A myriad of structurally and functionally diverse non-coding RNAs (ncRNAs) have recently been implicated in numerous human diseases including cancer. Small nucleolar RNAs (snoRNAs), the most abundant group of intron-encoded ncRNAs, are classified into two families (box C/D snoRNAs and box H/ACA snoRNAs) and are required for post-transcriptional modifications of ribosomal RNA (rRNA). There is now a growing appreciation that nucleotide modifications on rRNA may impart regulatory potential to the ribosome, however the functional consequence of site-specific snoRNA-guided modifications remains poorly defined. Discovered almost 20 years ago, H/ACA snoRNAs are required for the conversion of specific uridine residues to pseudouridine on rRNA. Interestingly, recent reports indicate that the levels of subsets of H/ACA snoRNAs required for pseudouridine modifications at specific sites on rRNA are altered in several diseases, particularly cancer. In this review, we describe recent advances in understanding the downstream consequences of H/ACA snoRNA-guided modifications on ribosome function, discuss the possible mechanism by which H/ACA snoRNAs may be regulated, and explore prospective expanding functions of H/ACA snoRNAs. Furthermore, we will discuss the potential biological implication of alterations in H/ACA snoRNA expression in several human diseases.

Summary Noncoding RNAs control critical cellular processes, although their contribution to disease remains largely unexplored. Dyskerin associates with hundreds of H/ACA small RNAs to generate a multitude of functionally distinct ribonucleoproteins (RNPs). The DKC1 gene, encoding dyskerin, is mutated in the multisystem disorder X-linked Dyskeratosis Congenita (X-DC). A central question is whether DKC1 mutations affect the stability of H/ACA RNPs including those modifying ribosomal RNA (rRNA). We carried out comprehensive profiling of dyskerin-associated H/ACA RNPs, revealing remarkable heterogeneity in the expression and function of subsets of H/ACA small RNAs in X-DC patient cells. Using a novel mass spectrometry approach, we uncovered single-nucleotide perturbations in dyskerin-guided rRNA modifications, providing functional readouts of small RNA dysfunction in X-DC. Strikingly, we identified that the catalytic activity of dyskerin is required for accurate hematopoietic stem cell differentiation. Altogether, these findings reveal that small noncoding RNA dysfunctions may contribute to the pleiotropic manifestation of human disease.

Recognizing that academic, scientific and technological strengths have become increasingly important in international relations, this study hypothesizes that the flow of knowledge resources among nations is interconnected with global political, economic and cultural relationships. As a means of validating this premise, this study analyzes one component of academic interaction -international study at the level of higher education. This article outlines changes in international study patterns in the decades following World War II and explores how the postwar context affected international exchange relationships. Intemational exchange during the 1960s and 1970s indicated strong participation by students from Third World nations and the popularity of five industrialized host nations. These relationships are explored through a statistical study of the flow of students from 18 developing nations out to the world and to the United States in particular. The findings assess the importance of key economic factors (such as involvement in global trade and concentration of trade), educational variables (including national emphasis on education and the availability of domestic opporttmities) and political arenas (such as international assistance and scholarship dependency) in determining intemational study patterns. As current shifts in our postwar world order unfold before us, better understanding of historical factors underlying international exchange may be instrumental as we anticipate its future within the context of new geopolitical alliances.

Small nucleolar RNAs (snoRNAs) are a diverse group of non-coding RNAs that direct chemical modifications at specific residues on other RNA molecules, primarily on ribosomal RNA (rRNA). SnoRNAs are altered in several cancers; however, their role in cell homeostasis as well as in cellular transformation remains poorly explored. Here, we show that specific subsets of snoRNAs are differentially regulated during the earliest cellular response to oncogenic RASG12V expression. We describe a novel function for one H/ACA snoRNA, SNORA24, which guides two pseudouridine modifications within the small ribosomal subunit, in RAS-induced senescence in vivo. We find that in mouse models, loss of Snora24 cooperates with RASG12V to promote the development of liver cancer that closely resembles human steatohepatitic hepatocellular carcinoma (HCC). From a clinical perspective, we further show that human HCCs with low SNORA24 expression display increased lipid content and are associated with poor patient survival. We next asked whether ribosomes lacking SNORA24-guided pseudouridine modifications on 18S rRNA have alterations in their biophysical properties. Single-molecule Fluorescence Resonance Energy Transfer (FRET) analyses revealed that these ribosomes exhibit perturbations in aminoacyl-transfer RNA (aa-tRNA) selection and altered pre-translocation ribosome complex dynamics. Furthermore, we find that HCC cells lacking SNORA24-guided pseudouridine modifications have increased translational miscoding and stop codon readthrough frequencies. These findings highlight a role for specific snoRNAs in safeguarding against oncogenic insult and demonstrate a functional link between H/ACA snoRNAs regulated by RAS and the biophysical properties of ribosomes in cancer.