Abstract:A recent outbreak of Zika virus in Brazil has led to a simultaneous increase in reports of neonatal microcephaly. Zika targets cerebral neural precursors, a cell population essential for cortical development, but the cause of this neurotropism remains obscure. Here we report that the neural RNA-binding protein Musashi-1 (MSI1) interacts with the Zika genome and enables viral replication. Zika infection disrupts the binding of MSI1 to its endogenous targets, thereby deregulating expression of factors implicated in neural stem cell function. We further show that MSI1 is highly expressed in neural progenitors of the human embryonic brain, and is mutated in individuals with autosomal recessive primary microcephaly. Selective MSI1 expression in neural precursors could therefore explain the exceptional vulnerability of these cells to Zika infection. Main text:Zika virus (ZIKV) recently emerged as a major public health risk because of its devastating effect on fetal neurodevelopment (1-3). ZIKV was first isolated in Uganda in 1947, and the virus subsequently spread through Asia, and from there to the Americas (4). A causal link between ZIKV infection and congenital brain malformations became apparent in 2016 following an outbreak in Brazil (1). Brazilian ZIKV is closely related to the Asian-lineage strain, which affected New Caledonia and French Polynesia, where cases of microcephaly were reported retrospectively (5).Intrauterine infections can impair neurodevelopment (6), but ZIKV is highly neurotropic and interferes specifically with fetal brain development causing microcephaly, cortical malformations and intracranial calcifications (7-10). We hypothesized that the singlestranded RNA flavivirus ZIKV may hijack RNA-binding factors present in the developing central nervous system (11). Host RNA-binding proteins are known to interact with untranslated regions (UTRs) to regulate replication, translation and stabilization of viral genomes (11). In silico analysis of the genomic RNA of the Brazilian ZIKV strain, PE243, revealed three consensus binding sites in the 3'UTR for the highly conserved Musashi family of RNA binding proteins, Musashi-1 (MSI1) and Musashi-2 (MSI2), both important translational regulators in stem cells (12)(13)(14)(15). Two sites were conserved between PE243 and the Ugandan MR766 strains (Sites 1, 2), whereas the third (Site 3) was found only in the Asian-lineage strains including PE243 ( Fig. 1A; Fig. S1A, B). By mapping these sites onto a predicted secondary structure of ZIKV 3'UTR, we found all the three to be present on stemloop structures, which are considered optimal for MSI binding (16,17). Moreover, a recent study revealed nucleotide substitutions proximal to Sites 1 and 2 in the Asian-lineage strains, which could indicate positive selection for MSI1 binding during ZIKV evolution (18).To address if the Musashi proteins interacted with ZIKV, we first tested their binding to ZIKV 3'UTR. RNA pull-downs identified binding of MSI1, but not MSI2, to the 3'UTR of PE243 (Fig. 1B) (15). Mutat...

The centrosome, a key microtubule organizing centre, is composed of centrioles, embedded in a protein-rich matrix. Centrosomes control the internal spatial organization of somatic cells, and as such contribute to cell division, cell polarity and migration. Upon exiting the cell cycle, most cell types in the human body convert their centrioles into basal bodies, which drive the assembly of primary cilia, involved in sensing and signal transduction at the cell surface. Centrosomal genes are targeted by mutations in numerous human developmental disorders, ranging from diseases exclusively affecting brain development, through global growth failure syndromes to diverse pathologies associated with ciliary malfunction. Despite our much-improved understanding of centrosome function in cellular processes, we know remarkably little of its role in the organismal context, especially in mammals. In this review, we examine how centrosome dysfunction impacts on complex physiological processes and speculate on the challenges we face when applying knowledge generated from in vitro and in vivo model systems to human development.

Disruption of the centromere protein J gene, CENPJ (CPAP, MCPH6, SCKL4), which is a highly conserved and ubiquitiously expressed centrosomal protein, has been associated with primary microcephaly and the microcephalic primordial dwarfism disorder Seckel syndrome. The mechanism by which disruption of CENPJ causes the proportionate, primordial growth failure that is characteristic of Seckel syndrome is unknown. By generating a hypomorphic allele of Cenpj, we have developed a mouse (Cenpjtm/tm) that recapitulates many of the clinical features of Seckel syndrome, including intrauterine dwarfism, microcephaly with memory impairment, ossification defects, and ocular and skeletal abnormalities, thus providing clear confirmation that specific mutations of CENPJ can cause Seckel syndrome. Immunohistochemistry revealed increased levels of DNA damage and apoptosis throughout Cenpjtm/tm embryos and adult mice showed an elevated frequency of micronucleus induction, suggesting that Cenpj-deficiency results in genomic instability. Notably, however, genomic instability was not the result of defective ATR-dependent DNA damage signaling, as is the case for the majority of genes associated with Seckel syndrome. Instead, Cenpjtm/tm embryonic fibroblasts exhibited irregular centriole and centrosome numbers and mono- and multipolar spindles, and many were near-tetraploid with numerical and structural chromosomal abnormalities when compared to passage-matched wild-type cells. Increased cell death due to mitotic failure during embryonic development is likely to contribute to the proportionate dwarfism that is associated with CENPJ-Seckel syndrome.