Proteins and noncoding RNAs that promote homologous chromosome recognition and pairing in fission yeast meiosis undergo condensate formation in vitro.
Pairing of homologous chromosomes during meiosis is crucial for successful sexual reproduction. Previous studies have shown that the fission yeast sme2 RNA, a meiosis-specific long noncoding RNA (lncRNA), accumulates at the sme2 locus and plays a key role in mediating robust pairing during meiosis. Several RNA-binding proteins accumulate at the sme2 and other lncRNA gene loci in conjunction with the lncRNAs transcribed from these loci. These lncRNA-protein complexes form condensates that exhibit phase separation properties on chromosomes and are necessary for robust pairing of homologous chromosomes. To further understand the mechanisms by which phase separation affects homologous chromosome pairing, we conducted an in vitro phase separation assay with the sme2 RNA-associated proteins (Smps) and RNAs. Our findings reveal that one of the Smps, Seb1, forms condensates resembling phase separation; the observed number and size of these condensates increase upon the addition of another Smp, Rhn1, and purified RNAs. Additionally, we have found that RNAs protect Smp condensates from treatment with 1,6-hexanediol. The Smp condensates containing different types of RNA display distinct FRAP profiles, and the Smp condensates containing the same type of RNA tend to fuse together more readily than those containing different types of RNAs. Collectively, these results indicate that the specific RNA species within condensates modulate their physical properties, potentially enabling the formation of regional RNA-Smp condensates with distinct characteristics that facilitate homologous chromosome pairing.
Ding DQ, Okamasa K, Yoshimura Y, Matsuda A, Yamamoto TG, Hiraoka Y, Nakayama JI