WDR55 Is a Nucleolar Modulator of Ribosomal RNA Synthesis, Cell Cycle Progression, and Teleost Organ Development

The thymus is a vertebrate-specific organ where T lymphocytes are generated. Genetic programs that lead to thymus development are incompletely understood. We previously screened ethylnitrosourea-induced medaka mutants for recessive defects in thymus development. Here we report that one of those mutants is caused by a missense mutation in a gene encoding the previously uncharacterized protein WDR55 carrying the tryptophan-aspartate-repeat motif. We find that WDR55 is a novel nucleolar protein involved in the production of ribosomal RNA (rRNA). Defects in WDR55 cause aberrant accumulation of rRNA intermediates and cell cycle arrest. A mutation in WDR55 in zebrafish also leads to analogous defects in thymus development, whereas WDR55-null mice are lethal before implantation. These results indicate that WDR55 is a nuclear modulator of rRNA synthesis, cell cycle progression, and embryonic organogenesis including teleost thymus development

Prognostic Value of Coronary Sinus Flow Quantification by Cardiac Magnetic Resonance Imaging in Patients With Acute Myocardial Infarction

Background This study aimed to evaluate the prognostic value of hyperemic coronary sinus flow (h‐CSF) and global coronary flow reserve (g‐CFR) obtained by phase‐contrast cine‐magnetic resonance imaging in patients with acute myocardial infarction (MI). Methods and Results This retrospective study analyzed patients with acute MI (n=523) who underwent primary (ST‐segment–elevation MI) or urgent (non–ST‐segment–elevation MI) percutaneous coronary intervention. Absolute coronary sinus blood flow (CSF) at rest and during vasodilator stress hyperemia was quantified at 30 days (24–36 days) after the index infarct‐related lesion percutaneous coronary intervention and revascularization of functionally significant non–infarct‐related lesions. We used Cox proportional hazards regression modeling to examine the association between h‐CSF, g‐CFR, and major adverse cardiac events defined as all‐cause death, nonfatal MI, hospitalization for congestive heart failure, and stroke. Finally, 325 patients with ST‐segment–elevation MI (62.1%) and 198 patients with non–ST‐segment–elevation MI (37.9%) were studied over a median follow‐up of 2.5 years. The rest CSF, h‐CSF, and g‐CFR were 0.94 (0.68–1.26) mL/min per g, 2.05 (1.42–2.73) mL/min per g, and 2.17 (1.54–3.03), respectively. Major adverse cardiac events occurred in 62 patients, and Cox proportional hazards analysis showed that h‐CSF and g‐CFR were independent predictors of major adverse cardiac events (h‐CSF: hazard ratio [HR], 0.64; 95% CI, 0.47–0.88; P=0.005; g‐CFR: HR, 0.62; 95% CI, 0.47–0.82; P=0.001). When stratified by h‐CSF and g‐CFR, cardiac event‐free survival was the worst in patients with concordantly impaired h‐CSF (<1.6 mL/min per g) and g‐CFR (<1.7) (P<0.001). Conclusions Global coronary sinus flow quantification using phase‐contrast cine‐magnetic resonance imaging provided significant prognostic information independent of infarction size and conventional risk factors in patients with acute MI undergoing revascularization

A missense mutation in <i>WDR55</i> is responsible for <i>hkc</i> phenotype.

<p>(A) <i>hkc</i> was mapped on linkage group (LG) 18 and confined in the 23 kb region on scaffold 567. Recombination rates of 407 <i>hkc</i> embryos from <i>hkc</i>/+ (cab-derived)×kaga crosses and cM distances from <i>hkc</i> to neighboring markers are shown. These markers are located in a single BAC Md0218G12. Indicated two genes were predicted in the mapped region. (B) Sequences within the <i>WDR55</i> coding region of WT (left) and <i>hkc</i> (right) genomic DNA and predicted amino acid sequences. (C) Predicted amino acid sequence of medaka (Ol) <i>WDR55</i> was compared with zebrafish (Dr), mouse (Mm), and human (Hs) <i>WDR55</i> sequences. Asterisks and dots indicate residues that are shared among all four species and three species, respectively. Arrows indicate WD repeat domains. Red box indicates glycine residue that is replaced with arginine in <i>hkc</i> mutants. (D) Predicted structure of medaka WDR55 protein. Filled boxes indicate WD repeat domains. Amino acid residues and predicted secondary structures of the second WD repeat domain are also shown. (E) 1-cell-stage embryos from <i>+</i>/<i>hkc</i>×<i>+</i>/<i>hkc</i> matings were injected with WT- or <i>hkc</i>-derived <i>WDR55</i> mRNA and <i>EGFP</i> mRNA, and whole-mount <i>in situ</i> hybridization using <i>rag1</i> probe was carried out at 6 dpf. P-values were calculated using κ-square test. (F) 50 µM of morpholino that blocks splicing of <i>WDR55</i> (sp-MO) was injected into WT embryos. Three images appearing on top left show dorsal views of control embryos (cont.) and morphants (sp-MO) at stage 25. Four images appearing at the bottom show ventral views of control (cont.) and 5-dpf morphants (sp-MO) hybridized with <i>rag1</i> probe. Numbers below images indicate the numbers of embryos showing phenotypes of the images over the numbers of total embryos examined. Top right images show ethidium bromide (EtBr)-stained gels of RT-PCR products for two <i>WDR55</i> exons neighboring the position of splicing-inhibiting morpholino. Total RNAs from two individual control embryos (cont.) and two individual morphants (sp-MO) at stage 25 were examined. cDNA was synthesized in the absence (−) or presence (+) of reverse transcriptase. Adult WT cDNA and genomic DNA were also amplified. cDNA for <i>cytoplasmic actin</i> (CA) was amplified to verify the quality of cDNA synthesized. (G) 50 µM of morpholino that was designed to block translation of <i>WDR55</i> mRNA was injected into WT embryos. Three images show ventral views of control (cont.) and 6-dpf morphants (ATG-MO) hybridized with <i>rag1</i> probe. Numbers below images indicate the numbers of embryos showing phenotypes of the images over the numbers of total embryos examined.</p