FIGURE 1.

Cell cycle or meiosis control of lncRNA in fungi. (A) In MATa or MATα haploid cells, the expression of IRT1 is induced by a transcription activator Rme1. Then transcribed IRT1 can recruit the histone methyltransferase Set2 and the histone deacetylase Set3 at the IME1 promoter, finally leading to the inhibit of IME1 expression. (B) In the homozygous MATa/α diploid cells, the a1/α2 heterodimer can inhibit the expression of REM1, so IRT1 can’t be expressed without the induction of Rme1. IME1 can successfully transcript without the repression of IRT1. (C) In MATa or MATα haploid cells, lncRNA REM2 inhibits transcription elongation of IME4 to prevent germ cell differentiation. However, in MATa/α diploid cells, the a1/α2 heterodimer represses the transcription of REM2 by binding at a conserved site located downstream of the IME4, thus allowing for induction of IME4. (D) meiRNA regulates the expression of meiotic gene and chromosome pairing. In meiotic cells, two isoforms of the meiRNA (i.e., meiRNA-S and meiRNA-L) are transcribed and form a meiRNA-Mei2 complex by interacting with RNA-binding protein Mei2. The Mei2-meiRNA complex blocks the RNA-binding protein Mmi1, thus allowing the sme2 to be translated, thus initiating meiosis. During meiotic prophase in S. pombe, the ends of each chromosome are tied up to the spindle pole body. At the sme2 loci on chromosome II, the formation of a robustly chromosome pairing is dependent on meiRNA. Interestingly, Mmi1 also inhibits Mei2 by forming a double negative feedback loop. In addition, Mmi1 can interact with a nuclear complex called Meiotic gene silencing complex MTREC/NURS MTREC (MTl1-REd1 Core) or NURS (NUclear RNA Silencing) in meiotic transcript elimination.