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Functional significance of nuclear export and mRNA binding of meiotic regulator Spo5 in fission yeast.

Togashi N, Yamashita A, Sato M, Yamamoto M - BMC Microbiol. (2014)

Bottom Line: Among the four family members, namely Pcr1, Atf1, Atf21, and Atf31, only the mRNA encoding Pcr1 binds to Spo5.Spo5 is exported from the nucleus with mRNAs via the Rae1-dependent pathway.RRMs are necessary for this process and also for the function of Spo5 after the nuclear export.

View Article: PubMed Central - HTML - PubMed

Affiliation: Kazusa DNA Research Institute, 2-6-7 Kazusa-kamatari, Kisarazu, Chiba 292-0818, Japan. yamamoto@nibb.ac.jp.

ABSTRACT

Background: Meiotic cells undergo two rounds of nuclear division and generate gametes. Previous studies have indicated that a number of transcription factors modulate the transcriptome in successive waves during meiosis and spore formation in fission yeast. However, the mechanisms underlying the post-transcriptional regulation in meiosis are not fully understood. The fission yeast spo5+ gene encodes a meiosis-specific RNA-binding protein, which is required for the progression of meiosis II and spore formation. However, the target RNA molecules of Spo5 are yet to be identified. Characterization of meiosis-specific RNA-binding proteins will provide insight into how post-transcriptional regulation influence gene expression during sexual differentiation.

Results: To assess the functional significance of RNA-recognition motifs (RRMs) of Spo5, we constructed a series of new spo5 truncated mutants and previously reported spo5 missense mutants. In addition, we isolated novel spo5 missense mutants. The phenotypic characteristics of these mutants indicated that the RRMs are essential for both the localization and function of the protein. Interestingly, Spo5 is exported from the nucleus to the cytoplasm via the Rae1-dependent mRNA export pathway, but is unlikely to be involved in global mRNA export. Furthermore, cytoplasmic localization of Spo5 is important for its function, which suggests the involvement of Spo5 in post-transcriptional regulation. We identified pcr1+ mRNA as one of the critical targets of Spo5. The pcr1+ gene encodes an activating transcription factor/cAMP response element binding (ATF/CREB) transcription factor family. Among the four family members, namely Pcr1, Atf1, Atf21, and Atf31, only the mRNA encoding Pcr1 binds to Spo5.

Conclusions: Spo5 is exported from the nucleus with mRNAs via the Rae1-dependent pathway. RRMs are necessary for this process and also for the function of Spo5 after the nuclear export. Spo5 appears to influence the activity of pcr1+ mRNA, and the mechanism of how Spo5 stimulates the mRNA to promote the progression of meiosis II and spore formation remains an intriguing question for future research.

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pcr1+ mRNA is one of the critical targets of Spo5. (A) The sporulation of the spo5(S365P) strain was detected by dark brown staining with iodine vapor when pcr1+ was overexpressed. Stained patches and DIC images of the cells are shown. Scale bar, 5 μm. (B) Sporulation defects of other spo5 mutants were also suppressed by the overexpression of pcr1+. Meiosis and sporulation were induced in cells harboring pPEP1 (vector) or pPEP3-pcr1+, and the sporulation efficiency was calculated (n > 500). Error bars indicate standard deviation. (C) Meiosis was induced in spo5∆ cells harboring plasmids containing spo5+, pcr1+, atf1+, atf21+, and atf31+, or the empty vector on SSA at 30°C for 3 days, and sporulation efficiency was calculated (n > 500). Error bars indicate standard deviation.
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Figure 4: pcr1+ mRNA is one of the critical targets of Spo5. (A) The sporulation of the spo5(S365P) strain was detected by dark brown staining with iodine vapor when pcr1+ was overexpressed. Stained patches and DIC images of the cells are shown. Scale bar, 5 μm. (B) Sporulation defects of other spo5 mutants were also suppressed by the overexpression of pcr1+. Meiosis and sporulation were induced in cells harboring pPEP1 (vector) or pPEP3-pcr1+, and the sporulation efficiency was calculated (n > 500). Error bars indicate standard deviation. (C) Meiosis was induced in spo5∆ cells harboring plasmids containing spo5+, pcr1+, atf1+, atf21+, and atf31+, or the empty vector on SSA at 30°C for 3 days, and sporulation efficiency was calculated (n > 500). Error bars indicate standard deviation.

Mentions: The relationship between Pcr1 and Spo5, however, has not been delineated. Transcription of pcr1+ was not lowered in the spo5 mutant, spo5∆ (Additional file 4: Figure S4A). The levels of pcr1+ transcripts gradually increase toward late meiosis [5] (after 4 h in Additional file 4: Figure S4A), suggesting that Pcr1 may also function in a meiotic process other than meiotic recombination. Overexpression of pcr1+ could suppress the sporulation deficiency of spo5(S365P) and other spo5 mutants including spo5∆ (Figure 4A,B). These data suggest that Pcr1 may act downstream of Spo5, and that meiotic progression can be promoted substantially without Spo5 if Pcr1 is expressed at sufficiently high levels.


Functional significance of nuclear export and mRNA binding of meiotic regulator Spo5 in fission yeast.

Togashi N, Yamashita A, Sato M, Yamamoto M - BMC Microbiol. (2014)

pcr1+ mRNA is one of the critical targets of Spo5. (A) The sporulation of the spo5(S365P) strain was detected by dark brown staining with iodine vapor when pcr1+ was overexpressed. Stained patches and DIC images of the cells are shown. Scale bar, 5 μm. (B) Sporulation defects of other spo5 mutants were also suppressed by the overexpression of pcr1+. Meiosis and sporulation were induced in cells harboring pPEP1 (vector) or pPEP3-pcr1+, and the sporulation efficiency was calculated (n > 500). Error bars indicate standard deviation. (C) Meiosis was induced in spo5∆ cells harboring plasmids containing spo5+, pcr1+, atf1+, atf21+, and atf31+, or the empty vector on SSA at 30°C for 3 days, and sporulation efficiency was calculated (n > 500). Error bars indicate standard deviation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4109790&req=5

Figure 4: pcr1+ mRNA is one of the critical targets of Spo5. (A) The sporulation of the spo5(S365P) strain was detected by dark brown staining with iodine vapor when pcr1+ was overexpressed. Stained patches and DIC images of the cells are shown. Scale bar, 5 μm. (B) Sporulation defects of other spo5 mutants were also suppressed by the overexpression of pcr1+. Meiosis and sporulation were induced in cells harboring pPEP1 (vector) or pPEP3-pcr1+, and the sporulation efficiency was calculated (n > 500). Error bars indicate standard deviation. (C) Meiosis was induced in spo5∆ cells harboring plasmids containing spo5+, pcr1+, atf1+, atf21+, and atf31+, or the empty vector on SSA at 30°C for 3 days, and sporulation efficiency was calculated (n > 500). Error bars indicate standard deviation.
Mentions: The relationship between Pcr1 and Spo5, however, has not been delineated. Transcription of pcr1+ was not lowered in the spo5 mutant, spo5∆ (Additional file 4: Figure S4A). The levels of pcr1+ transcripts gradually increase toward late meiosis [5] (after 4 h in Additional file 4: Figure S4A), suggesting that Pcr1 may also function in a meiotic process other than meiotic recombination. Overexpression of pcr1+ could suppress the sporulation deficiency of spo5(S365P) and other spo5 mutants including spo5∆ (Figure 4A,B). These data suggest that Pcr1 may act downstream of Spo5, and that meiotic progression can be promoted substantially without Spo5 if Pcr1 is expressed at sufficiently high levels.

Bottom Line: Among the four family members, namely Pcr1, Atf1, Atf21, and Atf31, only the mRNA encoding Pcr1 binds to Spo5.Spo5 is exported from the nucleus with mRNAs via the Rae1-dependent pathway.RRMs are necessary for this process and also for the function of Spo5 after the nuclear export.

View Article: PubMed Central - HTML - PubMed

Affiliation: Kazusa DNA Research Institute, 2-6-7 Kazusa-kamatari, Kisarazu, Chiba 292-0818, Japan. yamamoto@nibb.ac.jp.

ABSTRACT

Background: Meiotic cells undergo two rounds of nuclear division and generate gametes. Previous studies have indicated that a number of transcription factors modulate the transcriptome in successive waves during meiosis and spore formation in fission yeast. However, the mechanisms underlying the post-transcriptional regulation in meiosis are not fully understood. The fission yeast spo5+ gene encodes a meiosis-specific RNA-binding protein, which is required for the progression of meiosis II and spore formation. However, the target RNA molecules of Spo5 are yet to be identified. Characterization of meiosis-specific RNA-binding proteins will provide insight into how post-transcriptional regulation influence gene expression during sexual differentiation.

Results: To assess the functional significance of RNA-recognition motifs (RRMs) of Spo5, we constructed a series of new spo5 truncated mutants and previously reported spo5 missense mutants. In addition, we isolated novel spo5 missense mutants. The phenotypic characteristics of these mutants indicated that the RRMs are essential for both the localization and function of the protein. Interestingly, Spo5 is exported from the nucleus to the cytoplasm via the Rae1-dependent mRNA export pathway, but is unlikely to be involved in global mRNA export. Furthermore, cytoplasmic localization of Spo5 is important for its function, which suggests the involvement of Spo5 in post-transcriptional regulation. We identified pcr1+ mRNA as one of the critical targets of Spo5. The pcr1+ gene encodes an activating transcription factor/cAMP response element binding (ATF/CREB) transcription factor family. Among the four family members, namely Pcr1, Atf1, Atf21, and Atf31, only the mRNA encoding Pcr1 binds to Spo5.

Conclusions: Spo5 is exported from the nucleus with mRNAs via the Rae1-dependent pathway. RRMs are necessary for this process and also for the function of Spo5 after the nuclear export. Spo5 appears to influence the activity of pcr1+ mRNA, and the mechanism of how Spo5 stimulates the mRNA to promote the progression of meiosis II and spore formation remains an intriguing question for future research.

Show MeSH
Related in: MedlinePlus