July 2nd
Recent Publications Harnessing the Power of Translatomics.
Every week we provide a digest of a small number of recent interesting papers in the field of translatomics.
In this week’s Sunday papers, Tan et al. delve into the functionality of PRRC2A and its m6A recognition abilities in the process of meiosis and spermatogenesis. Later in the issue, another member of the Proline Rich Coiled-Coil 2 family, PRRC2B, is analysed by Jiang et al. for the role it plays within the realm of cell cycle progression. Sandwiched between these two insightful pieces, Wu et al. looks into the specifics of METTL3-meditated m6A modifications in chronic lymphocytic leukaemia.
The m6A reader PRRC2A is essential for meiosis I completion during spermatogenesis
Nature Communications, 2023
Tan, X., Zheng, C., Zhuang, Y., Jin, P. and Wang, F.
The m6A modification is the most prevalent mRNA modification in eukaryotic cells, and can have a range of impacts, influencing mRNA stability as well as translational efficiency. A number of m6A readers, along with writers and erasers, have previously been shown to be active in various aspects of spermatogenesis, including cell cycle control. However, no studies have investigated such modifications within the realm of meiotic metaphase. Here, the authors investigate a specific m6A reader, PRRC2A, and its potential role in such a function.
They find that PRRC2A is, compared to other tissues, highly expressed in the testes, with its knockout leading to a dramatic reduction in spermatogenesis. Underlying this, knockout also resulted in XY asynapsis, impaired meiotic sex chromosome inactivation, chromosomal misalignment and improper spindle assembly, along with arrest during meiotic metaphase. Ribosome profiling was able to reveal that PRRC2A expression decreased the mRNA levels of its targets, while improving their translation efficiency, many of which had functions in male fertility (e.g., cilium movement and spermatogenesis). Further analysis suggested that PRRC2A is crucial in the transition from early spermatogonia to later-phase spermatocytes. It also specifically promotes the translation of genes involved in meiotic cell division, such as CEP192 and Wnk1.
METTL3-Mediated m6A Modification Controls Splicing Factor Abundance and Contributes to Aggressive CLL
Blood Cancer Discovery, 2023
Wu, Y., Jin, M., Fernandez, M., Hart, K.L., Liao, A., Ge, X., Fernandes, S.M., McDonald, T., Chen, Z., Röth, D. and Ghoda, L.Y.
Chronic lymphocytic leukemia (CLL) is a form of mature B-cell leukemia, a hallmark of which is defects in the splicosomal machinery. While mutations in genes for such machinery (such as SF3B1) are comparatively common, their frequency cannot fully explain the splicosomal burden seen. More recently, the m6A modification of mRNA has been shown to be required for normal blood cell production, as well as in haematological malignancies. Here, the authors explore how such m6A modifications, and their writers, can contribute to such malignancies, such as CLL, and to what extent they may impact on RNA splicing dysregulation.
Early proteomic data suggested that RNA splicing factors were upregulated at a protein level, but not at an mRNA level, in CLL patients. Upregulation of such splicing factors was also associated with increased METTL3 levels. More specifically, the 3’ UTRs of transcripts in CLL cells displayed elevated m6A methylation levels. Furthermore, differentially methylated transcripts were enriched for RNA metabolism functions, including RNA splicing. The authors go on to demonstrate the mechanistic processes through METTL3 knockout, where they find that the stop codons of RNA splicing factor mRNAs are differentially hypomethylated, and subsequently display reduced translational efficiency. This is proposed to reduce the degree of ribosome recycling at the stop codon, leading to reduced translational efficiency overall. Interestingly, knockout also led to hypermethylation within the coding regions of splicing factor mRNAs, with increased pausing specifically localised to such methylation sites. Together, these results suggest a dual-mode of translational activity for METTL3 within conditions such as CLL.
RNA binding protein PRRC2B mediates translation of specific mRNAs and regulates cell cycle progression
Nucleic Acids Research, 2023
Jiang, F., Hedaya, O.M., Khor, E., Wu, J., Auguste, M. and Yao, P.
RNA binding proteins (RBPs) have wide-ranging roles in mRNA metabolism, such as transportation and degradation. However, certain RBPs are also able to influence the initiation rates of specific subsets of mRNAs. PRRC2B has been identified as an RNA-binding protein, and has been suggested to be a part of the eIF4G2 complex, itself associated with a range of atypical translation initiation mechanisms. While PRRC2B is known to be highly associated with rapidly proliferating tumours, the exact mechanics of its influence remains unclear. Here, the authors attempt to characterise PRRC2B in terms of its translational influence.
PAR-CLIP analysis was able to demonstrate that PRRC2B does indeed bind a subset of mRNAs, with a particular enrichment within 5’ UTRs, typically around 70 nucleotides upstream of the main ORF. Upon PRRC2B knockdown, there was a translational downregulation in a number of these RNAs, which displayed functions in stem cell maintenance. Additionally, knockdown resulted in a decrease in cells within the G1/S phase translation, partially attributed to a reduction in translation of cyclin D2. Immunoprecipitation analysis revealed protein-protein interactions between PRRC2B and eIF4G2, as well as eIF3. Removal of the eIF4G2 or eIF3 binding domains from PRRC2B displayed that such domains have high importance with regard to PRRC2B-selective translation.
