five polymorphic markers flanking or lying within the IL-IA , IL-JB, TNSALP, TNFA, and TNFRSFJ JA genes were used in a candidate gene approach to assess linkage and association with EARR in 38 pedigrees. Suggestive evidence for linkage between EARR and the polymorphic marker D18S64 was obtained with the analysis program MAPMAKER/SIBS (LOD score 2.51). The Q-TDT program showed highly significant (p = 0.0003) evidence of linkage disequilibrium of IL-1 B polymorphisms with EARR. Our analysis indicates that the JL -1 B polymorphism accounts for 15% of the total EARR variation. Experiment 3. Nine-week-old male mice were randomly selected as controls or for placement under anesthesia of an open coil spring ligated to the left maxillary first molar producing a force of approximately 25 g. The control (C) or treated (T) per strain were A/J (C=3,T=9), C57BL/6J (C=7,T=8), C3H/HeJ (C = 4,T=6), BALB/cJ (C=4,T=6), 129P3 /J (C=6,T=8), DBA/2J (C=8,T=9), SJL/J (C=8,T= 10), and AKR/J (C=9,T =8). Animals were sacrificed after nine days of treatment or control; maxillae were immediately removed, prepared, sectioned, mounted, stained with H&E, and observed microscopically at 1 OOX to determine root resorption. Mice were grouped into root resorption resistant (A/J, C57BL/6J and SJL/J); intermediate (C3H/HeJ and AKR/J); and susceptible (BALB/cJ, DBA/2J, and 129P3/J) strains. It was concluded that there were differential susceptibility or resistance to root resorption among inbred mouse strains, indicating that genotype is an influencing factor.

Yes / Abstract The budding yeast genome contains regions where meiotic recombination initiates more frequently than in others. This pattern parallels enrichment for the meiotic chromosome axis proteins Hop1 and Red1. These proteins are important for Spo11-catalyzed double strand break formation; their contribution to crossover recombination remains undefined. Using the sequence-specific VMA1-derived endonuclease (VDE) to initiate recombination in meiosis, we show that chromosome structure influences the choice of proteins that resolve recombination intermediates to form crossovers. At a Hop1-enriched locus, most VDE-initiated crossovers, like most Spo11-initiated crossovers, required the meiosis-specific MutLγ resolvase. In contrast, at a locus with lower Hop1 occupancy, most VDE-initiated crossovers were MutLγ-independent. In pch2 mutants, the two loci displayed similar Hop1 occupancy levels, and VDE-induced crossovers were similarly MutLγ-dependent. We suggest that meiotic and mitotic recombination pathways coexist within meiotic cells, and that features of meiotic chromosome structure determine whether one or the other predominates in different regions.

Polytäne Chromosomen von Drosophila sind in eine Abfolge von Banden und Interbanden unterschiedlichen Kompaktionsgrades gegliedert. Das Protein Z4 ist notwendig, um dieses Muster aufrecht zu erhalten (Eggert et al., 2004). Durch Koimmunpräzipitation mit Z4 wurde in unserer Arbeitsgruppe ein Chromodomänen Protein identifiziert, das von uns als Chriz bezeichnet wurde (Gortchakov et al., 2005). In meiner Arbeit testete ich die Interaktion zwischen den vollständigen Proteinen Chriz und Z4. Ich konnte dabei zeigen, dass beide Proteine in vivo direkt miteinander interagieren. Die kartierten Interaktionsdomänen am N-Terminus von Z4 und am C-Terminus von Chriz sind hinreichend für die wechselseitige Interaktion beider Proteine. Chriz ist wie Z4 in vielen Interbanden polytäner Interphasechromosomen gebunden. Die überexpression verschiedener Domänen von Chriz zeigte, dass sowohl der N- als auch der C-Terminus von Chriz für die Interbandenbindung von Chriz ausreichend sind. Der Chriz C-Terminus ist dar Über hinaus notwendig, um das überleben von Tieren mit einer Chriz Null Mutation bis in das larvale Stadium zu gewährleisten. Tiere mit induziertem Chriz RNAi knock down zeigten eine verringerte DNA Kondensation polytäner Chromosomen. Die Ähnlichkeit des chromosomalen Phänotyps von Z4 und Chriz Mutationen legt nahe, dass beide Proteine in einem gemeinsamen Komplex in Interbanden vorkommen. Unter Ausnutzung von Chriz RNAi bzw. Z4 RNAi konnte ich zeigen, dass die chromosomale Bindung von Z4 von Chriz abhängt. Weiterhin sind die Proteinkinase Jil-1 und an Serin 10 phosphoryliertes H3 (H3pS10), beides Marker für dekondensiertes Chromatin, in Chriz RNAi Tieren verringert. Aus meinen Daten schliesse ich, dass Chriz/Z4/Jil-1 in einem gemeinsamen Komplex an Interbanden gebunden sind. Chriz ist dabei fundamental wichtig für die zielgerichtete Bindung und Stabilität des Komplexes. Der Komplex selbst ist erforderlich, um die lokale Chromatinstruktur aufrecht zu erthalten. / Drosophila polytene chromosomes are compacted into a series of bands and interbands. Z4 is a protein to keep this pattern, since Z4 mutant larvae show a decompaction of chromosomes and a loss of banding pattern (Eggert et al., 2004). By coimmuno-precipitation, we identified a chromodomain protein, which we named Chriz, for chromodomain protein interacting with Z4 (Gortchakov et al., 2005). In my PhD thesis, I tested the interactions between the full length proteins and different fragments of Chriz and Z4 which showed that Chriz could directly interact with Z4 in vivo. The interaction domains were mapped and it was determined that the N terminus of Z4 and the C terminus of Chriz are sufficient for mutual interaction. GST pull down confirmed these data and more precisely localized the interaction domains. Chriz, like Z4, is present in many interbands of interphase polytene chromosomes. The overexpression of different domains of Chriz demonstrated that both the N and C terminus are sufficient for targeting of Chriz to interbands. The C terminus was shown to be sufficient for rescue of Chriz null mutations into larva stage. Chriz full length proteins, with site directed mutations within the chromodomain, could still partially rescue the null mutant. Chriz RNAi knock down resulted in a loss of structure of polytene chromosome. The similar chromosomal phenotype of Z4 and Chriz indicate that they cooperate in the formation of chromosomal structure. Using the Chriz RNAi, I showed that Z4 chromosomal binding is dependent on Chriz. However, by a similar assay I showed that Chriz binding did not depend on Z4. Finally, the decondensed interphase chromatin marker Jil-1, a H3S10 histone kinase, and H3pS10 are decreased in Chriz RNAi line. From these data, I conclude that Chriz/Z4/Jil-1 form an interband binding complex. Chriz is the fundamental factor for the chromosomal targeting and stabilitation of the complex that is required to maintain locally chromatin structure.