Hierarchical recruitment of Plk4 and regulation of centriole biogenesis by two centrosomal scaffolds,Cep192 and Cep152

Centrosomes play an important role in various cellular processes, including spindle formation and chromosome segregation. They are composed of two orthogonally arranged centrioles, whose duplication occurs only once per cell cycle. Accurate control of centriole numbers is essential for the maintenance of genomic integrity. Although it is well appreciated that polo-like kinase 4 (Plk4) plays a central role in centriole biogenesis, how it is recruited to centrosomes and whether this step is necessary for centriole biogenesis remain largely elusive. Here we showed that Plk4 localizes to distinct subcentrosomal regions in a temporally and spatially regulated manner, and that Cep192 and Cep152 serve as two distinct scaffolds that recruit Plk4 to centrosomes in a hierarchical order. Interestingly, Cep192 and Cep152 competitively interacted with the cryptic polo box of Plk4 through their homologous N-terminal sequences containing acidic-α-helix and N/Q-rich motifs. Consistent with these observations, the expression of either one of these N-terminal fragments was sufficient to delocalize Plk4 from centrosomes. Furthermore, loss of the Cep192- or Cep152-dependent interaction with Plk4 resulted in impaired centriole duplication that led to delayed cell proliferation. Thus, the spatiotemporal regulation of Plk4 localization by two hierarchical scaffolds, Cep192 and Cep152, is critical for centriole biogenesis.The centrosome is the main microtubule-organizing center in mammalian cells that plays a central role in spindle formation and chromosome segregation during mitosis. Centrosomes are composed of two orthogonally arranged centrioles surrounded by an amorphous mass of electron-dense pericentriolar material (PCM). Centrioles duplicate precisely once per cell cycle and serve as platforms for the assembly of centrosomes, primary cilia, and flagella (1–4).Centriole duplication is initiated by the assembly of a procentriole in early S phase. In Caenorhabditis elegans, a centrosomal scaffold protein, called Spd-2, is required for proper recruitment of a Ser/Thr kinase, Zyg-1 (5), to centrosomes, and this step in turn allows the recruitment of Sas-6, Sas-5, and Sas-4 to the site of procentriole assembly (6, 7). Sas6 plays a pivotal role in self-assembling a cartwheel-like structure at this site of the procentriole with Sas5 and Sas4 (8–12). In Drosophila, the overexpression of polo-like kinase 4 (Plk4; also called Sak), the Zyg-1 ortholog, is sufficient to induce centriole amplification, whereas the depletion of Plk4 disrupts centriole duplication (12, 13). Interestingly, however, Drosophila Spd-2 is dispensable for Plk4-mediated centriole duplication (14). Instead, another scaffold, Asterless, has been suggested to play a critical role in targeting Plk4 to centrosomes (15), hinting that the mechanism underlying Plk4 recruitment is distinct in different organisms.Accumulated evidence in humans suggests that Plk4 is a functional ortholog of C. elegans Zyg-1 and Drosophila Plk4, and that it plays a key role in centriole duplication (16, 17). When overexpressed, Plk4 can induce multiple centriole precursors surrounding a single parental centriole, and centrosomally localized Plk4 appears to be required for this event (16). The cryptic polo box (CPB) present at the upstream of the C-terminal polo box (PB) (18) is necessary and sufficient for targeting Plk4 to centrosomes (16, 19). Interestingly, the CPB comprises two structurally related motifs and forms a homodimer (19) to interact with its binding targets. However, the molecular basis of how Plk4 binds to its targets and localizes to centrosomes remains largely elusive.Studies have shown that Cep152, a human ortholog of Drosophila Asterless, interacts with Plk4 through the CPB (20, 21). However, the depletion of Cep152 does not significantly decrease the level of Plk4 at centrosomes. Recently, Sonnen et al. have shown that a C. elegans Spd-2 ortholog, Cep192, interacts with Plk4 and promotes the recruitment of Plk4 to centrosomes (22). Moreover, Cep192 binds to Cep152, and the depletion of both enhances the Plk4 localization defect (22). Based on these observations, Sonnen et al. proposed that Cep192 cooperates with Cep152 to properly recruit Plk4 to centrosomes and to promote centriole duplication (22).In this study, we demonstrated that disrupting either the Cep192–Plk4 interaction or the Cep152–Plk4 interaction was sufficient to impair centriole duplication. We further showed that Plk4 dynamically localizes to different subcentrosomal regions in a cell cycle-specific manner, and that Cep192 functions at a point upstream of Cep152 to regulate Plk4 localization. Thus, we propose that the spatiotemporal regulation of Plk4 localization by two hierarchical scaffolds, Cep192 and Cep152, is critical for Plk4-dependent centriole biogenesis.     

Preventive action of food seasoning spices mixture on fructose-induced lipid abnormalities

High fructose feeding in rats induces insulin resistance, hyperinsulinemia, hyperglycemia and dyslipidemia. The present study was undertaken to determine the hypolipidemic effect of food seasoning spices mixture on fructose-fed insulin resistant rats. Male Wistar rats received a daily diet containing either 60% fructose or 60% starch. They were administered with the spices mixture at three different doses (10 mg, 30 mg or 50 mg/day/rat) orally 15 days later. At the end of 45 days of the experimental period fructose-fed rats displayed elevated plasma glucose and insulin levels and dyslipidemia which included elevated levels of cholesterol, triglycerides, free fatty acids, reduced high density lipoprotein cholesterol and increased very low density lipoprotein cholesterol. Alterations in tissue lipid levels were also observed. Simultaneous treatment with spices mixture along with fructose diet resulted in the normalization of plasma glucose and insulin levels and restoration of lipid levels in plasma and tissues. The insulin potentiating action of the active principles in these spices may contribute to the hypolipidemic effect of spices mixture in high fructose-fed rats.     

Cecal volvulus occurring after laparoscopic appendectomy.

Less than 2% of cases of intestinal obstruction in adults is caused by cecal volvulus. Although recent abdominal surgery has been implicated, no previous case of cecal volvulus has been reported after laparoscopic appendectomy.     

Backscattered Dose Perturbation Effects at Metallic Interfaces Irradiated by High-Energy X- and Gamma-Ray Therapeutic Beams

PURPOSE: To analyze backscattered dose enhancements near different metallic interfaces for cobalt-60 ((60)Co) gamma rays and 6- and 18-MV photon beams. MATERIAL AND METHODS: Measurements were carried out with a PTW thin-window, parallel-plate ionization chamber and an RDM-1F electrometer. Thin sheets of aluminum, mild steel, copper, cadmium and lead were used as inhomogeneities. The chamber was positioned below the inhomogenities with the gantry maintained under the couch. RESULTS: It can be noticed that the backscatter dose factor (BSDF) reaches the saturation value within few millimeters of all inhomogeneities and the thickness at which the saturation value is reached depends on the atomic number of the inhomogeneity. The amount of backscattered radiation was noticed to be greater with lesser-energy photons ((60)Co) compared to the high erenergy photons. The BSDF varies across the beam when the inhomogeneity is present due to the change in beam quality. The backscattered electrons from lead inhomogeneity have a range in the order of 5-7 mm. CONCLUSION: Higher atomic number inhomogeneities result in an increase in BSDF, as they have higher scattering cross section for the secondary electrons. The increase in dose was noticed for few millimeters upstream from the metallic inhomogeneity, which suggests that the range of backscattered electrons is very small. Since the factors affecting the BSDF at the interface are energy dependent, it is expected that the variation in BSDF will also be sensitive to the beam energy.     

Endobronchial pseudo-tumour caused by herpes simplex.

Herpes simplex virus (HSV) causes tracheobronchitis and pneumonitis; however, to date, there has only been one report of an endobronchial mass caused by HSV type II. This case study describes a 68-yr-old female with severe kyphoscoliosis who was intubated for acute on chronic hypercapnic respiratory failure and developed blood-tinged endotracheal secretions. Fibreoptic bronchoscopy demonstrated an endobronchial mass in the right middle lobe. Cultures grew HSV type I and biopsy specimens demonstrated cytopathological changes consistent with HSV infection. This is the first reported case of HSV type I presenting as an endobronchial tumour.     

Tissue-associated self-antigens containing exosomes: Role in allograft rejection

Exosomes are extracellular vesicles that express self-antigens (SAgs) and donor human leukocyte antigens. Tissue-specific exosomes can be detected in the circulation following lung, heart, kidney and islet cell transplantations. We collected serum samples from patients who had undergone lung (n?=?30), heart (n?=?8), or kidney (n?=?15) transplantations to isolate circulating exosomes. Exosome purity was analyzed by Western blot, using CD9 exosome-specific markers. Tissue-associated lung SAgs, collagen V (Col-V) and K-alpha 1 tubulin (Kα1T), heart SAgs, myosin and vimentin, and kidney SAgs, fibronectin and collagen IV (Col-IV), were identified using western blot. Lung transplant recipients diagnosed with bronchiolitis obliterans syndrome had exosomes with higher expression of Col-V (4.2-fold) and Kα1T (37.1-fold) than stable. Exosomes isolated from heart transplant recipients diagnosed with coronary artery vasculopathy had a 3.9-fold increase in myosin and a 4.7-fold increase in vimentin compared with stable. Further, Kidney transplant recipients diagnosed with transplant glomerulopathy had circulating exosomes with a 2-fold increased expression of fibronectin and 2.5-fold increase in Col-IV compared with stable. We conclude that circulating exosomes with tissue associated SAgs have the potential to be a noninvasive biomarker for allograft rejection.     

Receptor for Advanced Glycation End Products (RAGE) and Implications for the Pathophysiology of Heart Failure

The receptor for advanced glycation end products (RAGE) is expressed in the heart in cardiomyocytes, vascular cells, fibroblasts, and in infiltrating inflammatory cells. Experiments in murine, rat, and swine models of injury suggest that RAGE and the ligands of RAGE are upregulated in key injuries to the heart, including ischemia/reperfusion injury, diabetes, and inflammation. Pharmacological antagonism of RAGE or genetic deletion of the receptor in mice is strikingly protective in models of these stresses. Data emerging from human studies suggest that measurement of levels of RAGE ligands or soluble RAGEs in plasma or serum may correlate with the degree of heart failure. Taken together, the ligand-RAGE axis is implicated in heart failure and we predict that therapeutic antagonism of RAGE might be a unique target for therapeutic intervention in this disorder.