A newly identified coronavirus, 2019-nCoV, has been posing significant threats to public health since December 2019. ACE2, the host cell receptor for severe acute respiratory syndrome coronavirus (SARS), has recently been demonstrated in mediating 2019-nCoV infection. Interestingly, besides the respiratory system, substantial proportion of SARS and 2019-nCoV patients showed signs of various degrees of liver damage, the mechanism and implication of which have not yet been determined. Here, we performed an unbiased evaluation of cell type specific expression of ACE2 in healthy liver tissues using single cell RNA-seq data of two independent cohorts, and identified specific expression in cholangiocytes. The results indicated that virus might directly bind to ACE2 positive cholangiocytes but not necessarily hepatocytes. This finding suggested the liver abnormalities of SARS and 2019-nCoV patients may not be due to hepatocyte damage, but cholangiocyte dysfunction and other causes such as drug induced and systemic inflammatory response induced liver injury. Our findings indicate that special care of liver dysfunction should be installed in treating 2019-nCoV patients during the hospitalization and shortly after cure.

N6 methylation at adenosine 1832 (m⁶A1832) of mammalian 18S rRNA, occupying a critical position within the decoding center, is modified by a conserved methyltransferase, METTL5. Here, we find that METTL5 shows strong substrate preference toward the 18S A1832 motif but not the other reported m⁶A motifs. Comparison with a yeast ribosome structural model unmodified at this site indicates that the modification may facilitate mRNA binding by inducing conformation changes in the mammalian ribosomal decoding center. METTL5 promotes p70-S6K activation and proper translation initiation, and the loss of METTL5 significantly reduces the abundance of polysome. METTL5 expression is elevated in breast cancer patient samples and is required for growth of several breast cancer cell lines. We further find that Caenorhabditis elegans lacking the homolog metl-5 develop phenotypes known to be associated with impaired translation. Altogether, our findings uncover critical and conserved roles of METTL5 in the regulation of translation.

Coronavirus disease 2019 (COVID-19) has become a worldwide threat to humans, and neutralizing antibodies have therapeutic potential. We have purified more than 1,000 memory B cells specific to SARS-CoV-2 S1 or its RBD (receptor binding domain) and obtain 729 paired heavy- and light-chain fragments. Among these, 178 antibodies test positive for antigen binding, and the majority of the top 17 binders with EC50 below 1 nM are RBD binders. Furthermore, we identify 11 neutralizing antibodies, eight of which show IC50 within 10 nM, and the best one, 414-1, with IC50 of 1.75 nM. Through epitope mapping, we find three main epitopes in RBD recognized by these antibodies, and epitope-B antibody 553-15 could substantially enhance the neutralizing abilities of most of the other antibodies. We also find that 515-5 could cross neutralize the SARS-CoV pseudovirus. Altogether, our study provides 11 potent human neutralizing antibodies for COVID-19 as therapeutic candidates.