Organoids-or pluripotent stem cell-derived in vitro-grown simplified mini organs-have become a tremendously important model to study human organ development and disease. To restrict the noise inherent to the heterogeneous cell mixtures derived from organoid cultures, we developed a new technique of fluorescence-assisted cell sorting (FACS) of virus-infected cerebral organoid cultures. This method still includes the advantage of growing cells in a more natural environment than traditional cell culture, but now renders samples suitable for downstream cell type-specific multi-omics analyses. The protocol starts from stem cell-derived mature brain organoids and includes steps for: preparing the culture for viral infection, production of the viral stocks, FACS sample preparation, and gating and sorting implementation. The protocol has been developed for Zika virus infection, but can be extrapolated to other viruses or fluorescent marker expression as illustrated in an alternate protocol using a single-cycle lentivirus expressing a fluorescent reporter protein. © 2018 by John Wiley & Sons, Inc.

Ronin (THAP11), a DNA-binding protein that evolved from a primordial DNA transposon by molecular domestication, recognizes a hyperconserved promoter sequence to control developmentally and metabolically essential genes in pluripotent stem cells. However, it remains unclear whether Ronin or related THAP proteins perform similar functions in development. Here, we present evidence that Ronin functions within the nascent heart as it arises from the mesoderm and forms a four-chambered organ. We show that Ronin is vital for cardiogenesis during midgestation by controlling a set of critical genes. The activity of Ronin coincided with the recruitment of its cofactor, Hcf-1, and the elevation of H3K4me3 levels at specific target genes, suggesting the involvement of an epigenetic mechanism. On the strength of these findings, we propose that Ronin activity during cardiogenesis offers a template to understand how important gene programs are sustained across different cell types within a developing organ such as the heart.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2019 has triggered an ongoing global pandemic of the severe pneumonia-like disease coronavirus disease 2019 (COVID-19)1. The development of a vaccine is likely to take at least 12-18 months, and the typical timeline for approval of a new antiviral therapeutic agent can exceed 10 years. Thus, repurposing of known drugs could substantially accelerate the deployment of new therapies for COVID-19. Here we profiled a library of drugs encompassing approximately 12,000 clinical-stage or Food and Drug Administration (FDA)-approved small molecules to identify candidate therapeutic drugs for COVID-19. We report the identification of 100 molecules that inhibit viral replication of SARS-CoV-2, including 21 drugs that exhibit dose-response relationships. Of these, thirteen were found to harbour effective concentrations commensurate with probable achievable therapeutic doses in patients, including the PIKfyve kinase inhibitor apilimod2-4 and the cysteine protease inhibitors MDL-28170, Z LVG CHN2, VBY-825 and ONO 5334. Notably, MDL-28170, ONO 5334 and apilimod were found to antagonize viral replication in human pneumocyte-like cells derived from induced pluripotent stem cells, and apilimod also demonstrated antiviral efficacy in a primary human lung explant model. Since most of the molecules identified in this study have already advanced into the clinic, their known pharmacological and human safety profiles will enable accelerated preclinical and clinical evaluation of these drugs for the treatment of COVID-19.

During implantation, the murine embryo transitions from a "quiet" into an active metabolic/proliferative state, which kick-starts the growth and morphogenesis of the post-implantation conceptus. Such transition is also required for embryonic stem cells to be established from mouse blastocysts, but the factors regulating this process are poorly understood. Here, we show that Ronin plays a critical role in the process by enabling active energy production, and the loss of Ronin results in the establishment of a reversible quiescent state in which naïve pluripotency is promoted. In addition, Ronin fine-tunes the expression of genes that encode ribosomal proteins and is required for proper tissue-scale organisation of the pluripotent lineage during the transition from blastocyst to egg cylinder stage. Thus, Ronin function is essential for governing the metabolic capacity so that it can support the pluripotent lineage's high-energy demands for cell proliferation and morphogenesis.

Genes that are key to cell identity are generally regulated by cell-type-specific enhancer elements bound by transcription factors, some of which facilitate looping to distant gene promoters. In contrast, genes that encode housekeeping functions, whose regulation is essential for normal cell metabolism and growth, generally lack interactions with distal enhancers. We find that Ronin (Thap11) assembles multiple promoters of housekeeping and metabolic genes to regulate gene expression. This behavior is analogous to how enhancers are brought together with promoters to regulate cell identity genes. Thus, Ronin-dependent promoter assemblies provide a mechanism to explain why housekeeping genes can forgo distal enhancer elements and why Ronin is important for cellular metabolism and growth control. We propose that clustering of regulatory elements is a mechanism common to cell identity and housekeeping genes but is accomplished by different factors binding distinct control elements to establish enhancer-promoter or promoter-promoter interactions, respectively.

Spinocerebellar ataxias (SCAs) are a group of genetically heterogeneous inherited neurodegenerative disorders characterized by progressive ataxia and cerebellar degeneration. Here, we used a mouse model to test a possible connection between SCA and Ronin (Thap11), a polyglutamine-containing transcriptional regulator encoded in a region of human chromosome 16q22.1 that has been genetically linked to SCA type 4. We report that transgenic expression of Ronin in mouse cerebellar Purkinje cells leads to detrimental loss of these cells and the development of severe ataxia as early as 10 weeks after birth. Mechanistically, we find that several SCA-causing genes harbor Ronin DNA-binding motifs and are transcriptionally deregulated in transgenic animals. In addition, ectopic expression of Ronin in embryonic stem cells significantly increases the protein level of Ataxin-1, the protein encoded by Atxn1, alterations of which cause SCA type 1. This increase is also seen in the cerebellum of transgenic animals, although the latter was not statistically significant. Hence, our data provide evidence for a link between Ronin and SCAs, and suggest that Ronin may be involved in the development of other neurodegenerative diseases.

SARS-CoV-2 lineages have diverged into highly prevalent variants termed "variants of concern" (VOCs). Here, we characterized emerging SARS-CoV-2 spike polymorphisms in vitro and in vivo to understand their impact on transmissibility and virus pathogenicity and fitness. We demonstrate that the substitution S:655Y, represented in the gamma and omicron VOCs, enhances viral replication and spike protein cleavage. The S:655Y substitution was transmitted more efficiently than its ancestor S:655H in the hamster infection model and was able to outcompete S:655H in the hamster model and in a human primary airway system. Finally, we analyzed a set of emerging SARS-CoV-2 variants to investigate how different sets of mutations may impact spike processing. All VOCs tested exhibited increased spike cleavage and fusogenic capacity. Taken together, our study demonstrates that the spike mutations present in VOCs that become epidemiologically prevalent in humans are linked to an increase in spike processing and virus transmission.

Human foreskin fibroblasts from a commercial source were reprogrammed into induced pluripotent stem cells to establish a clonal stem cell line, hiPSTZ16 (ISMMSi003-A). These cells show a normal karyotype and full differentiation potential in teratoma assays. The described cells provide a useful resource in combination with other iPS cell lines generated from normal human foreskin fibroblasts to study source- and reprogramming method-independent effects in downstream applications.

A fundamental principle governing organ size and function is the fine balance between cell proliferation and cell differentiation. Here, we identify RONIN (THAP11) as a key transcriptional regulator of retinal progenitor cell (RPC) proliferation. RPC-specific loss of Ronin results in a phenotype strikingly similar to that resulting from the G1- to S-phase arrest and photoreceptor degeneration observed in the Cyclin D1 null mutants. However, we determined that, rather than regulating canonical cell-cycle genes, RONIN regulates a cohort of mitochondrial genes including components of the electron transport chain (ETC), which have been recently implicated as direct regulators of the cell cycle. Coincidentally, with premature cell-cycle exit, Ronin mutants exhibited deficient ETC activity, reduced ATP levels, and increased oxidative stress that we ascribe to specific loss of subunits within complexes I, III, and IV. These data implicate RONIN as a positive regulator of mitochondrial gene expression that coordinates mitochondrial activity and cell-cycle progression.

Early mammalian embryonic cells must maintain a particularly robust DNA repair system, as mutations at this developmental point have detrimental consequences for the organism. How the repair system can be tuned to fulfill such elevated requirements is largely unknown, but it may involve transcriptional regulation. Ronin (Thap11) is a transcriptional regulator responsible for vital programs in pluripotent cells. Here, we report that this protein also modulates the DNA damage response of such cells. We show that conditional Ronin knockout sensitizes embryonic stem cells (ESCs) to UV-C-induced DNA damage in association with Atr pathway activation and G2/M arrest. Ronin binds to and regulates the genes encoding several DNA repair factors, including Gtf2h4 and Rad18, providing a potential mechanism for this phenotype. Our results suggest that the unique DNA repair requirements of the early embryo are not met by a static system, but rather via highly regulated processes.

Zika virus (ZIKV) infection during early pregnancy can cause microcephaly and associated defects at birth, but whether it can induce neurologic sequelae that appear later in life remains unclear. Using a model of the developing brain based on embryonic stem cell-derived brain organoids, we studied the impact of ZIKV infection on the DNA methylation pattern across the entire genome in selected neural cell types. The virus unexpectedly alters the DNA methylome of neural progenitors, astrocytes, and differentiated neurons at genes that have been implicated in the pathogenesis of a number of brain disorders, most prominently mental retardation and schizophrenia. Our results suggest that ZIKV infection during fetal development could lead to a spectrum of delayed-onset neuropsychiatric complications. IMPORTANCE Scientific research on human neural stem cells and cerebral organoids has confirmed the congenital neurotropic and neurodestructive nature of the Zika virus. However, the extent to which prenatal ZIKV infection is associated with more subtle brain alterations, such as epigenetic changes, remains ill defined. Here, we address the question of whether ZIKV infection induces DNA methylation changes with the potential to cause brain disorders later in life.