Myelin biogenesis:Dynamics of MBP, PLP and galactolipids

De aanmaak en het onderhoud van myeline membranen vereisen een nauwgezette regulering van complexe intracellulaire transportroutes, die zorg dragen voor het transport van myeline lipiden en eiwitten naar hun eindbestemming, waar ze hun functie kunnen uitoefenen. Omdat de functie van myeline eiwitten en lipide nauw verbonden is met hun lokalisatie kan elke verandering daarin gepaard gaan met ingrijpende veranderingen in de vorming van deze gespecialiseerde membranen. Zo zijn bijvoorbeeld de lokalisatie en organisatie van myeline specifieke componenten ontregeld in de ziekte multiple sclerose (MS) en is de aanmaak van ‘nieuwe’ myeline verstoord. Dit wordt onder meer veroorzaakt door een veranderding in de omgeving van cellen die verantwoordelijk zijn voor die aanmaak. Het in dit proefschrift beschreven onderzoek heeft nieuw en gedetailleerd inzicht gegeven in de mechanismen die het transport, lokalisatie, en laterale organisatie in het membraan van de belangrijkste myeline eiwitten PLP en MBP reguleren. Daarbij zijn effecten van intracellulaire componenten zoals de myeline galactolipiden, galactosylceramide en sulfatide onderzocht maar ook de invloed van cellulaire omgevingsfactoren, zoals fysologische en ziekte-geassocieerde extracellulaire matrix eiwitten en pro-inflammatoire cytokines. De verkregen kennis draagt bij aan het beter begrijpen waarom de (her)aanmaak en het onderhoud van myeline faalt in MS, en biedt daardoor perspectief voor het verder ontwikkelen van therapeutische mogelijkheden voor een ziekte waarvan het ontstaan nog grotendeels onbekend is

PERFORMANCE APPRAISAL PRACTICES AT TOURIST ACCOMODATION AND HOSPITALITY ORGANIZATIONS

Performance appraisal is a tool that provides management with valuable information regarding the quality of the human resources the organizations possess which may serve as a basis for important human resource decisions that may result in motivation and / or demotivation of the employees. The labor intensive characteristics of the tourist accommodation and hospitality organizations make the management of human resources in these organizations a key element in managing. Because of the above mentioned reasons, a study which involves the evaluation of he findings regarding the performance appraisal practices et these organizations located in the Turkish Republic of Northern Cyprus presented

Regulation of cell proliferation by nucleocytoplasmic dynamics of postnatal and embryonic exon-II-containing MBP isoforms

AbstractThe only known structural protein required for formation of myelin, produced by oligodendrocytes in the central nervous system, is myelin basic protein (MBP). This peripheral membrane protein has different developmentally-regulated isoforms, generated by alternative splicing. The isoforms are targeted to distinct subcellular locations, which is governed by the presence or absence of exon-II, although their functional expression is often less clear. Here, we investigated the role of exon-II-containing MBP isoforms and their link with cell proliferation. Live-cell imaging and FRAP analysis revealed a dynamic nucleocytoplasmic translocation of the exon-II-containing postnatal 21.5-kDa MBP isoform upon mitogenic modulation. Its nuclear export was blocked upon treatment with leptomycin B, an inhibitor of nuclear protein export. Next to the postnatal MBP isoforms, embryonic exon-II-containing MBP (e-MBP) is expressed in primary (immature) oligodendrocytes. The e-MBP isoform is exclusively present in OLN-93 cells, a rat-derived oligodendrocyte progenitor cell line, and interestingly, also in several non-CNS cell lines. As seen for postnatal MBPs, a similar nucleocytoplasmic translocation upon mitogenic modulation was observed for e-MBP. Thus, upon serum deprivation, e-MBP was excluded from the nucleus, whereas re-addition of serum re-established its nuclear localization, with a concomitant increase in proliferation. Knockdown of MBP by shRNA confirmed a role for e-MBP in OLN-93 proliferation, whereas the absence of e-MBP similarly reduced the proliferative capacity of non-CNS cell lines. Thus, exon-II-containing MBP isoforms may regulate cell proliferation via a mechanism that relies on their dynamic nuclear import and export, which is not restricted to the oligodendrocyte lineage

The Lateral Membrane Organization and Dynamics of Myelin Proteins PLP and MBP Are Dictated by Distinct Galactolipids and the Extracellular Matrix

In the central nervous system, lipid-protein interactions are pivotal for myelin maintenance, as these interactions regulate protein transport to the myelin membrane as well as the molecular organization within the sheath. To improve our understanding of the fundamental properties of myelin, we focused here on the lateral membrane organization and dynamics of peripheral membrane protein 18.5-kDa myelin basic protein (MBP) and transmembrane protein proteolipid protein (PLP) as a function of the typical myelin lipids galactosylceramide (GalC),and sulfatide, and exogenous factors such as the extracellular matrix proteins laminin-2 and fibronectin, employing an oligodendrocyte cell line, selectively expressing the desired galactolipids. The dynamics of MBP were monitored by z-scan point fluorescence correlation spectroscopy (FCS) and raster image correlation spectroscopy (RICS),while PLP dynamics in living cells were investigated by circular scanning FCS. The data revealed that on an inert substrate the diffusion rate of 18.5-kDa MBP increased in GalC-expressing cells, while the diffusion coefficient of PLP was decreased in sulfatide-containing cells. Similarly, when cells were grown on myelination-promoting laminin-2, the lateral diffusion coefficient of PLP was decreased in sulfatide-containing cells. In contrast, PLP's diffusion rate increased substantially when these cells were grown on myelination-inhibiting fibronectin. Additional biochemical analyses revealed that the observed differences in lateral diffusion coefficients of both proteins can be explained by differences in their biophysical, i.e., galactolipid environment, specifically with regard to their association with lipid rafts. Given the persistence of pathological fibronectin aggregates in multiple sclerosis lesions, this fundamental insight into the nature and dynamics of lipid-protein interactions will be instrumental in developing myelin regenerative strategies

Oligodendroglial membrane dynamics in relation to myelin biogenesis

In the central nervous system, oligodendrocytes synthesize a specialized membrane, the myelin membrane, which enwraps the axons in a multilamellar fashion to provide fast action potential conduction and to ensure axonal integrity. When compared to other membranes, the composition of myelin membranes is unique with its relatively high lipid to protein ratio. Their biogenesis is quite complex and requires a tight regulation of sequential events, which are deregulated in demyelinating diseases such as multiple sclerosis. To devise strategies for remedying such defects, it is crucial to understand molecular mechanisms that underlie myelin assembly and dynamics, including the ability of specific lipids to organize proteins and/or mediate protein-protein interactions in healthy versus diseased myelin membranes. The tight regulation of myelin membrane formation has been widely investigated with classical biochemical and cell biological techniques, both in vitro and in vivo. However, our knowledge about myelin membrane dynamics, such as membrane fluidity in conjunction with the movement/diffusion of proteins and lipids in the membrane and the specificity and role of distinct lipid-protein and protein-protein interactions, is limited. Here, we provide an overview of recent findings about the myelin structure in terms of myelin lipids, proteins and membrane microdomains. To give insight into myelin membrane dynamics, we will particularly highlight the application of model membranes and advanced biophysical techniques, i. e., approaches which clearly provide an added value to insight obtained by classical biochemical techniques

Clinical and Radiological Findings in Patients with Newly Diagnosed Graves’ Ophthalmopathy

Background. Graves’ ophthalmopathy is the most common extrathyroidal manifestation of Graves’ disease. The objective of this study was to investigate the clinical ophthalmological and MRI findings in newly diagnosed Graves’ ophthalmopathy. Methods. This study included 36 newly diagnosed Graves’ disease patients and 23 control participants. Patients and control participants underwent detailed ophthalmologic examination. In addition, all subjects underwent orbital MRI examination; and sizes, cross-sectional areas, and signal intensities of extraocular muscles were also measured. Results. Based on MRI measurements, the mean exophthalmos in the left eye was significantly higher in the patient group when compared to those of controls (2.04 ± 0.29 vs. 1.85 ± 0.15 cm, p = 0.003). The mean long diameter of inferior oblique muscle in both the right and left eyes were significantly shorter in patients when compared to those of controls (p = 0.001, p = 0.002, resp.); however, the mean long diameter of superior oblique in the left eye was longer in patients than those of controls (p = 0.001). Patients had significantly higher superior oblique muscle signal intensity than those of controls in the right eye (p = 0.01). There was no significant difference for the other parameters between the patient and control groups. Conclusion. Our findings suggest that there is no obvious change in MRI examination despite clinical ophthalmological findings in patients with newly diagnosed Graves’ ophthalmopathy. Unnecessary MRI examination should be avoided in this patient group due to unsatisfactory cost-effectiveness