Thesis defense: Marion Peuch
recombinaison
crossing over
synaptonemal complex
chromosomes
Tuesday, September 23rd 2025 2 pm - INRAE, Versailles
Understanding the structure of the synaptonemal complex in Arabidopsis thaliana
Meiosis is a type of cell division that creates haploid cells that are precursors of gametes, the specialized cell which carry genetic information during sexual reproduction. In Arabidopsis thaliana as in other model organisms used to study meiosis, identification and characterization of meiotic genes is an ongoing research field. This thesis reports the identification of three new A. thaliana meiotic genes, which are necessary to ensure correct segregation of homologous chromosomes in meiosis I, and display conservation across a range of angiosperm species.
The synaptonemal complex is a hallmark structure of meiosis: it forms between homologous chromosomes in meiotic prophase I, and, depending on the species, is involved in the formation and/or regulation of crossovers. The first part of this thesis describes the identification and characterization of SCEP1 and SCEP2, two new A. thaliana synaptonemal complex central element proteins. These are necessary for the formation of the synaptonemal complex and locate at its center. Their absence deregulates the formation of crossovers: more crossovers form, but their usual patterning is disrupted.
The second part of this thesis focuses on the functions of a third meiotic protein, named MPOZ1. Contrary to the other two proteins, absence of this protein yields a decrease in crossover numbers and in crossover-precursor complexes. In fact, genetic interaction studies revealed that HEI10 is epistatic to MPOZ1, a class I pro-crossover gene. Evaluation of the characteristics of the synaptonemal complex in the mpoz1 mutant revealed several anomalies compared to wild type synaptonemal complex dynamics. Most strikingly, lateral element remodeling is delayed or does not fully occur in mpoz1. Additionally, non-homologous synapsis and abnormal synaptonemal structures such as polycomplexes were occasionally observed. These results thus point towards an early-prophase role of MPOZ1, and highlights the interconnection between meiotic homologous recombination and synaptonemal complex dynamics.
Meiosis is a type of cell division that creates haploid cells that are precursors of gametes, the specialized cell which carry genetic information during sexual reproduction. In Arabidopsis thaliana as in other model organisms used to study meiosis, identification and characterization of meiotic genes is an ongoing research field. This thesis reports the identification of three new A. thaliana meiotic genes, which are necessary to ensure correct segregation of homologous chromosomes in meiosis I, and display conservation across a range of angiosperm species.
The synaptonemal complex is a hallmark structure of meiosis: it forms between homologous chromosomes in meiotic prophase I, and, depending on the species, is involved in the formation and/or regulation of crossovers. The first part of this thesis describes the identification and characterization of SCEP1 and SCEP2, two new A. thaliana synaptonemal complex central element proteins. These are necessary for the formation of the synaptonemal complex and locate at its center. Their absence deregulates the formation of crossovers: more crossovers form, but their usual patterning is disrupted.
The second part of this thesis focuses on the functions of a third meiotic protein, named MPOZ1. Contrary to the other two proteins, absence of this protein yields a decrease in crossover numbers and in crossover-precursor complexes. In fact, genetic interaction studies revealed that HEI10 is epistatic to MPOZ1, a class I pro-crossover gene. Evaluation of the characteristics of the synaptonemal complex in the mpoz1 mutant revealed several anomalies compared to wild type synaptonemal complex dynamics. Most strikingly, lateral element remodeling is delayed or does not fully occur in mpoz1. Additionally, non-homologous synapsis and abnormal synaptonemal structures such as polycomplexes were occasionally observed. These results thus point towards an early-prophase role of MPOZ1, and highlights the interconnection between meiotic homologous recombination and synaptonemal complex dynamics.
Directors: Mathilde Grelon & Christine Mézard, "Meiosis Mechanisms" MeioMe team, INRAE, IJPB, Versailles
Jury members
> Valérie Borde (Rapportrice) - CNRS, Institut Curie, Chromosome Dynamics and Recombination, Paris
> Thomas Robert (Rapporteur) - CNRS, CBS, Montpellier
> Kirsten Bomblies (Examinatrice) - ETH Zürich, Plant Evolutionary Genetics, Suisse
> Marianne Delarue (Examinatrice) - Université Paris-Saclay, IPS2, CHROMD, Gif-sur-Yvette,
> Chloé Girard (Examinatrice) - CNRS, I2BC,Meiotic Recombination and Pairing, Gif-sur-Yvette
Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences.
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