 mmi1  and  rep2  mRNAs are novel RNA targets of the Mei2 RNA-binding protein during early meiosis in  Schizosaccharomyces pombe .
The RNA-binding protein Mei2 is crucial for meiosis in  Schizosaccharomyces pombe.  In  mei2  mutants, pre-meiotic S-phase is blocked, along with meiosis. Mei2 binds a long non-coding RNA (lncRNA) called meiRNA, which is a 'sponge RNA' for the meiotic inhibitor protein Mmi1. The interaction between Mei2, meiRNA and Mmi1 protein is essential for meiosis. But  mei2  mutants have stronger and different phenotypes than meiRNA mutants, since  mei2Δ  arrests before pre-meiotic S, while the meiRNA mutant arrests after pre-meiotic S but before meiosis. This suggests Mei2 may bind additional RNAs. To identify novel RNA targets of Mei2, which might explain how Mei2 regulates pre-meiotic S, we used RNA immunoprecipitation and cross-linking immunoprecipitation. In addition to meiRNA, we found the mRNAs for  mmi1  (which encodes Mmi1) and for the S-phase transcription factor  rep2  There were also three other RNAs of uncertain relevance. We suggest that at meiotic initiation, Mei2 may sequester  rep2  mRNA to help allow pre-meiotic S, and then may bind both meiRNA and  mmi1  mRNA to inactivate Mmi1 at two levels, the protein level (as previously known), and also the mRNA level, allowing meiosis. We call Mei2-meiRNA a 'double sponge' (i.e. binding both an mRNA and its encoded protein).
Mukherjee K, Futcher B, Leatherwood J