SUMMARY Ribosome biogenesis is a highly regulated, essential cellular process. Although studies in yeast have established some of the biological principles of ribosome biogenesis, many of the intricacies of its regulation in higher eukaryotes remain unknown. To understand how ribosome biogenesis is globally integrated in human cells, we conducted a genome-wide siRNA screen for regulators of nucleolar number. We found 139 proteins whose depletion changed the number of nucleoli per nucleus from 2–3 to only 1 in human MCF10A cells. Follow-up analyses on 20 hits found many (90%) to be essential for the nucleolar functions of rDNA transcription (7), pre-ribosomal RNA (pre-rRNA) processing (16), and/or global protein synthesis (14). This genome-wide analysis exploits the relationship between nucleolar number and function to discover diverse cellular pathways that regulate the making of ribosomes and paves the way for further exploration of the links between ribosome biogenesis and human disease.
Nucleoli are dynamic nuclear condensates in eukaryotic cells that originate through ribosome biogenesis at loci that harbor the ribosomal DNA. These loci are known as nucleolar organizer regions (NORs) and there are 10 in a human diploid genome. While there are 10 NORs, however, the number of nucleoli observed in cells is variable. Furthermore, changes in number are associated with disease, with increased numbers and size common in aggressive cancers. In the near-diploid human breast epithelial cell line, MCF10A, the most frequently observed number of nucleoli is 2-3 per cell. Here, to identify novel regulators of ribosome biogenesis we used high-throughput quantitative imaging of MCF10A cells to identify proteins that, when depleted, increase the percentage of nuclei with ≥5 nucleoli. Unexpectedly, this unique screening approach led to identification of proteins associated with the cell cycle. Functional analysis on a subset of hits further revealed not only proteins required for progression through S and G2/M phase, but also proteins required explicitly for the regulation of RNA polymerase I transcription and protein synthesis. Thus, results from this screen for increased nucleolar number highlight the significance of the nucleolus in human cell cycle regulation, linking RNA polymerase I transcription to cell cycle progression.
Purpose To produce a physician and scientific workforce capable of delivering high quality, culturally competent health care and research, academic medical centers must assess their capacity for diversity and inclusion and respond to identified opportunities. Thus, the Diversity Engagement Survey (DES) is presented as a diagnostic and benchmarking tool. Method The 22-item DES connects workforce engagement theory with inclusion and diversity constructs. Face and content validity were established based on decades of previous work to promote institutional diversity. The survey was pilot tested at a single academic medical center and subsequently administered at 13 additional academic medical centers. Cronbach alphas assessed internal consistency and Confirmatory Factor Analysis (CFA) established construct validity. Criterion validity was assessed by observed separation in scores for groups traditionally recognized to have less workforce engagement. Results The sample consisted of 13,694 individuals at 14 medical schools from across the U.S. who responded to the survey administered between 2011– 2012. The Cronbach alphas for inclusion and engagement factors (range: 0.68 to 0.85), CFA fit indices, and item correlations with latent constructs, indicated an acceptable model fit and that questions measured the intended concepts. DES scores clearly distinguished higher and lower performing institutions. The DES detected important disparities for black, women, and those who did not have heterosexual orientation. Conclusions This study demonstrated that the DES is a reliable and valid instrument for internal assessment and evaluation or external benchmarking of institutional progress in building inclusion and engagement.
Nucleolar function and the cellular response to DNA damage have long been studied as distinct disciplines. New research and a new appreciation for proteins holding multiple functional roles, however, is beginning to change the way we think about the crosstalk among distinct cellular processes. Here, we focus on the crosstalk between the DNA damage response and the nucleolus, including a comprehensive review of the literature that reveals a role for conventional DNA repair proteins in ribosome biogenesis, and conversely, ribosome biogenesis proteins in DNA repair. Furthermore, with recent advances in nucleolar proteomics and a growing list of proteins that localize to the nucleolus, it is likely that we will continue to identify new DNA repair proteins with a nucleolar-specific role. Given the importance of ribosome biogenesis and DNA repair in essential cellular processes and the role that they play in diverse pathologies, continued elucidation of the overlap between these two disciplines will be essential to the advancement of both fields and to the development of novel therapeutics.
Fanconi anemia (FA) is a disease of DNA repair characterized by bone marrow failure and a reduced ability to remove DNA interstrand cross-links. Here, we provide evidence that the FA protein FANCI also functions in ribosome biogenesis, the process of making ribosomes that initiates in the nucleolus. We show that FANCI localizes to the nucleolus and is functionally and physically tied to the transcription of pre-ribosomal RNA (pre-rRNA) and to large ribosomal subunit (LSU) pre-rRNA processing independent of FANCD2. While FANCI is known to be monoubiquitinated when activated for DNA repair, we find that it is predominantly in the deubiquitinated state in the nucleolus, requiring the nucleoplasmic deubiquitinase (DUB) USP1 and the nucleolar DUB USP36. Our model suggests a possible dual pathophysiology for FA that includes defects in DNA repair and in ribosome biogenesis.
HIV-infected individuals are at risk for psychological distress, including depression, sadness, and suicidality. The purpose of this qualitative descriptive study was to examine 22 HIV-infected African American women's experiences of psychological distress and use of coping strategies. Data were collected through in-person one-on-one interviews until conceptual saturation was reached. Data were analyzed using inductive content analysis. Four themes were found: (a) psychoemotional suffering, (b) contextual factors negatively influence the everydayness of living with HIV infection, (c) HIV-related stigma perpetuates isolation and loneliness, and (d) creating a safe haven. Implications for nurses and other health care providers include (a) holistic assessment to include evaluation of emotional and mental state, and (b) coping strategies. Integration of spiritual practices into plan of care is also important. Development and evaluation of individualized coping interventions that address stigma and psychological distress through holistic modalities is warranted.
BackgroundModern flamingos (Phoenicopteridae) occupy a highly specialized ecology unique among birds and represent a potentially powerful model system for informing the mechanisms by which a lineage of birds adapts and radiates. However, despite a rich fossil record and well-studied feeding morphology, molecular investigations of the evolutionary progression among modern flamingos have been limited. Here, using three mitochondrial (mtDNA) markers, we present the first DNA sequence-based study of population genetic variation in the widely distributed Chilean Flamingo and, using two mtDNA and 10 nuclear (nDNA) markers, recover the species tree and divergence time estimates for the six extant species of flamingos. Phylogenetic analyses include likelihood and Bayesian frameworks and account for potential gene tree discordance. Analyses of divergence times are fossil calibrated at the divergence of Mirandornithes (flamingos + grebes) and the divergence of crown grebes.ResultsmtDNA sequences confirmed the presence of a single metapopulation represented by two minimally varying mtDNA barcodes in Chilean flamingos. Likelihood and Bayesian methods recovered identical phylogenies with flamingos falling into shallow-keeled (comprising the Greater, American and Chilean Flamingos) and deep-keeled (comprising the Lesser, Andean and James’s Flamingos) sub-clades. The initial divergence among flamingos occurred at or shortly after the Mio-Pliocene boundary (6–3 Ma) followed by quick consecutive divergences throughout the Plio-Pleistocene. There is significant incongruence between the ages recovered by the mtDNA and nDNA datasets, likely due to mutational saturation occurring in the mtDNA loci.ConclusionThe finding of a single metapopulation in the widespread Chilean Flamingo confirms similar findings in other widespread flamingo species. The robust species phylogeny is congruent with previous classifications of flamingos based on feeding morphology. Modern phoenicopterids likely originated in the New World with each sub-clade dispersing across the Atlantic at least once. Our divergence time estimates place flamingos among the youngest families of birds, counter to the classical notion of flamingos as among the oldest based on biogeography and the fossil record. Finally, we designate ‘Phoeniconaias’ as a junior synonym of ‘Phoenicoparrus’ and redefine the latter genus as containing all flamingos more closely related to Phoenicoparrus andinus than Phoenicopterus roseus.
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