Interfacial binding and aggregation of lamin A tail domains associated with Hutchinson–Gilford progeria syndrome

Hutchinson–Gilford progeria syndrome is a premature aging disorder associated with the expression of ∆50 lamin A (∆50LA), a mutant form of the nuclear structural protein lamin A (LA). ∆50LA is missing 50 amino acids from the tail domain and retains a C-terminal farnesyl group that is cleaved from the wild-type LA. Many of the cellular pathologies of HGPS are thought to be a consequence of protein–membrane association mediated by the retained farnesyl group. To better characterize the protein–membrane interface, we quantified binding of purified recombinant ∆50LA tail domain (∆50LA-TD) to tethered bilayer membranes composed of phosphatidylserine and phosphocholine using surface plasmon resonance. Farnesylated ∆50LA-TD binds to the membrane interface only in the presence of Ca[superscript 2 +] or Mg[superscript 2 +] at physiological ionic strength. At extremely low ionic strength, both the farnesylated and non-farnesylated forms of ∆50LA-TD bind to the membrane surface in amounts that exceed those expected for a densely packed protein monolayer. Interestingly, the wild-type LA-TD with no farnesylation also associates with membranes at low ionic strength but forms only a single layer. We suggest that electrostatic interactions are mediated by charge clusters with a net positive charge that we calculate on the surface of the LA-TDs. These studies suggest that the accumulation of ∆50LA at the inner nuclear membrane observed in cells is due to a combination of aggregation and membrane association rather than simple membrane binding; electrostatics plays an important role in mediating this association.National Institute of General Medical Sciences (U.S.) (1R01-GM101647)United States. Office of Naval Research. Presidential Early Career Award for Scientists and Engineers (N000141010562)National Institutes of Health (U.S.) (U01 EB014976

Single wall carbon nanotubes enter cells by endocytosis and not membrane penetration

<p>Abstract</p> <p>Background</p> <p>Carbon nanotubes are increasingly being tested for use in cellular applications. Determining the mode of entry is essential to control and regulate specific interactions with cells, to understand toxicological effects of nanotubes, and to develop nanotube-based cellular technologies. We investigated cellular uptake of Pluronic copolymer-stabilized, purified ~145 nm long single wall carbon nanotubes (SWCNTs) through a series of complementary cellular, cell-mimetic, and in vitro model membrane experiments.</p> <p>Results</p> <p>SWCNTs localized within fluorescently labeled endosomes, and confocal Raman spectroscopy showed a dramatic reduction in SWCNT uptake into cells at 4°C compared with 37°C. These data suggest energy-dependent endocytosis, as shown previously. We also examined the possibility for non-specific physical penetration of SWCNTs through the plasma membrane. Electrochemical impedance spectroscopy and Langmuir monolayer film balance measurements showed that Pluronic-stabilized SWCNTs associated with membranes but did not possess sufficient insertion energy to penetrate through the membrane. SWCNTs associated with vesicles made from plasma membranes but did not rupture the vesicles.</p> <p>Conclusions</p> <p>These measurements, combined, demonstrate that Pluronic-stabilized SWCNTs only enter cells via energy-dependent endocytosis, and association of SWCNTs to membrane likely increases uptake.</p

Single wall carbon nanotubes enter cells by endocytosis and not membrane penetration

<p>Abstract</p> <p>Background</p> <p>Carbon nanotubes are increasingly being tested for use in cellular applications. Determining the mode of entry is essential to control and regulate specific interactions with cells, to understand toxicological effects of nanotubes, and to develop nanotube-based cellular technologies. We investigated cellular uptake of Pluronic copolymer-stabilized, purified ~145 nm long single wall carbon nanotubes (SWCNTs) through a series of complementary cellular, cell-mimetic, and in vitro model membrane experiments.</p> <p>Results</p> <p>SWCNTs localized within fluorescently labeled endosomes, and confocal Raman spectroscopy showed a dramatic reduction in SWCNT uptake into cells at 4°C compared with 37°C. These data suggest energy-dependent endocytosis, as shown previously. We also examined the possibility for non-specific physical penetration of SWCNTs through the plasma membrane. Electrochemical impedance spectroscopy and Langmuir monolayer film balance measurements showed that Pluronic-stabilized SWCNTs associated with membranes but did not possess sufficient insertion energy to penetrate through the membrane. SWCNTs associated with vesicles made from plasma membranes but did not rupture the vesicles.</p> <p>Conclusions</p> <p>These measurements, combined, demonstrate that Pluronic-stabilized SWCNTs only enter cells via energy-dependent endocytosis, and association of SWCNTs to membrane likely increases uptake.</p

SN 2011ht: Confirming a Class of Interacting Supernovae with Plateau Light Curves (Type IIn-P)

We present photometry and spectroscopy of the Type IIn supernova (SN) 2011ht, identified previously as a SN impostor. The light curve exhibits an abrupt transition from a well-defined ~120 day plateau to a steep bolometric decline. Leading up to peak brightness, a hot emission-line spectrum exhibits signs of interaction with circumstellar material (CSM), in the form of relatively narrow P-Cygni features of H I and He I superimposed on broad Lorentzian wings. For the remainder of the plateau phase the spectrum exhibits strengthening P-Cygni profiles of Fe II, Ca II, and H-alpha. By day 147, after the plateau has ended, the SN entered the nebular phase, heralded by the appearance of forbidden transitions of [O I], [O II], and [Ca II] over a weak continuum. At this stage, the light curve exhibits a low luminosity that is comparable to that sub-luminous Type II-P supernovae, and a relatively fast visual-wavelength decline that is significantly steeper than the Co-56 decay rate. However, the total bolometric decline, including the IR luminosity, is consistent with Co-56 decay, and implies a low Ni-56 mass of ~0.01 M(Sun). We therefore characterize SN 2011ht as a bona-fide core-collapse SN very similar to the peculiar SNe IIn 1994W and 2009kn. These three SNe define a subclass, which are Type IIn based on their spectrum, but that also exhibit well-defined plateaus and produce low Ni-56 yields. We therefore suggest Type IIn-P as a name for this subclass. Possible progenitors of SNe IIn-P, consistent with the available data, include 8-10 M(Sun) stars, which undergo core collapse as a result of electron capture after a brief phase of enhanced mass loss, or more massive M>25 M(Sun) progenitors, which experience substantial fallback of the metal-rich radioactive ejecta. In either case, the energy radiated by these three SNe during their plateau must be dominated by CSM interaction (abridged).Comment: accepted, post-proof version (includes new data

Strong Ultraviolet Pulse From a Newborn Type Ia Supernova

Type Ia supernovae are destructive explosions of carbon oxygen white dwarfs. Although they are used empirically to measure cosmological distances, the nature of their progenitors remains mysterious, One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion. Here we report observations of strong but declining ultraviolet emission from a Type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star, and therefore provides evidence that some Type Ia supernovae arise from the single degenerate channel.Comment: Accepted for publication on the 21 May 2015 issue of Natur

PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy

We present the discovery and characterisation of PTF10iya, a short-lived (dt ~ 10 d, with an optical decay rate of ~ 0.3 mag per d), luminous (M_g ~ -21 mag) transient source found by the Palomar Transient Factory. The ultraviolet/optical spectral energy distribution is reasonably well fit by a blackbody with T ~ 1-2 x 10^4 K and peak bolometric luminosity L_BB ~ 1-5 x 10^44 erg per s (depending on the details of the extinction correction). A comparable amount of energy is radiated in the X-ray band that appears to result from a distinct physical process. The location of PTF10iya is consistent with the nucleus of a star-forming galaxy (z = 0.22405 +/- 0.00006) to within 350 mas (99.7 per cent confidence radius), or a projected distance of less than 1.2 kpc. At first glance, these properties appear reminiscent of the characteristic "big blue bump" seen in the near-ultraviolet spectra of many active galactic nuclei (AGNs). However, emission-line diagnostics of the host galaxy, along with a historical light curve extending back to 2007, show no evidence for AGN-like activity. We therefore consider whether the tidal disruption of a star by an otherwise quiescent supermassive black hole may account for our observations. Though with limited temporal information, PTF10iya appears broadly consistent with the predictions for the early "super-Eddington" phase of a solar-type star disrupted by a ~ 10^7 M_sun black hole. Regardless of the precise physical origin of the accreting material, the large luminosity and short duration suggest that otherwise quiescent galaxies can transition extremely rapidly to radiate near the Eddington limit; many such outbursts may have been missed by previous surveys lacking sufficient cadence.Comment: 18 pages, 8 figures; revised following referee's comment

Spectra of Hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory

Most Type I superluminous supernovae (SLSNe-I) reported to date have been identified by their high peak luminosities and spectra lacking obvious signs of hydrogen. We demonstrate that these events can be distinguished from normal-luminosity SNe (including Type Ic events) solely from their spectra over a wide range of light-curve phases. We use this distinction to select 19 SLSNe-I and four possible SLSNe-I from the Palomar Transient Factory archive (including seven previously published objects). We present 127 new spectra of these objects and combine these with 39 previously published spectra, and we use these to discuss the average spectral properties of SLSNe-I at different spectral phases. We find that Mn II most probably contributes to the ultraviolet spectral features after maximum light, and we give a detailed study of the O II features that often characterize the early-time optical spectra of SLSNe-I. We discuss the velocity distribution of O II, finding that for some SLSNe-I this can be confined to a narrow range compared to relatively large systematic velocity shifts. Mg II and Fe II favor higher velocities than O II and C II, and we briefly discuss how this may constrain power-source models. We tentatively group objects by how well they match either SN 2011ke or PTF12dam and discuss the possibility that physically distinct events may have been previously grouped together under the SLSN-I label

cDNA Immunization of Mice with Human Thyroglobulin Generates Both Humoral and T Cell Responses: A Novel Model of Thyroid Autoimmunity

Thyroglobulin (Tg) represents one of the largest known self-antigens involved in autoimmunity. Numerous studies have implicated it in triggering and perpetuating the autoimmune response in autoimmune thyroid diseases (AITD). Indeed, traditional models of autoimmune thyroid disease, experimental autoimmune thyroiditis (EAT), are generated by immunizing mice with thyroglobulin protein in conjunction with an adjuvant, or by high repeated doses of Tg alone, without adjuvant. These extant models are limited in their experimental flexibility, i.e. the ability to make modifications to the Tg used in immunizations. In this study, we have immunized mice with a plasmid cDNA encoding the full-length human Tg (hTG) protein, in order to generate a model of Hashimoto's thyroiditis which is closer to the human disease and does not require adjuvants to breakdown tolerance. Human thyroglobulin cDNA was injected and subsequently electroporated into skeletal muscle using a square wave generator. Following hTg cDNA immunizations, the mice developed both B and T cell responses to Tg, albeit with no evidence of lymphocytic infiltration of the thyroid. This novel model will afford investigators the means to test various hypotheses which were unavailable with the previous EAT models, specifically the effects of hTg sequence variations on the induction of thyroiditis

Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star

Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining1. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability2,3,4,5. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required