Chez les animaux, la conformation unique du noyau du spermatozoïde dont la chromatine est organisée avec des protéines chromosomiques spécifiques telles que les protamines le rend totalement inactif. Le remodelage de la chromatine paternelle à la fécondation par des activités d'origine maternelle sont donc des processus essentiels à la formation d'un embryon diploïde, dont les mécanismes restent très mal connus. Lors de ma thèse j'ai essayé de mieux comprendre ces processus par l'étude, chez la drosophile, d'un mutant létal embryonnaire à effet maternel : maternal haploid (mh). Ce mutant affecte l'incorporation des chromosomes paternels à la première division zygotique menant à la formation d'embryons haploïdes gynogénétiques. L'identification du gène de mh comme CG9203 m'ont permis de caractériser sa fonction. Dans les œufs mh, les chromosomes paternels se condensent anormalement et ne parviennent pas à se diviser correctement lors de la première mitose de l'embryon. Récemment, des études sur son orthologue humain, appelé Spartan/DVC1, ont montré qu'il était impliqué dans la synthèse translésionnelle (TLS), un mécanisme de tolérance aux dommages d'ADN. J'ai pu démontrer que dans les cellules somatiques, la fonction de Spartan dans le TLS est conservée chez la drosophile. Cependant, la fonction maternelle de MH ne relève pas du TLS canonique, mais permet de maintenir l'intégrité de l'ADN paternel avant la réplication. Ensemble, mes travaux soulignent la singularité du pronoyau mâle et la complexité que présente le maintien de son intégrité à la fécondation / In animals, sexual reproduction requires the union between two distinct parental gametes: the spermatozoon and the oocyte. The unique nuclear conformation of the sperm, in which the chromatin is organized with sperm-specific chromosomal protein like protamines, abolishes its activity. The paternal chromatin remodeling and the maintenance of its integrity at fertilization by maternal activities are therefore essential processes for zygote formation. However, although their mechanisms are crucial, they remain poorly understood. During my thesis, I tried to better understand the processes involved during de novo paternal chromatin assembly in Drosophila through the study of a maternal embryonic lethal mutation: maternal haploid (mh). The mutant affects the incorporation of paternal chromosomes during the first zygotic division, leading to the development of gynogenetic haploid embryos. The identification of the mh gene as CG9203, and the generation of the null allele mh2 allowed me to characterize its function. In eggs led by mh mutant females, paternal chromosomes abnormally condense and fail to divide leading to the formation of chromatin bridges at the first embryonic division. Recently, its human ortholog Spartan/DVC1, has been described to be involved in translesion synthesis (TLS), a DNA damage tolerance pathway that ensures replication fork progression. Combining genetic and cytological approaches, I demonstrated that the Spartan function in TLS is conserved in Drosophila. However, I discovered that the critical function of MH during the first embryonic division, was not consistent with a canonical TLS. Alternatively, it is specifically required to maintain paternal integrity and to allow its proper replication at the first cycle. The mh phenotype characterization, led me to compare it with others phenotypes induced by the knock-down of replication factors and to study parental chromosome condensation in the zygote. Surprisingly, one of the proteins allowing the establishment of the pre-replication complex is dispensable for the proper paternal chromosome segregation contrarily to the maternal counterpart. Altogether, these works highlight the difference that exists between the two parental pronuclei and the complexity of maintaining their integrity at fertilization
| Identifer | oai:union.ndltd.org:theses.fr/2014LYO10280 |
| Date | 08 December 2014 |
| Creators | Delabaere, Laetitia |
| Contributors | Lyon 1, Loppin, Benjamin |
| Source Sets | Dépôt national des thèses électroniques françaises |
| Language | French |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation, Text |
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