An amphipathic helix in Brl1 is required for nuclear pore complex biogenesis in S. cerevisiae

The nuclear pore complex (NPC) is the central portal for macromolecular exchange between the nucleus and cytoplasm. In all eukaryotes, NPCs assemble into an intact nuclear envelope (NE) during interphase, but the process of NPC biogenesis remains poorly characterized. Furthermore, little is known about how NPC assembly leads to the fusion of the outer and inner NE, and no factors have been identified that could trigger this event. Here, we characterize the transmembrane protein Brl1 as an NPC assembly factor required for NE fusion in budding yeast. Brl1 preferentially associates with NPC assembly intermediates and its depletion halts NPC biogenesis, leading to NE herniations that contain inner and outer ring nucleoporins but lack the cytoplasmic export platform. Furthermore, we identify an essential amphipathic helix in the luminal domain of Brl1 that mediates interactions with lipid bilayers. Mutations in this amphipathic helix lead to NPC assembly defects, and cryo-electron tomography analyses reveal multilayered herniations of the inner nuclear membrane with NPC-like structures at the neck, indicating a failure in NE fusion. Taken together, our results identify a role for Brl1 in NPC assembly and suggest a function of its amphipathic helix in mediating the fusion of the inner and outer nuclear membranes.publishedVersio

An amphipathic helix in Brl1 is required for nuclear pore complex biogenesis in S. cerevisiae

The nuclear pore complex (NPC) is the central portal for macromolecular exchange between the nucleus and cytoplasm. In all eukaryotes, NPCs assemble into an intact nuclear envelope (NE) during interphase, but the process of NPC biogenesis remains poorly characterized. Furthermore, little is known about how NPC assembly leads to the fusion of the outer and inner NE, and no factors have been identified that could trigger this event. Here, we characterize the transmembrane protein Brl1 as an NPC assembly factor required for NE fusion in budding yeast. Brl1 preferentially associates with NPC assembly intermediates and its depletion halts NPC biogenesis, leading to NE herniations that contain inner and outer ring nucleoporins but lack the cytoplasmic export platform. Furthermore, we identify an essential amphipathic helix in the luminal domain of Brl1 that mediates interactions with lipid bilayers. Mutations in this amphipathic helix lead to NPC assembly defects, and cryo-electron tomography analyses reveal multilayered herniations of the inner nuclear membrane with NPC-like structures at the neck, indicating a failure in NE fusion. Taken together, our results identify a role for Brl1 in NPC assembly and suggest a function of its amphipathic helix in mediating the fusion of the inner and outer nuclear membranes

Spatial control of nucleoporin condensation by fragile X-related proteins

Nucleoporins (Nups) build highly organized nuclear pore complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve-like hydrogel within the central channel of the NPCs. In the cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here, we show that fragile X-related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule-dependent mechanism. Downregulation of FXR1 or closely related orthologs FXR2 and fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granule-containing cells show defects in protein export, nuclear morphology and cell cycle progression. Our results reveal an unexpected role for the FXR protein family in the spatial regulation of nucleoporin condensation

Contrôle spatial de la condensation des nucléoporines par les protéines liées à l’X fragile

Nucleoporins (Nups) build highly organized Nuclear Pore Complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve-like hydrogel within the central channel of the NPCs. In the cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here we show that Fragile X-related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule-dependent mechanism. Downregulation of FXR1 or closely related paralogs FXR2 and Fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of Fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granules-containing cells show defects in protein export, nuclear morphology and cell cycle progression. These results reveal an unexpected role for the FXR protein family in the spatial regulation of Nup condensation.Les nucléoporines (Nups) construisent des complexes de pores nucléaires (NPC) hautement organisés au niveau de l'enveloppe nucléaire (NE). Dans le cytoplasme, les Nups solubles existent, mais on ignore pour l'instant comment leur assemblage se limite à la NE. Nous montrons ici que la protéine 1 liée au X fragile (FXR1) peut interagir avec plusieurs Nups et faciliter leur localisation vers NE pendant l'interphase par un mécanisme dépendant des microtubules. La régulation négative de la FXR1 ou des paralogues FXR2 et la protéine de retard mental du X fragile (FMRP) conduit à l'accumulation de condensats de Nups cytoplasmiques. De même, les modèles du syndrome du X fragile (SXF), caractérisés par une perte de FMRP, accumulent des granules de Nups. Les cellules contenant des granules de Nups présentent des défauts dans l'exportation des protéines, la morphologie nucléaire et la progression du cycle cellulaire. Ces résultats révèlent un rôle inattendu pour la famille des protéines FXR dans la régulation spatiale de la condensation des Nups

Contrôle spatial de la condensation des nucléoporines par les protéines liées à l’X fragile

Nucleoporins (Nups) build highly organized Nuclear Pore Complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve-like hydrogel within the central channel of the NPCs. In the cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here we show that Fragile X-related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule-dependent mechanism. Downregulation of FXR1 or closely related paralogs FXR2 and Fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of Fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granules-containing cells show defects in protein export, nuclear morphology and cell cycle progression. These results reveal an unexpected role for the FXR protein family in the spatial regulation of Nup condensation.Les nucléoporines (Nups) construisent des complexes de pores nucléaires (NPC) hautement organisés au niveau de l'enveloppe nucléaire (NE). Dans le cytoplasme, les Nups solubles existent, mais on ignore pour l'instant comment leur assemblage se limite à la NE. Nous montrons ici que la protéine 1 liée au X fragile (FXR1) peut interagir avec plusieurs Nups et faciliter leur localisation vers NE pendant l'interphase par un mécanisme dépendant des microtubules. La régulation négative de la FXR1 ou des paralogues FXR2 et la protéine de retard mental du X fragile (FMRP) conduit à l'accumulation de condensats de Nups cytoplasmiques. De même, les modèles du syndrome du X fragile (SXF), caractérisés par une perte de FMRP, accumulent des granules de Nups. Les cellules contenant des granules de Nups présentent des défauts dans l'exportation des protéines, la morphologie nucléaire et la progression du cycle cellulaire. Ces résultats révèlent un rôle inattendu pour la famille des protéines FXR dans la régulation spatiale de la condensation des Nups

Contrôle spatial de la condensation des nucléoporines par les protéines liées à l’X fragile

Les nucléoporines (Nups) construisent des complexes de pores nucléaires (NPC) hautement organisés au niveau de l'enveloppe nucléaire (NE). Dans le cytoplasme, les Nups solubles existent, mais on ignore pour l'instant comment leur assemblage se limite à la NE. Nous montrons ici que la protéine 1 liée au X fragile (FXR1) peut interagir avec plusieurs Nups et faciliter leur localisation vers NE pendant l'interphase par un mécanisme dépendant des microtubules. La régulation négative de la FXR1 ou des paralogues FXR2 et la protéine de retard mental du X fragile (FMRP) conduit à l'accumulation de condensats de Nups cytoplasmiques. De même, les modèles du syndrome du X fragile (SXF), caractérisés par une perte de FMRP, accumulent des granules de Nups. Les cellules contenant des granules de Nups présentent des défauts dans l'exportation des protéines, la morphologie nucléaire et la progression du cycle cellulaire. Ces résultats révèlent un rôle inattendu pour la famille des protéines FXR dans la régulation spatiale de la condensation des Nups.Nucleoporins (Nups) build highly organized Nuclear Pore Complexes (NPCs) at the nuclear envelope (NE). Several Nups assemble into a sieve-like hydrogel within the central channel of the NPCs. In the cytoplasm, the soluble Nups exist, but how their assembly is restricted to the NE is currently unknown. Here we show that Fragile X-related protein 1 (FXR1) can interact with several Nups and facilitate their localization to the NE during interphase through a microtubule-dependent mechanism. Downregulation of FXR1 or closely related paralogs FXR2 and Fragile X mental retardation protein (FMRP) leads to the accumulation of cytoplasmic Nup condensates. Likewise, models of Fragile X syndrome (FXS), characterized by a loss of FMRP, accumulate Nup granules. The Nup granules-containing cells show defects in protein export, nuclear morphology and cell cycle progression. These results reveal an unexpected role for the FXR protein family in the spatial regulation of Nup condensation

Fragile X–Related Protein 1 Regulates Nucleoporin Localization in a Cell Cycle–Dependent Manner

International audienceNuclear pore complexes (NPCs) are embedded in the nuclear envelope (NE) where they ensure the transport of macromolecules between the nucleus and the cytoplasm. NPCs are built from nucleoporins (Nups) through a sequential assembly order taking place at two different stages during the cell cycle of mammalian cells: at the end of mitosis and during interphase. In addition, fragile X–related proteins (FXRPs) can interact with several cytoplasmic Nups and facilitate their localization to the NE during interphase likely through a microtubule-dependent mechanism. In the absence of FXRPs or microtubule-based transport, Nups aberrantly localize to the cytoplasm forming the so-called cytoplasmic nucleoporin granules (CNGs), compromising NPCs’ function on protein export. However, it remains unknown if Nup synthesis or degradation mechanisms are linked to the FXRP–Nup pathway and if and how the action of FXRPs on Nups is coordinated with the cell cycle progression. Here, we show that Nup localization defects observed in the absence of FXR1 are independent of active protein translation. CNGs are cleared in an autophagy- and proteasome-independent manner, and their presence is restricted to the early G1 phase of the cell cycle. Our results thus suggest that a pool of cytoplasmic Nups exists that contributes to the NPC assembly specifically during early G1 to ensure NPC homeostasis at a short transition from mitosis to the onset of interphase

Charge conversion nanocarriers based on amphiphilic polypetides

Trabajo presentado al European Congress and Exhibition on Advanced Materials and Processes (EUROMAT), celebrado en Tesalónica (Grecia9 del 17 al 22 de septiembre de 2017.Peer Reviewe

A PKD-MFF signaling axis couples mitochondrial fission to mitotic progression

International audienceMitochondria are highly dynamic organelles subjected to fission and fusion events. During mitosis, mitochondrial fission ensures equal distribution of mitochondria to daughter cells. If and how this process can actively drive mitotic progression remains largely unknown. Here, we discover a pathway linking mitochondrial fission to mitotic progression in mammalian cells. The mitochondrial fission factor (MFF), the main mitochondrial receptor for the Dynamin-related protein 1 (DRP1), is directly phosphorylated by Protein Kinase D (PKD) specifically during mitosis. PKD-dependent MFF phosphorylation is required and sufficient for mitochondrial fission in mitotic but not in interphasic cells. Phosphorylation of MFF is crucial for chromosome segregation and promotes cell survival by inhibiting adaptation of the mitotic checkpoint. Thus, PKD/MFF-dependent mitochondrial fission is critical for the maintenance of genome integrity during cell division