Integrating Wheat Nucleolus Structure and Function: Variation in the Wheat Ribosomal RNA and Protein Genes

We review the coordinated production and integration of the RNA (ribosomal RNA, rRNA) and protein (ribosomal protein, RP) components of wheat cytoplasmic ribosomes in response to changes in genetic constitution, biotic and abiotic stresses. The components examined are highly conserved and identified with reference to model systems such as human, Arabidopsis, and rice, but have sufficient levels of differences in their DNA and amino acid sequences to form fingerprints or gene haplotypes that provide new markers to associate with phenotype variation. Specifically, it is argued that populations of ribosomes within a cell can comprise distinct complements of rRNA and RPs to form units with unique functionalities. The unique functionalities of ribosome populations within a cell can become central in situations of stress where they may preferentially translate mRNAs coding for proteins better suited to contributing to survival of the cell. In model systems where this concept has been developed, the engagement of initiation factors and elongation factors to account for variation in the translation machinery of the cell in response to stresses provided the precedents. The polyploid nature of wheat adds extra variation at each step of the synthesis and assembly of the rRNAs and RPs which can, as a result, potentially enhance its response to changing environments and disease threats.

The pseudouridine synthase dyskerin binds to cytoplasmic H/ACA-box snoRNA retaining transcripts affecting nuclear hormone receptor dependence

ABSTRACTDyskerin is a nuclear protein involved in H/ACA box snoRNA-guided uridine modification of RNA. Since its defective function induces specific alterations in gene expression, we sought to unbiasedly identify mRNAs regulated by dyskerin. We found that dyskerin depletion affects the expression or the association with polysomes of selected mRNA isoforms characterized by the retention of H/ACA box snoRNA-containing introns. These snoRNA retaining transcripts (snoRTs) are bound by dyskerin and can interact with cytoplasmic ribosomes. We then characterized the cytoplasmic dyskerin RNA interactome finding both H/ACA box snoRTs and protein-coding transcripts. Since a fraction of these latter transcripts is involved in the nuclear hormone receptor binding, we tested to see if this specific activity is affected by dyskerin. Results indicate that dyskerin dysregulation may alter the dependence on nuclear hormone receptor ligands in breast cancer. Our work suggests a cytoplasmic function for dyskerin which could affect mRNA post-transcriptional networks relevant for nuclear hormone receptor functions.

Ribosomal Protein L10: From Function to Dysfunction

Eukaryotic cytoplasmic ribosomes are highly structured macromolecular complexes made up of four different ribosomal RNAs (rRNAs) and 80 ribosomal proteins (RPs), which play a central role in the decoding of genetic code for the synthesis of new proteins. Over the past 25 years, studies on yeast and human models have made it possible to identify RPL10 (ribosomal protein L10 gene), which is a constituent of the large subunit of the ribosome, as an important player in the final stages of ribosome biogenesis and in ribosome function. Here, we reviewed the literature to give an overview of the role of RPL10 in physiologic and pathologic processes, including inherited disease and cancer.

Assembly of the peripheral stalk of ATP synthase in human mitochondria

The adenosine triphosphate (ATP) synthase in human mitochondria is a membrane bound assembly of 29 proteins of 18 kinds organized into F1-catalytic, peripheral stalk (PS), and c8-rotor ring modules. All but two membrane components are encoded in nuclear genes, synthesized on cytoplasmic ribosomes, imported into the mitochondrial matrix, and assembled into the complex with the mitochondrial gene products ATP6 and ATP8. Intermediate vestigial ATPase complexes formed by disruption of nuclear genes for individual subunits provide a description of how the various domains are introduced into the enzyme. From this approach, it is evident that three alternative pathways operate to introduce the PS module (including associated membrane subunits e, f, and g). In one pathway, the PS is built up by addition to the core subunit b of membrane subunits e and g together, followed by membrane subunit f. Then this b-e-g-f complex is bound to the preformed F1-c8module by subunits OSCP and F6. The final component of the PS, subunit d, is added subsequently to form a key intermediate that accepts the two mitochondrially encoded subunits. In another route to this key intermediate, first e and g together and then f are added to a preformed F1-c8-OSCP-F6-b-d complex. A third route involves the addition of the c8-ring module to the complete F1-PS complex. The key intermediate then accepts the two mitochondrially encoded subunits, stabilized by the addition of subunit j, leading to an ATP synthase complex that is coupled to the proton motive force and capable of making ATP.

Selective over-synthesis and rapid turnover of mitochondrial protein components of respiratory complexes

Mammalian mitochondria assemble four complexes of the respiratory chain (RCI, III, IV and V) by combining 13 polypeptides synthesized within mitochondria on mitochondrial ribosomes (mitoribosomes) with over 70 polypeptides encoded in nuclear DNA, translated on cytoplasmic ribosomes and imported into mitochondria. We report that pulse-chase SILAC can also serve as a valuable approach to study RC assembly as it reveals considerable differences in the rates and efficiency of assembly of different complexes. While assembly of RCV, ATPase, was rapid with little excess synthesis of subunits, RCI, NADH dehydrogenase, assembly was far less efficient with dramatic over-synthesis of numerous proteins, particularly in the matrix exposed N- and Q- Domains. Subunits that do not engage in assembly are generally degraded within three hours. Differential assembly kinetics were also observed for individual complexes immunoprecipitated with complex-specific antibodies. Immunoprecipitation with an antibody that recognizes the ND1 subunit of RCI co-precipitated a number of proteins implicated in FeS cluster assembly as well as newly-synthesized UQCRFS1, the Rieske FeS protein in RCIII, reflecting a degree of coordination of RCI and RCIII assembly.

Translation attenuation by minocycline enhances longevity and proteostasis in old post-stress-responsive organisms

Aging impairs the activation of stress signaling pathways (SSPs), preventing the induction of longevity mechanisms late in life. Here, we show that the antibiotic minocycline increases lifespan and reduces protein aggregation even in old, SSP-deficient Caenorhabditis elegans by targeting cytoplasmic ribosomes, preferentially attenuating translation of highly translated mRNAs. In contrast to most other longevity paradigms, minocycline inhibits rather than activates all major SSPs and extends lifespan in mutants deficient in the activation of SSPs, lysosomal or autophagic pathways. We propose that minocycline lowers the concentration of newly synthesized aggregation-prone proteins, resulting in a relative increase in protein-folding capacity without the necessity to induce protein-folding pathways. Our study suggests that in old individuals with incapacitated SSPs or autophagic pathways, pharmacological attenuation of cytoplasmic translation is a promising strategy to reduce protein aggregation. Altogether, it provides a geroprotecive mechanism for the many beneficial effects of tetracyclines in models of neurodegenerative disease.Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (<xref ref-type="decision-letter" rid="SA1">see decision letter</xref>).

Translation Attenuation by Minocycline Increases Lifespan and Improves Proteostasis in Old Post-Stress-Responsive Organisms

SummaryAging impairs the activation of Stress Signaling Pathways (SSPs), preventing the induction of longevity mechanisms late in life. Here we show that the antibiotic minocycline increases lifespan and reduces protein aggregation even in old, SSP-deficient C. elegans by targeting cytoplasmic ribosomes, preferentially attenuating translation of highly translated mRNAs. In contrast to most other longevity paradigms, minocycline inhibits rather than activates all major SSPs and extends lifespan in mutants deficient in the activation of SSPs, lysosomal or autophagic pathways. We propose that minocycline lowers the concentration of newly synthesized aggregation-prone proteins, resulting in a relative increase in protein-folding capacity without the necessity to induce protein-folding pathways. Our study suggests that in old individuals with incapacitated SSPs or autophagic pathways, pharmacological attenuation of cytoplasmic translation is a promising strategy to reduce protein aggregation. Altogether, it provides a geroprotecive mechanism for the many beneficial effects of tetracyclines in models of neurodegenerative disease.

Changes in chloroplastic and cytoplasmic ribosomal protein after GA3-treatment of Zea mays leaves

Protein was isolated from chioroplastic and cytoplasmic ribosomes of 14-day-old maize leaves subjected to the action of gibberellic acid. The proteins were separated electrophoretically on polyacrylamide gel. Fourteen fractions of ribosomal protein were obtained exhibiting wide electrophoretic differences. Qualitative differences were found between the chloroplastic and cytoplasmic ribosomes. Gibberellic acid caused the appearance of an additional protein Traction in cytoplasmic ribosomes. It did not, however, affect the qualitative composition of ribosome proteins from chloroplasts.