Gain-of-function assay for SARS-CoV-2 Mpro inhibition in living cells

The main protease, Mpro, of SARS-CoV-2 is required to cleave the viral polyprotein into precise functional units for virus replication and pathogenesis. Here we demonstrate a quantitative reporter for Mpro function in living cells, in which protease inhibition by genetic or chemical methods results in strong eGFP fluorescence. This robust gain-of-function system readily distinguishes between inhibitor potencies and can be scaled-up to high-throughput platforms for drug testing.

Visualizing bovine leukemia virus (BLV)-infected cells and measuring BLV proviral loads in the milk of BLV seropositive dams

Bovine leukemia virus (BLV) infects cattle and causes serious problems for the cattle industry, worldwide. Vertical transmission of BLV occurs via in utero infection and ingestion of infected milk and colostrum. The aim of this study was to clarify whether milk is a risk factor in BLV transmission by quantifying proviral loads in milk and visualizing the infectivity of milk. We collected blood and milk from 48 dams (46 BLV seropositive dams and 2 seronegative dams) from seven farms in Japan and detected the BLV provirus in 43 blood samples (89.6%) but only 22 milk samples (45.8%) using BLV-CoCoMo-qPCR-2. Although the proviral loads in the milk tended to be lower, a positive correlation was firstly found between the proviral loads with blood and milk. Furthermore, the infectivity of milk cells with BLV was visualized ex vivo using a luminescence syncytium induction assay (LuSIA) based on CC81-GREMG cells, which form syncytia expressing enhanced green fluorescent protein (EGFP) in response to BLV Tax and Env expressions when co-cultured with BLV-infected cells. Interestingly, in addition to one BLV-infected dam with lymphoma, syncytia with EGFP fluorescence were observed in milk cells from six BLV-infected, but healthy, dams by an improved LuSIA, which was optimized for milk cells. This is the first report demonstrating the infectious capacity of cells in milk from BLV-infected dams by visualization of BLV infection ex vivo. Thus, our results suggest that milk is a potential risk factor for BLV vertical spread through cell to cell transmission.

Fluorescent Reporter Zebrafish Line for Estrogenic Compound Screening Generated Using a CRISPR/Cas9-Mediated Knock-in System

An increasing number of compounds in our diet and environment are being identified as estrogenic, causing serious and detrimental effects on human, animal, and ecosystem health. Time- and cost-effective biological tools to detect and screen these compounds with potential high-throughput capabilities are in ever-growing demand. We generated a knock-in zebrafish transgenic line with enhanced green fluorescent protein (EGFP) driven by the regulatory region upstream of vitellogenin 1 (vtg1), a well-studied biomarker for estrogenic exposure, using CRISPR/Cas9 technology. Exposure to 17β-estradiol (E2: 0–625 nM) starting at 4-h post-fertilization in dechorionated embryos resulted in the significant induction of hepatic EGFP with ≥5 nM E2 as early as 3-days post-fertilization. Concentration- and time-dependent increase in the percentage of hepatic EGFP-positive larvae and extent of fluorescence expression, categorized into 3 expression levels, were observed with E2 exposure. A strong correlation between the levels of EGFP mRNA, vtg1 mRNA, and EGFP fluorescence levels were detected. Image analysis of the area and intensity of hepatic EGFP fluorescence resulted in high-fidelity quantitative measures that could be used in automated screening applications. In addition, exposure to bisphenol A (0–30 μM) resulted in quantitative responses showing promise for the use of this transgenic line to assess estrogenic activity of endocrine-disrupting chemicals. These results demonstrate that this novel knock-in zebrafish reporter allows for distinct screening of in vivo estrogenic effects, endpoints of which can be used for laboratory testing of samples for estimation of possible human and environmental risks.

Auxin-mediated rapid degradation of selective proteins in hippocampal neurons

Genetic manipulation of protein levels is a promising approach to identify the function of a specific protein in living organisms. Previous studies demonstrated that the auxin-inducible degron (AID) strategy provides rapid and reversible degradation of various proteins in fungi and mammalian mitotic cells. In this study, we employed this technology to postmitotic neurons to address whether the AID system could be applied to the nervous system. Using adeno-associated viruses, we simultaneously introduced EGFP fused with an AID tag, and an F-box family protein, TIR1 fromOryza sativa(OsTIR1) into hippocampal neurons. In dissociated hippocampal neurons, EGFP fluorescence signals rapidly decreased when adding a plant hormone, auxin. Further, auxin-induced EGFP degradation was also observed in hippocampal acute slices. Taken together, these results open the door for neuroscientists to manipulate protein expression levels by the AID-system in a temporally-controlled manner.

198 Germline-Specific Expression of the Murine Oct4-EGFP Transgene in the Pig

The Oct4 gene is crucial for undisturbed early embryonic development and maintenance of pluripotency in the mouse. It is found in mouse pre-implantation embryos after embryonic genome activation. After gastrulation, expression is restricted to germ cells. Limited research has been performed on OCT4 expression in the domestic pig, which is a valuable large animal model in biomedicine. Previously, we generated Oct4-EGFP reporter pigs carrying the genomic sequence of the murine Oct4 gene fused to the EGFP cDNA (Nowak-Imialek et al. 2011 Stem Cells Dev. 20, 1563-1575, 10.1089/scd.2010.0399). In the present study, we used this animal model to analyse the expression profile of the murine Oct4-EGFP transgene in porcine oocytes, in vivo-derived embryos (4-cell embryos, 8- to 16-cell embryos, morulae, and blastocysts) and ovaries. We studied whether the murine Oct4-EGFP transgene mimics the expression pattern of the endogenous OCT4 protein in transgenic pigs. Immature oocytes were isolated from ovaries of Oct4-EGFP transgenic sows (n = 5) using slicing methods. For collection of porcine embryos, wild-type sows were inseminated with sperm from an Oct4-EGFP transgenic boar. Sows were sacrificed 3, 4, and 5 days after insemination, and embryos were recovered by flushing oviducts and uterus and analysed by confocal microscopy. Ovaries obtained from female animals (5–12 months) were enzymatically dissociated and analysed using flow cytometry. Immature oocytes (n = 19) showed a very low, diffuse EGFP signal in cytoplasm. Embryos up to the 4-cell stage (n = 45) did not show Oct4-EGFP transgene expression. For the first time, EGFP fluorescence was detected at the 8-cell stage (n = 29) and a strong EGFP signal was observed in 16-cell stages and morulae (n = 53). In blastocysts from Day 5 (n = 40) EGFP fluorescence was not restricted to the inner cell mass (ICM), but was also seen in the trophectoderm (TE). Expression of EGFP was not detected in ovarian cells (n = 12). Thereafter, we analysed the expression pattern of endogenous OCT4 protein by immunostaining in nontransgenic porcine oocytes and pre-implantation embryos. As in Oct4-EGFP transgenic embryos, no expression of OCT4 was observed in 4-cell embryos (n = 12). Nuclear staining first became visible at the 8-cell stage (n = 12), with a strong signal observed in 16-cell stages and morulae (n = 18). In blastocysts from Day 5 (n = 26), both ICM and TE cell nuclei showed expression of OCT4 protein. These results demonstrate that the Oct4-EGFP transgene expression pattern reproduces the endogenous OCT4 protein expression profile in porcine oocytes and pre-implantation embryos. The Oct4-EGFP transgene was first detected at the 8-cell stage, consistent with embryonic genome activation, which is initiated at the 4-cell stage. However, Oct4-EGFP expression was not detected in ovarian cells. This might be related to the very low expression pattern of the Oct4-EGFP transgene in primary oocytes. In summary, the Oct4-EGFP transgene in the pig provides a useful marker for monitoring pluripotency in pre-implantation embryos after embryonic genome activation. In ongoing experiments, we are analysing the expression profile of the Oct4-EGFP transgene and endogenous OCT4 protein in porcine pre-implantation embryos from Days 8 and 11.

A transgenic mouse model ubiquitously overexpressing Dnmt1s mRNA lacks increased protein levels

Several types of cancer are characterized by global hypomethylation accompanied by regional hypermethylation and overexpression of DNA methyltransferase (cytosine-5) 1 (Dnmt1). In addition to the established role of Dnmt1 as maintenance methyltransferase, it has been suggested that Dnmt1 might also methylate certain target sites de novo. We created a transgenic mouse model to investigate whether the overexpression of the somatic form of Dnmt1, Dnmt1s, is sufficient to cause erroneous methylation and disease. Because ubiquitous Dnmt1 overexpression has been reported to be embryonic lethal, we designed a CAG promoter-driven Cre-loxP conditional transgene containing a floxed EGFP sequence followed by the Dnmt1s coding sequence. The EGFP sequence is excised and transgenic Dnmt1s expression is activated at specific time points or in specific tissues depending on the Cre deleter strain used for cross-ins. Pronucleus injections with the Dnmt1s transgene construct resulted in six founder lines as verified by PCR, Southern blot and EGFP fluorescence. We performed cross-ins with a CMV-Cre deleter strain to clarify if ubiquitous overexpression of Dnmt1s alone causes the previously observed embryonic lethality. Unexpectedly, these cross-ins yielded viable recombined offspring that ubiquitously overexpressed Dnmt1 mRNA at tissue-dependent levels of up to 229-fold. However, the recombined offspring did not significantly overexpress Dnmt1 protein and showed no apparent signs of disease or pathological phenotype. Here, we describe the establishment of our Dnmt1s-transgenic mouse model and propose possibilities for the absence of transgenic protein.

A transgenic mouse model ubiquitously overexpressing Dnmt1s mRNA lacks increased protein levels

Several types of cancer are characterized by global hypomethylation accompanied by regional hypermethylation and overexpression of DNA methyltransferase (cytosine-5) 1 (Dnmt1). In addition to the established role of Dnmt1 as maintenance methyltransferase, it has been suggested that Dnmt1 might also methylate certain target sites de novo. We created a transgenic mouse model to investigate whether the overexpression of the somatic form of Dnmt1, Dnmt1s, is sufficient to cause erroneous methylation and disease. Because ubiquitous Dnmt1 overexpression has been reported to be embryonic lethal, we designed a CAG promoter-driven Cre-loxP conditional transgene containing a floxed EGFP sequence followed by the Dnmt1s coding sequence. The EGFP sequence is excised and transgenic Dnmt1s expression is activated at specific time points or in specific tissues depending on the Cre deleter strain used for cross-ins. Pronucleus injections with the Dnmt1s transgene construct resulted in six founder lines as verified by PCR, Southern blot and EGFP fluorescence. We performed cross-ins with a CMV-Cre deleter strain to clarify if ubiquitous overexpression of Dnmt1s alone causes the previously observed embryonic lethality. Unexpectedly, these cross-ins yielded viable recombined offspring that ubiquitously overexpressed Dnmt1 mRNA at tissue-dependent levels of up to 229-fold. However, the recombined offspring did not significantly overexpress Dnmt1 protein and showed no apparent signs of disease or pathological phenotype. Here, we describe the establishment of our Dnmt1s-transgenic mouse model and propose possibilities for the absence of transgenic protein.

Abstract MP05: Mineralocorticoid And Angiotensin II Type 1 Receptors In The Subfornical Organ Mediate Angiotensin II Hypertension In Rats

Circulating Ang II increases BP through both peripheral and central mechanisms. Activation of both AT 1 R and MR in the CNS plays a critical role in Ang II-induced hypertension. The subfornical organ (SFO) contains both MR and AT 1 R and can relay the signals of circulating Ang II to downstream nuclei such as the PVN. In this study, we evaluated the effect of intra-SFO infusion of AAV-MR-siRNA or AAV-AT 1a R-siRNA on MR or AT 1 R mRNA expression in the SFO and PVN and Ang II induced hypertension as assessed by telemetry. Two week sc infusion of Ang II at 500 ng/kg/min in Wistar rats on regular salt diet increased BP by 60~65 mmHg. This pressor effect of Ang II was largely prevented by AAV-MR-siRNA or AAV-AT 1 R-siRNA in the SFO (Figure). Ang II increased AT 1 R mRNA expression (1.7± 0.4 vs 0.8 ± 0.04 х10 -1 , p<0.05) in the SFO. Both MR- and AT 1 R-siRNA in the SFO prevented this increase (1.1 ± 0.2х10 -1 and 1.0± 0.3х10 -1 ). In contrast, Ang II decreased MR mRNA expression (3.2 ± 0.2 vs. 4.1 ± 0.2х10 -2 , p<0.05) in the SFO. Both MR- and AT 1 R-siRNA further decreased MR mRNA expression (2.7 ± 0.2 х10 -2 and 2.3 ± 0.3 х10 -2 ). In the PVN, Ang II increased AT 1 R mRNA by ~100% and MR mRNA by ~20%. Only AT 1 R-siRNA in the SFO prevented these increases in the PVN. AAV mediated eGFP fluorescence expression was observed in the SFO but not the PVN. These results suggest that circulating Ang II differentially regulates MR and AT 1 R expression in the SFO. Prevention of Ang II induced AT 1 R up-regulation by knockdown of either AT 1 R or MR suggests a MR dependent regulation of AT 1 R in the SFO. MR-AT 1 R signaling in the SFO appears to play a major role in Ang II-induced hypertension in rats. * p<0.05, vs. baseline values; a: p<0.05, vs. AAV-SCM-siRNA