Dissecting the Mer3 Helicase Network: Structural, Biochemical, and Genetic Insights into Meiotic Crossover Regulation

• Applicant: Dr. John Weir
• Subject Area: Cell Biology ; General Genetics and Functional Genome Biology ; Biochemistry ; Structural Biology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 567435826

Meiosis is the special type of cell division that creates sperm or egg cells in many organisms, including humans. During meiosis, chromosomes exchange segments of DNA in a process called “homologous recombination,” which promotes genetic diversity and proper chromosome separation. Mistakes in this exchange can lead to infertility or genetic disorders. Our focus is the helicase enzyme Mer3, found in the budding yeast model system but also present in other species, including humans. Helicases act like tiny molecular motors that can separate or unwind DNA strands. Mer3 doesn’t just unwind DNA; it also works closely with partner proteins (RPA, Rad52, and Dmc1) to protect and stabilise essential DNA structures known as D-loops. These D-loops form when one chromosome strand invades a similar or identical DNA molecule, setting the stage for crossover events. We will focus on the following areas: 1. Unravelling Protein Partnerships. We aim to understand precisely how Mer3 interacts with each partner—RPA (a protein that keeps single-stranded DNA stable), Rad52 (key for DNA strand pairing), and Dmc1 (a recombinase that promotes genetic exchanges). By mapping out where these binding “hotspots” occur and determining the biochemical details, we learn how Mer3 coordinates the steps needed to form healthy crossovers. 2. Structural Insights. Alongside partner labs, we use techniques like cryo-electron microscopy, cross-linking mass spectrometry, and AlphaFold predictive modelling to visualise how Mer3 assembles in different complexes. Additionally, we will employ single-molecule methods—especially magnetic tweezers—to observe how Mer3 unwinds DNA in real time and cooperates with its partner proteins. Understanding the shape and arrangement of these protein-DNA complexes reveals how Mer3 holds everything together at the right place and time. 3. Meiotic Mechanics and Genetic Outcomes. By creating “separation-of-function” mutants—versions of Mer3 that are normal in some abilities but faulty in others—we test the exact contributions of each protein interaction. With these mutants, we measure crossover frequency, spore viability, and chromosome segregation accuracy. This pinpoints how each piece of the Mer3 puzzle affects fertility and genetic diversity. Ultimately, this work helps decode the finely tuned dance of DNA during meiosis. Because Mer3 has counterparts in plants and animals (including humans), our insights may shed light on fertility issues and even inform breeding strategies for crops. Understanding how cells maintain genome integrity also hints at broader applications, such as cancer therapies targeting recombination pathways.

• DFG Programme: Research Grants