Plants can produce organs throughout their entire life from pluripotent stem cells located at their growing tip, the shoot apical meristem (SAM). At the time of flowering, the SAM of Arabidopsis thaliana switches fate and starts producing flowers instead of leaves. Correct timing of flowering in part determines reproductive success, and is therefore under environmental and endogenous control. How epigenetic regulation contributes to the floral transition has eluded analysis so far, mostly because of the poor accessibility of the SAM. Here we report the temporal dynamics of the chromatin modifications H3K4me3 and H3K27me3 and their correlation with transcriptional changes at the SAM in response to photoperiod-induced flowering. Emphasizing the importance of tissue-specific epigenomic analyses we detect enrichments of chromatin states in the SAM that were not apparent in whole seedlings. Furthermore, our results suggest that regulation of translation might be involved in adjusting meristem function during the induction of flowering.

The SARS-CoV-2 pandemic has led to hundreds of thousands of deaths and billions of dollars in economic damage. The immune response elicited from this virus is poorly understood. An alarming number of cases have arisen where COVID-19 patients develop complications on top of the symptoms already associated with SARS, such as thrombosis, injuries of vascular system, kidney, and liver, as well as Kawasaki disease. In this review, we have used a bioinformatics approach to elucidate the immune response triggered by SARS-CoV-2 infection in primary human lung epithelial and transformed human lung alveolar. Additionally, we have examined the potential mechanism behind several complications that have been associated with COVID-19 and determined that a specific cytokine storm is leading to excessive neutrophil recruitment. These neutrophils are directly leading to thrombosis, organ damage, and complement activation via neutrophil extracellular trap release.

ProblemEmbryo implantation depends on the interactions between the developing embryo and the maternal endometrium. Signals originating from the decidua play a critical role in the process of implantation and trophoblast invasion; however, the molecular mechanisms mediating this interaction are poorly understood. The objective of this study was to develop in vitro models that would mimic the processes of attachment, migration, and early invasion of the trophoblast.Methods of studyFirst trimester trophoblast cells (Sw.71 cells) were cultured in low attachment plates to form blastocyst‐like spheroids (BLS). Epithelial‐mesenchymal transition (EMT) characterization during BLS formation was determined by RT‐PCR and Western Blot. The two 3D in vitro culture models consist of (a) trophoblast migration: BLS cultured in suspension (b) trophoblast invasion: human endometrium stromal cells (HESC) plated in the bottom of a 96‐well plate, covered by Matrigel and BLS transferred on top. Matrigel was used to mimic the human endometrial extracellular matrix.ResultsUsing 3D cell culture systems and real‐time imaging, we are able to determine the impact of endometrial factors on trophoblast cell function. Endometrial stromal cells promote blastocyst‐like spheroid migration of trophoblast cells and invasion of the extracellular matrix.ConclusionWe report the characterization of 3D in vitro models to evaluate the interaction between endometrial cells and trophoblast during the process of migration and invasion. The models are useful tools in order to further study the molecular mechanism of embryo‐maternal uterine cells interactions.

Problem: Zika virus (ZIKV) has gained public concern for its association with microcephaly in infants born to ZIKV-infected mothers. To reach the fetus the virus must overcome the defense mechanisms provided by trophoblast cells. Additionally, in the first trimester, the integrity of the placenta is critical for fetal protection as damage to differentiating trophoblast can affect placental formation and function. We sought to investigate the effect of ZIKV infection on trophoblast cells and the factors that might increase the risk for ZIKV infection during pregnancy.Methods: First-trimester human trophoblast cells, Swan 7.1, were infected with ZIKV, herpes simplex virus-2 (HSV-2), and yellow fiver (YFV). C57BL/6 pregnant mice were infected with HSV-2, ZIKV, or coinfection. Placental viral titers were determined by RT-PCR.Results: ZIKV infection induces apoptosis in first-trimester trophoblasts and prevents differentiation of these cells. Furthermore, HSV-2 infection enhances placental sensitivity to ZIKV by enhancing the expression of TAM receptors, which facilitate ZIKV cell entry. Conclusion:These findings may explain the mechanism by which ZIKV breaches the placental barrier to access the fetus. Furthermore, our results suggest that patients with HSV-2 infection are at a higher risk for the teratogenic effects induced by ZIKV.

Decidual macrophages are in close contact with trophoblast cells during placenta development, and an appropriate crosstalk between these cellular compartments is crucial for the establishment and maintenance of a healthy pregnancy. During different phases of gestation, macrophages undergo dynamic changes to adjust to the different stages of fetal development. Trophoblast‐secreted factors are considered the main modulators responsible for macrophage differentiation and function. However, the phenotype of these macrophages induced by trophoblast‐secreted factors and the factors responsible for their polarization has not been elucidated. In this study, we characterized the phenotype and function of human trophoblast‐induced macrophages. Using in vitro models, we found that human trophoblast‐educated macrophages were CD14+CD206+CD86− and presented an unusual transcriptional profile in response to TLR4/LPS activation characterized by the expression of type I IFN‐β expression. IFN‐β further enhances the constitutive production of soluble programmed cell death ligand 1 (PD‐L1) from trophoblast cells. PD‐1 blockage inhibited trophoblast‐induced macrophage differentiation. Soluble PD‐L1 (sPD‐L1) was detected in the blood of pregnant women and increased throughout the gestation. Collectively, our data suggest the existence of a regulatory circuit at the maternal fetal interface wherein IFN‐β promotes sPD‐L1 expression/secretion by trophoblast cells, which can then initiate a PD‐L1/PD‐1‐mediated macrophage polarization toward an M2 phenotype, consequently decreasing inflammation. Macrophages then maintain the expression of sPD‐L1 by the trophoblasts through IFN‐β production induced through TLR4 ligation.

Pregnancy is a unique immunologic and microbial condition that requires an adequate level of awareness to provide a fast and protective response against pathogens as well as to maintain a state of tolerance to paternal antigens. Dysregulation of inflammatory pathways in the placenta triggered by pathogens is one of the main factors responsible for pregnancy complications. Type I IFNs are key molecules modulating immune responses at the level of the placenta and are crucial for protection of the pregnancy via their antiviral and immune modulatory properties. In this study, we elucidate the mechanisms controlling the basal expression of IFNβ and its negative feedback. Using in vitro and in vivo animal models, we found that TLR signaling maintains basal IFNβ levels through the TLR4-MyD88-independent TBK/IRF3 signaling pathway. We describe the role of the TAM receptor Axl in the regulation of IFNβ function in human and mouse trophoblast cells. The absence of TAM receptors in vivo is associated with fetal demise due to dysregulation of IFNβ expression and its pro-apoptotic downstream effectors. Collectively, our data describe a feedback signaling pathway controlling the expression and function of IFNβ in the trophoblast that is essential for an effective response during viral and microbial infections.

Barley yellow mosaic virus (BaYMV), the type species of the genus Bymovirus in the family Potyviridae in the picornavirus-like superfamily, causes a yellow mosaic disease of winter barley with significant yield losses in Europe and East Asia. Until now, infectious in vitro transcripts for the bipartite plus-sense RNA genome of any bymovirus species have not been available, rendering molecular analyses of bymovirus pathogenicity and the host resistance mechanisms difficult. In this study, we constructed the first cDNA clones of BaYMV RNA1 and RNA2, from which infectious RNA can be transcribed in vitro. Using in vitro transcripts, we showed that RNA1, which encodes eight proteins, including a viral proteinase NIa-Pro, the RNA-dependent RNA polymerase NIb, genome-linked viral protein VPg and the capsid protein CP, replicated autonomously in barley mesophyll protoplasts in the absence of RNA2 optimally at 15 degrees C, a temperature similar to the optimum for causing disease in barley fields. For systemic infection of barley plants, RNA1 alone was not sufficient and RNA2 was also required. Of the two proteins encoded on RNA2 (P1 with cysteine proteinase activity and P2 with unknown functions), P1 was essential and P2 was dispensable for systemic infectivity. The expression of both P1 and P2, but not the precursor polyprotein, together with RNA1 increased systemic infection and caused mosaic leaf symptoms. The infectious cDNA clones of BaYMV will be vital for future studies of bymovirus-host-vector interactions at the molecular level.

The phloem plays essential roles in the source-to-sink relationship and in long-distance communication, and thereby coordinates growth and development throughout the plant. Here we employed isolation of nuclei tagged in specific cell types coupled with low-input, high-throughput sequencing approaches to analyze the changes of the chromatin modifications H3K4me3 and H3K27me3 and their correlation with gene expression in the phloem companion cells (PCCs) of Arabidopsis (Arabidopsis thaliana) shoots in response to changes in photoperiod. We observed a positive correlation between changes in expression and H3K4me3 levels of genes that are involved in essential PCC functions, including regulation of metabolism, circadian rhythm, development, and epigenetic modifications. By contrast, changes in H3K27me3 signal appeared to contribute little to gene expression changes. These genomic data illustrate the complex gene-regulatory networks that integrate plant developmental and physiological processes in the PCCs. Emphasizing the importance of cell-specific analyses, we identified a previously uncharacterized MORN-motif repeat protein, MORN-MOTIF REPEAT PROTEIN REGULATING FLOWERING1 (MRF1), that was strongly up-regulated in the PCCs in response to inductive photoperiod. The mrf1 mutation delayed flowering, whereas MRF1 overexpression had the opposite effect, indicating that MRF1 acts as a floral promoter.