Wnt/beta-catenin and Fgf signaling control collective cell migration by restricting chemokine receptor expression

KIAA1199 is a secreted molecule that enhances osteoblastic stem cell migration and recruitment

Factors mediating mobilization of osteoblastic stem and progenitor cells from their bone marrow niche to be recruited to bone formation sites during bone remodeling are poorly known. We have studied secreted factors present in the bone marrow microenvironment and identified KIAA1199 (also known as CEMIP, cell migration inducing hyaluronan binding protein) in human bone biopsies as highly expressed in osteoprogenitor reversal cells (Rv.C) recruited to the eroded surfaces (ES), which are the future bone formation sites. In vitro, KIAA1199 did not affect the proliferation of human osteoblastic stem cells (also known as human bone marrow skeletal or stromal stem cells, hMSCs); but it enhanced cell migration as determined by scratch assay and trans-well migration assay. KIAA1199 deficient hMSCs (KIAA1199down) exhibited significant changes in cell size, cell length, ratio of cell width to length and cell roundness, together with reduction of polymerization actin (F-actin) and changes in phos-CFL1 (cofflin1), phos-LIMK1 (LIM domain kinase 1) and DSTN (destrin), key factors regulating actin cytoskeletal dynamics and cell motility. Moreover, KIAA1199down hMSC exhibited impaired Wnt signaling in TCF-reporter assay and decreased expression of Wnt target genes and these effects were rescued by KIAA1199 treatment. Finally, KIAA1199 regulated the activation of P38 kinase and its associated changes in Wnt-signaling. Thus, KIAA1199 is a mobilizing factor that interacts with P38 and Wnt signaling, and induces changes in actin cytoskeleton, as a mechanism mediating recruitment of hMSC to bone formation sites.

Crosstalk of Intercellular Signaling Pathways in the Generation of Midbrain Dopaminergic Neurons In Vivo and from Stem Cells

Dopamine-synthesizing neurons located in the mammalian ventral midbrain are at the center stage of biomedical research due to their involvement in severe human neuropsychiatric and neurodegenerative disorders, most prominently Parkinson’s Disease (PD). The induction of midbrain dopaminergic (mDA) neurons depends on two important signaling centers of the mammalian embryo: the ventral midline or floor plate (FP) of the neural tube, and the isthmic organizer (IsO) at the mid-/hindbrain boundary (MHB). Cells located within and close to the FP secrete sonic hedgehog (SHH), and members of the wingless-type MMTV integration site family (WNT1/5A), as well as bone morphogenetic protein (BMP) family. The IsO cells secrete WNT1 and the fibroblast growth factor 8 (FGF8). Accordingly, the FGF8, SHH, WNT, and BMP signaling pathways play crucial roles during the development of the mDA neurons in the mammalian embryo. Moreover, these morphogens are essential for the generation of stem cell-derived mDA neurons, which are critical for the modeling, drug screening, and cell replacement therapy of PD. This review summarizes our current knowledge about the functions and crosstalk of these signaling pathways in mammalian mDA neuron development in vivo and their applications in stem cell-based paradigms for the efficient derivation of these neurons in vitro.

Modeling Wnt signaling by CRISPR-Cas9 genome editing recapitulates neoplasia in human Barrett epithelial organoids

Primary organoid cultures generated from patient biopsies comprise a novel improved platform for disease modeling, being genetically stable and closely recapitulating in vivo scenarios. Barrett esophagus (BE) is the major risk factor for esophageal adenocarcinoma. There has been a dearth of long-term in vitro expansion models of BE neoplastic transformation. We generated a long-term virus-free organoid expansion model of BE neoplasia from patient biopsies. Both wild-type and paired APC-knockout (APCKO) BE organoids genome-edited by CRISPR-Cas9 showed characteristic goblet cell differentiation. Autonomous Wnt activation was confirmed in APCKO organoids by overexpression of Wnt target genes and nuclear-translocated β-catenin expression after withdrawal of Wnt-3A and R-spondin-1. Wnt-activated organoids demonstrated histologic atypia, higher proliferative and replicative activity, reduced apoptosis, and prolonged culturability. Wnt-activated organoids also showed sustained protrusive migration ability accompanied by disrupted basement membrane reorganization and integrity. This CRISPR-Cas9 editing human-derived organoid model recapitulates the critical role of aberrant Wnt/β-catenin signaling activation in BE neoplastic transformation. This system can be used to study other 'driver' pathway alterations in BE-associated neoplasia, avoiding signaling noise present in immortalized or cancer-derived cell lines.

Modeling Wnt signaling by CRISPR-Cas9 genome editing recapitulates neoplasia in human Barrett epithelial organoids

Primary organoid cultures generated from patient biopsies comprise a novel improved platform for disease modeling, being genetically stable and closely recapitulating in vivo scenarios. Barrett esophagus (BE) is the major risk factor for esophageal adenocarcinoma. There has been a dearth of long-term in vitro expansion models of BE neoplastic transformation. We generated a long-term virus-free organoid expansion model of BE neoplasia from patient biopsies. Both wild-type and paired APC-knockout (APC^KO) BE organoids genome-edited by CRISPR-Cas9 showed characteristic goblet cell differentiation. Autonomous Wnt activation was confirmed in APC^KO organoids by overexpression of Wnt target genes and nuclear-translocated β-catenin expression after withdrawal of Wnt-3A and R-spondin-1. Wnt-activated organoids demonstrated histologic atypia, higher proliferative and replicative activity, reduced apoptosis, and prolonged culturability. Wnt-activated organoids also showed sustained protrusive migration ability accompanied by disrupted basement membrane reorganization and integrity. This CRISPR-Cas9 editing human-derived organoid model recapitulates the critical role of aberrant Wnt/β-catenin signaling activation in BE neoplastic transformation. This system can be used to study other 'driver' pathway alterations in BE-associated neoplasia, avoiding signaling noise present in immortalized or cancer-derived cell lines.

Left/right asymmetric collective migration of parapineal cells is mediated by focal FGF signaling activity in leading cells

The ability of cells to collectively interpret surrounding environmental signals underpins their capacity to coordinate their migration in various contexts, including embryonic development and cancer metastasis. One tractable model for studying collective migration is the parapineal, a left-sided group of neurons that arises from bilaterally positioned precursors that undergo a collective migration to the left side of the brain. In zebrafish, the migration of these cells requires Fgf8 and, in this study, we resolve how FGF signaling correlates with-and impacts the migratory dynamics of-the parapineal cell collective. The temporal and spatial dynamics of an FGF reporter transgene reveal that FGF signaling is activated in only few parapineal cells usually located at the leading edge of the parapineal during its migration. Overexpressing a constitutively active Fgf receptor compromises parapineal migration in wild-type embryos, while it partially restores both parapineal migration and mosaic expression of the FGF reporter transgene in fgf8 ^-/- mutant embryos. Focal activation of FGF signaling in few parapineal cells is sufficient to promote the migration of the whole parapineal collective. Finally, we show that asymmetric Nodal signaling contributes to the restriction and leftwards bias of FGF pathway activation. Our data indicate that the first overt morphological asymmetry in the zebrafish brain is promoted by FGF pathway activation in cells that lead the collective migration of the parapineal to the left. This study shows that cell-state differences in FGF signaling in front versus rear cells is required to promote migration in a model of FGF-dependent collective migration.

Galectin-3 promotes CXCR2 to augment the stem-like property of renal cell carcinoma

Although targeted therapy is usually the first‐line treatment for advanced renal cell carcinoma (RCC), some patients can experience drug resistance. Cancer stem cells are tumour‐initiating cells that play a vital role in drug resistance, metastasis and cancer relapse, while galectins (Gal) participate in tumour progression and drug resistance. However, the exact role of galectins in RCC stemness is yet unknown. In this study, we grew a subpopulation of RCC cells as tumour spheres with higher levels of stemness‐related genes, such as Oct4, Sox2 and Nanog. Among the Gal family, Gal‐3 in particular was highly expressed in RCC tumour spheres. To further investigate Gal‐3's role in the stemness of RCC, lentivirus‐mediated knockdown and overexpression of Gal‐3 in RCC cells were used to examine both in vitro and in vivo tumorigenicity. We further assessed Gal‐3 expression in RCC tissue microarray using immunohistochemistry. Upon suppressing Gal‐3 in parental RCC cells, invasion, colony formation, sphere‐forming ability, drug resistance and stemness‐related gene expression were all significantly decreased. Furthermore, CXCL6, CXCL7 and CXCR2 were down‐regulated in Gal‐3‐knockdown tumour spheres, while CXCR2 overexpression in Gal‐3‐knockdown RCC restored the ability of sphere formation. Gal‐3 overexpression in RCC promoted both in vitro and in vivo tumorigenicity, and its expression was correlated with CXCR2 expression and tumour progression in clinical tissues. RCC patients with higher co‐expressions of Gal‐3 and CXCR2 demonstrated a worse survival rate. These results indicate that highly expressed Gal‐3 may up‐regulate CXCR2 to augment RCC stemness. Gal‐3 may be a prognostic and innovative target of combined therapy for treating RCC.

Protective effects of 2,3,5,4-tetrahydroxystilbene-2-o-β-D-glucoside against osteoporosis: Current knowledge and proposed mechanisms

AIM

The aim of this study was to explore the mechanism underlying the protective effects of 2,3,5,4-tetrahydroxystilbene-2-o-β-D-glucoside (TSG) against osteoporosis.

METHOD

MC3T3-E1 mouse osteoblast precursor cells were used to analyze the protective effects of TSG on osteoblast apoptosis and differential inhibition induced by oxidative stress to determine the gene expression of forkhead transcription factor FKHRL1 (FoxO3a), T cell factors (TCFs), and downstream genes. A mouse model was used to assess the protective effects of TSG on ovariectomy-induced osteoporosis as well as on Cell Counting Kit-8 (CCK) gene expression, including that of FoxO3a. The mechanism underlying the protective effects of TSG against osteoporosis was further explored using high-throughput sequencing data.

RESULTS

A CCK-8 assay in MC3T3-E1 cells and hematoxylin and eosin staining in mouse tissue indicated that cell viability and bone tissue development were inhibited by oxidative stress and ovariectomy and that TSG neutralized or attenuated this effect. The expression levels of FoxO3a, TCF, and downstream genes and the indices of oxidative stress were the same in MC3T3-E1 cells and the bone tissues of the mouse model. Bioinformatics analysis indicated that the cardiac muscle contraction and chemokine signaling pathway were disturbed in MC3T3-E1 cells treated with hydrogen peroxide. Gene ontology-biological process analysis revealed the influence of TSG treatment.

CONCLUSION

Osteoporosis and cardiac diseases appear to share a common mechanism. In addition to Wnt/FoxO3a signaling, the immune system and the chemokine signaling pathway may contribute to the protective mechanism of TSG.

Concise Review: Prostate Cancer Stem Cells: Current Understanding

Prostate cancer (PCa) is heterogeneous, harboring phenotypically diverse cancer cell types. PCa cell heterogeneity is caused by genomic instability that leads to the clonal competition and evolution of the cancer genome and by epigenetic mechanisms that result in subclonal cellular differentiation. The process of tumor cell differentiation is initiated from a population of prostate cancer stem cells (PCSCs) that possess many phenotypic and functional properties of normal stem cells. Since the initial reports on PCSCs in 2005, there has been much effort to elucidate their biological properties, including unique metabolic characteristics. In this Review, we discuss the current methods for PCSC enrichment and analysis, the hallmarks of PCSC metabolism, and the role of PCSCs in tumor progression. Stem Cells 2018;36:1457-1474.

Using Zebrafish to Study Collective Cell Migration in Development and Disease

Cellular migration is necessary for proper embryonic development as well as maintenance of adult health. Cells can migrate individually or in groups in a process known as collective cell migration. Collectively migrating cohorts maintain cell-cell contacts, group polarization, and exhibit coordinated behavior. This mode of migration is important during numerous developmental processes including tracheal branching, blood vessel sprouting, neural crest cell migration and others. In the adult, collective cell migration is important for proper wound healing and is often misappropriated during cancer cell invasion. A variety of genetic model systems are used to examine and define the cellular and molecular mechanisms behind collective cell migration including border cell migration and tracheal branching in Drosophila melanogaster, neural crest cell migration in chick and Xenopus embryos, and posterior lateral line primordium (pLLP) migration in zebrafish. The pLLP is a group of about 100 cells that begins migrating around 22 hours post-fertilization along the lateral aspect of the trunk of the developing embryo. During migration, clusters of cells are deposited from the trailing end of the pLLP; these ultimately differentiate into mechanosensory organs of the lateral line system. As zebrafish embryos are transparent during early development and the pLLP migrates close to the surface of the skin, this system can be easily visualized and manipulated in vivo. These advantages together with the amenity to advance genetic methods make the zebrafish pLLP one of the premier model systems for studying collective cell migration. This review will describe the cellular behaviors and signaling mechanisms of the pLLP and compare the pLLP to collective cell migration in other popular model systems. In addition, we will examine how this type of migration is hijacked by collectively invading cancer cells.

Anosmin1 Shuttles Fgf to Facilitate Its Diffusion, Increase Its Local Concentration, and Induce Sensory Organs

Growth factors induce and pattern sensory organs, but how their distribution is regulated by the extracellular matrix (ECM) is largely unclear. To address this question, we analyzed the diffusion behavior of Fgf10 molecules during sensory organ formation in the zebrafish posterior lateral line primordium. In this tissue, secreted Fgf10 induces organ formation at a distance from its source. We find that most Fgf10 molecules are highly diffusive and move rapidly through the ECM. We identify Anosmin1, which when mutated in humans causes Kallmann Syndrome, as an ECM protein that binds to Fgf10 and facilitates its diffusivity by increasing the pool of fast-moving Fgf10 molecules. In the absence of Anosmin1, Fgf10 levels are reduced and organ formation is impaired. Global overexpression of Anosmin1 slows the fast-moving Fgf10 molecules and results in Fgf10 dispersal. These results suggest that Anosmin1 liberates ECM-bound Fgf10 and shuttles it to increase its signaling range.

FLYWCH1, a Novel Suppressor of Nuclear β-Catenin, Regulates Migration and Morphology in Colorectal Cancer

Wnt/β-catenin signaling plays a critical role during development of both normal and malignant colorectal cancer tissues. Phosphorylation of β-catenin protein alters its trafficking and function. Such conventional allosteric regulation usually involves a highly specialized set of molecular interactions, which may specifically turn on a particular cell phenotype. This study identifies a novel transcription modulator with an FLYWCH/Zn-finger DNA-binding domain, called "FLYWCH1." Using a modified yeast-2-hybrid based Ras-Recruitment system, it is demonstrated that FLYWCH1 directly binds to unphosphorylated (nuclear) β-catenin efficiently suppressing the transcriptional activity of Wnt/β-catenin signaling that cannot be rescued by TCF4. FLYWCH1 rearranges the transcriptional activity of β-catenin/TCF4 to selectively block the expression of specific downstream genes associated with colorectal cancer cell migration and morphology, including ZEB1, EPHA4, and E-cadherin. Accordingly, overexpression of FLYWCH1 reduces cell motility and increases cell attachment. The expression of FLYWCH1 negatively correlates with the expression level of ZEB1 and EPHA4 in normal versus primary and metastatic colorectal cancer tissues in patients. Thus, FLYWCH1 antagonizes β-catenin/TCF4 signaling during cell polarity/migration in colorectal cancer. IMPLICATIONS: This study uncovers a new molecular mechanism by which FLYWCH1 with a possible tumor suppressive role represses β-catenin-induced ZEB1 and increases cadherin-mediated cell attachment preventing colorectal cancer metastasis.

FGFR1-Activated Translation of WNT Pathway Components with Structured 5' UTRs Is Vulnerable to Inhibition of EIF4A-Dependent Translation Initiation

Cooperativity between WNT and FGF signaling is well documented in embryonic development and cancer progression, but the molecular mechanisms underlying this cross-talk remain elusive. In this study, we interrogated the dynamics of RNA levels, ribosome occupancy, and protein expression as a function of inducible FGF signaling in mouse mammary glands with constitutive WNT hyperactivation. Multiomics correlation analysis revealed a substantial discrepancy between RNA and ribosome occupancy levels versus protein levels. However, this discrepancy decreased as cells became premalignant and dynamically responded to FGF signaling, implicating the importance of stringent gene regulation in nontransformed cells. Analysis of individual genes demonstrated that acute FGF hyperactivation increased translation of many stem cell self-renewal regulators, including WNT signaling components, and decreased translation of genes regulating cellular senescence. WNT pathway components translationally upregulated by FGF signaling had long and structured 5' UTRs with a high frequency of polypurine sequences, several of which harbored (CGG)4 motifs that can fold into either stable G-quadruplexes or other stable secondary structures. The FGF-mediated increase in translation of WNT pathway components was compromised by silvestrol, an inhibitor of EIF4A that clamps EIF4A to polypurine sequences to block 43S scanning and inhibits its RNA-unwinding activity important for translation initiation. Moreover, silvestrol treatment significantly delayed FGF-WNT-driven tumorigenesis. Taken together, these results suggest that FGF signaling selectively enhances translation of structured mRNAs, particularly WNT signaling components, and highlight their vulnerability to inhibitors that target the RNA helicase EIF4A.Significance: The RNA helicase EIF4A may serve as a therapeutic target for breast cancers that require FGF and WNT signaling. Cancer Res; 78(15); 4229-40. ©2018 AACR.

Cxcl12a induces snail1b expression to initiate collective migration and sequential Fgf-dependent neuromast formation in the zebrafish posterior lateral line primordium

The zebrafish posterior lateral line primordium migrates along a path defined by the chemokine Cxcl12a, periodically depositing neuromasts, to pioneer formation of the zebrafish posterior lateral line system. snail1b, known for its role in promoting cell migration, is expressed in leading cells of the primordium in response to Cxcl12a, whereas its expression in trailing cells is inhibited by Fgf signaling. snail1b knockdown delays initiation of primordium migration. This delay is associated with aberrant expansion of epithelial cell adhesion molecule (epcam) and reduction of cadherin 2 expression in the leading part of the primordium. Co-injection of snail1b morpholino with snail1b mRNA prevents the initial delay in migration and restores normal expression of epcam and cadherin 2 The delay in initiating primordium migration in snail1b morphants is accompanied by a delay in sequential formation of trailing Fgf signaling centers and associated protoneuromasts. This delay is not specifically associated with knockdown of snail1b but also with other manipulations that delay migration of the primordium. These observations reveal an unexpected link between the initiation of collective migration and sequential formation of protoneuromasts in the primordium.

Functions of EpCAM in physiological processes and diseases (Review)

EpCAM (epithelial cell adhesion molecule) is a type I transmembrane glycoprotein, which was originally identified as a tumor-associated antigen due to its high expression level in rapidly growing epithelial tumors. Germ line mutations of the human EpCAM gene have been indicated as the cause of congenital tufting enteropathy. Previous studies based on cell models have revealed that EpCAM contributes to various biological processes including cell adhesion, signaling, migration and proliferation. Due to the previous lack of genetic animal models, the in vivo functions of EpCAM remain largely unknown. However, EpCAM genetic animal models have recently been generated, and are useful for understanding the functions of EpCAM. The authors here briefly review the functions and mechanisms of EpCAM in physiological processes and different diseases.

PathCORE-T: identifying and visualizing globally co-occurring pathways in large transcriptomic compendia

Background

Investigators often interpret genome-wide data by analyzing the expression levels of genes within pathways. While this within-pathway analysis is routine, the products of any one pathway can affect the activity of other pathways. Past efforts to identify relationships between biological processes have evaluated overlap in knowledge bases or evaluated changes that occur after specific treatments. Individual experiments can highlight condition-specific pathway-pathway relationships; however, constructing a complete network of such relationships across many conditions requires analyzing results from many studies.

Results

We developed PathCORE-T framework by implementing existing methods to identify pathway-pathway transcriptional relationships evident across a broad data compendium. PathCORE-T is applied to the output of feature construction algorithms; it identifies pairs of pathways observed in features more than expected by chance as functionally co-occurring. We demonstrate PathCORE-T by analyzing an existing eADAGE model of a microbial compendium and building and analyzing NMF features from the TCGA dataset of 33 cancer types. The PathCORE-T framework includes a demonstration web interface, with source code, that users can launch to (1) visualize the network and (2) review the expression levels of associated genes in the original data. PathCORE-T creates and displays the network of globally co-occurring pathways based on features observed in a machine learning analysis of gene expression data.

Conclusions

The PathCORE-T framework identifies transcriptionally co-occurring pathways from the results of unsupervised analysis of gene expression data and visualizes the relationships between pathways as a network. PathCORE-T recapitulated previously described pathway-pathway relationships and suggested experimentally testable additional hypotheses that remain to be explored.

Electronic supplementary material

The online version of this article (10.1186/s13040-018-0175-7) contains supplementary material, which is available to authorized users.

Prion gene paralogs are dispensable for early zebrafish development and have nonadditive roles in seizure susceptibility

Normally folded prion protein (PrP^C) and its functions in healthy brains remain underappreciated compared with the intense study of its misfolded forms ("prions," PrP^Sc) during the pathobiology of prion diseases. This impedes the development of therapeutic strategies in Alzheimer's and prion diseases. Disrupting the zebrafish homologs of PrP^C has provided novel insights; however, mutagenesis of the zebrafish paralog prp2 did not recapitulate previous dramatic developmental phenotypes, suggesting redundancy with the prp1 paralog. Here, we generated zebrafish prp1 loss-of-function mutant alleles and dual prp1^-/-;prp2^-/- mutants. Zebrafish prp1^-/- and dual prp1^-/-;prp2^-/- mutants resemble mammalian Prnp knockouts insofar as they lack overt phenotypes, which surprisingly contrasts with reports of severe developmental phenotypes when either prp1 or prp2 is knocked down acutely. Previous studies suggest that PrP^C participates in neural cell development/adhesion, including in zebrafish where loss of prp2 affects adhesion and deposition patterns of lateral line neuromasts. In contrast with the expectation that prp1's functions would be redundant to prp2, they appear to have opposing functions in lateral line neurodevelopment. Similarly, loss of prp1 blunted the seizure susceptibility phenotypes observed in prp2 mutants, contrasting the expected exacerbation of phenotypes if these prion gene paralogs were serving redundant roles. In summary, prion mutant fish lack the overt phenotypes previously predicted, and instead they have subtle phenotypes similar to mammals. No evidence was found for functional redundancy in the zebrafish prion gene paralogs, and the phenotypes observed when each gene is disrupted individually are consistent with ancient functions of prion proteins in neurodevelopment and modulation of neural activity.

Lpar2b Controls Lateral Line Tissue Size by Regulating Yap1 Activity in Zebrafish

LPA signaling plays important roles during cell migration and proliferation in normal and pathological conditions. However, its role during sensory organ development remains unknown. Here we show a LPA receptor Lpar2b is expressed in the posterior lateral line primordium (pLLP) and mechanosensory organs called neuromasts (NMs) in zebrafish embryos. Lpar2b loss-of-function significantly reduces the number of NMs and hair cells in the posterior lateral line (pLL). Further analysis reveals that Lpar2b regulates the patterning and tissue size of the pLLP. Interestingly, we show that knocking down a Hippo effector Yap1 phenocopies the result of Lpar2b depletion, and Lpar2b regulates the phosphorylation and activity of Yap1 in the pLLP. Importantly, a phosphorylation-resistant Yap1 rescues pLLP size and NM number in Lpar2b-depleted embryos. Our results indicate Lpar2b controls primordium size and NM number by regulating Yap1 activity in the lateral line system.

Urban stormwater runoff negatively impacts lateral line development in larval zebrafish and salmon embryos

After a storm, water often runs off of impervious urban surfaces directly into aquatic ecosystems. This stormwater runoff is a cocktail of toxicants that have serious effects on the ecological integrity of aquatic habitats. Zebrafish that develop in stormwater runoff suffer from cardiovascular toxicity and impaired growth, but the effects of stormwater on fish sensory systems are not understood. Our study investigated the effect of stormwater on hair cells of the lateral line in larval zebrafish and coho salmon. Our results showed that although toxicants in stormwater did not kill zebrafish hair cells, these cells did experience damage. Zebrafish developing in stormwater also experienced impaired growth, fewer neuromasts in the lateral line, and fewer hair cells per neuromast. A similar reduction in neuromast number was observed in coho salmon reared in stormwater. Bioretention treatment, intended to filter out harmful constituents of stormwater, rescued the lateral line defects in zebrafish but not in coho salmon, suggesting that not all of the harmful constituents were removed by the filtration media and that salmonids are particularly sensitive to aquatic toxicants. Collectively, these data demonstrate that sub-lethal exposure to stormwater runoff negatively impacts a fish sensory system, which may have consequences for organismal fitness.

A framework for understanding morphogenesis and migration of the zebrafish posterior Lateral Line primordium

A description of zebrafish posterior Lateral Line (pLL) primordium development at single cell resolution together with the dynamics of Wnt, FGF, Notch and chemokine signaling in this system has allowed us to develop a framework to understand the self-organization of cell fate, morphogenesis and migration during its early development. The pLL primordium migrates under the skin, from near the ear to the tip of the tail, periodically depositing neuromasts. Nascent neuromasts, or protoneuromasts, form sequentially within the migrating primordium, mature, and are deposited from its trailing end. Initially broad Wnt signaling inhibits protoneuromast formation. However, protoneuromasts form sequentially in response to FGF signaling, starting from the trailing end, in the wake of a progressively shrinking Wnt system. While proliferation adds to the number of cells, the migrating primordium progressively shrinks as its trailing cells stop moving and are deposited. As it shrinks, the length of the migrating primordium correlates with the length of the leading Wnt system. Based on these observations we show how measuring the rate at which the Wnt system shrinks, the proliferation rate, the initial size of the primordium, its speed, and a few additional parameters allows us to predict the pattern of neuromast formation and deposition by the migrating primordium in both wild-type and mutant contexts. While the mechanism that links the length of the leading Wnt system to that of the primordium remains unclear, we discuss how it might be determined by access to factors produced in the leading Wnt active zone that are required for collective migration of trailing cells. We conclude by reviewing how FGFs, produced in response to Wnt signaling in leading cells, help determine collective migration of trailing cells, while a polarized response to a self-generated chemokine gradient serves as an efficient mechanism to steer primordium migration along its relatively long journey.

Notch and Fgf signaling during electrosensory versus mechanosensory lateral line organ development in a non-teleost ray-finned fish

The lateral line system is a useful model for studying the embryonic and evolutionary diversification of different organs and cell types. In jawed vertebrates, this ancestrally comprises lines of mechanosensory neuromasts over the head and trunk, flanked on the head by fields of electrosensory ampullary organs, all innervated by lateral line neurons in cranial lateral line ganglia. Both types of sense organs, and their afferent neurons, develop from cranial lateral line placodes. Current research primarily focuses on the posterior lateral line primordium in zebrafish, which migrates as a cell collective along the trunk; epithelial rosettes form in the trailing zone and are deposited as a line of neuromasts, within which hair cells and supporting cells differentiate. However, in at least some other teleosts (e.g. catfishes) and all non-teleosts, lines of cranial neuromasts are formed by placodes that elongate to form a sensory ridge, which subsequently fragments, with neuromasts differentiating in a line along the crest of the ridge. Furthermore, in many non-teleost species, electrosensory ampullary organs develop from the flanks of the sensory ridge. It is unknown to what extent the molecular mechanisms underlying neuromast formation from the zebrafish migrating posterior lateral line primordium are conserved with the as-yet unexplored molecular mechanisms underlying neuromast and ampullary organ formation from elongating lateral line placodes. Here, we report experiments in an electroreceptive non-teleost ray-finned fish, the Mississippi paddlefish Polyodon spathula, that suggest a conserved role for Notch signaling in regulating lateral line organ receptor cell number, but potentially divergent roles for the fibroblast growth factor signaling pathway, both between neuromasts and ampullary organs, and between paddlefish and zebrafish.

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Notch and Fgf pathway genes are expressed during paddlefish lateral line development.

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Fgf ligand genes are differentially expressed in neuromasts and ampullary organs.

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DAPT treatment results in irregular organ spacing and supernumerary receptor cells.

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SU5402 treatment yields fewer neuromasts, but ampullary organs form precociously.

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SU5402 treatment also results in supernumerary receptor cells.

Epithelial cell behaviours during neurosensory organ formation

Perception of the environment in vertebrates relies on a variety of neurosensory mini-organs. These organs develop via a multi-step process that includes placode induction, cell differentiation, patterning and innervation. Ultimately, cells derived from one or more different tissues assemble to form a specific mini-organ that exhibits a particular structure and function. The initial building blocks of these organs are epithelial cells that undergo rearrangements and interact with neighbouring tissues, such as neural crest-derived mesenchymal cells and sensory neurons, to construct a functional sensory organ. In recent years, advances in in vivo imaging methods have allowed direct observation of these epithelial cells, showing that they can be displaced within the epithelium itself via several modes. This Review focuses on the diversity of epithelial cell behaviours that are involved in the formation of small neurosensory organs, using the examples of dental placodes, hair follicles, taste buds, lung neuroendocrine cells and zebrafish lateral line neuromasts to highlight both well-established and newly described modes of epithelial cell motility.

Retinoic acid is required and Fgf, Wnt, and Bmp signaling inhibit posterior lateral line placode induction in zebrafish

The lateral line system is a mechanosensory systems present in aquatic animals. The anterior and posterior lateral lines develop from anterior and posterior lateral line placodes (aLLp and pLLp), respectively. Although signaling molecules required for the induction of other cranial placodes have been well studied, the molecular mechanisms underlying formation of the lateral line placodes are unknown. In this study we tested the requirement of multiple signaling pathways, such as Wnt, Bmp Fgf, and Retinoic Acid for aLLp and pLLp induction. We determined that aLLp specification requires Fgf signaling, whilst pLLp specification requires retinoic acid which inhibits Fgf signaling. pLLp induction is also independent of Wnt and Bmp activities, even though these pathways limit the boundaries of the pLLp. This is the first report that the aLLp and pLLp depend on different inductive mechanisms and that pLLp induction requires the inhibition of Fgf, Wnt and Bmp signaling.

Screening of cancer tissue arrays identifies CXCR4 on adrenocortical carcinoma: correlates with expression and quantification on metastases using 64Cu-plerixafor PET

Expression of the chemokine receptor CXCR4 by many cancers correlates with aggressive clinical behavior. As part of the initial studies in a project whose goal was to quantify CXCR4 expression on cancers non-invasively, we examined CXCR4 expression in cancer samples by immunohistochemistry using a validated anti-CXCR4 antibody. Among solid tumors, we found expression of CXCR4 on significant percentages of major types of kidney, lung, and pancreatic adenocarcinomas, and, notably, on metastases of clear cell renal cell carcinoma and squamous cell carcinoma of the lung. We found particularly high expression of CXCR4 on adrenocortical cancer (ACC) metastases. Microarrays of ACC metastases revealed correlations between expression of CXCR4 and other chemokine system genes, particularly CXCR7/ACKR3, which encodes an atypical chemokine receptor that shares a ligand, CXCL12, with CXCR4. A first-in-human study using ⁶⁴Cu-plerixafor for PET in an ACC patient prior to resection of metastases showed heterogeneity among metastatic nodules and good correlations among PET SUVs, CXCR4 staining, and CXCR4 mRNA. Additionally, we were able to show that CXCR4 expression correlated with the rates of growth of the pulmonary lesions in this patient. Further studies are needed to understand better the role of CXCR4 in ACC and whether targeting it may be beneficial. In this regard, non-invasive methods for assessing CXCR4 expression, such as PET using ⁶⁴Cu-plerixafor, should be important investigative tools.

Insm1a Is Required for Zebrafish Posterior Lateral Line Development

Insulinoma-associated 1 (Insm1), a zinc-finger transcription factor, is widely expressed in the developing nervous system and plays important roles in cell cycle progression and cell fate specification. However, the functions of Insm1 in the embryonic development of the sensory system and its underlying molecular mechanisms remain largely unexplored. Here, through whole-mount in situ hybridization, we found that the zebrafish insm1a gene was expressed in the posterior lateral line (pLL) system, including both the migrating pLL primordium and the deposited neuromast cells. In order to decipher the specific roles of insm1a in zebrafish pLL development, we inhibited insm1a expression by using a morpholino knockdown strategy. The insm1a morphants exhibited primordium migration defects that resulted in reduced numbers of neuromasts. The inactivation of insm1a reduced the numbers of hair cells in neuromasts, and this defect could be a secondary consequence of disrupting rosette formation in the pLL primordium. Additionally, we showed that insm1a knockdown decreased the proliferation of pLL primordium cells, which likely contributed to these pLL defects. Furthermore, we showed that loss of insm1a resulted in elevated Wnt/β-catenin signaling and downregulation of Fgf target genes in the primordium. Insm1a knockdown also perturbed the expression patterns of chemokine signaling genes. Taken together, this study reveals a pivotal role for Insm1a in regulating pLL development during zebrafish embryogenesis.

Ror2 Signaling and Its Relevance in Breast Cancer Progression

Breast cancer is a heterogeneous disease and has been classified into five molecular subtypes based on gene expression profiles. Signaling processes linked to different breast cancer molecular subtypes and different clinical outcomes are still poorly understood. Aberrant regulation of Wnt signaling has been implicated in breast cancer progression. In particular Ror1/2 receptors and several other members of the non-canonical Wnt signaling pathway were associated with aggressive breast cancer behavior. However, Wnt signals are mediated via multiple complex pathways, and it is clinically important to determine which particular Wnt cascades, including their domains and targets, are deregulated in poor prognosis breast cancer. To investigate activation and outcome of the Ror2-dependent non-canonical Wnt signaling pathway, we overexpressed the Ror2 receptor in MCF-7 and MDA-MB231 breast cancer cells, stimulated the cells with its ligand Wnt5a, and we knocked-down Ror1 in MDA-MB231 cells. We measured the invasive capacity of perturbed cells to assess phenotypic changes, and mRNA was profiled to quantify gene expression changes. Differentially expressed genes were integrated into a literature-based non-canonical Wnt signaling network. The results were further used in the analysis of an independent dataset of breast cancer patients with metastasis-free survival annotation. Overexpression of the Ror2 receptor, stimulation with Wnt5a, as well as the combination of both perturbations enhanced invasiveness of MCF-7 cells. The expression-responsive targets of Ror2 overexpression in MCF-7 induced a Ror2/Wnt module of the non-canonical Wnt signaling pathway. These targets alter regulation of other pathways involved in cell remodeling processing and cell metabolism. Furthermore, the genes of the Ror2/Wnt module were assessed as a gene signature in patient gene expression data and showed an association with clinical outcome. In summary, results of this study indicate a role of a newly defined Ror2/Wnt module in breast cancer progression and present a link between Ror2 expression and increased cell invasiveness.

Convergence of signaling pathways underlying habenular formation and axonal outgrowth in zebrafish

The habenular nuclei are a conserved integrating center in the vertebrate epithalamus, where they modulate diverse behaviors. Despite their importance, our understanding of habenular development is incomplete. Time-lapse imaging and fate mapping demonstrate that the dorsal habenulae (dHb) of zebrafish are derived from dbx1b-expressing (dbx1b⁺ ) progenitors, which transition into cxcr4b-expressing neuronal precursors. The precursors give rise to differentiated neurons, the axons of which innervate the midbrain interpeduncular nucleus (IPN). Formation of the dbx1b⁺ progenitor population relies on the activity of the Shh, Wnt and Fgf signaling pathways. Wnt and Fgf function additively to generate dHb progenitors. Surprisingly, Wnt signaling also negatively regulates fgf8a, confining expression to a discrete dorsal diencephalic domain. Moreover, the Wnt and Fgf pathways have opposing roles in transcriptional regulation of components of the Cxcr4-chemokine signaling pathway. The chemokine pathway, in turn, directs the posterior outgrowth of dHb efferents toward the IPN and, when disrupted, results in ectopic, anteriorly directed axonal projections. The results define a signaling network underlying the generation of dHb neurons and connectivity with their midbrain target.

Control of signaling molecule range during developmental patterning

Tissue patterning, through the concerted activity of a small number of signaling pathways, is critical to embryonic development. While patterning can involve signaling between neighbouring cells, in other contexts signals act over greater distances by traversing complex cellular landscapes to instruct the fate of distant cells. In this review, we explore different strategies adopted by cells to modulate signaling molecule range to allow correct patterning. We describe mechanisms for restricting signaling range and highlight how such short-range signaling can be exploited to not only control the fate of adjacent cells, but also to generate graded signaling within a field of cells. Other strategies include modulation of signaling molecule action by tissue architectural properties and the use of cellular membranous structures, such as signaling filopodia and exosomes, to actively deliver signaling ligands to target cells. Signaling filopodia can also be deployed to reach out and collect particular signals, thereby precisely controlling their site of action.

Pioneer neurog1 expressing cells ingress into the otic epithelium and instruct neuronal specification

Neural patterning involves regionalised cell specification. Recent studies indicate that cell dynamics play instrumental roles in neural pattern refinement and progression, but the impact of cell behaviour and morphogenesis on neural specification is not understood. Here we combine 4D analysis of cell behaviours with dynamic quantification of proneural expression to uncover the construction of the zebrafish otic neurogenic domain. We identify pioneer cells expressing neurog1 outside the otic epithelium that migrate and ingress into the epithelialising placode to become the first otic neuronal progenitors. Subsequently, neighbouring cells express neurog1 inside the placode, and apical symmetric divisions amplify the specified pool. Interestingly, pioneer cells delaminate shortly after ingression. Ablation experiments reveal that pioneer cells promote neurog1 expression in other otic cells. Finally, ingression relies on the epithelialisation timing controlled by FGF activity. We propose a novel view for otic neurogenesis integrating cell dynamics whereby ingression of pioneer cells instructs neuronal specification.

DOI:http://dx.doi.org/10.7554/eLife.25543.001

The inner ear is responsible for our senses of hearing and balance, and is made up of a series of fluid-filled cavities. Sounds, and movements of the head, cause the fluid within these cavities to move. This activates neurons that line the cavities, causing them to increase their firing rates and pass on information about the sounds or head movements to the brain. Damage to these neurons can result in deafness or vertigo. But where do the neurons themselves come from?

It is generally assumed that all inner ear neurons develop inside an area of the embryo called the inner ear epithelium. Cells in this region are thought to switch on a gene called neurog1, triggering a series of changes that turn them into inner ear neurons. However, using advanced microscopy techniques in zebrafish embryos, Hoijman, Fargas et al. now show that this is not the whole story.

While zebrafish do not have external ears, they do possess fluid-filled structures for balance and hearing that are similar to those of other vertebrates. Zebrafish embryos are also transparent, which means that activation of genes can be visualized directly. By imaging zebrafish embryos in real time, Hoijman, Fargas et al. show that the first cells to switch on neurog1 do so outside the inner ear epithelium. These pioneer cells then migrate into the inner ear epithelium and switch on neurog1 in their new neighbors. A substance called fibroblast growth factor tells the inner ear epithelium to let the pioneers enter, and thereby controls the final number of inner ear neurons.

The work of Hoijman, Fargas et al. reveals how coordinated activation of genes and movement of cells gives rise to inner ear neurons. This should provide insights into the mechanisms that generate other types of sensory tissue. In the long term, the advances made in this study may lead to new strategies for repairing damaged sensory nerves.

DOI:http://dx.doi.org/10.7554/eLife.25543.002

Polarization and migration in the zebrafish posterior lateral line system

Collective cell migration plays an important role in development. Here, we study the posterior lateral line primordium (PLLP) a group of about 100 cells, destined to form sensory structures, that migrates from head to tail in the zebrafish embryo. We model mutually inhibitory FGF-Wnt signalling network in the PLLP and link tissue subdivision (Wnt receptor and FGF receptor activity domains) to receptor-ligand parameters. We then use a 3D cell-based simulation with realistic cell-cell adhesion, interaction forces, and chemotaxis. Our model is able to reproduce experimentally observed motility with leading cells migrating up a gradient of CXCL12a, and trailing (FGF receptor active) cells moving actively by chemotaxis towards FGF ligand secreted by the leading cells. The 3D simulation framework, combined with experiments, allows an investigation of the role of cell division, chemotaxis, adhesion, and other parameters on the shape and speed of the PLLP. The 3D model demonstrates reasonable behaviour of control as well as mutant phenotypes.

Feedback Activation of Basic Fibroblast Growth Factor Signaling via the Wnt/β-Catenin Pathway in Skin Fibroblasts

Skin wound healing is a complex process requiring the coordinated behavior of many cell types, especially in the proliferation and migration of fibroblasts. Basic fibroblast growth factor (bFGF) is a member of the FGF family that promotes fibroblast migration, but the underlying molecular mechanism remains elusive. The present RNA sequencing study showed that the expression levels of several canonical Wnt pathway genes, including Wnt2b, Wnt3, Wnt11, T-cell factor 7 (TCF7), and Frizzled 8 (FZD8) were modified by bFGF stimulation in fibroblasts. Enzyme-linked immunosorbent assay (ELISA) analysis also showed that Wnt pathway was activated under bFGF treatment. Furthermore, treatment of fibroblasts with lithium chloride or IWR-1, an inducer and inhibitor of the Wnt signaling pathway, respectively, promoted and inhibited cell migration. Also, levels of cytosolic glycogen synthase kinase 3 beta phosphorylated at serine⁹ (pGSK3β Ser⁹) and nuclear β-catenin were increased upon exposure to bFGF. Molecular and biochemical assays indicated that phosphoinositide 3-kinase (PI3K) signaling activated the GSK3β/β-catenin/Wnt signaling pathway via activation of c-Jun N-terminal kinase (JNK), suggesting that PI3K and JNK act at the upstream of β-catenin. In contrast, knock-down of β-catenin delayed fibroblast cell migration even under bFGF stimulation. RNA sequencing analysis of β-catenin knock-down fibroblasts demonstrated that β-catenin positively regulated the transcription of bFGF and FGF21. Moreover, FGF21 treatment activated AKT and JNK, and accelerated fibroblast migration to a similar extent as bFGF does. In addition, ELISA analysis demonstrated that both of bFGF and FGF21 were auto secretion factor and be regulated by Wnt pathway stimulators. Taken together, our analyses define a feedback regulatory loop between bFGF (FGF21) and Wnt signaling acting through β-catenin in skin fibroblasts.

Neurodevelopmental Perspectives on Wnt Signaling in Psychiatry

Mounting evidence indicates that Wnt signaling is relevant to pathophysiology of diverse mental illnesses including schizophrenia, bipolar disorder, and autism spectrum disorder. In the 35 years since Wnt ligands were first described, animal studies have richly explored how downstream Wnt signaling pathways affect an array of neurodevelopmental processes and how their disruption can lead to both neurological and behavioral phenotypes. Recently, human induced pluripotent stem cell (hiPSC) models have begun to contribute to this literature while pushing it in increasingly translational directions. Simultaneously, large-scale human genomic studies are providing evidence that sequence variation in Wnt signal pathway genes contributes to pathogenesis in several psychiatric disorders. This article reviews neurodevelopmental and postneurodevelopmental functions of Wnt signaling, highlighting mechanisms, whereby its disruption might contribute to psychiatric illness, and then reviews the most reliable recent genetic evidence supporting that mutations in Wnt pathway genes contribute to psychiatric illness. We are proponents of the notion that studies in animal and hiPSC models informed by the human genetic data combined with the deep knowledge base and tool kits generated over the last several decades of basic neurodevelopmental research will yield near-term tangible advances in neuropsychiatry.

Proliferation-independent regulation of organ size by Fgf/Notch signaling

Organ morphogenesis depends on the precise orchestration of cell migration, cell shape changes and cell adhesion. We demonstrate that Notch signaling is an integral part of the Wnt and Fgf signaling feedback loop coordinating cell migration and the self-organization of rosette-shaped sensory organs in the zebrafish lateral line system. We show that Notch signaling acts downstream of Fgf signaling to not only inhibit hair cell differentiation but also to induce and maintain stable epithelial rosettes. Ectopic Notch expression causes a significant increase in organ size independently of proliferation and the Hippo pathway. Transplantation and RNASeq analyses revealed that Notch signaling induces apical junctional complex genes that regulate cell adhesion and apical constriction. Our analysis also demonstrates that in the absence of patterning cues normally provided by a Wnt/Fgf signaling system, rosettes still self-organize in the presence of Notch signaling.

DOI:http://dx.doi.org/10.7554/eLife.21049.001

Sequential organogenesis sets two parallel sensory lines in medaka

Animal organs are typically formed during embryogenesis by following one specific developmental programme. Here, we report that neuromast organs are generated by two distinct and sequential programmes that result in parallel sensory lines in medaka embryos. A ventral posterior lateral line (pLL) is composed of neuromasts deposited by collectively migrating cells whereas a midline pLL is formed by individually migrating cells. Despite the variable number of neuromasts among embryos, the sequential programmes that we describe here fix an invariable ratio between ventral and midline neuromasts. Mechanistically, we show that the formation of both types of neuromasts depends on the chemokine receptor genes cxcr4b and cxcr7b, illustrating how common molecules can mediate different morphogenetic processes. Altogether, we reveal a self-organising feature of the lateral line system that ensures a proper distribution of sensory organs along the body axis.

Summary: Two parallel sensory lines in medaka share a common origin and are composed of identical organs that are, nevertheless, generated through different morphogenetic programmes.

MiR-218 Induces Neuronal Differentiation of ASCs in a Temporally Sequential Manner with Fibroblast Growth Factor by Regulation of the Wnt Signaling Pathway

Differentiation of neural lineages from mesenchymal stem cells has raised the hope of generating functional cells as seed cells for nerve tissue engineering. As important gene regulators, microRNAs (miRNAs) have been speculated to play a vital role in accelerating stem cell differentiation and repairing neuron damage. However, miRNA roles in directing differentiation of stem cells in current protocols are underexplored and the mechanisms of miRNAs as regulators of neuronal differentiation remain ambiguous. In this study, we have determined that miR-218 serves as crucial constituent regulator in neuronal differentiation of adipose stem cells (ASCs) through Wnt signaling pathway based on comprehensive annotation of miRNA sequencing data. Moreover, we have also discovered that miR-218 and Fibroblast Growth Factor-2 (FGF2) modulate neuronal differentiation in a sequential manner. These findings provide additional understanding of the mechanisms regulating stem cell neuronal differentiation as well as a new method for neural lineage differentiation of ASCs.

Roles of Ras Homolog A in Invasive Ductal Breast Carcinoma

Breast cancer has a poor prognosis owing to tumor cell invasion and metastasis. Although Ras homolog (Rho) A is involved in tumor cell invasion, its role in breast carcinoma is unclear. Here, RhoA expression was examined in invasive ductal carcinoma (IDC), with a focus on its relationships with epidermal-mesenchymal transition (EMT) and collective cell invasion. Forty-four surgical IDC tissue samples and two normal breast tissue samples were obtained. RhoA, E-cadherin, vimentin, and F-actin protein expression were analyzed by immunohistochemistry. RhoA, ROCK, mTOR, AKT1, and PIK3CA mRNA expression were conducted using laser microdissection and semi-nested quantitative reverse transcription-polymerase chain reaction. RhoA expression was stronger on the tumor interface of IDCs than the tumor center (P<0.001). RhoA expression was correlated with ROCK expression only in HER2-subtype IDC (P<0.05). In IDCs co-expressing RhoA and ROCK, F-actin expression was stronger on the tumor interface, particularly at the edges of tumor cells, than it was in ROCK-negative IDCs (P<0.0001). In conclusion, RhoA expression was not correlated with EMT in IDC, but enhanced F-actin expression was localized on the edge of tumor cells that co-expressed ROCK. RhoA/ROCK signaling may be associated with collective cell invasion, particularly in HER2-subtype IDC.

Transcriptional Control of Developmental Cell Behaviors

Tissue-specific transcription regulators emerged as key developmental control genes, which operate in the context of complex gene regulatory networks (GRNs) to coordinate progressive cell fate specification and tissue morphogenesis. We discuss how GRNs control the individual cell behaviors underlying complex morphogenetic events. Cell behaviors classically range from mesenchymal cell motility to cell shape changes in epithelial sheets. These behaviors emerge from the tissue-specific, multiscale integration of the local activities of universal and pleiotropic effectors, which underlie modular subcellular processes including cytoskeletal dynamics, cell-cell and cell-matrix adhesion, signaling, polarity, and vesicle trafficking. Extrinsic cues and intrinsic cell competence determine the subcellular spatiotemporal patterns of effector activities. GRNs influence most subcellular activities by controlling only a fraction of the effector-coding genes, which we argue is enriched in effectors involved in reading and processing the extrinsic cues to contextualize intrinsic subcellular processes and canalize developmental cell behaviors. The properties of the transcription-cell behavior interface have profound implications for evolution and disease.

Insights into sensory hair cell regeneration from the zebrafish lateral line

Loss of mechanosensory hair cells in the inner ear leads to loss of hearing. In humans this results in permanent deafness, as mammals are largely unable to regenerate hair cells. In contrast, zebrafish robustly regenerate hair cells in the sensory lateral line and ear and recent gene expression and time-lapse analyses of cell behaviors at the single cell level have greatly advanced our understanding of the mechanisms responsible for hair cell regeneration. In the lateral line, hair cell regeneration is controlled via dynamic interactions between Notch and Wnt/β-catenin signaling, and likely also between Fgf and the retinoic acid signaling pathways. Less is known about what initiates regeneration and we discuss potential pathways that may trigger proliferation after hair cell damage.

Inhibition of H3K9me2 Reduces Hair Cell Regeneration after Hair Cell Loss in the Zebrafish Lateral Line by Down-Regulating the Wnt and Fgf Signaling Pathways

The activation of neuromast (NM) supporting cell (SC) proliferation leads to hair cell (HC) regeneration in the zebrafish lateral line. Epigenetic mechanisms have been reported that regulate HC regeneration in the zebrafish lateral line, but the role of H3K9me2 in HC regeneration after HC loss remains poorly understood. In this study, we focused on the role of H3K9me2 in HC regeneration following neomycin-induced HC loss. To investigate the effects of H3K9me2 in HC regeneration, we took advantage of the G9a/GLP-specific inhibitor BIX01294 that significantly reduces the dimethylation of H3K9. We found that BIX01294 significantly reduced HC regeneration after neomycin-induced HC loss in the zebrafish lateral line. BIX01294 also significantly reduced the proliferation of NM cells and led to fewer SCs in the lateral line. In situ hybridization showed that BIX01294 significantly down-regulated the Wnt and Fgf signaling pathways, which resulted in reduced SC proliferation and HC regeneration in the NMs of the lateral line. Altogether, our results suggest that down-regulation of H3K9me2 significantly decreases HC regeneration after neomycin-induced HC loss through inactivation of the Wnt/β-catenin and Fgf signaling pathways. Thus H3K9me2 plays a critical role in HC regeneration.

Localized Gene Induction by Infrared-Mediated Heat Shock

Genetic manipulations are a vital instrument for the study of embryonic development where to understand how genes work, it is necessary to provoke a loss or gain of function of a particular gene in a spatial and temporal manner. In the zebrafish embryo, the Hsp70 promoter is the most commonly used tool to induce a transient global gene expression of a desired gene, in a temporal manner. However, Hsp70-driven global gene induction presents caveats when studying gene function in a tissue of interest as gene induction in the whole embryo can lead to cell-autonomous and non-cell-autonomous phenotypes. In the current article, we describe an innovative and cost effective protocol to activate Hsp70-dependent expression in a small subset of cells in the zebrafish embryo, by utilizing a localized infrared (IR) laser. Our IR laser set up can be incorporated to any microscope platform without the requirement for expensive equipment. Furthermore, our protocol allows for controlled localized induction of specific proteins under the control of the hsp70 promoter in small subsets of cells. We use the migrating zebrafish sensory lateral line primordium as a model, because of its relative simplicity and experimental accessibility; however, this technique can be applied to any tissue in the zebrafish embryo.

Imaging collective cell migration and hair cell regeneration in the sensory lateral line

The accessibility of the lateral line system and its amenability to long-term in vivo imaging transformed the developing lateral line into a powerful model system to study fundamental morphogenetic events, such as guided migration, proliferation, cell shape changes, organ formation, organ deposition, cell specification and differentiation. In addition, the lateral line is not only amenable to live imaging during migration stages but also during postembryonic events such as sensory organ tissue homeostasis and regeneration. The robust regenerative capabilities of the mature, mechanosensory lateral line hair cells, which are homologous to inner ear hair cells and the ease with which they can be imaged, have brought zebrafish into the spotlight as a model to develop tools to treat human deafness. In this chapter, we describe protocols for long-term in vivo confocal imaging of the developing and regenerating lateral line.

Comparative transcriptomic profiling of hydrogen peroxide signaling networks in zebrafish and human keratinocytes: Implications toward conservation, migration and wound healing

Skin wounds need to be repaired rapidly after injury to restore proper skin barrier function. Hydrogen peroxide (H₂O₂) is a conserved signaling factor that has been shown to promote a variety of skin wound repair processes, including immune cell migration, angiogenesis and sensory axon repair. Despite growing research on H₂O₂ functions in wound repair, the downstream signaling pathways activated by this reactive oxygen species in the context of injury remain largely unknown. The goal of this study was to provide a comprehensive analysis of gene expression changes in the epidermis upon exposure to H₂O₂ concentrations known to promote wound repair. Comparative transcriptome analysis using RNA-seq data from larval zebrafish and previously reported microarray data from a human epidermal keratinocyte line shows that H₂O₂ activates conserved cell migration, adhesion, cytoprotective and anti-apoptotic programs in both zebrafish and human keratinocytes. Further assessment of expression characteristics and signaling pathways revealed the activation of three major H₂O₂–dependent pathways, EGF, FOXO1, and IKKα. This study expands on our current understanding of the clinical potential of low-level H₂O₂ for the promotion of epidermal wound repair and provides potential candidates in the treatment of wound healing deficits.

The front and rear of collective cell migration

Collective cell migration has a key role during morphogenesis and during wound healing and tissue renewal in the adult, and it is involved in cancer spreading. In addition to displaying a coordinated migratory behaviour, collectively migrating cells move more efficiently than if they migrated separately, which indicates that a cellular interplay occurs during collective cell migration. In recent years, evidence has accumulated confirming the importance of such intercellular communication and exploring the molecular mechanisms involved. These mechanisms are based both on direct physical interactions, which coordinate the cellular responses, and on the collective cell behaviour that generates an optimal environment for efficient directed migration. The recent studies have described how leader cells at the front of cell groups drive migration and have highlighted the importance of follower cells and cell-cell communication, both between followers and between follower and leader cells, to improve the efficiency of collective movement.

Autonomy and Non-autonomy of Angiogenic Cell Movements Revealed by Experiment-Driven Mathematical Modeling

Angiogenesis is a multicellular phenomenon driven by morphogenetic cell movements. We recently reported morphogenetic vascular endothelial cell (EC) behaviors to be dynamic and complex. However, the principal mechanisms orchestrating individual EC movements in angiogenic morphogenesis remain largely unknown. Here we present an experiment-driven mathematical model that enables us to systematically dissect cellular mechanisms in branch elongation. We found that cell-autonomous and coordinated actions governed these multicellular behaviors, and a cell-autonomous process sufficiently illustrated essential features of the morphogenetic EC dynamics at both the single-cell and cell-population levels. Through refining our model and experimental verification, we further identified a coordinated mode of tip EC behaviors regulated via a spatial relationship between tip and follower ECs, which facilitates the forward motility of tip ECs. These findings provide insights that enhance our mechanistic understanding of not only angiogenic morphogenesis, but also other types of multicellular phenomenon.

HDAC3 Is Required for Posterior Lateral Line Development in Zebrafish

Histone deacetylases (HDACs) are involved in multiple developmental processes, but their functions in the development of mechanosensory organs are largely unknown. In the present study, we report the presence of HDAC3 in the zebrafish posterior lateral line primordium and newly deposited neuromasts. We used morpholinos to show that HDAC3 knockdown severely disrupts the development of the posterior lateral line and reduces the numbers of neuromasts and sensory hair cells within these organs. In HDAC3 morphants, we also observed decreased cell proliferation and increased apoptosis, which might lead to these defects. Finally, we show that HDAC3 deficiency results in attenuated Fgf signaling in the migrating primordium. In situ hybridizations indicate aberrant expression patterns of Notch signaling pathway genes in HDAC3 morphants. In addition, inhibition of HDAC3 function diminishes cxcr7b and alters cxcl12a expression in the migrating primordium. Our results indicate that HDAC3 plays a crucial role in regulating posterior lateral line (PLL) formation and provide evidence for epigenetic regulation in auditory organ development.