Non-Plasmonic SERS with Silicon: Is It Really Safe? New Insights into the Optothermal Properties of Core/Shell Microbeads

Silicon is one of the most interesting candidates for plasmon-free surface-enhaced Raman scattering (SERS), because of its high-refractive index and thermal stability. However, here we demonstrate that the alleged thermal stability of silicon nanoshells irradiated by conventional Raman laser cannot be taken for granted. We investigated the opto-thermal behavior of SiO₂/Si core/shell microbeads (Si-rex) irradiated with three common Raman laser sources (λ = 532, 633, 785 nm) under real working conditions. We obtained an experimental proof of the critical role played by bead size and aggregation in heat and light management, demonstrating that, in the case of strong opto-thermal coupling, the temperature can exceed that of the melting points of both core and shell components. In addition, we also show that weakly coupled beads can be utilized as stable substrates for plasmon-free SERS experiments.

Improved Determination of Subnuclear Position Enabled by Three-Dimensional Membrane Reconstruction

Many aspects of chromatin biology are influenced by the nuclear compartment in which a locus resides, from transcriptional regulation to DNA repair. Further, the dynamic and variable localization of a particular locus across cell populations and over time makes analysis of a large number of cells critical. As a consequence, robust and automatable methods to measure the position of individual loci within the nuclear volume in populations of cells are necessary to support quantitative analysis of nuclear position. Here, we describe a three-dimensional membrane reconstruction approach that uses fluorescently tagged nuclear envelope or endoplasmic reticulum membrane marker proteins to precisely map the nuclear volume. This approach is robust to a variety of nuclear shapes, providing greater biological accuracy than alternative methods that enforce nuclear circularity, while also describing nuclear position in all three dimensions. By combining this method with established approaches to reconstruct the position of diffraction-limited chromatin markers-in this case, lac Operator arrays bound by lacI-GFP-the distribution of loci positions within the nuclear volume with respect to the nuclear periphery can be quantitatively obtained. This stand-alone image analysis pipeline should be of broad practical utility for individuals interested in various aspects of chromatin biology, while also providing, to our knowledge, a new conceptual framework for investigators who study organelle shape.

Surveillance of nuclear pore complex assembly by ESCRT-III/Vps4

The maintenance of nuclear compartmentalization by the nuclear envelope and nuclear pore complexes (NPCs) is essential for cell function; loss of compartmentalization is associated with cancers, laminopathies, and aging. We uncovered a pathway that surveils NPC assembly intermediates to promote the formation of functional NPCs. Surveillance is mediated by Heh2, a member of the LEM (Lap2-emerin-MAN1) family of integral inner nuclear membrane proteins, which binds to an early NPC assembly intermediate, but not to mature NPCs. Heh2 recruits the endosomal sorting complex required for transport (ESCRT)-III subunit Snf7 and the AAA-ATPase Vps4 to destabilize and clear defective NPC assembly intermediates. When surveillance or clearance is compromised, malformed NPCs accumulate in a storage of improperly assembled nuclear pore complexes compartment, or SINC. The SINC is retained in old mothers to prevent loss of daughter lifespan, highlighting a continuum of mechanisms to ensure nuclear compartmentalization.

Toward a consensus on the mechanism of nuclear pore complex inheritance

Nuclear compartmentalization is achieved through the enclosure of the genome by the nuclear envelope; the nuclear envelope is perforated by nuclear pore complexes (NPCs), which form portals that control molecular exchange between the nucleus and cytoplasm. The number of NPCs per nucleus establishes a limit to the flux of molecules across the nuclear envelope and might directly impact genome organization and gene expression in a cell type specific manner. Mechanisms that control NPC number remain ill defined. Our recent study implicates a cytoplasmic pool of the nucleoporin Nsp1 as a factor that controls NPC number during the asymmetric division of budding yeast; Nsp1 acts to ensure that daughters inherit NPCs. We place our data within an emerging model of NPC inheritance in yeast and consider potential analogous mechanisms in multicellular eukaryotes, including the functional conservation of a cytoplasmic pool of Nsp1.

The transmission of nuclear pore complexes to daughter cells requires a cytoplasmic pool of Nsp1

Nuclear pore complexes (NPCs) are essential protein assemblies that span the nuclear envelope and establish nuclear-cytoplasmic compartmentalization. We have investigated mechanisms that control NPC number in mother and daughter cells during the asymmetric division of budding yeast. By simultaneously tracking existing NPCs and newly synthesized NPC protomers (nups) through anaphase, we uncovered a pool of the central channel nup Nsp1 that is actively targeted to the bud in association with endoplasmic reticulum. Bud targeting required an intact actin cytoskeleton and the class V myosin, Myo2. Selective inhibition of cytoplasmic Nsp1 or inactivation of Myo2 reduced the inheritance of NPCs in daughter cells, leading to a daughter-specific loss of viability. Our data are consistent with a model in which Nsp1 releases a barrier that otherwise prevents NPC passage through the bud neck. It further supports the finding that NPC inheritance, not de novo NPC assembly, is primarily responsible for controlling NPC number in daughter cells.

Lumenal interactions in nuclear pore complex assembly and stability

A mechanism of nuclear pore complex assembly into intact nuclear envelopes remains elusive. We explore roles of conserved inner nuclear membrane proteins, Heh1p and Heh2p, in this process. The data support the existence of a lumenal bridge between Heh1p and the nucleoporin Pom152p, which might facilitate early nuclear pore complex assembly events.

Nuclear pore complexes (NPCs) provide a gateway for the selective transport of macromolecules across the nuclear envelope (NE). Although we have a solid understanding of NPC composition and structure, we do not have a clear grasp of the mechanism of NPC assembly. Here, we demonstrate specific defects in nucleoporin distribution in strains lacking Heh1p and Heh2p—two conserved members of the LEM (Lap2, emerin, MAN1) family of integral inner nuclear membrane proteins. These effects on nucleoporin localization are likely of functional importance as we have defined specific genetic interaction networks between HEH1 and HEH2, and genes encoding nucleoporins in the membrane, inner, and outer ring complexes of the NPC. Interestingly, expression of a domain of Heh1p that resides in the NE lumen is sufficient to suppress both the nucleoporin mislocalization and growth defects in heh1Δpom34Δ strains. We further demonstrate a specific physical interaction between the Heh1p lumenal domain and the massive cadherin-like lumenal domain of the membrane nucleoporin Pom152p. These findings support a role for Heh1p in the assembly or stability of the NPC, potentially through the formation of a lumenal bridge with Pom152p.

Total reflection X-ray fluorescence (TXRF) for direct analysis of aerosol particle samples

Atmospheric aerosol particles have a great impact on the environment and on human health. Routine analysis of the particles usually involves only the mass determination. However, chemical composition and phases provide fundamental information about the particles' origins and can help to prevent health risks. For example, these particles may contain heavy metals such as Pb, Ni and Cd, which can adversely affect human health. In this work, filter samples were collected in Brescia, an industrial town located in Northern Italy. In order to identify the chemical composition and the phases of the atmospheric aerosols, the samples were analysed by means of total reflection X-ray fluorescence (TXRF) spectrometry with a laboratory instrument and X-ray microdiffraction at Synchrotron Daresbury Laboratories, Warrington (Cheshire, UK). The results are discussed and correlated to identify possible pollution sources. The novelty of this analytical approach is that filter samples for TXRF were analysed directly and did not require chemical pretreatment to leach elements from the aerosol particulates. The results of this study clearly show that TXRF is a powerful technique for the analysis of atmospheric aerosols on 'as-received' filters, thereby leaving samples intact and unaltered for possible subsequent analyses by other methods. In addition, the low detection limits for many elements (low ng/cm2) indicate that this method may hold promise in various application fields, such as nanotechnology.

Polymer-coated quartz crystal microbalance chemical sensor for heavy cations in water

A flow type quartz crystal microbalance (QCM) (bio)chemical sensor was developed for the real time determination of heavy metal ions that is suitable for environmental monitoring. A new process has been developed which enables to obtain surface-modified gold electrodes with high heavy metal ions complexing ability. The sensing performances of the piezoelectric sensor used in a flow-through setup were investigated by monitoring the frequency variation induced by the presence of heavy metal ions, such as copper and lead, as model ions, in aqueous media. X-Ray Reflectivity (XRR) and Atomic Force Microscopy (AFM) were carried out to characterize the unmodified and modified gold surfaces.

Reproducibility in X-ray reflectometry: results from the first world-wide round-robin experiment

X-ray reflectometry (XRR) is a well established technique to evaluate quantitatively electron density, thickness and roughness of thin layers. In this paper, results of the first world-wide XRR round-robin experiment, involving 20 laboratories, are presented and discussed. The round-robin experiment was performed within the framework of the VAMAS Project `X-ray reflectivity measurements for evaluation of thin films and multilayers', the aim of which is to produce a `good practice' manual for XRR. The reproducibility of measurements obtained using different equipment has been investigated. The influence of the fitting of the experimental data was shown to be non-negligible compared with the experimental factors. The dynamic intensity range proves to be an important parameter for obtaining a good quality measurement. A simpler test sample which does not develop a surface oxide layer over time is now the subject of a follow-up study.

Molecular cloning and biochemical characterization of sialidases from zebrafish (Danio rerio)

Sialidases remove sialic acid residues from various sialo-derivatives. To gain further insights into the biological roles of sialidases in vertebrates, we exploited zebrafish (Danio rerio) as an animal model. A zebrafish transcriptome- and genome-wide search using the sequences of the human NEU polypeptides as templates revealed the presence of seven different genes related to human sialidases. neu1 and neu4 are the putative orthologues of the mammalian sialidases NEU1 and NEU4 respectively. Interestingly, the remaining genes are organized in clusters located on chromosome 21 and are all more closely related to mammalian sialidase NEU3. They were thus named neu3.1, neu3.2, neu3.3, neu3.4 and neu3.5. Using RT-PCR (reverse transcription-PCR) we detected transcripts for all genes, apart from neu3.4, and whole-mount in situ hybridization experiments show a localized expression pattern in gut and lens for neu3.1 and neu4 respectively. Transfection experiments in COS7 (monkey kidney) cells demonstrate that Neu3.1, Neu3.2, Neu3.3 and Neu4 zebrafish proteins are sialidase enzymes. Neu3.1, Neu3.3 and Neu4 are membrane-associated and show a very acidic pH optimum below 3.0, whereas Neu3.2 is a soluble sialidase with a pH optimum of 5.6. These results were further confirmed by subcellular localization studies carried out using immunofluorescence. Moreover, expression in COS7 cells of these novel zebrafish sialidases (with the exception of Neu3.2) induces a significant modification of the ganglioside pattern, consistent with the results obtained with membrane-associated mammalian sialidases. Overall, the redundancy of sialidases together with their expression profile and their activity exerted on gangliosides of living cells indicate the biological relevance of this class of enzymes in zebrafish.

Sialidase NEU3 is a peripheral membrane protein localized on the cell surface and in endosomal structures

Sialidase NEU3 is also known as the plasma-membrane-associated form of mammalian sialidases, exhibiting a high substrate specificity towards gangliosides. In this respect, sialidase NEU3 modulates cell-surface biological events and plays a pivotal role in different cellular processes, including cell adhesion, recognition and differentiation. At the moment, no detailed studies concerning the subcellular localization of NEU3 are available, and the mechanism of its association with cellular membranes is still unknown. In the present study, we have demonstrated that sialidase NEU3, besides its localization at the plasma membrane, is present in intracellular structures at least partially represented by a subset of the endosomal compartment. Moreover, we have shown that NEU3 present at the plasma membrane is internalized and locates then to the recycling endosomal compartment. The enzyme is associated with the outer leaflet of the plasma membrane, as shown by selective cell-surface protein biotinylation. This evidence is in agreement with the ability of NEU3 to degrade gangliosides inserted into the plasma membrane of adjacent cells. Moreover, the mechanism of the protein association with the lipid bilayer was elucidated by carbonate extraction. Under these experimental conditions, we have succeeded in solubilizing NEU3, thus demonstrating that the enzyme is a peripheral membrane protein. In addition, Triton X-114 phase separation demonstrates further the hydrophilic nature of the protein. Overall, these results provide important information about the biology of NEU3, the most studied member of the mammalian sialidase family.

Atomic force microscopy evaluation of the effects of a novel antimicrobial multimeric peptide on Pseudomonas aeruginosa

In this article we evaluated by atomic force microscopy (AFM) the effects of the (novel) tetrabranched antimicrobial peptide SB006 on morphology and mechanical properties of the gram-negative bacterium Pseudomonas aeruginosa. AFM imaging showed that SB006 causes the appearance of significant fragmentariness in the bacterial membrane and a severe volume decrease. Quantitative evaluation of the degree of fragmentariness was allowed by a new ad hoc image analysis procedure. The rigidity of the treated and untreated bacteria was measured through AFM tip nanoindentation measurements, and no differences registered. These results support the membrane interaction hypothesis, according to which SB006 targets the bacterial membranes and disrupts their permeability (allowing the leakage of cytoplasmic material and the subsequent shrinkage), but it does not affect the bacterium wall, which determines its rigidity.

Elastic and magnetic dynamics of nanomagnet-ordered arrays impulsively excited by subpicosecond laser pulses

This Letter reports on the first observation of elastic and magnetic dynamics of ordered arrays of permalloy nanodots excited by low-intensity 120 fs light pulses. The first order of the diffraction pattern, generated by the probe beam in a pump-probe configuration, is used for time-resolved reflectivity and time-resolved magneto-optical Kerr effect measurements. The nonadiabatical absorption of the pump triggers an acoustic standing wave, detected by the reflected probe signal, with a frequency related to the array wave vector. Instead, the magneto-optical signal exhibits, on the nanosecond time scale, the signature of the heat-exchange diffusion processes. In addition, a clear oscillation of the magnetic signal, at a frequency close to the frequency of the acoustic wave, is unambiguously detected. Finally, the interplay between the elastic and magnetic dynamics is analyzed and interpreted.

Glancing-incidence X-ray diffraction for depth profiling of polycrystalline layers

On the basis of glancing-incidence X-ray diffraction (GIXRD) spectra collected at different incidence angles, it is possible to obtain structural information at different depths. In the case of an ideal crystalline material, the integrated intensity of each crystalline-phase reflection is correlated to the irradiated volume of the phase. In this work, it is shown that quantitative information on the thickness of thin polycrystalline layers can be obtained by means of GIXRD. Experiments have been performed on thin films of gold with different thicknesses, sputtered on glass slides. The film thickness has been carefully evaluated by X-ray reflectivity (XRR) experiments. XRR and GIXRD data are compared, and the consistency of the thickness values of the crystalline gold layer is shown.

The unexpected structural role of glutamate synthase [4Fe-4S](+1,+2) clusters as demonstrated by site-directed mutagenesis of conserved C residues at the N-terminus of the enzyme beta subunit

Azospirillum brasilense glutamate synthase (GltS) is a complex iron-sulfur flavoprotein whose catalytically active alphabeta protomer (alpha subunit, 162kDa; beta subunit, 52.3 kDa) contains one FAD, one FMN, one [3Fe-4S](0,+1), and two [4Fe-4S](+1,+2) clusters. The structure of the alpha subunit has been determined providing information on the mechanism of ammonia transfer from L-glutamine to 2-oxoglutarate through a 30 A-long intramolecular tunnel. On the contrary, details of the electron transfer pathway from NADPH to the postulated 2-iminoglutarate intermediate through the enzyme flavin co-factors and [Fe-S] clusters are largely indirect. To identify the location and role of each one of the GltS [4Fe-4S] clusters, we individually substituted the four cysteinyl residues forming the first of two conserved C-rich regions at the N-terminus of GltS beta subunit with alanyl residues. The engineered genes encoding the beta subunit variants (and derivatives carrying C-terminal His6-tags) were co-expressed with the wild-type alpha subunit gene. In all cases the C/A substitutions prevented alpha and beta subunits association to yield the GltS alphabeta protomer. This result is consistent with the fact that these residues are responsible for the formation of glutamate synthase [4Fe-4S](+1,+2) clusters within the N-terminal region of the beta subunit, and that these clusters are implicated not only in electron transfer between the GltS flavins, but also in alphabeta heterodimer formation by structuring an N-terminal [Fe-S] beta subunit interface subdomain, as suggested by the three-dimensional structure of dihydropyrimidine dehydrogenase, an enzyme containing an N-terminal beta subunit-like domain.

Diagnostic and surgical management of patients with aneurysms of the thoracic aorta with various causes. Echocardiography and contrast enhanced computed tomography in prophylactic replacement of the ascending aorta

Sixty eight patients with aneurysms of the thoracic aorta were studied. Forty one had aortic dissection, 24 had dilatation only, and three had transverse aortic rupture. Sixteen had Marfan's syndrome; 17 had hypertension; and in eight there were other causal factors. In 17 the cause of the aneurysm was unknown. Histological examination did not help to establish the cause of aneurysm. Echocardiography failed to detect dissection of the ascending aorta in four (21%) out of 19 cases studied. The mortality rate in the whole series was 26%. Early (operative and hospital) and late deaths occurred in 20% and 6% of patients respectively. The early mortality rate was 40% in the 24 emergency cases of dissection of the ascending aorta, 9% in patients operated on for dilatation of the ascending and transverse aorta without dissection, and 8% in patients with chronic dissection of the ascending aorta who had elective operation. Early and late mortality rates were no higher in patients with Marfan's disease than in any of the other groups. It is suggested that contrast enhanced computer tomography should be performed in all patients with pronounced aortic root dilatation and in patients with Marfan's disease with symptoms which suggest dissection, even if they have only slight aortic root dilatation. Preventive replacement of the ascending aorta should be considered in more patients to reduce the number of emergency operations, in which the mortality rate is high. There is no definite limit of aortic root dilatation above which preventive replacement of the ascending aorta should be routinely considered.

Pulmonary valve agenesis and supravalvular pulmonary stenosis. Report of a case and review of literature

Pulmonary valve agenesis is a rare malformation, and is usually associated with a ventricular septal defect. Occasionally it may be associated also with right ventricular outflow obstruction. Children with this syndrome usually die early in infancy either of intractable heart failure or of severe respiratory distress. Rare instances of association with peripheral pulmonary stenoses have also been reported. We report the case of a three-year-old girl, asymptomatic except for failure to thrive, with pulmonary valve agenesis and coarctation of the pulmonary artery trunk.

[Emergencies in valvular surgery]

Ninety patients who underwent emergency cardiac valve surgery from January 1976 to December 1981 are reported. Patients were divided in two groups: those operated on native valves are included in group I; patients with prosthetic valves operated because of leakage or malfunction, in group II. In group I (57 patients) the aetiology was: rheumatic heart disease (34 cases); acute endocarditis (16 cases); sequelae of recent endocarditis (2 cases); luetic infection (1 case); sequelae of myocardial infarction (1 case); rupture of mitral chordae in mixomatous valve (3 cases). The emergency operation was prompted in 22 patients by cardiogenic shock, in 13 patients by intractable pulmonary edema, in 21 patients by low output syndrome, in one case by ventricular arrhythmias. In group II (33 cases) the causes of reoperation were: in 27 cases leakage (in 13 due to active endocarditis); in 6 cases variance of the occluder or thrombosis. The emergency originated in 12 cases from cardiogenic shock, in 11 cases from intractable pulmonary edema, in 9 cases from low output syndrome, in 1 case from ventricular arrhythmias. Twenty-six patients died perioperatively in group I and 17 in group II. Mean follow-up in group I was 26 months. Among 27 patients there were two deaths; 25 patients are alive and well (one has been reoperated again). Mean follow-up in group II was 21 months. Among the 15 patients observed there were 6 deaths (3 after re-reoperation); 9 patients are alive and well (one has been re-reoperated).' The Authors feel that surgery is mandatory in all such patients to ensure satisfying long term results, in spite of high perioperative mortality rate.

Aneurysms involving the aortic arch. Report on thirteen surgically treated patients

Since the beginning of 1980, 13 patients with aneurysms of the aortic arch have been operated in our department. In 4 cases the aneurysm was limited to the aortic arch, while in 10 patients the ascending aorta was involved. In 7 patients an emergency procedure was required. Eleven patients were operated using deep hypothermia and circulatory arrest, in 2 right axillary and femoral artery cannulation with moderate hypothermia was used. In 5 patients a concomitant aortic insufficiency was corrected with a mechanical valve. Three patients died in the hospital. Transient cerebral dysfunctions occurred in 4 patients. Deep hypothermia and circulatory arrest provided a convenient method especially in older patients. Bleeding due to generalized coagulopathy and bleeding diathesis was one of the major problems. The methods adopted to avoid these complications are reported and discussed in detail.

An unusual case of congenital double coronary arteriovenous fistula

A double coronary arteriovenous fistula (CAVF) was observed in a ten-year-old girl. A large, tortuous, and elongated right coronary artery, communicating with the right ventricle, was detected by two-dimensional echocardiography and confirmed at angiography. To our knowledge, no echocardiographic recognition of the origin and termination of a CAVF has been reported previously. Moreover, another fistula, connecting the left anterior descending coronary artery with the main pulmonary artery was also detected by selective left coronary arteriography. The anatomy of double CAVF was confirmed on surgery. A right CAVF draining into the right ventricle and a left CAVF draining into the main pulmonary artery seemed to be a very unusual combination.