Abstract
Meiosis is a cellular differentiation process in which hundreds of genes are temporally induced. Because the expression of meiotic genes during mitosis is detrimental to proliferation, meiotic genes must be negatively regulated in the mitotic cell cycle. Yet, little is known about mechanisms used by mitotic cells to repress meiosis-specific genes. Here we show that the poly(A)-binding protein Pab2, the fission yeast homolog of mammalian PABPN1, controls the expression of several meiotic transcripts during mitotic division. Our results from chromatin immunoprecipitation and promoter-swapping experiments indicate that Pab2 controls meiotic genes post-transcriptionally. Consistently, we show that the nuclear exosome complex cooperates with Pab2 in the negative regulation of meiotic genes. We also found that Pab2 plays a role in the RNA decay pathway orchestrated by Mmi1, a previously described factor that functions in the post-transcriptional elimination of meiotic transcripts. Our results support a model in which Mmi1 selectively targets meiotic transcripts for degradation via Pab2 and the exosome. Our findings have therefore uncovered a mode of gene regulation whereby a poly(A)-binding protein promotes RNA degradation in the nucleus to prevent untimely expression.
Highlights
Meiosis is a key differentiation process essential for the generation of genetically distinct individuals
Meiotic Differentiation Genes Are Up-regulated in the Absence of Pab2—DNA microarrays were previously used to investigate the expression profile of fission yeast cells that have a deletion for the gene encoding Pab2 [27]
These results demonstrate that specific meiotic transcripts accumulate in pab2⌬ cells during the mitotic cycle
Summary
Strains and Growth—All the S. pombe strains used in this study are listed in supplemental Table 1. Real-time Quantitative PCR—Real-time quantitative PCR analysis using fission yeast total RNA was performed as described previously [37]. Unless specified otherwise, -fold changes are relative to the wild-type strain and normalized to the nda mRNA. The -fold changes were calculated relative to the signal of meiRNA in the wild-type strain, and the signal was normalized to the 5 S rRNA. The -fold changes were calculated relative to the WT strain for each temperature and normalized to the srp RNA. RNA Immunoprecipitation—RNA immunoprecipitations were performed as described previously [27] using extracts prepared from an rrp6⌬ strain that expresses a functional TAP-tagged version of Pab from its endogenous promoter (FBY347). The -fold changes were calculated relative to an untagged control strain and normalized to srp RNA. Sporulation Assay—FBY200, FBY335, and FBY394 homothallic h90 cells were counted using a hemocytometer, and equal numbers of cells were spotted on minimal media and incubated
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