Nature Communications volume 10, Article number: 4549 (2019)

S. De León Reyes, S. Mederos, I. Varela, L. A. Weiss, G. Perea, M. J. Galazo & M. Nieto

Abstract

Interhemispheric axons of the corpus callosum (CC) facilitate the higher order functions of the cerebral cortex. According to current views, callosal and non-callosal fates are determined early after a neuron’s birth, and certain populations, such as cortical layer (L) 4 excitatory neurons of the primary somatosensory (S1) barrel, project only ipsilaterally. Using a novel axonal-retrotracing strategy and GFP-targeted visualization of Rorb+ neurons, we instead demonstrate that L4 neurons develop transient interhemispheric axons. Locally restricted L4 connectivity emerges when exuberant contralateral axons are refined in an area- and layer-specific manner during postnatal development. Surgical and genetic interventions of sensory circuits demonstrate that refinement rates depend on distinct inputs from sensory-specific thalamic nuclei. Reductions in input-dependent refinement result in mature functional interhemispheric hyperconnectivity, demonstrating the plasticity and bona fide callosal potential of L4 neurons. Thus, L4 neurons discard alternative interhemispheric circuits as instructed by thalamic input. This may ensure optimal wiring.

 DOI 10.1038/s41467-019-12495-w

• Investigadoras del CNB identifican mecanismos que generan conexiones inesperadas ante alteraciones en el desarrollo del individuo.
• Las neuronas de la corteza tienen la capacidad de generar circuitos alternativos con nuevas funciones optimizadas ante situaciones adversas o carencias de estímulos
• El trabajo aporta una nueva perspectiva para comprender la diversidad de circuitos y comportamientos, un factor muy importante para el manejo y el tratamiento de síndromes como el espectro autista.

Front Plant Sci. 2019 Sep 5;10:1044. eCollection 2019.

Contreras R, Kallemi P, González-García MP, Lazarova A, Sánchez-Serrano JJ, Sanmartín M, Rojo E.

Abstract

The transition of stem cells from self-renewal into differentiation is tightly regulated to assure proper development of the organism. Arabidopsis MINIYO (IYO) and its mammalian orthologue RNA polymerase II associated protein 1 (RPAP1) are essential factors for initiating stem cell differentiation in plants and animals. Moreover, there is evidence suggesting that the translocation of IYO and RPAP1 from the cytosol into the nucleus functions as a molecular switch to initiate this cell fate transition. Identifying the determinants of IYO subcellular localization would allow testing if, indeed, nuclear IYO migration triggers cell differentiation and could provide tools to control this crucial developmental transition. Through transient and stable expression assays in Nicotiana benthamiana and Arabidopsis thaliana, we demonstrate that IYO contains two nuclear localization signals (NLSs), located at the N- and C-terminus of the protein, which mediate the interaction with the NLS-receptor IMPA4 and the import of the protein into the nucleus. Interestingly, IYO also interacts with GPN GTPases, which are involved in selective nuclear import of RNA polymerase II. This interaction is prevented when the G1 motif in GPN1 is mutated, suggesting that IYO binds specifically to the nucleotide-bound form of GPN1. In contrast, deleting the NLSs in IYO does not prevent the interaction with GPN1, but it interferes with import of GPN1 into the nucleus, indicating that IYO and GPN1 are co-transported as a complex that requires the IYO NLSs for import. This work unveils key domains and factors involved in IYO nuclear import, which may prove instrumental to determine how IYO and RPAP1 control stem cell differentiation.

doi: 10.3389/fpls.2019.01044.

Adv Virus Res. 2019;105:1-33.

Sachse M, Fernández de Castro I, Tenorio R, Risco C.

Abstract

Transmission electron microscopy (TEM) has been crucial to study viral infections. As a result of recent advances in light and electron microscopy, we are starting to be aware of the variety of structures that viruses assemble inside cells. Viruses often remodel cellular compartments to build their replication factories. Remarkably, viruses are also able to induce new membranes and new organelles. Here we revise the most relevant imaging technologies to study the biogenesis of viral replication organelles. Live cell microscopy, correlative light and electron microscopy, cryo-TEM, and three-dimensional imaging methods are unveiling how viruses manipulate cell organization. In particular, methods for molecular mapping in situ in two and three dimensions are revealing how macromolecular complexes build functional replication complexes inside infected cells. The combination of all these imaging approaches is uncovering the viral life cycle events with a detail never seen before.

doi: 10.1016/bs.aivir.2019.07.005.

PLoS Comput Biol. 2019 Sep 17;15(9):e1007353.

Chagoyen M, Poyatos JF.

Abstract

Environmental or genetic perturbations lead to gene expression changes. While most analyses of these changes emphasize the presence of qualitative differences on just a few genes, we now know that changes are widespread. This large-scale variation has been linked to the exclusive influence of a global transcriptional program determined by the new physiological state of the cell. However, given the sophistication of eukaryotic regulation, we expect to have a complex architecture of specific control affecting this program. Here, we examine this architecture. Using data of Saccharomyces cerevisiae expression in different nutrient conditions, we first propose a five-sector genome partition, which integrates earlier models of resource allocation, as a framework to examine the deviations from the global control. In this scheme, we recognize invariant genes, whose regulation is dominated by physiology, specific genes, which substantially depart from it, and two additional classes that contain the frequently assumed growth-dependent genes. Whereas the invariant class shows a considerable absence of specific regulation, the rest is enriched by regulation at the level of transcription factors (TFs) and epigenetic modulators. We nevertheless find markedly different strategies in how these classes deviate. On the one hand, there are TFs that act in a unique way between partition constituents, and on the other, the action of chromatin modifiers is significantly diverse. The balance between regulatory strategies ultimately modulates the action of the general transcription machinery and therefore limits the possibility of establishing a unifying program of expression change at a genomic scale.

doi: 10.1371/journal.pcbi.1007353

• La infección por la bacteria E. coli enterohemorrágica (EHEC) se transmite por alimentos contaminados produciendo colitis hemorrágicas, anemia hemolítica e insuficiencia renal, lo que puede llegar a causar graves secuelas y la muerte.
• No existe en la actualidad vacuna o una terapia eficiente, pero investigadores del CSIC han encontrado una novedosa estrategia que puede bloquear la infección.

La bacteria E. coli enterohemorrágica (EHEC) se encuentra a menudo presente en el intestino del ganado bovino sin causar síntomas, pero desde estos animales puede llegar a contaminar alimentos (p.ej. carne picada, vegetales, zumos) si no se toman las medidas sanitarias adecuadas durante su elaboración. Tras la ingestión de alimentos contaminados EHEC infecta el colon humano y produce toxinas que causan colitis hemorrágica, anemia hemolítica e insuficiencia renal, lo que puede generar graves efectos secundarios e incluso la muerte. Estas infecciones suponen un riesgo para la salud pública ya que no existe vacuna ni una terapia efectiva frente a EHEC, ya que el uso de antibióticos puede inducir una mayor liberación de toxinas.

Arranca el curso: El próximo 20 de septiembre comienza el XXIV Ciclo de Seminarios del CNB y el XIII Ciclo de Seminarios Junior del CNB con una ponencia inaugural impartida por la Prof. Patricia Fara, directora del Departamento de Historia y Filosofía de la Ciencia del Clare College, University of Cambridge. .

Los seminarios tendrán lugar los viernes a las 12:00 en el Salón de Actos del Centro Nacional de Biotecnología del CSIC.

Ayer se celebró en Madrid la entrega de las acreditaciones Severo Ochoa y María de Maeztu. Pedro Duque, ministro en funciones de Ciencia, Innovación y Universidades entregó las distinciones a los centros y unidades elegidos, que destacan por su alta competitividad, sus ambiciosos planes estratégicos, una producción científica de máxima calidad y una gran capacidad para atraer talento nacional e internacional.  

Para el CNB, esta es la segunda acreditación Severo Ochoa tras la recibida en el año 2013. Fernando Rojo, director del centro, destacó en la ceremonia como la acreditación Severo Ochoa ha supuesto un cambio importante para el CNB, promoviendo la realización de un plan estratégico del centro a medio y largo plazo donde se han identificado las fortalezas del centro de cara a garantizar la calidad, excelencia y el impacto de nuestra investigación en el futuro.

PLoS Pathog. 2019 Aug 29;15(8):e1008031.

Ruano-Gallego D, Yara DA, Di Ianni L, Frankel G, Schüller S, Fernández LA.

Abstract

Enterohemorrhagic E. coli (EHEC) is a human intestinal pathogen that causes hemorrhagic colitis and hemolytic uremic syndrome. No vaccines or specific therapies are currently available to prevent or treat these infections. EHEC tightly attaches to the intestinal epithelium by injecting the intimin receptor Tir into the host cell via a type III secretion system (T3SS). In this project, we identified a camelid single domain antibody (nanobody), named TD4, that recognizes a conserved Tir epitope overlapping the binding site of its natural ligand intimin with high affinity and stability. We show that TD4 inhibits attachment of EHEC to cultured human HeLa cells by preventing Tir clustering by intimin, activation of downstream actin polymerization and pedestal formation. Furthermore, we demonstrate that TD4 significantly reduces EHEC adherence to human colonic mucosa in in vitro organ cultures. Altogether, these results suggest that nanobody-based therapies hold potential in the development of much needed treatment and prevention strategies against EHEC infection.

doi: 10.1371/journal.ppat.1008031.

MBio. 2019 Aug 27;10(4). pii: e01839-19.

DeDiego ML, Nogales A, Martinez-Sobrido L, Topham DJ.

Abstract

Using multiple viral systems, and performing silencing approaches, overexpression approaches, and experiments in knockout cells, we report, for the first time, that interferon (IFN)-induced protein 44 (IFI44) positively affects virus production and negatively modulates innate immune responses induced after viral infections. Moreover, IFI44 is able to rescue poly(I·C)- and IFN-mediated inhibition of virus growth. Furthermore, we report a novel interaction of IFI44 with the cellular factor FK506-binding protein 5 (FKBP5), which binds to cellular kinases such as the inhibitor of nuclear factor kappa B (IκB) kinases (IKKα, IKKβ, and IKKε). Importantly, in the presence of FKBP5, IFI44 decreases the ability of IKKβ to phosphorylate IκBα and the ability of IKKε to phosphorylate interferon regulatory factor 3 (IRF-3), providing a novel mechanism for the function of IFI44 in negatively modulating IFN responses. Remarkably, these new IFI44 functions may have implications for diseases associated with excessive immune signaling and for controlling virus infections mediated by IFN responses.IMPORTANCE Innate immune responses mediated by IFN and inflammatory cytokines are critical for controlling virus replication. Nevertheless, exacerbated innate immune responses could be detrimental for the host and feedback mechanisms are needed to maintain the cellular homeostasis. In this work, we describe a completely novel function for IFI44 in negatively modulating the innate immune responses induced after viral infections. We show that decreasing IFI44 expression by using small interfering RNAs (siRNAs) or by generating knockout (KO) cells impairs virus production and increases the levels of IFN responses. Moreover, we report a novel interaction of IFI44 with the cellular protein FKBP5, which in turn interacts with kinases essential for type I and III IFN induction and signaling, such as the inhibitor of nuclear factor kappa B (IκB) kinases IKKα, IKKβ, and IKKε. Our data indicate that binding of IFI44 to FKBP5 decreased the phosphorylation of IRF-3 and IκBα mediated by IKKε and IKKβ, respectively, providing a likely explanation for the function of IFI44 in negatively modulating IFN responses. These results provide new insights into the induction of innate immune responses and suggest that IFI44 is a new potential antiviral target for reducing virus replication.

doi: 10.1128/mBio.01839-19.