Crossover (CO) formation through homologous recombination is critical for accurate chromosome segregation during meiosis. Errors in this process can lead to congenital defects and infertility. Despite the hundreds of programmed double-strand breaks (DSBs) at the onset of meiosis, only a small subset matures into COs. Understanding how CO frequency and distribution are regulated in mammalian prophase I remains a key challenge in the field.

Recent studies emphasize the importance of ubiquitination and SUMOylation pathways in CO formation. E3 ligases RNF212 and HEI10 are indispensable for CO selection and maturation. Recently, genome-wide association studies have identified a novel E3 ligase, RNF212B, as a potential contributor to recombination rate variation. However, a precise role for RNF212B in meiosis remains unexplored. To explore this, RNF212B-specific antibodies and mutant mouse models were developed. RNF212B colocalizes with RNF212 along chromosomes from zygonema onward in a synapsis-dependent, DSB-independent manner. By late pachynema, RNF212B, like RNF212, consolidates at maturing CO sites, colocalizing with HEI10, CNTD1, and MLH1. RNF212B foci formation depends on Rnf212, while turnover requires Hei10 and Cntd1. Mutant Rnf212b mice exhibit meiotic defects, including reduced testis weights, metaphase I arrest, mild synaptic abnormalities, and impaired localization of pro-CO factors (e.g., MSH4, TEX11, and MLH1). SUMOylome analysis in Rnf212b mutant testis and immunoprecipitation of tagged SUMO and ubiquitin in HeLa cells, suggest that RNF212B is an E3-ligase with ubiquitin activity, serving as a crucial factor for CO maturation.

This study characterizes RNF212B as a novel pro-CO factor, underscoring the critical roles of ubiquitination and SUMOylation in CO formation and regulation. Congratulations to Ian, Stephanie, and Rachel for their outstanding contributions to this publication— fantastic work all around!