Molecular Architecture of Meiotic Chromosomes

• Applicant: Professor Dr. Ricardo Benavente
• Subject Area: Cell Biology
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 273125261

Meiosis is essential for sexual reproduction in that it enables the generation of haploid cells. It consists of two successive cellular divisions without intervening DNA replication. During the first meiotic prophase homologous chromosomes pair, synapse and recombine. These processes are essential to ensure correct chromosome segregation during the reductional first meiotic division. During the second division, sister chromatids are separated leading to the formation of haploid gametes. As a result of recombination between the homologous chromosomes and their independent assortment during meiosis I, germ cells are genetically different from the original mother cell (spermatogonia or oogonia). The high biological relevance of meiosis is beyond question: it provides the basis for sexual reproduction and represents the largest natural source of genetic variability. Meiotic chromosome synapsis and meiotic recombination depend on the formation of meiosis-specific structures: synaptonemal complexes, cohesin axes and recombination nodules. Remarkably, formation of these structures revealed to be interdependent processes that take place in the meiotic chromosome axis. Thus, defining the molecular organization of the meiotic chromosome axis is a key aspect for the understanding of genome stability in the germ line. Protein localization of meiotic chromosome axial structures has been approached by immunofluorescence microscopy, but the resolution achieved is only about 200 nm. The localization of some of the axial chromosome components has also been approached by immunogold EM. Here, proteins can be localized with nm resolution, whereas the localization precision is mainly limited by the size of the primary and secondary antibody and the size of the gold particle. Sample preparation is usually time consuming and quantitative analysis tedious, because of the low amount of gold particles. Since the structural resolution achievable is determined not only by the localization precision but also by the signal density as described by the Nyquist-Shannon sampling theorem, the construction of proteins localization maps of different proteins by immunogold EM remains challenging. To circumvent these obstacles we propose to investigate the molecular architecture and interactions of meiotic chromosome axial structures to each other and with the nuclear envelope by providing quantitative protein distribution maps. To this end, super-resolution imaging (dSTORM) in combination with one- and dual-color single localization microscopy and average position determination with nanometer position will be applied to wild-type and selected knockout mice, together with electron microscope tomography as well as molecular and biochemical approaches. As infertility and aneuploidies (i.e. Down syndrome) are often the consequence of a defective meiosis, these investigations would be of relevance for the field of animal and human reproductive health.

• DFG Programme: Research Grants