RESUMEN
Bicontinuous membranes in cell organelles epitomize nature's ability to create complex functional nanostructures. Like their synthetic counterparts, these membranes are characterized by continuous membrane sheets draped onto topologically complex saddle-shaped surfaces with a periodic network-like structure. Their structure sizes, (around 50-500 nm), and fluid nature make transmission electron microscopy (TEM) the analysis method of choice to decipher their nanostructural features. Here we present a tool, Surface Projection Image Recognition Environment (SPIRE), to identify bicontinuous structures from TEM sections through interactive identification by comparison to mathematical "nodal surface" models. The prolamellar body (PLB) of plant etioplasts is a bicontinuous membrane structure with a key physiological role in chloroplast biogenesis. However, the determination of its spatial structural features has been held back by the lack of tools enabling the identification and quantitative analysis of symmetric membrane conformations. Using our SPIRE tool, we achieved a robust identification of the bicontinuous diamond surface as the dominant PLB geometry in angiosperm etioplasts in contrast to earlier long-standing assertions in the literature. Our data also provide insights into membrane storage capacities of PLBs with different volume proportions and hint at the limited role of a plastid ribosome localization directly inside the PLB grid for its proper functioning. This represents an important step in understanding their as yet elusive structure-function relationship.
Asunto(s)
Membrana Celular/fisiología , Membrana Celular/ultraestructura , Productos Agrícolas/crecimiento & desarrollo , Productos Agrícolas/ultraestructura , Plastidios/fisiología , Plastidios/ultraestructura , Avena/crecimiento & desarrollo , Avena/ultraestructura , Cucumis sativus/crecimiento & desarrollo , Cucumis sativus/ultraestructura , Microscopía Electrónica de Transmisión/métodos , Modelos Teóricos , Pisum sativum/crecimiento & desarrollo , Pisum sativum/ultraestructura , Phaseolus/crecimiento & desarrollo , Phaseolus/ultraestructura , Programas Informáticos , Zea mays/crecimiento & desarrollo , Zea mays/ultraestructuraRESUMEN
The quantizer problem is a tessellation optimization problem where point configurations are identified such that the Voronoi cells minimize the second moment of the volume distribution. While the ground state (optimal state) in 3D is almost certainly the body-centered cubic lattice, disordered and effectively hyperuniform states with energies very close to the ground state exist that result as stable states in an evolution through the geometric Lloyd's algorithm [M. A. Klatt et al. Nat. Commun. 10, 811 (2019)]. When considered as a statistical mechanics problem at finite temperature, the same system has been termed the "Voronoi liquid" by Ruscher, Baschnagel, and Farago [Europhys. Lett. 112, 66003 (2015)]. Here, we investigate the cooling behavior of the Voronoi liquid with a particular view to the stability of the effectively hyperuniform disordered state. As a confirmation of the results by Ruscher et al., we observe, by both molecular dynamics and Monte Carlo simulations, that upon slow quasi-static equilibrium cooling, the Voronoi liquid crystallizes from a disordered configuration into the body-centered cubic configuration. By contrast, upon sufficiently fast non-equilibrium cooling (and not just in the limit of a maximally fast quench), the Voronoi liquid adopts similar states as the effectively hyperuniform inherent structures identified by Klatt et al. and prevents the ordering transition into a body-centered cubic ordered structure. This result is in line with the geometric intuition that the geometric Lloyd's algorithm corresponds to a type of fast quench.
RESUMEN
Environmental signals shape host physiology and fitness. Microbiota-derived cues are required to program conventional dendritic cells (cDCs) during the steady state so that they can promptly respond and initiate adaptive immune responses when encountering pathogens. However, the molecular underpinnings of microbiota-guided instructive programs are not well understood. Here, we report that the indigenous microbiota controls constitutive production of type I interferons (IFN-I) by plasmacytoid DCs. Using genome-wide analysis of transcriptional and epigenetic regulomes of cDCs from germ-free and IFN-I receptor (IFNAR)-deficient mice, we found that tonic IFNAR signaling instructs a specific epigenomic and metabolic basal state that poises cDCs for future pathogen combat. However, such beneficial biological function comes with a trade-off. Instructed cDCs can prime T cell responses against harmless peripheral antigens when removing roadblocks of peripheral tolerance. Our data provide fresh insights into the evolutionary trade-offs that come with successful adaptation of vertebrates to their microbial environment.
Asunto(s)
Células Dendríticas/inmunología , Interferón Tipo I/inmunología , Microbiota/inmunología , Inmunidad Adaptativa/inmunología , Inmunidad Adaptativa/fisiología , Animales , Linfocitos T CD8-positivos/inmunología , Células Dendríticas/microbiología , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Microbiota/fisiología , Receptor de Interferón alfa y beta/metabolismo , Transducción de Señal/inmunologíaRESUMEN
Confinement or geometric frustration is known to alter the structure of soft matter, including copolymeric melts, and can consequently be used to tune structure and properties. Here we investigate the self-assembly of ABC and ABB 3-miktoarm star copolymers confined to a spherical shell using coarse-grained dissipative particle dynamics simulations. In bulk and flat geometries the ABC stars form hexagonal tilings, but this is topologically prohibited in a spherical geometry which normally is alleviated by forming pentagonal tiles. However, the molecular architecture of the ABC stars implies an additional 'color constraint' which only allows even tilings (where all polygons have an even number of edges) and we study the effect of these simultaneous constraints. We find that both ABC and ABB systems form spherical tiling patterns, the type of which depends on the radius of the spherical substrate. For small spherical substrates, all solutions correspond to patterns solving the Thomson problem of placing mobile repulsive electric charges on a sphere. In ABC systems we find three coexisting, possibly different tilings, one in each color, each of them solving the Thomson problem simultaneously. For all except the smallest substrates, we find competing solutions with seemingly degenerate free energies that occur with different probabilities. Statistically, an observer who is blind to the differences between B and C can tell from the structure of the A domains if the system is an ABC or an ABB star copolymer system.
RESUMEN
Dendritic cells (DCs) are important inducers and regulators of T-cell responses. They are able to activate and modulate the differentiation of CD4+ and CD8+ T cells. In the skin, there are at least five phenotypically distinct DC subpopulations that can be distinguished by differential expression of the cell surface markers CD207, CD103, and CD11b. Previous studies have suggested that dermal CD11b-CD207+ conventional type 1 DCs are indispensable for the priming of a skin homing cytotoxic T-lymphocyte response. However, conventional type 1 DCs are also the only skin DC subset capable of cross-presenting exogenous antigens on major histocompatibility complex class I. Thus, it remained unclear whether for antigens that do not require cross-presentation, such as viruses that infect DCs, other DC subtypes in the skin can contribute to cytotoxic T-lymphocyte priming. To address this question, we used a transgenic mouse model that allows inducible expression and presentation of a model antigen on selected subsets of dermal DCs. We show that for antigens presented via the conventional major histocompatibility complex class I presentation pathway, CD207- dermal DCs are fully competent to prime a skin homing cytotoxic T-lymphocyte response that is capable of protection against a local virus challenge and gives rise to skin resident memory CD8+ T cells.
Asunto(s)
Linfocitos T CD8-positivos/inmunología , Reactividad Cruzada , Células de Langerhans/inmunología , Piel/inmunología , Linfocitos T Citotóxicos/inmunología , Animales , Modelos Animales de Enfermedad , Epítopos de Linfocito T/genética , Epítopos de Linfocito T/inmunología , Epítopos de Linfocito T/metabolismo , Antígenos de Histocompatibilidad Clase I/inmunología , Antígenos de Histocompatibilidad Clase I/metabolismo , Humanos , Memoria Inmunológica , Células de Langerhans/metabolismo , Ratones , Ratones Transgénicos , Piel/citología , Enfermedades Cutáneas Virales/inmunología , Enfermedades Cutáneas Virales/virología , Linfocitos T Citotóxicos/metabolismo , Virus Vaccinia/inmunologíaRESUMEN
Coevolution of ticks and the vertebrate immune system has led to the development of immunosuppressive molecules that prevent immediate response of skin-resident immune cells to quickly fend off the parasite. In this article, we demonstrate that the tick-derived immunosuppressor sialostatin L restrains IL-9 production by mast cells, whereas degranulation and IL-6 expression are both unaffected. In addition, the expression of IL-1ß and IRF4 is strongly reduced in the presence of sialostatin L. Correspondingly, IRF4- or IL-1R-deficient mast cells exhibit a strong impairment in IL-9 production, demonstrating the importance of IRF4 and IL-1 in the regulation of the Il9 locus in mast cells. Furthermore, IRF4 binds to the promoters of Il1b and Il9, suggesting that sialostatin L suppresses mast cell-derived IL-9 preferentially by inhibiting IRF4. In an experimental asthma model, mast cell-specific deficiency in IRF4 or administration of sialostatin L results in a strong reduction in asthma symptoms, demonstrating the immunosuppressive potency of tick-derived molecules.
Asunto(s)
Cistatinas/farmacología , Inmunidad Innata/efectos de los fármacos , Inmunosupresores/farmacología , Factores Reguladores del Interferón/inmunología , Interleucina-9/inmunología , Mastocitos/efectos de los fármacos , Animales , Asma/genética , Asma/inmunología , Asma/patología , Sitios de Unión , Degranulación de la Célula/inmunología , Cistatinas/inmunología , Regulación de la Expresión Génica , Interacciones Huésped-Parásitos/inmunología , Factores Reguladores del Interferón/deficiencia , Factores Reguladores del Interferón/genética , Interleucina-1beta/genética , Interleucina-1beta/inmunología , Interleucina-6/genética , Interleucina-6/inmunología , Interleucina-9/antagonistas & inhibidores , Interleucina-9/genética , Mastocitos/inmunología , Mastocitos/patología , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Ratones Noqueados , Regiones Promotoras Genéticas , Unión Proteica , Receptores de Interleucina-1/genética , Receptores de Interleucina-1/inmunología , Transducción de Señal , Transcripción GenéticaRESUMEN
Dendritic cells (DCs) are the key APCs not only for the priming of naïve T cells, but also for the induction and maintenance of peripheral T-cell tolerance. We have recently shown that cognate interactions between Foxp3(+) Tregs and steady-state DCs are crucial to maintain the tolerogenic potential of DCs. Using DIETER mice, which allow the induction of antigen presentation selectively on DCs without altering their maturation status, we show here that breakdown of CD8(+) T-cell tolerance, which ensues after depletion of suppressive CD4(+) T cells, is driven by a positive feedback loop in which autoreactive CD8(+) T cells activate DCs via CD40. These data identify ligation of CD40 on DCs as a stimulus that promotes autoreactive T-cell priming when regulatory T-cell suppression fails and suggest that feedback from autoreactive T cells to DCs may contribute to the well-documented involvement of CD40 in many autoimmune diseases.
Asunto(s)
Linfocitos T CD4-Positivos/inmunología , Antígenos CD40/inmunología , Ligando de CD40/inmunología , Linfocitos T CD8-positivos/inmunología , Tolerancia Inmunológica/inmunología , Animales , Anticuerpos Monoclonales/farmacología , Presentación de Antígeno/inmunología , Trasplante de Médula Ósea , Linfocitos T CD4-Positivos/metabolismo , Antígenos CD40/genética , Antígenos CD40/metabolismo , Ligando de CD40/genética , Ligando de CD40/metabolismo , Linfocitos T CD8-positivos/metabolismo , Línea Celular Tumoral , Células Dendríticas/inmunología , Células Dendríticas/metabolismo , Retroalimentación Fisiológica/efectos de los fármacos , Citometría de Flujo , Tolerancia Inmunológica/genética , Coriomeningitis Linfocítica/inmunología , Coriomeningitis Linfocítica/virología , Virus de la Coriomeningitis Linfocítica/inmunología , Virus de la Coriomeningitis Linfocítica/fisiología , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Linfocitos T Citotóxicos/inmunología , Linfocitos T Citotóxicos/metabolismo , Quimera por Trasplante/sangre , Quimera por Trasplante/inmunologíaRESUMEN
Proteasomes are the main cytosolic proteases responsible for generating peptides for antigen processing and presentation in the MHC (major histocompatibility complex) class-I pathway. Purified 20S and 26S proteasomes have been widely used to study both specificity and efficiency of antigen processing. Here, we describe the purification of active human 20S and 26S proteasomes from human erythrocytes by DEAE-ion exchange chromatography, ammonium sulfate precipitation, glycerol density gradient centrifugation, and Superose-6 size exclusion chromatography and their characterization using fluorogenic substrates and specific inhibitors.