Nuclear CCT chaperonin regulates meiotic chromosome morphogenesis through assembly of meiotic HORMAD proteins

A key feature of meiotic prophase entry is the assembly of a meiotic chromosome, which includes organizing the meiotic chromatin of the replicated chromosomes into an array of loops secured by a chromosome axis. The axes are comprised of meiosis-specific cohesion complexes, and in most species by members of a protein family containing a HORMA domain (for Hop1, Rev7p, and MAD2). Across eukaryotic phyla, the meiotic HORMA domain proteins have essential functions at chromosome axes where they promote meiotic DSB formation, homolog pairing, SC formation, and multiple steps in the formation of crossovers from recombination intermediates. The nematode C. elegans has four HORMA domain proteins that physically interact and are recruited to the chromosomes in a stepwise hierarchy during axis formation. We have investigated the function of the nematode HORMAD proteins during meiosis with the goal of understanding how their recruitment to chromosomes is co-ordinated with their distinct functions in meiotic events. Our recent work has revealed a nuclear role for the CCT/TRiC chaperonin complex in meiotic axis morphogenesis and an unappreciated role for CCT-mediated folding in regulating meiotic events.