RNF212B E3 ligase is crucial for crossover designation and maturation during mouse meiosis
Raquel Sainz Urruela
Centro de Investigación del Cáncer (CSIC-Universidad de Salamanca)
Meiosis relies on precise initiation, maturation and resolution of crossovers (COs) during prophase I to ensure an accurate segregation of homologs. In mammals, this process is regulated by the interplay of RING-E3 ligases such as RNF212 and HEI10.
In this study, we firstly identified and functionally characterized a RING-E3 ligase, RNF212B. RNF212B colocalizes and interacts with RNF212 and HEI10, forming foci along chromosome axes from zygonema onwards in a synapsis-dependent and DSB-independent manner. These consolidate into larger foci at maturing COs, colocalizing with HEI10, CNTD1 and MLH1 by late pachynema. Genetically, RNF212B foci formation depends on Rnf212 but not on Msh4, Hei10 and Cntd1, while the unloading of RNF212B at the end of pachynema is dependent on Hei10 and Cntd1.
Mice lacking RNF212B, or expressing a catalytically inactive RNF212B protein, exhibit modest synapsis defects, a reduction in the localization of pro-CO factors (MSH4, TEX11, RPA, MZIP2) and an absence of late CO-intermediates (MLH1). This loss of most COs by diakinesis results in mostly univalent chromosomes at metaphase I. Double mutants for Rnf212b and Rnf212 exhibit an identical phenotype to that of Rnf212b and Rnf212 single mutants, while double heterozygous demonstrate a dosage-dependent reduction in CO number, indicating a functional interplay between paralogs. SUMOylome analysis of testes from Rnf212b mutants and pull-down analysis of Sumo- and Ubiquitin-tagged HeLa cells, suggest that RNF212B is a E3-ligase with Ubiquitin activity. Thus, the RING-finger E3 ligases RNF212 and RNF212B play vital, yet overlapping roles, in ensuring CO homeostasis through their distinct E3 ligase activities.