A minimal model for the role of Rim4-mRNA aggregates in regulating meiotic exit in budding yeast

Meiosis ensures the formation of haploid gametes through two rounds of chromosome segregation after one round of DNA replication. How this complex cell cycle process is limited to two and only two divisions is poorly understood. In budding yeast, RNA-binding protein Rim4 forms aggregated fibrils that bind various mRNAs to prevent their translation. At the onset of meiosis II, degradation of Rim4 triggered by Ime2 kinase activity and concomitant release of sequestered mRNA has been shown to be important in ensuring fidelity of meiotic exit. Indeed, phase separated condensates consisting of key molecules together with other proteins or RNA are crucial for the spatial and temporal regulation of various cellular processes. Several mRNAs bound by Rim4 encode important regulators of meiotic exit. We present a parsimonious model of meiotic termination that recapitulates the role of Rim4-mRNA aggregates in regulating exit, consistent with experimental results for the deletion of key network constituents. Notably, we show that when dissociation of Rim4-mRNA aggregates is disrupted, oscillations in cyclin dependent kinases persist, and exit does not occur. We extend our phenomenological description of Rim4-mRNA aggregation and dissociation to include preliminary results on their phosphorylation-mediated regulation with implications for the fidelity of exit.