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Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 5 uppsatser.

Les gènes du chromosomeX sont majoritairement inactivés au cours de la méiose mâle. Chez la souris, seulement 6% d’entre eux sont réactivés au cours des stades post-méiotiques. Parmi eux le gène Uba1X codant pour l’enzyme activatrice de l'ubiquitine, UBA1 qui produit trois transcrits dont deux sont ubiquitaires mais le troisième prédomine dans les cellules post¬-méiotiques : les spermatides. Nos travaux montrent que les 5’UTR, seul différence entre ces trois transcrits, déterminent la localisation et la dose relative des isoformes nucléaire et cytoplasmique de la protéine UBA1. Nous avons mis en évidence chez la souris que le transcrit spermatide-spécifique code pour l'isoforme nucléaire, exprimée fortement dans les spermatides suggérant un rôle de la protéine UBA1 dans la dégradation des histones lors du remodelage chromatinien. Nous avons détecté deux mutations dans la région spermatide-spécifique du gène : une délétion de 13pb et une transition G>A, chacune portée par un patient infertile, et non retrouvée dans notre population témoin. Les analyses ont montré que la délétion de 13pb induit un épissage anormal du transcrit spermatide-spécifique et que la transition G>A pouvait réduire le taux d’expression du transcrit spermatide-spécifique. Ces mutations pourraient induire l'infertilité des deux patients. En parallèle nous avons pu démontrer que les mutations dans le gène codant pour la protamine PRM1 décrites dans la littérature c.102G>T et c.-107G>C ne sont pas liées à l'infertilité masculine et que le variant est un polymorphisme fréquemment retrouvé dans la population congolaise. / The majority of genes on the X chromosome are repressed during meiosis and only 6% of them are expressed in post meiotic germ cells. One of these genes is Ubal, encoding the ubiquitin-activating enzyme UBA1. Ubal produces three different transcripts, two of which are ubiquitously expressed while the third is predominant in the post meiotic germ cells: the spermatids. Our study shows that the 5’UTR, which is the only difference between these transcripts, determines the localization and the relative dose of the nuclear and cytoplasmic isoform of the UBA1 protein. The spermatid-specific transcript encodes for the nuclear isoform in the spermatids in the mouse suggesting that the UBA1 protein is implicated in chromatin remodeling during spermiogenesis. We have detected two mutations in the spermatid-specific region of the UBA1 gene in two infertile men: a deletion of 13bp and a G>A transition, neither of which was found in our cohort of fertile men. The deletion of 13bp diminishes the correct splicing of the spermatid-specific transcript and that the G>A transition may reduce expression of the spermatid-specific transcript. These results show that the UBA1 gene is involved in spermiogenesis, and reactivated in spermatids by its spermatid-specific transcript and that the mutations identified may induce infertility by reducing UBA1 levels in spermatids. We have also demonstrated that two variants described in the protamine codant gene PRM1C.102G>T and c.-107G>C are clearly not associated with male infertility and that the c.-107G>C is polymorphism frequently found in the congolese population.

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A infertilidade é uma doença do sistema reprodutivo considerada um problema de saúde pública global, afetando aproximadamente 15% dos casais e 7% dos homens. Falência espermatogênica primária é definida como incapacidade dos testículos produzirem espermatozoides, apesar do suporte hormonal adequado. Esse estudo é o primeiro a comparar dois grupos de pacientes com falência espermatogênica primária por meio da técnica array-CGH+SNP, utilizando a plataforma 4X180 (Agilent®). Adicionalmente, foram comparados os resultados obtidos por essa técnica com bancos de dados genômicos de expressão. Foram analisados vinte e três pacientes com falência espermatogênica primária, sendo sete com oligozoospermia extrema e dezesseis com azoospermia não obstrutiva, assim como seis homens comprovadamente férteis (grupo controle). A análise genômica foi realizada pelo software Nexus 8.0 e as análises de bancos de dados genômicos de expressão por meio do software Nexus Expression 3.0 com nível de significância de 5%. Os primeiros resultados evidenciaram diferenças de número e de tamanho das alterações genômicas (CNVs e LOHs) entre os dois grupos da amostra e o grupo controle, sendo a diferença do número de CNVs de perdas do grupo com oligozoospermia significativamente maior do que no grupo controle. O grupo de pacientes com azoospermia apresentou alterações genômicas de maior tamanho, entre 552pb a 11.3MB, quando comparado aos homens oligozoospérmicos e ao grupo controle. A análise descritiva permitiu identificação de um gene candidato a fenótipo de falência espermatogênica primária na região 12q21.1-q21.2, o gene GLIPR1L1. Por meio da análise individualizada, identificamos dois genes candidatos ao fenótipo de infertilidade, o SHH, localizado na região 7q21.3, e o TMEM184A, localizado na região 7p22.3. Foram também descritas oito novas regiões de CNVs e LOHs nos dois grupos da amostra, direcionando novos estudos para correlação entre genótipo e fenótipo. / Infertility is a disease of the reproductive system and a global public health problem affecting approximately 15% of couples and 7% of men. Primary spermatogenic failure is defined as the inability of the testes to produce sperm although there is adequate hormonal support. This study is the first to compare two groups of patients with primary spermatogenic failure using array-CGH + SNP technique with the 4X180 (Agilent®) platform. Also, we compared the results obtained by this technique with genomic expression databases. Twenty-three patients with primary spermatogenic failure were analyzed, seven with extreme oligozoospermia and sixteen with nonobstructive azoospermia. We used six proven fertile men as a control group. Genomic analysis was performed by Nexus 8.0 software and analysis of genomic databases of expression was performed using the Nexus Expression 3.0 software with 5% significance level. Initial results showed differences in both the number and size of genomic alterations (CNVs and LOHs) between the two sampled infertility groups and the control group. The main difference was that the number of overall CNVs losses which was significantly higher in the oligozoospermia group than in the control group. The group of patients with azoospermia showed larger genomic alterations, between 552bp and 11.3MB size, compared to oligozoospermic men and the control group. A descriptive analysis was used to identify a candidate gene, GLIPR1L1, for the primary spermatogenic failure phenotype in the region 12q21.1-q21.2. Through individualized analysis, we identified two other candidate genes that may have a relationship with the infertility phenotype, SHH, located in the 7q21.3 region, and TMEM184A, located on the 7p22.3 region. Eight new areas of CNV and LOHs have also been described in the two sample groups, for more extensive genotype and phenotype correlative studies.

While the introduction of intracytoplasmic sperm injection (ICSI) has revolutionized the treatment of male infertility, concerns have been raised regarding the risk of chromosomal abnormalities in pregnancies derived from ICSI. Studies on sperm from infertile men have suggested that this population may produce higher rates of aneuploid sperm. Thus, we hypothesized that defects in early meiotic events may contribute to both male infertility and the production of aneuploid sperm. We used immunofluorescent techniques to observe the synapsis and recombination of chromosomes during meiosis, and fluorescent in-situ hybridization (FISH) to assess sperm aneuploidy. We analyzed testicular tissue from thirty-one men (10 fertile and 21 infertile men). We observed that ~36% (5/14) of men with impaired spermatogenesis displayed reduced genome-wide recombination. When all men were pooled, we observed an inverse correlation between the frequency of sex chromosome recombination and XY disomy in the sperm. We combined immunofluorescent and FISH techniques to study recombination patterns on chromosomes 13, 18 and 21 in fifteen men (5 fertile and 10 infertile men). Four of the infertile men displayed altered recombination distributions on at least one of the chromosome arms studied. Finally, we examined early meiotic events in two biopsies from an azoospermic t(8;13) carrier. While global recombination rates were not altered, recombination frequencies were reduced specifically on the rearranged chromosomes. Asynapsed quadrivalents were observed in 90% and 87% of pachytene nuclei from the first and second biopsies, respectively, and were frequently associated with the sex chromosomes. BRCA1 and γH2AX, two proteins implicated in meiotic sex chromosome inactivation, localized along asynapsed regions regardless of whether or not they were associated with the sex chromosomes, suggesting that regions of autosomal chromosomes that fail to synapse undergo transcriptional silencing in humans. In summary, we observed that a subset of infertile men display alterations in the number and position of meiotic crossovers, which may contribute to both infertility and an increased risk of sperm aneuploidy. The fidelity of synapsis is also a critical factor in determining the outcome of gametogenesis in humans, as the transcriptional inactivation of asynapsed regions may silence meiotic genes, leading to meiotic arrest and infertility.