RSV Promotes Epithelial Neuroendocrine Phenotype Differentiation through NODAL Signaling Pathway.

BACKGROUND: Respiratory syncytial virus (RSV) infects infants and children, predisposing them to development of asthma during adulthood. Epithelial neuroendocrine phenotypes may be associated with development of asthma. This study hopes to ascertain if RSV infection promotes epithelial neuroendocrine phenotypes through the NODAL signaling pathway. METHODS: The GSE6802 data set was obtained from the GEO database, and the differential genes were analyzed using the R language. An in vitro model was constructed with RSV infected human respiratory epithelial cells, and then real-time qPCR and immunofluorescence were used to detect the expression of different epithelial biomarkers and airway neuropeptides. The acute and chronic infection model of RSV infection was established by intranasal injection of RSV into guinea pigs. Immunohistochemistry and Western blot were used to detect the expression of pulmonary neuroendocrine cells markers ENO2 and neuropeptides. RESULTS: The expression levels of ENO2, SP, CGRP, and NODAL/ACTRII were significantly higher in the RSV infection group than those of the control group, which were abrogated by siRNA-NODAL. In vivo, we found that the expression levels of ENO2, SP, and CGRP were significantly higher than that of the control group. CONCLUSION: RSV promotes epithelial neuroendocrine phenotypes through the NODAL signaling pathway.

Maternal and zygotic activin signaling promotes adequate pattern and differentiation of mesoderm through regulation of pluripotency genes during zebrafish development.

To investigate the role of maternal Activin-like factors in the preservation of stemness and mesendoderm induction, their effects were promoted and inhibited using synthetic human Activin A or SB-505124 treatments, respectively, before the maternal to zygotic transition (MZT). To study the role of zygotic Activin-like factors, SB-505124 treatment was also used after the MZT. Promoting the signaling intensity of maternal Activin-like factors led to premature differentiation, loss of stemness, and no mesendoderm malformation, while its alleviation delayed the differentiation and caused various malformations. Inhibition of the zygotic Activin-like factors was associated with suppressing the ndr1, ndr2, oct4 (pou5f3), mycb and notail transcription as well as differentiation retardation at the oblong stage, and a broad spectrum of anomalies in a dose-dependent manner. Together, promoting the signal intensity of maternal Activin-like factors drove development along with mesendodermal differentiation, while suppression of the maternal or zygotic ones maintained the pluripotent state and delayed differentiation.

Nr5a homologues in the ricefield eel Monopterus albus: Alternative splicing, tissue-specific expression, and differential roles on the activation of cyp19a1a promoter in vitro.

Nr5a (Fushi tarazu factor 1, Ftz-F1) homologues belong to the nuclear receptor superfamily, and are involved in the regulation of reproduction in vertebrates. Four genes encoding Nr5a homologues were present in the genome of ricefield eel, which are designated as nr5a1a, nr5a1b, nr5a2, and nr5a5 in the present study. Alternatively spliced transcripts were identified for nr5a1a and nr5a1b genes. Sequence analysis indicated that nr5a5 is possibly a paralog of nr5a2, and nr5a1b is lost during evolution in some teleosts including tilapia and medaka. Ricefield eel nr5a genes exhibit tissue-specific expression patterns, with nr5a1a and nr5a1b resembling that of the SF-1/Ad4BP (NR5A1) subfamily, and nr5a2 and nr5a5 resembling that of the NR5A2/LRH/FTF subfamily. Transcriptomic analysis revealed parallel expression profiles of nr5a1a, foxl2, and cyp19a1a in ovarian follicles during vitellogenesis, with peak values at the late vitellogenic stage. Real-time PCR indicated that the expression levels of nr5a1a and foxl2 in gonads were decreased significantly during the sexual transition from female to the late intersexual stage. In vitro transient transfection assay showed that Nr5a1a up-regulated ricefield eel cyp19a1a promoter activities synergistically with Foxl2. However, Nr5a1b, Nr5a2, and Nr5a5 could neither activate ricefield eel cyp19a1a promoter alone nor enhance the stimulatory effects of Foxl2 on cyp19a1a promoter activities. Collectively, the above data suggest that Nr5a homologues may have diverse and differential roles in the tissues of ricefield eels. The up-regulation of gonadal nr5a1a and foxl2 during vitellogenesis may be important for the ovarian development whereas their down-regulation during the sexual transition period may be important for the sex change process of ricefield eels, possibly through the regulation of cyp19a1a gene expression.

The effect of Activin pathway modulation on the expression of both pluripotency and differentiation markers during early zebrafish development compared with other vertebrates.

Activin-like factors control many developmental processes, including pluripotency maintenance and differentiation. Although Activin-like factors' action in mesendoderm induction has been demonstrated in zebrafish, their involvement in preserving the stemness remains unknown. To investigate the role of maternal Activin-like factors, their effects were promoted or blocked using synthetic human Activin A or SB-431542 treatments respectively until the maternal to zygotic transition. To study the role of zygotic Activin-like factors, SB-431542 treatment was also applied after the maternal to zygotic transition. The effect of the pharmacological modulations of the Activin/Smad pathway was then studied on the mRNA expressions of the ndr1, ndr2, tbxta (no tail/ntl) as the differentiation index, mych, nanog, and oct4 (pou5f3) as the pluripotency markers of the zebrafish embryonic cells as well as sox17 as a definitive endoderm marker. Expression of the target genes was measured at the 16-cell, 256-cell, 1K-cell, oblong, dome, and shield stages using the real-time quantitative polymerase chain reaction (RT-qPCR). Activation of the maternal Activin signaling pathway led to an increase in zygotic expression of the tbxta, particularly marked at the oblong stage. In other words, promotion of the maternal Activin/Smad pathway induced differentiation by advancing the major peaks of ndr1 and nanog, thereby eliciting tbxta expression. Whereas suppression of the maternal or zygotic Activin/Smad pathway sustained the pluripotency by preventing the major peaks of ndr1 and nanog as well as tbxta encoding.

The pattern of nodal morphogen signaling is shaped by co-receptor expression.

Embryos must communicate instructions to their constituent cells over long distances. These instructions are often encoded in the concentration of signals called morphogens. In the textbook view, morphogen molecules diffuse from a localized source to form a concentration gradient, and target cells adopt fates by measuring the local morphogen concentration. However, natural patterning systems often incorporate numerous co-factors and extensive signaling feedback, suggesting that embryos require additional mechanisms to generate signaling patterns. Here, we examine the mechanisms of signaling pattern formation for the mesendoderm inducer Nodal during zebrafish embryogenesis. We find that Nodal signaling activity spans a normal range in the absence of signaling feedback and relay, suggesting that diffusion is sufficient for Nodal gradient formation. We further show that the range of endogenous Nodal ligands is set by the EGF-CFC co-receptor Oep: in the absence of Oep, Nodal activity spreads to form a nearly uniform distribution throughout the embryo. In turn, increasing Oep levels sensitizes cells to Nodal ligands. We recapitulate these experimental results with a computational model in which Oep regulates the diffusive spread of Nodal ligands by setting the rate of capture by target cells. This model predicts, and we confirm in vivo, the surprising observation that a failure to replenish Oep transforms the Nodal signaling gradient into a travelling wave. These results reveal that patterns of Nodal morphogen signaling are shaped by co-receptor-mediated restriction of ligand spread and sensitization of responding cells.

Basement membrane remodelling regulates mouse embryogenesis.

Tissue sculpting during development has been attributed mainly to cellular events through processes such as convergent extension or apical constriction1,2. However, recent work has revealed roles for basement membrane remodelling in global tissue morphogenesis3-5. Upon implantation, the epiblast and extraembryonic ectoderm of the mouse embryo become enveloped by a basement membrane. Signalling between the basement membrane and these tissues is critical for cell polarization and the ensuing morphogenesis6,7. However, the mechanical role of the basement membrane in post-implantation embryogenesis remains unknown. Here we demonstrate the importance of spatiotemporally regulated basement membrane remodelling during early embryonic development. Specifically, we show that Nodal signalling directs the generation and dynamic distribution of perforations in the basement membrane by regulating the expression of matrix metalloproteinases. This basement membrane remodelling facilitates embryo growth before gastrulation. The establishment of the anterior-posterior axis8,9 further regulates basement membrane remodelling by localizing Nodal signalling-and therefore the activity of matrix metalloproteinases and basement membrane perforations-to the posterior side of the embryo. Perforations on the posterior side are essential for primitive-streak extension during gastrulation by rendering the basement membrane of the prospective primitive streak more prone to breaching. Thus spatiotemporally regulated basement membrane remodelling contributes to the coordination of embryo growth, morphogenesis and gastrulation.

Nodal regulates ovarian functions in zebrafish.

Nodal, a member of the transforming growth factor-ß (TGF-ß) superfamily, plays critical roles during embryo development. Several studies suggest that Nodal also regulates reproduction. The objective of this study was to investigate if Nodal is expressed in zebrafish ovary and if it is involved in the regulation of ovarian functions. Using real-time PCR, we detected two Nodal homologs, nodal-related (ndr)1, and ndr2 in zebrafish ovarian follicles. We further compared the mRNA levels of ndr1, ndr2, and their receptors between maturational incompetent early vitellogenic follicles (stage IIIa) and mid- to late-vitellogenic follicles (stage IIIb) which are capable of undergoing maturation when they are induced by hormones. We found that mRNAs for ndr1 and ndr2, as well as a type I receptor, acvr1ba, were significantly increased in follicular cells isolated from stage IIIb follicles. In primary cultures of ovarian follicular cells, treatment with recombinant human Nodal inhibited cell proliferation. On the other hand, Nodal increased the mRNA levels of two steroidogenic enzymes hsd3b2 and cyp17a1, as well as paqr8, which encodes the membrane progestin receptor-ß (mPR-ß). Conversely, knockdown of ndr1 and ndr2 using siRNAs decreased the mRNA levels of hsd3b2, cyp17a1, and paqr8. Finally, treatment of Nodal significantly induced oocyte maturation. Taken together, these findings suggest that Nodal exerts multiple effects on zebrafish ovary to regulate follicle growth, steroidogenesis, and oocyte maturation.

Naïve human pluripotent stem cells respond to Wnt, Nodal and LIF signalling to produce expandable naïve extra-embryonic endoderm.

Embryonic stem cells (ESCs) exist in at least two states that transcriptionally resemble different stages of embryonic development. Naïve ESCs resemble peri-implantation stages and primed ESCs the pre-gastrulation epiblast. In mouse, primed ESCs give rise to definitive endoderm in response to the pathways downstream of Nodal and Wnt signalling. However, when these pathways are activated in naïve ESCs, they differentiate to a cell type resembling early primitive endoderm (PrE), the blastocyst-stage progenitor of the extra-embryonic endoderm. Here, we apply this context dependency to human ESCs, showing that activation of Nodal and Wnt signalling drives the differentiation of naïve pluripotent cells toward extra-embryonic PrE, or hypoblast, and these can be expanded as an in vitro model for naïve extra-embryonic endoderm (nEnd). Consistent with observations made in mouse, human PrE differentiation is dependent on FGF signalling in vitro, and we show that, by inhibiting FGF receptor signalling, we can simplify naïve pluripotent culture conditions, such that the inhibitor requirements closer resemble those used in mouse. The expandable nEnd cultures reported here represent stable extra-embryonic endoderm, or human hypoblast, cell lines.This article has an associated 'The people behind the papers' interview.

Aplnra/b Sequentially Regulate Organ Left-Right Patterning via Distinct Mechanisms.

The G protein-coupled receptor APJ/Aplnr has been widely reported to be involved in heart and vascular development and disease, but whether it contributes to organ left-right patterning is largely unknown. Here, we show that in zebrafish, aplnra/b coordinates organ LR patterning in an apela/apln ligand-dependent manner using distinct mechanisms at different stages. During gastrulation and early somitogenesis, aplnra/b loss of function results in heart and liver LR asymmetry defects, accompanied by disturbed KV/cilia morphogenesis and disrupted left-sided Nodal/spaw expression in the LPM. In this process, only aplnra loss of function results in KV/cilia morphogenesis defect. In addition, only apela works as the early endogenous ligand to regulate KV morphogenesis, which then contributes to left-sided Nodal/spaw expression and subsequent organ LR patterning. The aplnra-apela cascade regulates KV morphogenesis by enhancing the expression of foxj1a, but not fgf8 or dnh9, during KV development. At the late somite stage, both aplnra and aplnrb contribute to the expression of lft1 in the trunk midline but do not regulate KV formation, and this role is possibly mediated by both endogenous ligands, apela and apln. In conclusion, our study is the first to identify a role for aplnra/b and their endogenous ligands apela/apln in LR patterning, and it clarifies the distinct roles of aplnra-apela and aplnra/b-apela/apln in orchestrating organ LR patterning.

Role of Nodal signalling in testis development and initiation of testicular cancer.

Testicular development from the initially bipotential gonad is a tightly regulated process involving a complex signalling cascade to ensure proper sequential expression of signalling factors and secretion of steroid hormones. Initially, Sertoli cell specification facilitates differentiation of the steroidogenic fetal Leydig cells and establishment of the somatic niche, which is critical in supporting the germ cell population. Impairment of the somatic niche during fetal life may lead to development of male reproductive disorders, including arrest of gonocyte differentiation, which is considered the first step in the testicular cancer pathogenesis. In this review, we will outline the signalling pathways involved in fetal testis development focusing on the Nodal pathway, which has recently been implicated in several aspects of testicular differentiation in both mouse and human studies. Nodal signalling plays important roles in germ cell development, including regulation of pluripotency factor expression, proliferation and survival. Moreover, the Nodal pathway is involved in establishment of the somatic niche, including formation of seminiferous cords, steroidogenesis and Sertoli cell function. In our outline of fetal testis development, important differences between human and mouse models will be highlighted to emphasise that information obtained from mouse studies cannot always be directly translated to humans. Finally, the implications of dysregulated Nodal signalling in development of the testicular cancer precursor, germ cell neoplasia in situ, and testicular dysgenesis will be discussed - none of which arise in rodents, emphasising the importance of human models in the effort to increase our understanding of origin and early development of these disorders.

Nodal and BMP dispersal during early zebrafish development.

The secreted TGF-ß superfamily signals Nodal and BMP coordinate the patterning of vertebrate embryos. Nodal specifies endoderm and mesoderm during germ layer formation, and BMP specifies ventral fates and patterns the dorsal/ventral axis. Five major models have been proposed to explain how the correct distributions of Nodal and BMP are achieved within tissues to orchestrate embryogenesis: source/sink, transcriptional determination, relay, self-regulation, and shuttling. Here, we discuss recent experiments probing these signal dispersal models, focusing on early zebrafish development.

Conserved regulation of Nodal-mediated left-right patterning in zebrafish and mouse.

Nodal is the major effector of left-right axis development. In mice, Nodal forms heterodimers with Gdf1 and is inhibited by Cerl2/Dand5 at the node, and by Lefty1 in the lateral plate mesoderm (LPM). Studies in zebrafish have suggested some parallels, but also differences, between left-right patterning in mouse and zebrafish. To address these discrepancies, we generated single and double zebrafish mutants for southpaw (spaw, the Nodal ortholog), dand5 and lefty1, and performed biochemical and activity assays with Spaw and Vg1/Gdf3 (the Gdf1 ortholog). Contrary to previous findings, spaw mutants failed to initiate spaw expression in the LPM, and asymmetric heart looping was absent, similar to mouse Nodal mutants. In blastoderm assays, Vg1 and Spaw were interdependent for target gene induction, and contrary to previous results, formed heterodimers. Loss of Dand5 or Lefty1 caused bilateral spaw expression, similar to mouse mutants, and Lefty1 was replaceable with a uniform Nodal signaling inhibitor. Collectively, these results indicate that Dand5 activity biases Spaw-Vg1 heterodimer activity to the left, Spaw around Kupffer's vesicle induces the expression of spaw in the LPM and global Nodal inhibition maintains the left bias of Spaw activity, demonstrating conservation between zebrafish and mouse mechanisms of left-right patterning.

Long-Range Signaling Activation and Local Inhibition Separate the Mesoderm and Endoderm Lineages.

Specification of the three germ layers by graded Nodal signaling has long been seen as a paradigm for patterning through a single morphogen gradient. However, by exploiting the unique properties of the zebrafish embryo to capture the dynamics of signaling and cell fate allocation, we now demonstrate that Nodal functions in an incoherent feedforward loop, together with Fgf, to determine the pattern of endoderm and mesoderm specification. We show that Nodal induces long-range Fgf signaling while simultaneously inducing the cell-autonomous Fgf signaling inhibitor Dusp4 within the first two cell tiers from the margin. The consequent attenuation of Fgf signaling in these cells allows specification of endoderm progenitors, while the cells further from the margin, which receive Nodal and/or Fgf signaling, are specified as mesoderm. This elegant model demonstrates the necessity of feedforward and feedback interactions between multiple signaling pathways for providing cells with temporal and positional information.

Translational co-regulation of a ligand and inhibitor by a conserved RNA element.

In many organisms, transcriptional and post-transcriptional regulation of components of pathways or processes has been reported. However, to date, there are few reports of translational co-regulation of multiple components of a developmental signaling pathway. Here, we show that an RNA element which we previously identified as a dorsal localization element (DLE) in the 3'UTR of zebrafish nodal-related1/squint (ndr1/sqt) ligand mRNA, is shared by the related ligand nodal-related2/cyclops (ndr2/cyc) and the nodal inhibitors, lefty1 (lft1) and lefty2 mRNAs. We investigated the activity of the DLEs through functional assays in live zebrafish embryos. The lft1 DLE localizes fluorescently labeled RNA similarly to the ndr1/sqt DLE. Similar to the ndr1/sqt 3'UTR, the lft1 and lft2 3'UTRs are bound by the RNA-binding protein (RBP) and translational repressor, Y-box binding protein 1 (Ybx1), whereas deletions in the DLE abolish binding to Ybx1. Analysis of zebrafish ybx1 mutants shows that Ybx1 represses lefty1 translation in embryos. CRISPR/Cas9-mediated inactivation of human YBX1 also results in human NODAL translational de-repression, suggesting broader conservation of the DLE RNA element/Ybx1 RBP module in regulation of Nodal signaling. Our findings demonstrate translational co-regulation of components of a signaling pathway by an RNA element conserved in both sequence and structure and an RBP, revealing a 'translational regulon'.

Toddler signaling regulates mesodermal cell migration downstream of Nodal signaling.

Toddler/Apela/Elabela is a conserved secreted peptide that regulates mesendoderm development during zebrafish gastrulation. Two non-exclusive models have been proposed to explain Toddler function. The 'specification model' postulates that Toddler signaling enhances Nodal signaling to properly specify endoderm, whereas the 'migration model' posits that Toddler signaling regulates mesendodermal cell migration downstream of Nodal signaling. Here, we test key predictions of both models. We find that in toddler mutants Nodal signaling is initially normal and increasing endoderm specification does not rescue mesendodermal cell migration. Mesodermal cell migration defects in toddler mutants result from a decrease in animal pole-directed migration and are independent of endoderm. Conversely, endodermal cell migration defects are dependent on a Cxcr4a-regulated tether of the endoderm to mesoderm. These results suggest that Toddler signaling regulates mesodermal cell migration downstream of Nodal signaling and indirectly affects endodermal cell migration via Cxcr4a-signaling.

Xenopus pitx3 target genes lhx1 and xnr5 are identified using a novel three-fluor flow cytometry-based analysis of promoter activation and repression.

BACKGROUND: Pitx3 plays a well understood role in directing development of lens, muscle fiber, and dopaminergic neurons; however, in Xenopus laevis, it may also play a role in early gastrulation and somitogenesis. Potential downstream targets of pitx3 possess multiple binding motifs that would not be readily accessible by conventional promoter analysis. RESULTS: We isolated and characterized pitx3 target genes lhx1 and xnr5 using a novel three-fluor flow cytometry tool that was designed to dissect promoters with multiple binding sites for the same transcription factor. This approach was calibrated using a known pitx3 target gene, Tyrosine hydroxylase. CONCLUSIONS: We demonstrate how flow cytometry can be used to detect gene regulatory changes with exquisite precision on a cell-by-cell basis, and establish that in HEK293 cells, pitx3 directly activates lhx1 and represses xnr5. Developmental Dynamics 246:657-669, 2017. © 2017 Wiley Periodicals, Inc.

p38 MAPK as an essential regulator of dorsal-ventral axis specification and skeletogenesis during sea urchin development: a re-evaluation.

Dorsal-ventral axis formation in the sea urchin embryo relies on the asymmetrical expression of the TGFß Nodal. The p38-MAPK pathway has been proposed to be essential for dorsal-ventral axis formation by acting upstream of nodal expression. Here, we report that, in contrast to previous studies that used pharmacological inhibitors of p38, manipulating the activity of p38 by genetic means has no obvious impact on morphogenesis. Instead, we discovered that p38 inhibitors strongly disrupt specification of all germ layers by blocking signalling from the Nodal receptor and by interfering with the ERK pathway. Strikingly, while expression of a mutant p38 that is resistant to SB203580 did not rescue dorsal-ventral axis formation or skeletogenesis in embryos treated with this inhibitor, expression of mutant Nodal receptors that are resistant to SB203580 fully restored nodal expression in SB203580-treated embryos. Taken together, these results establish that p38 activity is not required for dorsal-ventral axis formation through nodal expression nor for skeletogenesis. Our results prompt a re-evaluation of the conclusions of several recent studies that linked p38 activity to dorsal-ventral axis formation and to patterning of the skeleton.

Nodal signalling in Xenopus: the role of Xnr5 in left/right asymmetry and heart development.

Nodal class TGF-ß signalling molecules play essential roles in establishing the vertebrate body plan. In all vertebrates, nodal family members have specific waves of expression required for tissue specification and axis formation. In Xenopus laevis, six nodal genes are expressed before gastrulation, raising the question of whether they have specific roles or act redundantly with each other. Here, we examine the role of Xnr5. We find it acts at the late blastula stage as a mesoderm inducer and repressor of ectodermal gene expression, a role it shares with Vg1. However, unlike Vg1, Xnr5 depletion reduces the expression of the nodal family member xnr1 at the gastrula stage. It is also required for left/right laterality by controlling the expression of the laterality genes xnr1, antivin (lefty) and pitx2 at the tailbud stage. In Xnr5-depleted embryos, the heart field is established normally, but symmetrical reduction in Xnr5 levels causes a severely stunted midline heart, first evidenced by a reduction in cardiac troponin mRNA levels, while left-sided reduction leads to randomization of the left/right axis. This work identifies Xnr5 as the earliest step in the signalling pathway establishing normal heart laterality in Xenopus.

Cilia are required for asymmetric nodal induction in the sea urchin embryo.

BACKGROUND: Left-right (LR) organ asymmetries are a common feature of metazoan animals. In many cases, laterality is established by a conserved asymmetric Nodal signaling cascade during embryogenesis. In most vertebrates, asymmetric nodal induction results from a cilia-driven leftward fluid flow at the left-right organizer (LRO), a ciliated epithelium present during gastrula/neurula stages. Conservation of LRO and flow beyond the vertebrates has not been reported yet. RESULTS: Here we study sea urchin embryos, which use nodal to establish larval LR asymmetry as well. Cilia were found in the archenteron of embryos undergoing gastrulation. Expression of foxj1 and dnah9 suggested that archenteron cilia were motile. Cilia were polarized to the posterior pole of cells, a prerequisite of directed flow. High-speed videography revealed rotating cilia in the archenteron slightly before asymmetric nodal induction. Removal of cilia through brief high salt treatments resulted in aberrant patterns of nodal expression. Our data demonstrate that cilia - like in vertebrates - are required for asymmetric nodal induction in sea urchin embryos. CONCLUSIONS: Based on these results we argue that the anterior archenteron represents a bona fide LRO and propose that cilia-based symmetry breakage is a synapomorphy of the deuterostomes.

Extracellular interactions and ligand degradation shape the nodal morphogen gradient.

The correct distribution and activity of secreted signaling proteins called morphogens is required for many developmental processes. Nodal morphogens play critical roles in embryonic axis formation in many organisms. Models proposed to generate the Nodal gradient include diffusivity, ligand processing, and a temporal activation window. But how the Nodal morphogen gradient forms in vivo remains unclear. Here, we have measured in vivo for the first time, the binding affinity of Nodal ligands to their major cell surface receptor, Acvr2b, and to the Nodal inhibitor, Lefty, by fluorescence cross-correlation spectroscopy. We examined the diffusion coefficient of Nodal ligands and Lefty inhibitors in live zebrafish embryos by fluorescence correlation spectroscopy. We also investigated the contribution of ligand degradation to the Nodal gradient. We show that ligand clearance via degradation shapes the Nodal gradient and correlates with its signaling range. By computational simulations of gradient formation, we demonstrate that diffusivity, extra-cellular interactions, and selective ligand destruction collectively shape the Nodal morphogen gradient.