Influenza A viruses (IAVs) are a major global health threat and in the future, may cause the next pandemic. Although studies have partly uncovered the molecular mechanism of IAV–host interaction, it requires further research. In this study, we explored the roles of transportin-3 (TNPO3) in IAV infection. We found that TNPO3-deficient cells inhibited infection with four different IAV strains, whereas restoration of TNPO3 expression in knockout (KO) cells restored IAV infection. TNPO3 overexpression in wild-type (WT) cells promoted IAV infection, suggesting that TNPO3 is involved in the IAV replication. Furthermore, we found that TNPO3 depletion restrained the uncoating in the IAV life cycle, thereby inhibiting the process of viral ribonucleoprotein (vRNP) entry into the nucleus. However, KO of TNPO3 did not affect the virus attachment, endocytosis, or endosomal acidification processes. Subsequently, we found that TNPO3 can colocalize and interact with viral proteins M1 and M2. Taken together, the depletion of TNPO3 inhibits IAV uncoating, thereby inhibiting IAV replication. Our study provides new insights and potential therapeutic targets for unraveling the mechanism of IAV replication and treating influenza disease.

The ectopic overexpression of foreign genes in animal genomes is an important strategy for gain-of-function study and establishment of transgenic animal models. Previous studies showed that two loci (Rosa26 and pH11) were identified as safe harbor locus in pig genomes, which means foreign genes can be integrated into this locus for stable expression. Moreover, integration of a transgene may interfere with the endogenous gene expression of the target locus after the foreign fragments are inserted. Here, we provide a new strategy for efficient transgene knock-in in the endogenous GAPDH gene via CRISPR/Cas9 mediated homologous recombination. This strategy has no influence on the expression of the endogenous GAPDH gene. Thus, the GAPDH locus is a new alternative safe harbor locus in the pig genome for foreign gene knock-ins. This strategy is promising for agricultural breeding and biomedical model applications.

Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic flavivirus that causes encephalitis and reproductive disorders in mammalian species. However, key host genes involved in the JEV life cycle and cell death are poorly understood. Here, we designed 85,674 single guide RNAs (sgRNAs) targeting 17,743 protein-coding genes, 11,053 long ncRNAs (lncRNAs), and 551 microRNAs (miRNAs) in the porcine genome, and subsequently developed a porcine sgRNA library and genome-scale CRISPR/Cas9 knockout (PigGeCKO) system. These sgRNAs were delivered into porcine kidney-15 (PK-15) cells that constitutively express Cas9, positive selection screening of the resulting PigGeCKO cell collection for resistance to JEV-induced cell death led to the identification of several previously unreported genes required for JEV infection. We conducted follow-up studies to verify the dependency of JEV on these genes, and identified functional contributions for six of the many candidate JEV-related host genes, including an endoplasmic reticulum membrane protein complex subunit 3 (EMC3) and calreticulin (CALR). Additionally, we identified that four genes associated with heparan sulfate proteoglycans (HSPGs) metabolism, specifically those responsible for HSPG sulfurylation, facilitated JEV entry into PK-15 cells. Thus, beyond our development of the largest CRISPR-based functional genomic screening platform for pig research to date, this work deepens our basic understanding of flavivirus infection and identifies multiple potentially vulnerable targets for the development of medical and breeding technologies to prevent and treat diseases caused by Japanese encephalitis virus.