SUMMARY The suspected link between infection by Zika virus (ZIKV), a re-emerging flavivirus, and microcephaly is an urgent global health concern. The direct target cells of ZIKV in the developing human fetus are not clear. Here we show that a strain of the ZIKV MR766, serially passaged in monkey and mosquito cells, efficiently infects human cortical neural progenitor cells (hNPCs) derived from induced pluripotent stem cells. Infected hNPCs further release infectious ZIKV particles. Importantly, ZIKV infection increases cell death and dysregulates cell cycle progression, resulting in attenuated hNPC growth. Global gene expression analysis of infected hNPCs reveals transcriptional dysregulation, notably of cell cycle-related pathways. Our results identify human cortical neural precursor cells as a direct ZIKV target. In addition, we establish a tractable experimental model system to investigate the impact and mechanism of ZIKV on human brain development and provide a platform to screen therapeutic compounds.

Fat mass and obesity-associated gene (FTO) is a member of the Fe (II)- and oxoglutarate-dependent AlkB dioxygenase family and is linked to both obesity and intellectual disability. The role of FTO in neurodevelopment and neurogenesis, however, remains largely unknown. Here we show that FTO is expressed in adult neural stem cells and neurons and displays dynamic expression during postnatal neurodevelopment. The loss of FTO leads to decreased brain size and body weight. We find that FTO deficiency could reduce the proliferation and neuronal differentiation of adult neural stem cells in vivo, which leads to impaired learning and memory. Given the role of FTO as a demethylase of N6-methyladenosine (m6A), we went on to perform genome-wide m6A profiling and observed dynamic m6A modification during postnatal neurodevelopment. The loss of FTO led to the altered expression of several key components of the brain derived neurotrophic factor pathway that were marked by m6A. These results together suggest FTO plays important roles in neurogenesis, as well as in learning and memory.

Methionine aminopeptidase (MetAP) catalyzes the hydrolytic cleavage of the N-terminal methionine from newly synthesized polypeptides. The extent of methionyl removal from a protein is dictated by its N-terminal peptide sequence. Earlier studies revealed that MetAPs require amino acids containing small side chains (e.g., Gly, Ala, Ser, Cys, Pro, Thr, and Val) as the P1' residue, but their specificity at positions P2' and beyond remains incompletely defined. In this work, the substrate specificities of Escherichia coli MetAP1, human MetAP1, and human MetAP2 were systematically profiled by screening against a combinatorial peptide library and kinetic analysis of individually synthesized peptide substrates. Our results show that although all three enzymes require small residues at the P1' position, they have differential tolerance for Val and Thr at this position. The catalytic activity of human MetAP2 toward Met-Val peptides is consistently two orders of magnitude higher than that of MetAP1, suggesting that MetAP2 is responsible for processing proteins containing N-terminal Met-Val and Met-Thr sequences in vivo. At positions P2' to P5', all three MetAPs have broad specificity, but are poorly active toward peptides containing a proline at the P2' position. In addition, the human MetAPs disfavor acidic residues at the P2' to P5' positions. The specificity data have allowed us to formulate a simple set of rules that can reliably predict the N-terminal processing of E. coli and human proteins. KeywordsMethionine aminopeptidase; N-terminal processing; substrate specificity; kinetics; peptide library Ribosomal protein synthesis is universally initiated with methionine (in eukaryotic cytoplasm) or N-formylmethionine (in prokaryotes, mitochondria, and chloroplasts). During protein maturation, the N-formyl group is removed by peptide deformylase, leaving methionine with a free NH 2 group (1). Subsequently, the initiator methionine is removed from many but not all of the proteins by methionine aminopeptidase(s) (MetAPs). For example, in a cytosolic extract of Escherichia coli, only 40% of the polypeptides retain the initiator methionine, whereas the majority of the polypeptides display alanine, serine, or threonine at their N-termini (2). There are two types of MetAPs, MetAP1 and MetAP2.

SUMMARY Zika virus (ZIKV) directly infects neural progenitors and impairs their proliferation. How ZIKV interacts with the host molecular machinery to impact neurogenesis in vivo is not well understood. Here, by systematically introducing individual proteins encoded by ZIKV into the embryonic mouse cortex, we show that expression of ZIKV-NS2A, but not Dengue virus (DENV)-NS2A, leads to reduced proliferation and premature differentiation of radial glial cells, and aberrant positioning of newborn neurons. Mechanistically, in vitro mapping of protein-interactomes and biochemical analysis suggest interactions between ZIKA-NS2A and multiple adherens junction complex (AJ) components. Functionally, ZIKV-NS2A, but not DENV-NS2A, destabilizes the AJ complex, resulting in impaired AJ formation and aberrant radial glial fiber scaffolding in the embryonic mouse cortex. Similarly, ZIKA-NS2A, but not DENV-NS2A, reduces radial glial cell proliferation and causes AJ deficits in human forebrain organoids. Together, our results reveal pathogenic mechanisms underlying ZIKV infection in the developing mammalian brain.

Background N6-methyladenosine (m6A) modification is known to impact many aspects of RNA metabolism, including mRNA stability and translation, and is highly prevalent in the brain. Results We show that m6A modification displays temporal and spatial dynamics during neurodevelopment and aging. Genes that are temporally differentially methylated are more prone to have mRNA expression changes and affect many pathways associated with nervous system development. Furthermore, m6A shows a distinct tissue-specific methylation profile, which is most pronounced in the hypothalamus. Tissue-specific methylation is associated with an increase in mRNA expression and is associated with tissue-specific developmental processes. During the aging process, we observe significantly more m6A sites as age increases, in both mouse and human. We show a high level of overlap between mouse and human; however, humans at both young and old ages consistently show more m6A sites compared to mice. Differential m6A sites are found to be enriched in alternative untranslated regions of genes that affect aging-related pathways. These m6A sites are associated with a strong negative effect on mRNA expression. We also show that many Alzheimer-related transcripts exhibit decreased m6A methylation in a mouse model of Alzheimer’s disease, which is correlated with reduced protein levels. Conclusions Our results suggest that m6A exerts a critical function in both early and late brain development in a spatio-temporal fashion. Furthermore, m6A controls protein levels of key genes involved in Alzheimer’s disease-associated pathways, suggesting that m6A plays an important role in aging and neurodegenerative disease.