Thesis defense: Mariana Tiscareño-Andrade
meiosis
chromosome
nucleus
recombination
movement
Thursday, December 12th 2024, 2 pm, INRAE, Versailles
Characterization of chromosome dynamics during meiotic prophase in Arabidopsis thaliana
Meiosis is a specialized cell division that generates haploid cells, which give rise to gametes. In sexually reproducing eukaryotes, meiosis is crucial to introduce genetic variation from one generation to the other, notably through the formation of genetic exchanges between homologous chromosomes called crossovers (COs). These COs arise by recombination, during meiotic prophase I and are essential for proper chromosome segregation at anaphase I. During prophase I, chromosomes are subject to several dynamic processes: (i) pairing, where homologous chromosomes align along their length; (ii) synapsis, the union of homologs via the synaptonemal complex; (iii) telomere attachment and clustering to the nuclear envelope (NE) and (iv) significant chromosome mobility, known as “Rapid Prophase movements” (RPMs). The molecular mechanisms behind these events, particularly in plants, and their link to recombination are still not fully understood. Using live-cell imaging, I characterized, for the first time in Arabidopsis thaliana, the meiotic RPMs during prophase I in male meiocytes. Our findings revealed that A. thaliana meiotic centromeres exhibit rapid (up to 500 nm/s) and uncoordinated movements during the zygotene and pachytene stages. These movements are autonomous, not driven by global nuclear rotation, and remain unaffected by mutations modifying synapsis progression, chromosome structure, or recombination. I also identified several regulators of these RPMs. They are located in the NE, and form a meiotic LINC (Linker of Nucleoskeleton and Cytoskeleton) complex together with its associated kinesin-motor protein, PSS1. Through live imaging and 3D immunolocalization, I analyzed the structural changes occurring in the NE during prophase I. I showed that the PSS1-LINC complex exhibits polarization in the NE and focal agglomerations at telomere attachment points. I showed that the PSS1-LINC complex promotes telomere attachment and clustering at the NE. In mutants lacking the PSS1-LINC complex, these processes, along with centromere movement, were disrupted, leading to defects in synapsis and recombination. This suggests that meiotic RPMs play a conserved role in ensuring proper homologous pairing and recombination during prophase I in A. thaliana.
Meiosis is a specialized cell division that generates haploid cells, which give rise to gametes. In sexually reproducing eukaryotes, meiosis is crucial to introduce genetic variation from one generation to the other, notably through the formation of genetic exchanges between homologous chromosomes called crossovers (COs). These COs arise by recombination, during meiotic prophase I and are essential for proper chromosome segregation at anaphase I. During prophase I, chromosomes are subject to several dynamic processes: (i) pairing, where homologous chromosomes align along their length; (ii) synapsis, the union of homologs via the synaptonemal complex; (iii) telomere attachment and clustering to the nuclear envelope (NE) and (iv) significant chromosome mobility, known as “Rapid Prophase movements” (RPMs). The molecular mechanisms behind these events, particularly in plants, and their link to recombination are still not fully understood. Using live-cell imaging, I characterized, for the first time in Arabidopsis thaliana, the meiotic RPMs during prophase I in male meiocytes. Our findings revealed that A. thaliana meiotic centromeres exhibit rapid (up to 500 nm/s) and uncoordinated movements during the zygotene and pachytene stages. These movements are autonomous, not driven by global nuclear rotation, and remain unaffected by mutations modifying synapsis progression, chromosome structure, or recombination. I also identified several regulators of these RPMs. They are located in the NE, and form a meiotic LINC (Linker of Nucleoskeleton and Cytoskeleton) complex together with its associated kinesin-motor protein, PSS1. Through live imaging and 3D immunolocalization, I analyzed the structural changes occurring in the NE during prophase I. I showed that the PSS1-LINC complex exhibits polarization in the NE and focal agglomerations at telomere attachment points. I showed that the PSS1-LINC complex promotes telomere attachment and clustering at the NE. In mutants lacking the PSS1-LINC complex, these processes, along with centromere movement, were disrupted, leading to defects in synapsis and recombination. This suggests that meiotic RPMs play a conserved role in ensuring proper homologous pairing and recombination during prophase I in A. thaliana.
Director: Mathilde Grelon - INRAE, IJPB, Versailles, MeioMe team
Co-Supervisor: Laurence Cromer - INRAE, IJPB, Versailles, MeioMe team
Members of the jury
> Jean-René Huynh (Rapporteur) - Collège de France, CIRB, Paris
> Christophe Tatout (Rapporteur) - University Clermont Auvergne, iGReD, Clermont-Ferrand
> Emmanuelle Fabre (Examinatrice) - CNRS, BDC, Paris
> Simone Koehler (Examinatrice) - EMBL, Heidelberg, Allemagne
> Mariane Delarue (Examinatrice) - Université Paris-Saclay, IPS2, Gif-sur-Yvette
To attend, contact, Mathilde Grelon
Research developed at the Institute Jean-Pierre Bourgin for Plant Sciences.
Back
