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The supramolecular organization of a new polychlorotriphenyl (PTM) radical bearing three long alkyl chains has been studied by scanning tunneling microscopy (STM) at the liquid-solid interface. This radical hierarchically self-assembles on graphite forming head-to-head dimers that organize in rows following an interesting spin-containing two-leg molecular ladder topology, in which the alkyl chains determine the space between the radical rows and act as diamagnetic barriers. In addition, these double-rows also self-assemble three-dimensionally, leading to a multilayer organization which is still influenced by the HOPG substrate symmetry. The observed nanostructures are sustained by different intermolecular interactions such as Cl...Cl, Cl...Ph, pi-pi, van der Waals, and CH...pi interactions. Theoretical calculations were used to model the observed assemblies, and the results were in complete agreement with the experimental data. Remarkably, atomic force microscopy (AFM) studies confirmed that this tendency to form double rows composed by the PTM magnetic heads surrounded by the alkyl chains is maintained after the complete evaporation of the solvent. The electrochemical and magnetic properties of these PTM nanostructures were also demonstrated.

A series of polyphenylene dendrimers (PDs) incorporating additional pentafluorophenyl units have been synthesized. A key building block thereby is the tetrakis(pentafluorophenyl)cyclopentadienone, which serves as the end-capper for making the outer shells of the dendrimers. The variation of the peripheral pentafluorophenyl content was varied using desymmetrized tetraphenylmethane cores for the divergent construction of the dendrimers. The self-assembled nanostructures, prepared by drop-casting solutions of the second-generation species on highly oriented pyrolytic graphite (HOPG), have been investigated by tapping mode atomic force microscopy (AFM). Besides isotropic globular aggregates and percolated networks of nanometer size anisotropic objects, the herein presented dendrimers self-organize into micrometer long nanofibers. The formation of a certain morphology depends upon the amount of pentafluorophenyl rings at the periphery of the dendrimers. Furthermore, it has been observed that by the progressive...

Shape-persistent macrocycles with interiors in the nanometer regime were prepared by the oxidative cyclization of the appropriate bisacetylene precursors under high-dilution conditions. These compounds contain polycyclic aromatic hydrocarbons in the ring backbone and are decorated with extra annular oligoalkyl or silyl side groups. Interestingly, after depositing them on different surfaces and investigating the self-assembled structures by means of scanning tunneling microscopy (STM) and atomic force microscopy (AFM), various nanostructures were observed. STM showed that these macrocycles are organized in two-dimensional (2D) layers, whereas AFM showed, in addition, the formation of 2D crystallites and one-dimensional fibrils. These results reveal the importance of the extra annular substitution of the macrocycles in creating patterned surfaces and nanoscale objects.

The synthesis, properties, and conformation of shape-persistent macrocycles with extraannular oligo-alkyl groups and an intraannular bis(hydroxymethyl)biphenylene diester are investigated. The key step in the preparation is the template-supported Glaser coupling of rigid bisacetylenes which allows obtaining the cyclic product in 81% yield. Contrary to the initial expectations, the compounds do not exhibit liquid crystalline phases. This could be explained by a nonplanar conformation of the molecules because the biphenylene bridge is longer than the diameter of the rings. On the other hand, scanning tunneling microscopy investigations indicate that the intraannular biphenylene bridge can be located in the same plane as the aromatic backbone of the macrocycles on graphite. Modeling involving molecular mechanics and molecular dynamics simulations unraveled this apparent inconsistency by showing that the molecules adopt a nonplanar conformation in the absence of the solid support whereas planarization takes p...

SERCA2a is the cardiac-specific isoform of Ca 2+ -ATPase of the sarcoplasmic reticulum (SR). A reduction of SERCA2a has been implicated in the contractile dysfunction of heart failure, and partial knockout of the SERCA2 gene ( Atp2a2 +/− mice) reiterated many of the features of heart failure. Yet, mice with a mutation of Atp2a2 , resulting in full suppression of the SERCA2a isoform and expression of the SERCA2b isoform only ( SERCA2 b/b ), showed only moderate functional impairment, despite a reduction by 40% of the SERCA2 protein levels. We examined in more detail the Ca 2+ handling in isolated cardiac myocytes from SERCA2 b/b . At 0.25 Hz stimulation, the amplitude of the [Ca 2+ ] i transients, SR Ca 2+ content, diastolic [Ca 2+ ] i , and density of I CaL were comparable between WT and SERCA2 b/b . However, the decline of [Ca 2+ ] i was slower (t 1/2 154±7 versus 131±5 ms; P 2+ ] i transient (eg, SR depletion), removed the differences in [Ca 2+ ] i decline. In contrast, increasing the Ca 2+ load revealed pronounced reduction of SR Ca 2+ uptake at high [Ca 2+ ] i . There was no increase in Na + -Ca 2+ exchange protein or function. Theoretical modeling indicated that in the SERCA2 b/b mouse, the higher Ca 2+ affinity of SERCA2b partially compensates for the 40% reduction of SERCA expression. The lack of SR depletion in the SERCA2 b/b may also be related to the absence of upregulation of Na + -Ca 2+ exchange. We conclude that for SERCA isoforms with increased affinity for Ca 2+ , a reduced expression level is better tolerated as Ca 2+ uptake and storage are impaired only at higher Ca 2+ loads.

Myostatin is a newly described member of the TGF-beta superfamily acting as a secreted negative regulator of skeletal muscle mass in several species, but whose mode of action remains largely unknown. In the present work, we followed the myostatin mRNA and protein levels in rat soleus and extensor digitorum longus (EDL) muscles regenerating in vivo from notexin-induced necrosis, and the myostatin transcript levels in two different in vitro myogenic differentiation models: i.e. in mouse BC3H1 and C2Cl2 cultured cells. The in vivo regenerating rat skeletal muscles showed a characteristic time-dependent expression of myostatin mRNA. After notexin injection, the transcript levels dropped below the detection limit on day 1 in soleus and close to the detection limit on day 3 in EDL, then increased to a maximum on day 7 in soleus and after 28 days finally reached the control values in both types of muscles. In contrast, the myostatin protein levels increased dramatically on the first days of regeneration in both muscles, i.e. at the time when its transcript level was low. Later on the myostatin protein level gradually declined to normal in soleus while in EDL it stayed high some days longer and decreased to normal on days 21-28. In vitro proliferating myoblasts produced low level of myostatin mRNA, which increased upon induction of differentiation suggesting that functional innervation is no prerequisite for myostatin expression. Myostatin production in vitro seems not to be dependent on myocyte fusion either, since it is observed in differentiated BC3H1 cells, which are defective in myofiber formation.

Two conjugated oligomers, representing elementary segments of fluorene - thiophene copolymers, are compared in terms of the microscopic morphology and the optical properties of thin deposits. The atomic force microscopy morphological data and the solid-state absorption and emission spectra are interpreted in terms of the assembly of the conjugated molecules. The compound with a terthiophene central unit and fluorene end-groups shows well-defined monolayer-by-monolayer assembly into micrometer- long stripe-like structures, with a crystalline herringbone-type organization within the monolayers. Polarized confocal microscopy indicates a strong orientation of the crystalline domains within the stripes. In contrast, the compound with a terfluorene central unit and thiophene end groups forms no textured aggregates and the optical spectra in the solid-state are very similar to those recorded in solution, suggesting that the molecules interact only weakly in the solid. The difference in behaviour between the two compounds most probably originates from their different capability to form densely-packed assemblies of interacting pi-systems.

The synthesis of new fluorescent indicators for Na+, Benz-15-5 or Diaz-15-5, and for K+, Benz-18-6 or Diaz-18-6, respectively, is reported. They consist of a benzocrown or a diazacrown ether linked to a pyrazoline fluorophore substituted with carboxylate groups to ensure water solubility. They were obtained via reaction of an α,β-unsaturated ketone with an aryl hydrazine. The fluorescence intensity of Benz-15-5 is nearly insensitive to Na+. Benz-18-6 displays a four-fold selectivity for K+ over Na+, with a dissociation constant of 3.6 mM for the K+: indicator complex. Diaz-15-5 and Diaz-18-6 have only a weak affinity for monovalent cations, so that they only can be used for the determination of high Na+ and K+ concentrations.

The synthesis and the spectral and cation binding properties of new fluorescent indicators for Na+, dicaesium 5-[5-(2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin-15-yl)-2-thienyl]isophthalate (Benzos), and for K+, dicaesium 5-[5-(2,3,5,6,8,9,11,12,14,15-decahydro-1,4,7,10,13,16-benzohexaoxacyclooctadecin-18-yl)-2-thienyl]isophthalate (Benzop), are reported. Both indicators consist of a benzocrown ether with an appropriate cavity for the sodium and the potassium cation, respectively, linked to an aryl thiophene fluorophore. In aqueous solution, the indicators have an absorption maximum at 340 nm and an emission maximum at 430 nm. The chelating abilities of Benzos and Benzop with Na+, K+, Li+, Cs+, Mg2+ and Ca2+ were studied by means of their fluorescence properties. Upon cation binding, a change in the fluorescence intensity is observed, whereas the spectral distribution remains unaltered. While Benzos cannot discriminate between Na+ and other monovalent cations, Benzop shows a three-fold selectivity for K+ over Na+.

Round and round: Covalently bound spokes induce an efficient template-directed cyclization towards a rigid molecular wheel (see figure) and afford dramatically increased shape-persistence properties compared with non-strutted macrocycles.The synthesis and characterization of a shape-persistent two-dimensional (2D) organic compound is described in detail. In a rational modular synthesis of a dodecaacetylene precursor and its subsequent template-aided cyclization, we obtained a molecularly defined, stable, C(6)-symmetric, rigid, spoked wheel. Peripheral tert-butyl groups and alkyl chains attached to the plane of the molecule provide sufficient solubility, so that the 2D oligomer can be fully characterized by MALDI-MS, GPC, and (1)H NMR, UV/Vis absorption, and fluorescence spectroscopy. Molecular mechanics and dynamics simulations indicate that the most stable conformer of the molecule in vacuum is a shallow boat conformation with a small dihedral angle. Comparisons with the precursor as well as a ring-only structure clearly reveal the high rigidity of the title compound. Small-angle neutron scattering (SANS) experiments in [D(8)]THF and CDCl(3) affirm the rigid backbone structure in solution, that is, a radius of about 2.7 nm and a thickness of about 0.22 nm. STM investigations illustrate that the wheel molecules adsorb with their molecular plane parallel to the surface and can form hexagonal crystalline domains (unit cell parameters are a=b=6.0+/-0.2 nm and theta=60+/-2 degrees ), with the tert-butyl groups on the apexes staggered. Such staggering induces chirality in the organized domains. AFM investigations demonstrate that the wheel molecules inside overlayers organize in the same way as in the layer directly in contact with the surface. This indicates an epitaxial growth characteristic of the film.

A second-generation polyphenylene dendrimer 1 is shown to self-assemble into nanofibers. To guide the formation of the dendrimer fibers into well-defined patterns, 1H,1H,2H,2H-perfluorodecyltrichlorosilane is grafted in the gas phase onto a silicon substrate. De-wetting of the solution on the nanopatterned surface results in the formation of a nanostructured template, into which fiber growth subsequently occurs under the constraints set by the de-wetted morphology.

De vraag naar vernieuwende technieken om structuren op te bouwen vanuit moleculaire bouwstenen groeit omwille van de nood aan productiemethodes met een hoge precisie op moleculair niveau om gelijke tred te kunnen hou den met de schaalverkleining van bijvoorbeeld elektronica. Deze thesis d raagt bij tot het ontrafelen en sturen van moleculaire zelf-assemblage o p substraten. Zelf-assemblage is een fenomeen dat spontaan optreedt in d e nano-wereld. Het gebruik van vormvaste organische molecules met een we lgedefinieerde vorm, zoals dendrimeren en macrocycles, werd onderzocht i n deze thesis met als doel het combineren van moleculaire zelf-assemblag e met bestaande processen en technieken om met grote precisie structuren te creëren op nanometerschaal. De parameters die het resultaat van deze organische zelf-assemblerende systemen bepalen, werden geëvalueerd om i nzicht te krijgen in het zelf-assemblage proces. Deze kennis kan in een later stadium gebruikt worden om het zelf-assemblage proces te sturen. Het resultaat van de zelf-assemblage van organische systemen werd bestud eerd met een reeks technieken zoals lichtverstrooiing (in oplossing) en vooral rastersondemicroscopie (op substraten). Tweede generatie polyfeny leendendrimeren werden gebruikt om nanovezels te creëren op substraten. De invloed van substraat, concentratie van de dendrimeeroplossing, omgev ingsfactoren tijdens staalbereiding, oplosmiddel en perifere functionele groepen van de molecules werden bestudeerd. Het aanbrengen van een dend rimeer-THF-oplossing in een THF-verzadigde tank op een siliciumsubstraat dat vooraf werd gereinigd in piranha-oplossing bleek de optimale staalb ereidingsmethode. Het aggregatiegedrag van vormvaste macrocyclische mole cules werd eveneens onderzocht om het potentieel van zelf-assemblage van deze molecules ter vorming van nanostructuren te evalueren. De resultat en hiervan tonen het belang aan van intra- en extra-annulaire substituti e van de macrocyclische molecules in het creëren van oppervlaktepatronen en nano-objecten. Een tweede aspect betreft de plaats en oriëntatie van de zelf-geassemble erde nanostructuren op het substraatoppervlak. Het zelf-assemblageproces van het tweede generatie polyfenyleendendrimeer werd aangewend in een a antal methodes om nanostructuren te produceren. Lithografie met stempels en mallen werd met succes gebruikt om het zelf-assemblage proces naar s peficieke plaatsen op het substraat te sturen. In tegenstelling tot deze methode kon een sjabloon met binaire patronen niet enkel de plaats van de aggregaten op het substraat sturen, maar was het ook mogelijk om de v orm van de structuren te beïnvloeden. Nanovezels werden uitgelijnd volge ns het sjabloon op het substraat door gebruik te maken van de optimale s taalbereidingsmethode. Een andere methode, gebruik makend van een sterk magnetisch veld (tot 20 T), werd gebruikt om het zelf-assemblageproces v an zowel een dendrimeersysteem als macrocyclisch systeem te beïnvloeden. Enkel in het geval van het macrocyclisch systeem bleek het magnet isch veld een uitlijnend effect te vertonen. Dit effect wordt toegeschre ven aan de juiste (parallelle) oriëntatie van de fenylgroepen in deze ze lf-geassembleerde vezels, wat niet mogelijk is voor de fenylgroepen in d e dendrimeervezels. Het resultaat van deze studie illustreert het potentieel en de uitdaging en van moleculaire zelf-assemblage in combinatie met een oriëntatiesture nde aanpak en opent de weg voor verder onderzoek naar de combinatie tuss en top-down en bottom-up methodes. status: published

De toenemende vraag naar thuiszorg brengt een stijging van het aantal arbeidsplaatsen voor verzorgenden (de vroegere gezins- en bejaardenhelpsters) in de gezinszorg mee. Anno 2003 waren er in België een 250-tal diensten gezinszorg die samen meer dan 20 000 verzorgenden tewerkstelden. Om nu en in de toekomst voldoende geschikte verzorgenden aan te trekken en te behouden voor de gezinszorg, is het belangrijk om de kwaliteit van de arbeid te bewaken en zo nodig te verbeteren. Vandaar ontstond het idee om een project, genaamd PROXIMA, uit te voeren met als doel de kwaliteit van de arbeid van gezinsverzorgenden in België te onderzoeken en aanbevelingen te doen om deze te verbeteren. De promotor van het onderzoek is de Federale Overheidsdienst Werkgelegenheid, Arbeid en Sociaal Overleg. Het onderzoek wordt gecofinancierd door het ESF en uitgevoerd door het Hoger instituut voor de arbeid (HIVA) van de K.U. Leuven en de faculteit Psychologie van de universiteit van Bergen. Om de kwaliteit van de arbeid van de verzorgenden te onderzoeken, deden we een bevraging in bijna 90 verschillende diensten gezinszorg, verspreid over Vlaanderen, Wallonië en Brussel. We bevroegen er meer dan 1000 verzorgenden aan de hand van een schriftelijke vragenlijst. Deze vragenlijst was vooral gericht op hun arbeidssituatie en de manier waarop ze hun werk beleven. Daarnaast interviewden we per dienst een verantwoordelijke over het beleid en de organisatie van de dienst. No ISBN nrpages: 388 status: published

De toenemende vraag naar thuiszorg brengt een stijging van het aantal arbeidsplaatsen voor verzorgenden (de vroegere gezins- en bejaardenhelpsters) in de gezinszorg mee. Anno 2003 waren er in België een 250-tal diensten gezinszorg die samen meer dan 20 000 verzorgenden tewerkstelden. Om nu en in de toekomst voldoende geschikte verzorgenden aan te trekken en te behouden voor de gezinszorg, is het belangrijk om de kwaliteit van de arbeid te bewaken en zo nodig te verbeteren. Vandaar ontstond het idee om een project, genaamd PROXIMA, uit te voeren met als doel de kwaliteit van de arbeid van gezinsverzorgenden in België te onderzoeken en aanbevelingen te doen om deze te verbeteren. De promotor van het onderzoek is de Federale Overheidsdienst Werkgelegenheid, Arbeid en Sociaal Overleg. Het onderzoek wordt gecofinancierd door het ESF en uitgevoerd door het Hoger instituut voor de arbeid (HIVA) van de K.U. Leuven en de faculteit Psychologie van de universiteit van Bergen. Om de kwaliteit van de arbeid van de verzorgenden te onderzoeken, deden we een bevraging in bijna 90 verschillende diensten gezinszorg, verspreid over Vlaanderen, Wallonië en Brussel. We bevroegen er meer dan 1000 verzorgenden aan de hand van een schriftelijke vragenlijst. Deze vragenlijst was vooral gericht op hun arbeidssituatie en de manier waarop ze hun werk beleven. Daarnaast interviewden we per dienst een verantwoordelijke over het beleid en de organisatie van de dienst. Klik op de grijs-rode download-button om de tussentijdse samenvatting van de onderzoeksresultaten van de verzorgenden te bekijken. nrpages: 12 status: published

Met het oog op de ondersteuning van het maatschappelijk debat over de herwaardering van de leerkracht liet het departement Onderwijs van de Vlaamse overheid door het HIVA en door het ACMS (Universiteit Antwerpen) de tijdsbesteding en taakbelasting van leerkrachten op een wetenschappelijke wijze in kaart brengen. De onderzoeksvragen die aan de basis liggen van dit onderzoek, zijn: Hoe ziet het takenpakket van leerkrachten eruit anno 2001? Wat is hierin veranderd ten aanzien van 1990 (De Wilde & Van Hooreweghe, 1991; Van Hooreweghe & De Wilde, 1991a)? Hoeveel tijd spenderen leerkrachten aan de uitvoering van hun job en aan de verschillende activiteiten waaruit hun job bestaat? Zijn er verschuivingen in de tijdsbesteding merkbaar ten aanzien van tien jaar geleden? Zijn er bepaalde groepen van leerkrachten die meer of minder tijd aan hun beroep en/of aan de verschillende activiteiten afzonderlijk spenderen? Hoe beleven leerkrachten hun activiteiten en hun job? Hoe belastend is een functie als leerkracht? Welke school-, job- en individuele kenmerken spelen hier een rol bij Om een antwoord te formuleren op de verschillende vragen, werden verschillende methodes aangewend. Om zicht te krijgen op het takenpakket van de leerkrachten en de verschuivingen hierin ten aanzien van een decennium geleden, werden gesprekken gevoerd met een vijfentwintig-tal bevoorrechte getuigen uit het onderwijsveld zoals leerkrachten, directies, medewerkers van de inspectie en van de pedagogische begeleidingsdiensten. Om zicht te krijgen op de tijdsbesteding van leerkrachten, vroegen we alle leerkrachten van 73 scholen (37 basisscholen en 36 secundaire scholen) om gedurende twee schoolweken (inclusief twee weekends) een tijdsbestedingsagenda bij te houden waarin ze zowel de aard als de duur van hun beroepsactiviteiten noteerden. De tijdsbestedingsagenda was vergezeld van een korte schriftelijke vragenlijst over de wijze waarop leerkrachten hun job en de verschillende activiteiten van hun job beleven. De taakbelasting en de antecedenten ervan -zoals jobkenmerken, arbeidsorganisatie, taakbeleid, personeelsbeleid, schoolbeleid,….- werden onderzocht via een schriftelijke bevraging van de leerkrachten en een mondelinge bevraging van de directies. Deze studie werd uitgevoerd in het kader van het programma 'Onderwijskundig Beleids- en Praktijkgericht Wetenschappelijk Onderzoek' (OBPWO). Dit programma is een initiatief van de Vlaamse minister van Onderwijs. nrpages: 52 status: published

Uit het Europees waardeonderzoek blijkt dat een meerderheid van de Belgen het aanvragen van sociale uitkeringen waar je geen recht op hebt, veroordeelt. Driekwart vindt dit in geen enkel geval gerechtvaardigd (Dobbelaere et al., 2000). Over de omvang en de achtergrondkenmerken van zulke sociale fraude in België is echter weinig geweten. Het afgelopen decennium werd in ons land immers nauwelijks onderzoek verricht naar dit fenomeen. Dit was één van de uitgangspunten van een multidisciplinaire studie naar sociale fraude in opdracht van het Fonds voor Wetenschappelijk Onderzoek-Vlaanderen. Naast een juridisch en economisch luik (Van Rompaey, 1997; Pacolet & Marchal, 2001) bevat deze studie een sociaal-psychologisch luik. Dit laatste luik is gericht op uitkeringsfraude bij volledig uitkeringsgerechtigde werklozen. ispartof: Over.werk. Tijdschrift van het Steunpunt WSE vol:12 issue:3 pages:192-196 status: published

The cardiac sarco(endo)plasmic reticulum Ca 2+ -ATPase gene ( ATP2A2 ) encodes the following two different protein isoforms: SERCA2a (muscle-specific) and SERCA2b (ubiquitous). We have investigated whether this isoform specificity is required for normal cardiac function. Gene targeting in mice successfully disrupted the splicing mechanism responsible for generating the SERCA2a isoform. Homozygous SERCA2a −/− mice displayed a complete loss of SERCA2a mRNA and protein resulting in a switch to the SERCA2b isoform. The expression of SERCA2b mRNA and protein in hearts of SERCA2a −/− mice corresponded to only 50% of wild-type SERCA2 levels. Cardiac phospholamban mRNA levels were unaltered in SERCA2a −/− mice, but total phospholamban protein levels increased 2-fold. The transgenic phenotype was characterized by a ≈20% increase in embryonic and neonatal mortality (early phenotype), with histopathologic evidence of major cardiac malformations. Adult SERCA2a −/− animals (adult phenotype) showed a reduced spontaneous nocturnal activity and developed a mild compensatory concentric cardiac hypertrophy with impaired cardiac contractility and relaxation, but preserved β-adrenergic response. Ca 2+ uptake levels in SERCA2a −/− cardiac homogenates were reduced by ≈50%. In isolated cells, relaxation and Ca 2+ removal by the SR were significantly reduced. Comparison of our data with those obtained in mice expressing similar cardiac levels of SERCA2a instead of SERCA2b indicate the importance of the muscle-specific SERCA2a isoform for normal cardiac development and for the cardiac contraction-relaxation cycle.

The mouse has been used extensively for generating transgenic animal models to study cardiovascular disease. Recently, a number of transgenic mouse models have been created to investigate the importance of sarcoplasmic reticulum (SR) Ca(2+)transport proteins in cardiac pathophysiology. However, the expression and regulation of cardiac SR Ca(2+)ATPase and other Ca(2+)transport proteins have not been studied in detail in the mouse. In this study, we used multiplex RNase mapping analysis to determine SERCA2, phospholamban (PLB), and Na(+)/Ca(2+)-exchanger (NCX-1) gene expression throughout mouse heart development and in hypo/hyperthyroid animals. Our results demonstrate that the expression of SERCA2 and PLB mRNA increase eight-fold from fetal to adult stages, indicating that SR function increases with heart development. In contrast, the expression of the Na(+)/Ca(2+)-exchanger gene is two-fold higher in fetal heart compared to adult. Our study also makes the important observation that in hypothyroidic hearts the NCX-1 mRNA and protein levels were upregulated, whereas the SERCA2 mRNA/protein levels were downregulated. In hyperthyroidic hearts, however, an opposite response was identified. These findings are important and point out that the expression of NCX-1 is regulated antithetically to that of SERCA2 during heart development and in response to alterations in thyroid hormone levels.

Deze brochure is een samenvatting van het rapport 'Organisatieverandering in de Belgische overheidsdiensten. Een enquête bij de betrokken werknemers'. nrpages: 36 status: published

We have used magnetic-field-induced birefringence as a new sensitive technique to probe the aggregation kinetics of macrocyclic molecules in solution. We have found three consecutive aggregation stages: disordered objects, ordered fibers, and a network. The transition from disordered objects to ordered fibers is found to be slow, taking days or weeks to complete. We attribute this to the molecular tails of the macrocycles, which hamper fiber formation. We anticipate that linking aggregation kinetics to molecular properties will lead to a better understanding of the mechanisms by which molecules self-assemble, allowing for a more rational design of the molecular building blocks.

Summary Expression levels of fast-twitch (SERCA1), slow-twitch (SERCA2a) and “housekeeping” (SERCA2 b) isoforms of the sarcoplasmic reticulum Ca 2+ -transport ATPase were monitored during regeneration of rat soleus muscles following necrosis induced by the toxin notexin at the tissue level by Western blot analysis and at the cellular level by immunocytochemical analysis. Due to necrosis, levels of muscle-specific SERCA1 and SERCA2 a isoforms dropped to low levels on the third day after injection of the toxin. Subsequently, during regeneration both isoforms recovered but with a different time course. Expression of the fast type SERCA1 increased first. This type showed its most pronounced increase between day 3 and 10. Expression of the slow type SERCA2 a was biphasic. After an increase to approximately one third of the control value on days 5-10, it showed its main increase up to the control level between day 10 and 21. Expression levels of the housekeeping SERCA2 b isoform remained relatively constant throughout the 4 weeks of regeneration. Between day 10 and 28, when new innervation is established, SERCA2 a expression spread gradually over almost all fibers whereas the number of SERCA1-expressing fibers decreased and only a limited number of fibers co-expressed SERCA1 and SERCA2 a. At 4 weeks of regeneration, expression of the fast isoform was found only in 12% of the fibers, whereas the slow form was found in 98% of the fibers. In the contralateral untreated soleus muscles, 26% SERCA1-positive and 81% SERCA2 a-positive fibers were observed. Immunocytochemical analysis showed that SERCA1 and SERCA2 a were co-expressed with fast and slow myosin isoforms in fibers of normal muscles but in regenerated muscle only slow myosin and slow SERCA isoforms correlated. The results show that during regeneration levels of fast and slow SERCA proteins change in a similar way as their mRNAs do. However, in regenerated soleus, unlike in normal muscle, expression of slow SERCA is coregulated only with the slow myosin isoform. This finding is in agreement with the fact that the number of slow type fibers is increased in regenerated soleus.

Expression of the muscle-specific 2a isoform of the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2) requires activation of an inefficient optional splice process at the 3´ end of the primary gene transcript. The sequence elements required for this regulated splice event were studied by modifying a minigene containing the 3´ end of the SERCA2 gene. An important requirement appears to be a strong muscle-specific acceptor site, as replacing it by a weak one prevented the induction of muscle-type splicing during myogenic differentiation. The induction of muscle-type splicing did not depend on positive cis-active sequences in the muscle-specific exon. On the other hand, replacement of a broad region around the acceptor site dramatically deregulated the expression pattern, as this modification strongly induced muscle-type splicing in undifferentiated muscle cells and in fibroblasts. This cis-active region is also involved in the suppression of the neuronal type of splicing. Furthermore selective replacement of the acceptor site as well as deletions or replacements in the muscle-specific exon induced muscle-type splicing to various extents in undifferentiated myogenic cells. Therefore sequence elements in the distal part of the optional intron and in the muscle-specific exon contribute to the suppression of muscle-specific SERCA2 splicing.

The relative mRNA levels corresponding to the different sarcoplasmic/endoplasmic-reticulum Ca2+-ATPase isoforms (SERCA1a, SERCA1b, SERCA2a, SERCA2b and SERCA3) were measured by reverse transcriptase–PCR in rat soleus muscles regenerating after notexin-induced necrosis. The succession of appearance of the different types of SERCA mRNA species in regenerating muscle largely recapitulates those observed during normal ontogenesis. The mRNA levels of the muscle-specific isoforms SERCA1a and SERCA2a became very low on the first and third days after injection of the snake venom. It was only on the fifth day of regeneration that the mRNA of the neonatal variant of the fast-twitch skeletal SERCA1b isoform began to rise, well before the other SERCA transcripts. At 7 and 10 days, i.e. at a time when the new myofibres normally become re-innervated, the mRNA level of SERCA1a and SERCA2a increased markedly, but the fast-twitch skeletal SERCA1a isoform was still the most prominent. On day 21, in the advanced stage of regeneration, a switch in the relative expression levels of SERCA1a and SERCA2a mRNA was observed and the ratio of both isoforms became similar to that found in the normal soleus muscles. This was followed by a decline in the level of all SERCA mRNA species, so that on day 28 the levels of the sarcoplasmic/endoplasmatic-reticulum Ca2+-pump RNAs was again lower but their ratio remained similar to that of the untreated control soleus.

Defined two-dimensional…organic structures in the 5 nm regime have been rarely produced without meeting the limits of solubility, synthetic feasibility, or uniformity. In their full paper on page 2518 ff., S. Hoger, S. De Feyter, R. Lazzaroni, S. Rosenfeldt et al. present a spoked wheel that is molecularly defined, shape-persistent, and yet fully characterizable. The 2D oligomer is formed by sixfold coupling of rim modules to a central hub and subsequent template-directed cyclization. The structure and rigidity are confirmed by detailed STM/AFM and SANS experiments.