No abstract

Dendritic cells (DCs) are critical for launching of protective T cell immunity in response to viral infection. Viruses can directly infect DCs, thereby compromising their viability and suppressing their ability to activate immune responses. How DC function is maintained in light of this paradox is not understood. By analyzing the susceptibility of primary human DC subsets to viral infections, we report that CD141+ DCs have an innate resistance to infection by a broad range of enveloped viruses, including human immunodeficiency virus (HIV) and influenza virus. In contrast, CD1c+ DCs are susceptible to infection which enables viral antigen production but impairs their immune functions and survival. The ability of CD141+ DCs to resist infection is conferred by RAB15, a vesicle trafficking protein constitutively expressed in this DC subset. We show that CD141+ DCs rely on viral antigens produced in bystander cells to launch cross-presentation driven T cell responses. By dissociating viral infection from antigen presentation, this mechanism protects the functional capacity of DCs to launch adaptive immunity against viral infection.

Background: To date, very few cellular factors required for secretion of flaviviruses have been described. Results: Simultaneous depletion of class II Arf (Arf4 and Arf5) blocks dengue flavivirus secretion, without altering the constitutive secretory pathway. Dengue glycoprotein prM interacts with Arf4 and Arf5. Conclusion: Arf4 and Arf5 play a crucial role in dengue flavivirus secretion. Significance: Our findings reveal a molecular mechanism of dengue flavivirus secretion.

The recent Zika outbreak in South America and French Polynesia was associated with an epidemic of microcephaly, a disease characterized by a reduced size of the cerebral cortex. Other members of the Flavivirus genus, including West Nile virus (WNV), can cause encephalitis but were not demonstrated to cause microcephaly. It remains unclear whether Zika virus (ZIKV) and other flaviviruses may infect different cell populations in the developing neocortex and lead to distinct developmental defects. Here, we describe an assay to infect mouse E15 embryonic brain slices with ZIKV, WNV and dengue virus serotype 4 (DENV-4). We show that this tissue is able to support viral replication of ZIKV and WNV, but not DENV-4. Cell fate analysis reveals a remarkable tropism of ZIKV infection for neural stem cells. Closely related WNV displays a very different tropism of infection, with a bias towards neurons. We further show that ZIKV infection, but not WNV infection, impairs cell cycle progression of neural stem cells. Both viruses inhibited apoptosis at early stages of infection. This work establishes a powerful comparative approach to identify ZIKV-specific alterations in the developing neocortex and reveals specific preferential infection of neural stem cells by ZIKV.

The role of the membrane protein (prM/M) in flavivirus life cycle remains unclear. Here, we identified a cellular interactor to the 40-residue-long ectodomain of prM/M (ectoM) using a yeast two-hybrid screen against a human cDNA library and GST pull-down assays. We showed that dynein light chain Tctex-1 interacts with the ectoM of dengue 1-4, West Nile, and Japanese encephalitis flaviviruses. No interaction was found with yellow fever and tick-borne flaviviruses. This interaction is highly specific since a single amino-acid change in the ectoM abrogates the interaction with Tctex-1. To understand the role of this interaction, silencing of Tctex-1 using siRNA was performed prior to infection. A significant decrease in progeny production was observed for dengue and West Nile viruses. Silencing Tctex-1 inhibited the production of recombinant dengue subviral particles (RSPs). Thus Tctex-1 may play a role in late stages of viral replication through its interaction with the membrane protein.

Highlights d Mitotic spindle architecture changes during mammalian neurogenesis d Early-stage spindles contain more astral MTs and less spindle MTs d TPX2 loading on spindle microtubules influences spindle morphology d Spindles are more prone to chromosome segregation errors during early neurogenesis

Neurons of the neocortex are generated by stem cells called radial glial cells. These polarized cells extend a short apical process toward the ventricular surface and a long basal fiber that acts as a scaffold for neuronal migration. How the microtubule cytoskeleton is organized in these cells to support long-range transport is unknown. Using subcellular live imaging within brain tissue, we show that microtubules in the apical process uniformly emanate for the pericentrosomal region, while microtubules in the basal fiber display a mixed polarity, reminiscent of the mammalian dendrite. We identify acentrosomal microtubule organizing centers localized in varicosities of the basal fiber. CAMSAP family members accumulate in these varicosities, where they control microtubule growth. Double knockdown of CAMSAP1 and 2 leads to a destabilization of the entire basal process. Finally, using live imaging of human fetal cortex, we reveal that this organization is conserved in basal radial glial cells, a related progenitor cell population associated with human brain size expansion.

Radial glial (RG) cells are the neural stem cells of the developing neocortex. Apical RG (aRG) cells can delaminate to generate basal RG (bRG) cells, a cell type associated with human brain expansion. Here, we report that aRG delamination is regulated by the post‐Golgi secretory pathway. Using in situ subcellular live imaging, we show that post‐Golgi transport of RAB6+ vesicles occurs toward the minus ends of microtubules and depends on dynein. We demonstrate that the apical determinant Crumbs3 (CRB3) is also transported by dynein. Double knockout of RAB6A/A' and RAB6B impairs apical localization of CRB3 and induces a retraction of aRG cell apical process, leading to delamination and ectopic division. These defects are phenocopied by knockout of the dynein activator LIS1. Overall, our results identify a RAB6‐dynein‐LIS1 complex for Golgi to apical surface transport in aRG cells, and highlights the role of this pathway in the maintenance of neuroepithelial integrity.