Skp1 proteins are structural components of the synaptonemal complex in C. elegans

Abstract

The synaptonemal complex (SC) is a zipper-like protein assembly that links homologous chromosomes to regulate recombination and segregation during meiosis. The SC has been notoriously refractory to in vitro reconstitution, thus leaving its molecular organization largely unknown. Here, we report a moonlighting function of two paralogous S-phase kinase-associated protein 1 (Skp1)–related proteins (SKR-1 and SKR-2), well-known adaptors of the Skp1–Cul1–F-box (SCF) ubiquitin ligase, as the key missing components of the SC in Caenorhabditis elegans . SKR proteins repurpose their SCF-forming interfaces to dimerize and interact with meiosis-specific SC proteins, thereby driving synapsis independent of SCF activity. SKR-1 enables the formation of the long-sought-after soluble complex with previously identified SC proteins in vitro, which we propose it to represent a complete SC building block. Our findings demonstrate how a conserved cell cycle regulator has been co-opted to interact with rapidly evolving meiotic proteins to construct the SC and provide a foundation for understanding its structure and assembly mechanisms.

Diffusion within the synaptonemal complex can account for signal transduction along meiotic chromosomes

“…The synaptonemal complex has been identified as a major regulator of crossover patterning. It comprises a linear axis parallel to the chromosomes made up of chromatin-associated axis proteins from the HORMA domain family (in worms, HTP-1/2/3 and HIM-3), and a central region (SC-CR) composed of proteins that span the inter-chromosomal space (in worms, SYP-1/2/3/4/5/6 and SKR-1/2 4,5 ). In addition to the intimate association between the parental chromosomes, the synaptonemal complex directly regulates crossovers: multiple proteins required for crossover formation are recruited by the SC-CR, and perturbation of the SC-CR alters crossover interference [6][7][8][9] .…”