Temporal and Functional Relationship between Synaptonemal Complex Morphogenesis and Recombination during Meiosis

Area of Science:

• Cell Biology
• Genetics
• Molecular Biology

Background:

• Meiosis I requires programmed double-strand breaks (DSBs) to form crossovers for homologous chromosome segregation.
• Crossovers arise from homologous recombination, closely linked to synaptonemal complex (SC) assembly during pachytene.
• The temporal and functional relationship between synapsis and recombination remains unclear.

Approach:

• Investigated the link between SC assembly and recombination dynamics in budding yeast.
• Analyzed the transition of DNA structures from D-loops to single-end invasions (SEIs).
• Examined the role of the SC central element protein Zip1 in recombination progression.

Key Points:

• SC assembly correlates with a threshold of unstable D-loops.
• Transition to plectonemic SEIs completes during mid-pachytene as SC fully assembles.
• Double Holliday junctions form at desynapsis and resolve into crossovers during diplonema.
• Zip1 shepherds recombination through strand exchange, end capture, and dHJ resolution.
• Zip1 mediates SEI formation independently of polymerization; precocious assembly hinders dHJ resolution.

Conclusions:

• The SC controls recombination during and after its assembly, potentially via spatial constraints.
• Findings elucidate the intricate regulation of meiotic recombination by chromosome structure.