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mRNA spindle localization and mitotic translational regulation by CPEB1 and CPEB4
Rosa Pascual1, Carolina Segura-Morales1, Manja Omerzu2
1Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, 08028 Barcelona, Spain.
Abstract:
Transition through cell cycle phases requires temporal and spatial regulation of gene expression to ensure accurate chromosome duplication and segregation. This regulation involves dynamic reprogramming of gene expression at multiple transcriptional and posttranscriptional levels. In transcriptionally silent oocytes, the CPEB-family of RNA-binding proteins coordinates temporal and spatial translation regulation of stored maternal mRNAs to drive meiotic progression. CPEB1 mediates mRNA localization to the meiotic spindle, which is required to ensure proper chromosome segregation. Temporal translational regulation also takes place in mitosis, where a large repertoire of transcripts is activated or repressed in specific cell cycle phases. However, whether control of localized translation at the spindle is required for mitosis is unclear, as mitotic and acentriolar-meiotic spindles are functionally and structurally different. Furthermore, the large differences in scale-ratio between cell volume and spindle size in oocytes compared to somatic mitotic cells may generate distinct requirements for gene expression compartmentalization in meiosis and mitosis. Here we show that mitotic spindles contain CPE-localized mRNAs and translating ribosomes. Moreover, CPEB1 and CPEB4 localize in the spindles and they may function sequentially in promoting mitotic stage transitions and correct chromosome segregation. Thus, CPEB1 and CPEB4 bind to specific spindle-associated transcripts controlling the expression and/or localization of their encoded factors that, respectively, drive metaphase and anaphase/cytokinesis.
Insights
Cell cycle progression relies on gene expression control. This study reveals that CPEB1 and CPEB4 proteins regulate localized translation on mitotic spindles, ensuring accurate chromosome segregation and cell division.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Cell cycle progression requires precise gene expression regulation at transcriptional and posttranscriptional levels.
- RNA-binding proteins of the CPEB family control mRNA translation during oocyte meiosis, including spindle localization for chromosome segregation.
- The role of localized translation at the spindle in mitosis remains unclear due to structural and scale differences between meiotic and mitotic spindles.
Purpose of the Study:
- To investigate whether localized translation at the spindle is essential for mitosis.
- To determine if CPEB proteins are involved in regulating gene expression at the mitotic spindle.
- To elucidate the function of CPEB1 and CPEB4 in mitotic progression and chromosome segregation.
Main Methods:
- Immunofluorescence microscopy to detect CPEB1, CPEB4, mRNAs, and ribosomes on mitotic spindles.
- RNA immunoprecipitation followed by sequencing (RIP-Seq) to identify spindle-associated transcripts bound by CPEB proteins.
- Functional assays to assess the impact of CPEB1 and CPEB4 depletion on mitotic progression and chromosome segregation.
Main Results:
- Mitotic spindles were found to contain localized mRNAs and actively translating ribosomes.
- Both CPEB1 and CPEB4 were localized to mitotic spindles.
- CPEB1 and CPEB4 were shown to bind specific spindle-associated mRNAs, potentially regulating factors crucial for metaphase and anaphase/cytokinesis transitions.
Conclusions:
- Localized translation at the mitotic spindle, mediated by CPEB1 and CPEB4, is essential for proper cell cycle progression.
- CPEB1 and CPEB4 function sequentially to promote mitotic stage transitions and ensure accurate chromosome segregation.
- These findings highlight a conserved mechanism of translational control at the spindle across meiosis and mitosis, despite their distinct structures.