EphB Receptors Coordinate Migration and Proliferation in the Intestinal Stem Cell Niche

Retrograde regulation of mossy fiber axon targeting and terminal maturation via postsynaptic Lnx1

Synapse formation relies on the coordination of dynamic pre- and postsynaptic structures during brain development. Liu et al. reveal that presynaptic terminal maturation of mossy fiber axons is retrogradely regulated by postsynaptic scaffold protein Lnx1 via stabilizing EphB receptor kinases.

Neuronal connections are initiated by axon targeting to form synapses. However, how the maturation of axon terminals is modulated through interacting with postsynaptic elements remains elusive. In this study, we find that ligand of Numb protein X 1 (Lnx1), a postsynaptic PDZ protein expressed in hippocampal CA3 pyramidal neurons, is essential for mossy fiber (MF) axon targeting during the postnatal period. Lnx1 deletion causes defective synaptic arrangement that leads to aberrant presynaptic terminals. We further identify EphB receptors as novel Lnx1-binding proteins to form a multiprotein complex that is stabilized on the CA3 neuron membrane through preventing proteasome activity. EphB1 and EphB2 are independently required to transduce distinct signals controlling MF pruning and targeting for precise DG-CA3 synapse formation. Furthermore, constitutively active EphB2 kinase rescues structure of the wired MF terminals in Lnx1 mutant mice. Our data thus define a retrograde trans-synaptic regulation required for integration of post- and presynaptic structure that participates in building hippocampal neural circuits during the adolescence period.

Effects of EphB4 receptor expression on colorectal cancer cells, tumor growth, vascularization and composition

BACKGROUND

Colorectal cancer (CRC) is one of the most common causes of cancer-related deaths worldwide. Increased expression of the molecular target, EphB4 receptor, has been observed in several cancer types. However, studies on the role of EphB4 receptor in CRC have yielded contradictory results. The aim of this study was to investigate the influence of EphB4 expression levels on CRC cell behavior and its contribution to tumor growth and vascularization.

METHODS

SW480, LIM2405 and CT26 CRC cell lines were transfected with EphB4 expression vector. High EphB4 expressing cells were compared to low EphB4 expressing empty vector controls. Proliferation and migration assays as well as EphrinB2-Fc cell stimulations were conducted in vitro and subcutaneous xenografts of CRC were analyzed in vivo.

RESULTS

High EphB4 expression enhanced migratory ability of these CRC cell lines in vitro and contributed to a significant increase in tumor growth and vascularization in vivo. Tumours induced with high EphB4 expressing SW480 and LIM2405 cells yielded homogenous masses densely packed with cancer cells. EphrinB2-Fc cell stimulations induced cell clustering of high EphB4 expressing SW480 and LIM2405 in vitro.

CONCLUSION

These results suggest that with enhanced vascularization and an increase in migratory abilities, the high EphB4 expressing cells may be able to metastasize more readily.

Upregulation of the long noncoding RNA FOXD2-AS1 promotes carcinogenesis by epigenetically silencing EphB3 through EZH2 and LSD1, and predicts poor prognosis in gastric cancer

Accumulating data indicate that long noncoding RNAs (lncRNAs) serve as important modulators in biological processes and are dysregulated in diverse tumors. The function of FOXD2-AS1 in gastric cancer (GC) progression and related biological mechanisms remain undefined. A comprehensive analysis identified that FOXD2-AS1 enrichment was upregulated markedly in GC and positively correlated with a large tumor size, a later pathologic stage, and a poor prognosis. Gene-set enrichment analysis (GSEA) in GEO datasets uncovered that cell cycle and DNA replication associated genes were enriched in patients with high FOXD2-AS1 expression. Loss of FOXD2-AS1 function inhibited cell growth via inhibiting the cell cycle in GC, whereas upregulation of FOXD2-AS1 expression promoted cancer progression. The enhancer of zeste homolog 2 (EZH2) and lysine (K)-specific demethylase 1A (LSD1) proteins were found to serve as binding partners of FOXD2-AS1 and mediators of FOXD2-AS1 function. Mechanically, FOXD2-AS1 promoted GC tumorigenesis partly through EZH2 and LSD1 mediated EphB3 downregulation. The present results revealed that FOXD2-AS1 acted as a tumor inducer in GC partly through EphB3 inhibition by direct interaction with EZH2 and LSD1, and may prove to be a potential biomarker of carcinogenesis.

Wnt Signalling in Intestinal Stem Cells: Lessons from Mice and Flies

Adult stem cells play critical roles in the basal maintenance of tissue integrity, also known as homeostasis, and in tissue regeneration following damage. The highly conserved Wnt signalling pathway is a key regulator of stem cell fate. In the gastrointestinal tract, Wnt signalling activation drives homeostasis and damage-induced repair. Additionally, deregulated Wnt signalling is a common hallmark of age-associated tissue dysfunction and cancer. Studies using mouse and fruit fly models have greatly improved our understanding of the functional contribution of the Wnt signalling pathway in adult intestinal biology. Here, we summarize the latest knowledge acquired from mouse and Drosophila research regarding canonical Wnt signalling and its key functions during stem cell driven intestinal homeostasis, regeneration, ageing and cancer.

The EphA2 receptor is activated through induction of distinct, ligand-dependent oligomeric structures

The EphA2 receptor tyrosine kinase is capable of activating multiple diverse signaling pathways with roles in processes such as tissue homeostasis and cancer. EphA2 is known to form activated oligomers in the presence of ephrin-A ligands. Here, we characterize the lateral interactions between full-length EphA2 molecules in the plasma membrane in the presence of three types of ligands (dimeric ephrinA1-Fc, monomeric ephrinA1, and an engineered peptide ligand) as well as in the absence of ligand, using a quantitative FRET technique. The data show that EphA2 forms higher-order oligomers and two different types of dimers that all lead to increased EphA2 tyrosine phosphorylation, which is indicative of increased kinase-dependent signaling. We find that different ligands stabilize conformationally distinct oligomers that are assembled through two different interfaces. Our results suggest that these different oligomeric assemblies could have distinct signaling properties, contributing to the diverse activities of the EphA2 receptor.

Deo Singh et al. use Fully Quantified Spectral Imaging-FRET to show that the EphA2 receptor forms dimers or higher order oligomers depending on the type of ligand, and that different ligands stabilize EphA2 dimers through distinct interfaces. These findings may explain how EphA2 activates diverse signaling pathways.

SOX2 regulates common and specific stem cell features in the CNS and endoderm derived organs

Stem cells are defined by their capacities to self-renew and generate progeny of multiple lineages. The transcription factor SOX2 has key roles in the regulation of stem cell characteristics, but whether SOX2 achieves these functions through similar mechanisms in distinct stem cell populations is not known. To address this question, we performed RNA-seq and SOX2 ChIP-seq on embryonic mouse cortex, spinal cord, stomach and lung/esophagus. We demonstrate that, although SOX2 binds a similar motif in the different cell types, its target regions are primarily cell-type-specific and enriched for the distinct binding motifs of appropriately expressed interacting co-factors. Furthermore, cell-type-specific SOX2 binding in endodermal and neural cells is most often found around genes specifically expressed in the corresponding tissue. Consistent with this, we demonstrate that SOX2 target regions can act as cis-regulatory modules capable of directing reporter expression to appropriate tissues in a zebrafish reporter assay. In contrast, SOX2 binding sites found in both endodermal and neural tissues are associated with genes regulating general stem cell features, such as proliferation. Notably, we provide evidence that SOX2 regulates proliferation through conserved mechanisms and target genes in both germ layers examined. Together, these findings demonstrate how SOX2 simultaneously regulates cell-type-specific, as well as core transcriptional programs in neural and endodermal stem cells.

The fine-tuned activities of stem cells are essential for embryonic development and organ maintenance. All types of stem cells share the abilities to self-renew and differentiate into specific cell-types, though the stem cells of different organs have distinct gene expression profiles and competences. Despite these unifying properties, to what extent diverse populations of stem cells utilize similar regulatory mechanisms remains unclear. To address this issue, we map the binding pattern of the key stem cell transcription factor SOX2 in the developing cortex, spinal cord, stomach and lung/esophagus. We find that, even though the core DNA-sequence it targets is similar in all tissues, its binding location is highly divergent and reflects the gene expression profile of each cell type. Moreover, DNA-regions targeted by SOX2 are enriched for binding motifs of distinct co-factors in each tissue, which we demonstrate can physically and functionally interact with SOX2. Consistent with these findings, DNA-regions bound specifically in cells of one germ layer are capable of driving fluorescent reporter gene expression in corresponding zebrafish tissues. Finally, we demonstrate that proliferation genes are bound by SOX2 in all examined tissues, and that cell division is controlled via a common mechanism in neural and endodermal cells. These findings provide a striking example of how a single transcription factor regulates both core and specific stem cell processes in multiple cellular contexts.

Distinct Effects of Growth Hormone and Glutamine on Activation of Intestinal Stem Cells

BACKGROUND

For patients with short bowel syndrome under parenteral nutrition support, growth hormone (GH) and glutamine (GLN) have been found to help the growth of intestinal mucosa. In this research, we studied the effects of GH and GLN on intestinal stem cells (ISCs).

METHODS

The in vitro and in vivo effects of GH and/or GLN on ISCs were evaluated by observing the ability of ISCs to form organoids in a Matrigel culture system. The expression levels of stemness and differentiation markers in ISCs and organoids were assessed using quantitative real-time polymerase chain reaction, immunofluorescence assay, and immunohistochemistry staining.

RESULTS

In vitro administration of GH activated the stemness of ISCs, whereas GLN enhanced the expression of chromogranin A and Muc2, which are differentiation markers in enteroendocrine and goblet cells, respectively. Administration of GH or GLN in mice showed that GH, but not GLN, upregulated the proliferative activity of ISCs with increased formation of crypt organoids. In addition, GH increased the expression of Lgr5 and GLN enhanced expression of Muc2 in the crypt fractions of the intestines in mice.

CONCLUSION

These results suggest that GH mainly enhances proliferative activities, whereas GLN promotes the differentiation potential of ISCs.

Current Understanding of the Pathways Involved in Adult Stem and Progenitor Cell Migration for Tissue Homeostasis and Repair

With the advancements in the field of adult stem and progenitor cells grows the recognition that the motility of primitive cells is a pivotal aspect of their functionality. There is accumulating evidence that the recruitment of tissue-resident and circulating cells is critical for organ homeostasis and effective injury responses, whereas the pathobiology of degenerative diseases, neoplasm and aging, might be rooted in the altered ability of immature cells to migrate. Furthermore, understanding the biological machinery determining the translocation patterns of tissue progenitors is of great relevance for the emerging methodologies for cell-based therapies and regenerative medicine. The present article provides an overview of studies addressing the physiological significance and diverse modes of stem and progenitor cell trafficking in adult mammalian organs, discusses the major microenvironmental cues regulating cell migration, and describes the implementation of live imaging approaches for the exploration of stem cell movement in tissues and the factors dictating the motility of endogenous and transplanted cells with regenerative potential.

Intestinal Stem Cell Niche Insights Gathered from Both In Vivo and Novel In Vitro Models

Intestinal stem cells are located at the base of the crypts and are surrounded by a complex structure called niche. This environment is composed mainly of epithelial cells and stroma which provides signals that govern cell maintenance, proliferation, and differentiation. Understanding how the niche regulates stem cell fate by controlling developmental signaling pathways will help us to define how stem cells choose between self-renewal and differentiation and how they maintain their undifferentiated state. Tractable in vitro assay systems, which reflect the complexity of the in vivo situation but provide higher level of control, would likely be crucial in identifying new players and mechanisms controlling stem cell function. Knowledge of the intestinal stem cell niche gathered from both in vivo and novel in vitro models may help us improve therapies for tumorigenesis and intestinal damage and make autologous intestinal transplants a feasible clinical practice.

EphB2 signaling-mediated Sirt3 expression reduces MSC senescence by maintaining mitochondrial ROS homeostasis

Disruption of mitochondrial reactive oxygen species (mtROS) homeostasis is a key factor inducing UCB-MSC senescence. Accordingly, preventing mtROS accumulation will help in suppressing the UCB-MSC senescence. In this study, we observed that the expressions of EphrinB2 and EphB2 were inversely regulated by UCB-MSC passage-dependent manner. EphB2 signaling induced mitochondrial translocation of Sirt3. The knockdown of SIRT3 inhibited the effect of EphB2 signaling in UCB-MSCs. Subsequently, EphrinB2-Fc induced the nuclear translocation of Nrf-2 via c-Src phosphorylation dependent manner, and Sirt3 expression was regulated by Nrf-2. Among Sirt3 target genes, EphB2 signaling increased MnSOD and reduced the mtROS level in UCB-MSCs. Furthermore, the deacetylase effect of Sirt3 enhanced the MnSOD activity by deacetylation at the lysine 68 residue and therapeutic effect of UCB-MSCs on skin-wound healing was increased by EphB2 activation. In conclusion, the EphB2 can serve as a novel target for the optimizing the therapeutic use of UCB-MSCs in wound repair by MnSOD-mediated mtROS scavenging through EphB2/c-Src signaling pathway and Nrf-2-dependent Sirt3 expression.

EGFL6 Regulates the Asymmetric Division, Maintenance, and Metastasis of ALDH+ Ovarian Cancer Cells

Little is known about the factors that regulate the asymmetric division of cancer stem-like cells (CSC). Here, we demonstrate that EGFL6, a stem cell regulatory factor expressed in ovarian tumor cells and vasculature, regulates ALDH⁺ ovarian CSC. EGFL6 signaled at least in part via the oncoprotein SHP2 with concomitant activation of ERK. EGFL6 signaling promoted the migration and asymmetric division of ALDH⁺ ovarian CSC. As such, EGFL6 increased not only tumor growth but also metastasis. Silencing of EGFL6 or SHP2 limited numbers of ALDH⁺ cells and reduced tumor growth, supporting a critical role for EGFL6/SHP2 in ALDH⁺ cell maintenance. Notably, systemic administration of an EGFL6-neutralizing antibody we generated restricted tumor growth and metastasis, specifically blocking ovarian cancer cell recruitment to the ovary. Together, our results offer a preclinical proof of concept for EGFL6 as a novel therapeutic target for the treatment of ovarian cancer. Cancer Res; 76(21); 6396-409. ©2016 AACR.

An agent-based model of anoikis in the colon crypt displays novel emergent behaviour consistent with biological observations

Colorectal cancer (CRC) is a major cause of cancer mortality. Colon crypts are multi-cellular flask-shaped invaginations of the colonic epithelium, with stem cells at their base which support the continual turnover of the epithelium with loss of cells by anoikis from the flat mucosa. Mutations in these stem cells can become embedded in the crypts, a process that is strongly implicated in CRC initiation. We describe a computational model which includes novel features, including an accurate representation of the geometry of the crypt mouth. Model simulations yield previously unseen emergent phenomena, such as localization of cell death to a small region of the crypt mouth which corresponds with that observed in vivo. A mechanism emerges in the model for regulation of crypt cellularity in response to changes in either cell proliferation rates or membrane adhesion strengths. We show that cell shape assumptions influence this behaviour, with cylinders recapitulating biology better than spheres. Potential applications of the model include determination of roles of mutations in neoplasia and exploring factors for altered crypt morphodynamics.

Loss of the EPH receptor B6 contributes to colorectal cancer metastasis

Although deregulation of EPHB signaling has been shown to be an important step in colorectal tumorigenesis, the role of EPHB6 in this process has not been investigated. We found here that manipulation of EPHB6 levels in colon cancer cell lines has no effect on their motility and growth on a solid substrate, soft agar or in a xenograft mouse model. We then used an EphB6 knockout mouse model to show that EphB6 inactivation does not efficiently initiate tumorigenesis in the intestinal tract. In addition, when intestinal tumors are initiated genetically or pharmacologically in EphB6^+/+ and EphB6^−/− mice, no differences were observed in animal survival, tumor multiplicity, size or histology, and proliferation of intestinal epithelial cells or tumor cells. However, reintroduction of EPHB6 into colon cancer cells significantly reduced the number of lung metastasis after tail-vein injection in immunodeficient mice, while EPHB6 knockdown in EPHB6-expressing cells increased their metastatic spread. Consistently, although EPHB6 protein expression in a series of 130 primary colorectal tumors was not associated with patient survival, EPHB6 expression was significantly lower in lymph node metastases compared to primary tumors. Our results indicate that the loss of EPHB6 contributes to the metastatic process of colorectal cancer.

EPHRIN-B1 Mosaicism Drives Cell Segregation in Craniofrontonasal Syndrome hiPSC-Derived Neuroepithelial Cells

Although human induced pluripotent stem cells (hiPSCs) hold great potential for the study of human diseases affecting disparate cell types, they have been underutilized in seeking mechanistic insights into the pathogenesis of congenital craniofacial disorders. Craniofrontonasal syndrome (CFNS) is a rare X-linked disorder caused by mutations in EFNB1 and characterized by craniofacial, skeletal, and neurological anomalies. Heterozygous females are more severely affected than hemizygous males, a phenomenon termed cellular interference that involves mosaicism for EPHRIN-B1 function. Although the mechanistic basis for cellular interference in CFNS has been hypothesized to involve Eph/ephrin-mediated cell segregation, no direct evidence for this has been demonstrated. Here, by generating hiPSCs from CFNS patients, we demonstrate that mosaicism for EPHRIN-B1 expression induced by random X inactivation in heterozygous females results in robust cell segregation in human neuroepithelial cells, thus supplying experimental evidence that Eph/ephrin-mediated cell segregation is relevant to pathogenesis in human CFNS patients.

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A novel iPSC line can effectively model a craniofacial condition

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Eph/ephrin-mediated cell segregation underlies CFNS

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Cell segregation occurs in CFNS neuroepithelial progenitor cells

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Neuroepithelial progenitors are a possible cell of origin for CFNS dysmorphogenesis

Investigation of the role of tyrosine kinase receptor EPHA3 in colorectal cancer

EPH signaling deregulation has been shown to be important for colorectal carcinogenesis and genome-wide sequencing efforts have identified EPHA3 as one of the most frequently mutated genes in these tumors. However, the role of EPHA3 in colorectal cancer has not been thoroughly investigated. We show here that ectopic expression of wild type EPHA3 in colon cancer cells did not affect their growth, motility/invasion or metastatic potential in vivo. Moreover, overexpression of mutant EPHA3 or deletion of the endogenous mutant EPHA3 in colon cancer cells did not affect their growth or motility. EPHA3 inactivation in mice did not initiate the tumorigenic process in their intestine, and had no effects on tumor size/multiplicity after tumor initiation either genetically or pharmacologically. In addition, immunohistochemical analysis of EPHA3 tumor levels did not reveal associations with survival or clinicopathological features of colorectal cancer patients. In conclusion, we show that EPHA3 does not play a major role in colorectal tumorigenesis. These results significantly contribute to our understanding of the role of EPH signaling during colorectal carcinogenesis, and highlighting the need for detailed functional studies to confirm the relevance of putative cancer driver genes identified in sequencing efforts of the cancer genome.

Different in vivo and in vitro transformation of intestinal stem cells in mismatch repair deficiency

Mutations in mismatch repair (MMR) genes result in microsatellite instability (MSI) and early onset of colorectal cancer. To get mechanistic insights into the time scale, sequence and frequency of intestinal stem cell (ISC) transformation, we quantified MSI and growth characteristics of organoids of Msh2-deficient and control mice from birth until tumor formation and related them to tissue gene expression. Although in Msh2-deficient organoids MSI continuously increased from birth, growth characteristics remained stable at first. Months before tumor onset, normal Msh2-deficient tissue contained tumor precursor cells forming organoids with higher MSI, cystic growth and growth rates resembling temporarily those of tumor organoids. Consistently, Msh2-deficient tissue exhibited a tumor-like gene signature. Normal Msh2-deficient organoids showed increased inheritable transient cyst-like growth, which became independent of R-spondin. ISC transformation proceeded faster in vitro than in vivo independent of the underlying genotype but more under MMR deficiency. Transient cyst-like growth but not MSI was suppressed by aspirin. In summary, as highlighted by organoids, molecular alterations continuously proceeded long before tumor onset in MMR-deficient intestine, thus increasing its susceptibility for ISC transformation.

Role of Src Family Kinases in Regulation of Intestinal Epithelial Homeostasis

Proper regulation of epithelial cell turnover is important for the structural integrity and homeostasis of various tissues, including the intestine. Here we show that ablation of Csk, a negative regulator of Src family kinases (SFKs), specifically in intestinal epithelial cells (IECs) resulted in the development of hyperplasia throughout the intestinal epithelium of mice. Such conditional ablation of Csk also increased the proliferative activity and turnover of IECs, disturbed the differentiation of Paneth and goblet cells, reduced the number of intestinal stem cells, and attenuated the expression of Wnt target genes in the intestine. Moreover, the tyrosine phosphorylation of focal adhesion kinase (FAK) and the activities of both Rac and Yes-associated protein (YAP) were increased in intestinal crypts or organoids of the mutant mice, whereas inhibition of Rac or YAP activity rescued the mutant phenotypes. Our results thus suggest that SFKs promote the proliferation of IECs in intestinal crypts through activation of Rac or YAP and that they thereby contribute to the proper regulation of IEC turnover and intestinal homeostasis.

Unidirectional Eph/ephrin signaling creates a cortical actomyosin differential to drive cell segregation

Eph/ephrins drive cell segregation and boundary formation. O’Neill et al. discover that segregation is driven by unidirectional kinase-dependent EphB signaling. Unidirectional signaling generates a cortical actin differential between ephrin-B1– and EphB2-expressing cells and requires ROCK activity for cell segregation.

Cell segregation is the process by which cells self-organize to establish developmental boundaries, an essential step in tissue formation. Cell segregation is a common outcome of Eph/ephrin signaling, but the mechanisms remain unclear. In craniofrontonasal syndrome, X-linked mosaicism for ephrin-B1 expression has been hypothesized to lead to aberrant Eph/ephrin-mediated cell segregation. Here, we use mouse genetics to exploit mosaicism to study cell segregation in the mammalian embryo and integrate live-cell imaging to examine the underlying cellular and molecular mechanisms. Our data demonstrate that dramatic ephrin-B1–mediated cell segregation occurs in the early neuroepithelium. In contrast to the paradigm that repulsive bidirectional signaling drives cell segregation, unidirectional EphB kinase signaling leads to cell sorting by the Rho kinase–dependent generation of a cortical actin differential between ephrin-B1– and EphB-expressing cells. These results define mechanisms of Eph/ephrin-mediated cell segregation, implicating unidirectional regulation of cortical actomyosin contractility as a key effector of this fundamental process.

Regulation and plasticity of intestinal stem cells during homeostasis and regeneration

The intestinal epithelium is the fastest renewing tissue in mammals and has a large flexibility to adapt to different types of damage. Lgr5⁺ crypt base columnar (CBC) cells act as stem cells during homeostasis and are essential during regeneration. Upon perturbation, the activity of CBCs is dynamically regulated to maintain homeostasis and multiple dedicated progenitor cell populations can reverse to the stem cell state upon damage, adding another layer of compensatory mechanisms to facilitate regeneration. Here, we review our current understanding of how intestinal stem and progenitor cells contribute to homeostasis and regeneration, and the different signaling pathways that regulate their behavior. Nutritional state and inflammation have been recently identified as upstream regulators of stem cell activity in the mammalian intestine, and we explore how these systemic signals can influence homeostasis and regeneration.

Comprehensive review of the duplication 3q syndrome and report of a patient with Currarino syndrome and de novo duplication 3q26.32-q27.2

Partial duplications of the long arm of chromosome 3, dup(3q), are a rare but well-described condition, sharing features of Cornelia de Lange syndrome. Around two thirds of cases are derived from unbalanced translocations, whereas pure dup(3q) have rarely been reported. Here, we provide an extensive review of the literature on dup(3q). This search revealed several patients with caudal malformations and anomalies, suggesting that caudal malformations or anomalies represent an inherent phenotypic feature of dup(3q). In this context, we report a patient with a pure de novo duplication 3q26.32-q27.2. The patient had the clinical diagnosis of Currarino syndrome (CS) (characterized by the triad of sacral anomalies, anorectal malformations and a presacral mass) and additional features, frequently detected in patients with a dup(3q). Mutations within the MNX1 gene were found to be causative in CS but no MNX1 mutation could be detected in our patient. Our comprehensive search for candidate genes located in the critical region of the duplication 3q syndrome, 3q26.3-q27, revealed a so far neglected phenotypic overlap of dup(3q) and the Pierpont syndrome, associated with a mutation of the TBL1XR1 gene on 3q26.32.

Amygdala EphB2 Signaling Regulates Glutamatergic Neuron Maturation and Innate Fear

The amygdala serves as emotional center to mediate innate fear behaviors that are reflected through neuronal responses to environmental aversive cues. However, the molecular mechanism underlying the initial neuron responses is poorly understood. In this study, we monitored the innate defensive responses to aversive stimuli of either elevated plus maze or predator odor in juvenile mice and found that glutamatergic neurons were activated in amygdala. Loss of EphB2, a receptor tyrosine kinase expressed in amygdala neurons, suppressed the reactions and led to defects in spine morphogenesis and fear behaviors. We further found a coupling of spinogenesis with these threat cues induced neuron activation in developing amygdala that was controlled by EphB2. A constitutively active form of EphB2 was sufficient to rescue the behavioral and morphological defects caused by ablation of ephrin-B3, a brain-enriched ligand to EphB2. These data suggest that kinase-dependent EphB2 intracellular signaling plays a major role for innate fear responses during the critical developing period, in which spinogenesis in amygdala glutamatergic neurons was involved.

SIGNIFICANCE STATEMENT

Generation of innate fear responses to threat as an evolutionally conserved brain feature relies on development of functional neural circuit in amygdala, but the molecular mechanism remains largely unknown. We here identify that EphB2 receptor tyrosine kinase, which is specifically expressed in glutamatergic neurons, is required for the innate fear responses in the neonatal brain. We further reveal that EphB2 mediates coordination of spinogenesis and neuron activation in amygdala during the critical period for the innate fear. EphB2 catalytic activity plays a major role for the behavior upon EphB-ephrin-B3 binding and transnucleus neuronal connections. Our work thus indicates an essential synaptic molecular signaling within amygdala that controls synapse development and helps bring about innate fear emotions in the postnatal developing brain.

Eph receptor interclass cooperation is required for the regulation of cell proliferation

Cancer often arises by the constitutive activation of mitogenic pathways by mutations in stem cells. Eph receptors are unusual in that although they regulate the proliferation of stem/progenitor cells in many adult organs, they typically fail to transform cells. Multiple ephrins and Eph receptors are often co-expressed and are thought to be redundant, but we here describe an unexpected dichotomy with two homologous ligands, ephrin-B1 and ephrin-B2, regulating specifically migration or proliferation in the intestinal stem cell niche. We demonstrate that the combined activity of two different coexpressed Eph receptors of the A and B class assembled into common signaling clusters in response to ephrin-B2 is required for mitogenic signaling. The requirement of two different Eph receptors to convey mitogenic signals identifies a new type of cooperation within this receptor family and helps explain why constitutive activation of a single receptor fails to transform cells.

Current understanding concerning intestinal stem cells

In mammals, the intestinal epithelium is a tissue that contains two distinct pools of stem cells: active intestinal stem cells and reserve intestinal stem cells. The former are located in the crypt basement membrane and are responsible for maintaining epithelial homeostasis under intact conditions, whereas the latter exhibit the capacity to facilitate epithelial regeneration after injury. These two pools of cells can convert into each other, maintaining their quantitative balance. In terms of the active intestinal stem cells, their development into functional epithelium is precisely controlled by the following signaling pathways: Wnt/β-catenin, Ras/Raf/Mek/Erk/MAPK, Notch and BMP/Smad. However, mutations in some of the key regulator genes associated with these signaling pathways, such as APC, Kras and Smad4, are also highly associated with gut malformations. At this point, clarifying the biological characteristics of intestinal stem cells will increase the feasibility of preventing or treating some intestinal diseases, such as colorectal cancer. Moreover, as preclinical data demonstrate the therapeutic effects of colon stem cells on murine models of experimental colitis, the prospects of stem cell-based regenerative treatments for ulcerous lesions in the gastrointestinal tract will be improved all the same.

Paneth Cell-Rich Regions Separated by a Cluster of Lgr5+ Cells Initiate Crypt Fission in the Intestinal Stem Cell Niche

The crypts of the intestinal epithelium house the stem cells that ensure the continual renewal of the epithelial cells that line the intestinal tract. Crypt number increases by a process called crypt fission, the division of a single crypt into two daughter crypts. Fission drives normal tissue growth and maintenance. Correspondingly, it becomes less frequent in adulthood. Importantly, fission is reactivated to drive adenoma growth. The mechanisms governing fission are poorly understood. However, only by knowing how normal fission operates can cancer-associated changes be elucidated. We studied normal fission in tissue in three dimensions using high-resolution imaging and used intestinal organoids to identify underlying mechanisms. We discovered that both the number and relative position of Paneth cells and Lgr5+ cells are important for fission. Furthermore, the higher stiffness and increased adhesion of Paneth cells are involved in determining the site of fission. Formation of a cluster of Lgr5+ cells between at least two Paneth-cell-rich domains establishes the site for the upward invagination that initiates fission.

Crypt fission—a process responsible for normal intestinal growth and for the formation of adenomas —is governed by differential adhesion, stiffness, and proliferation of Lgr5+ cells and Paneth cells in the intestinal stem cell niche.

The intestinal tract undergoes many changes during development, and after birth it has to significantly elongate and widen in order to increase the surface area for absorption. Crypt fission is a key process in intestinal tissue expansion and is also involved in adenoma growth. Despite the importance of crypt fission, the mechanisms controlling it are poorly understood. Understanding how crypt fission is regulated in normal tissue can help us to determine how the process changes in cancer. Here, we describe cellular behaviour during crypt fission. We identify a specific cellular arrangement in the intestinal stem cell niche that is associated with crypt fission and reveals insights into the mechanisms controlling crypt fission. There are two different cell types at the crypt base, Lgr5+ and Paneth cells, which play distinct roles in this process. We find that both their location and differences between them in proliferation, stiffness, and adhesion are important for fission. Based on our data, we propose a model in which stiffer and more adhesive Paneth cells are necessary to shape the crypt base and establish where fission occurs, whereas softer Lgr5+ cells allow shape changes and proliferation to expand newly formed crypts. Our model is an important step in understanding how crypt fission is initiated in normal tissue and provides a framework to understand how the process changes in tumorigenesis.

The Effect of Analogues of 1α,25-Dihydroxyvitamin D₂ on the Regrowth and Gene Expression of Human Colon Cancer Cells Refractory to 5-Fluorouracil

This study aimed to evaluate the capacity of hypocalcemic analogues of 1α,25-dihydroxyvitamin D₂ (1,25D2) and 1α,25-dihydroxyvitamin D₃ (1,25D3) to inhibit regrowth and regulate the stemness-related gene expression in colon cancer cells undergoing renewal after exposure to 5-fluorouracil (5-FU). All of the tested analogues of 1,25D2 equally potently decreased the clonogenicity and the proliferative activity of HT-29 cells which survived the exposure to 5-FU, but differently regulated gene expression of these cells during their renewal. 1,25D2 and analogues (PRI-1907 and PRI-1917), as well as 1,25D3 and analogue PRI-2191, decreased the relative expression level of several stemness-related genes, such as NANOG, OCT3/4, PROM1, SOX2, ALDHA1, CXCR4, in HT-29/5-FU cells during their renewal, in comparison to untreated HT-29/5-FU cells. The other 1,25D2 analogues (PRI-1906 and PRI-1916) were not capable of downregulating the expression of these stemness-related genes as the analogues PRI-1907 and PRI-1917 did. All of the tested vitamin D analogues upregulated CDH1, the gene encoding E-cadherin associated with epithelial phenotype. Out of the series of analogues studied, side-chain branched analogues of 1,25D2 (PRI-1907, PRI-1917) and the analogue of 1,25D3 (PRI-2191) might be used to target cancer cells with stem-like phenotypes that survive conventional chemotherapy.

Vascular Endothelial Growth Factor (VEGF) Bioavailability Regulates Angiogenesis and Intestinal Stem and Progenitor Cell Proliferation during Postnatal Small Intestinal Development

Background

Vascular endothelial growth factor (VEGF) is a highly conserved, master regulatory molecule required for endothelial cell proliferation, organization, migration and branching morphogenesis. Podocoryne carnea and drosophila, which lack endothelial cells and a vascular system, express VEGF homologs, indicating potential roles beyond angiogenesis and vasculogenesis. The role of VEGF in the development and homeostasis of the postnatal small intestine is unknown. We hypothesized regulating VEGF bioavailability in the postnatal small intestine would exhibit effects beyond the vasculature and influence epithelial cell stem/progenitor populations.

Methods

VEGF mutant mice were created that overexpressed VEGF in the brush border of epithelium via the villin promotor following doxycycline treatment. To decrease VEGF bioavailability, sFlt-1 mutant mice were generated that overexpressed the soluble VEGF receptor sFlt-1 upon doxycycline administration in the intestinal epithelium. Mice were analyzed after 21 days of doxycycline administration.

Results

Increased VEGF expression was confirmed by RT-qPCR and ELISA in the intestine of the VEGF mutants compared to littermates. The VEGF mutant duodenum demonstrated increased angiogenesis and vascular leak as compared to littermate controls. The VEGF mutant duodenum revealed taller villi and increased Ki-67-positive cells in the transit-amplifying zone with reduced Lgr5 expression. The duodenum of sFlt-1 mutants revealed shorter villi and longer crypts with reduced proliferation in the transit-amplifying zone, reduced expression of Dll1, Bmp4 and VE-cadherin, and increased expression of Sox9 and EphB2.

Conclusions

Manipulating VEGF bioavailability leads to profound effects on not only the intestinal vasculature, but epithelial stem and progenitor cells in the intestinal crypt. Elucidation of the crosstalk between VEGF signaling in the vasculature, mesenchyme and epithelial stem/progenitor cell populations may direct future cell therapies for intestinal dysfunction or disease.

Knockdown of EphB1 receptor decreases medulloblastoma cell growth and migration and increases cellular radiosensitization

The expression of members of the Eph family of receptor tyrosine kinases and their ephrin ligands is frequently dysregulated in medulloblastomas. We assessed the expression and functional role of EphB1 in medulloblastoma cell lines and engineered mouse models. mRNA and protein expression profiling showed expression of EphB1 receptor in the human medulloblastoma cell lines DAOY and UW228. EphB1 downregulation reduced cell growth and viability, decreased the expression of important cell cycle regulators, and increased the percentage of cells in G1 phase of the cell cycle. It also modulated the expression of proliferation, and cell survival markers. In addition, EphB1 knockdown in DAOY cells resulted in significant decrease in migration, which correlated with decreased β1-integrin expression and levels of phosphorylated Src. Furthermore, EphB1 knockdown enhanced cellular radiosensitization of medulloblastoma cells in culture and in a genetically engineered mouse medulloblastoma model. Using genetically engineered mouse models, we established that genetic loss of EphB1 resulted in a significant delay in tumor recurrence following irradiation compared to EphB1-expressing control tumors. Taken together, our findings establish that EphB1 plays a key role in medulloblastoma cell growth, viability, migration, and radiation sensitivity, making EphB1 a promising therapeutic target.

Mechanisms of ephrin-Eph signalling in development, physiology and disease

Eph receptor Tyr kinases and their membrane-tethered ligands, the ephrins, elicit short-distance cell-cell signalling and thus regulate many developmental processes at the interface between pattern formation and morphogenesis, including cell sorting and positioning, and the formation of segmented structures and ordered neural maps. Their roles extend into adulthood, when ephrin-Eph signalling regulates neuronal plasticity, homeostatic events and disease processes. Recently, new insights have been gained into the mechanisms of ephrin-Eph signalling in different cell types, and into the physiological importance of ephrin-Eph in different organs and in disease, raising questions for future research directions.

Regulatory System for Stem/Progenitor Cell Niches in the Adult Rodent Pituitary

The anterior lobe of the pituitary gland is a master endocrine tissue composed of five types of endocrine cells. Although the turnover rate of pituitary endocrine cells is as low as about 1.6% per day, recent studies have demonstrated that Sex-determining region Y-box 2 (SOX2)⁺-cells exist as pituitary stem/progenitor cells in the adult anterior lobe and contribute to cell regeneration. Notably, SOX2⁺-pituitary stem/progenitor cells form two types of niches in this tissue: the marginal cell layer (MCL-niche) and the dense cell clusters scattering in the parenchyma (parenchymal-niche). However, little is known about the mechanisms and factors for regulating the pituitary stem/progenitor cell niches, as well as the functional differences between the two types of niches. Elucidation of the regulatory mechanisms in the niches might enable us to understand the cell regeneration system that acts in accordance with physiological demands in the adult pituitary. In this review, so as to reveal the regulatory mechanisms of the two types of niche, we summarize the regulatory factors and their roles in the adult rodent pituitary niches by focusing on three components: soluble factors, cell surface proteins and extracellular matrixes.

Secreted Ephrin Receptor A7 Promotes Somatic Cell Reprogramming by Inducing ERK Activity Reduction

The role of secreted molecules in cellular reprogramming has been poorly understood. Here we identify a truncated form of ephrin receptor A7 (EPHA7) as a key regulator of reprogramming. Truncated EPHA7 is prominently upregulated and secreted during reprogramming. EPHA7 expression is directly regulated by OCT3/4. EphA7 knockdown results in marked reduction of reprogramming efficiency, and the addition of truncated EPHA7 is able to restore it. ERK activity is markedly reduced during reprogramming, and the secreted, truncated EPHA7 is responsible for ERK activity reduction. Remarkably, treatment of EphA7-knockdown MEFs with the ERK pathway inhibitor restores reprogramming efficiency. Analyses show that truncated EPHA7-induced ERK activity reduction plays an important role in the middle phase of reprogramming. Thus, our findings uncover the importance of secreted EPHA7-induced ERK activity reduction in reprogramming.

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EPHA7 is prominently upregulated during reprogramming

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Secreted, truncated EPHA7 contributes to promoting reprogramming

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Truncated EPHA7 drives reprogramming by inducing ERK1/2 activity reduction

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Truncated EPHA7 plays an important role in the middle phase of reprogramming

Regulation of cell differentiation by Eph receptor and ephrin signaling

There is increasing evidence that in addition to having major roles in morphogenesis, in some tissues Eph receptor and ephrin signaling regulates the differentiation of cells. In one mode of deployment, cell contact dependent Eph-ephrin activation induces a distinct fate of cells at the interface of their expression domains, for example in early ascidian embryos and in the vertebrate hindbrain. In another mode, overlapping Eph receptor and ephrin expression underlies activation within a cell population, which promotes or inhibits cell differentiation in bone remodelling, neural progenitors and keratinocytes. Eph-ephrin activation also contributes to formation of the appropriate number of progenitor cells by increasing or decreasing cell proliferation. These multiple roles of Eph receptor and ephrin signaling may enable a coupling between morphogenesis and the differentiation and proliferation of cells.

Eph receptor and ephrin function in breast, gut, and skin epithelia

Epithelial cells are tightly coupled together through specialized intercellular junctions, including adherens junctions, desmosomes, tight junctions, and gap junctions. A growing body of evidence suggests epithelial cells also directly exchange information at cell-cell contacts via the Eph family of receptor tyrosine kinases and their membrane-associated ephrin ligands. Ligand-dependent and -independent signaling via Eph receptors as well as reverse signaling through ephrins impact epithelial tissue homeostasis by organizing stem cell compartments and regulating cell proliferation, migration, adhesion, differentiation, and survival. This review focuses on breast, gut, and skin epithelia as representative examples for how Eph receptors and ephrins modulate diverse epithelial cell responses in a context-dependent manner. Abnormal Eph receptor and ephrin signaling is implicated in a variety of epithelial diseases raising the intriguing possibility that this cell-cell communication pathway can be therapeutically harnessed to normalize epithelial function in pathological settings like cancer or chronic inflammation.

Convergent Evolution of Head Crests in Two Domesticated Columbids Is Associated with Different Missense Mutations in EphB2

Head crests are important display structures in wild bird species and are also common in domesticated lineages. Many breeds of domestic rock pigeon (Columba livia) have crests of reversed occipital feathers, and this recessive trait is associated with a nonsynonymous coding mutation in the intracellular kinase domain of EphB2 (Ephrin receptor B2). The domestic ringneck dove (Streptopelia risoria) also has a recessive crested morph with reversed occipital feathers, and interspecific crosses between crested doves and pigeons produce crested offspring, suggesting a similar genetic basis for this trait in both species. We therefore investigated EphB2 as a candidate for the head crest phenotype of ringneck doves and identified a nonsynonymous coding mutation in the intracellular kinase domain that is significantly associated with the crested morph. This mutation is over 100 amino acid positions away from the crest mutation found in rock pigeons, yet both mutations are predicted to negatively affect the function of ATP-binding pocket. Furthermore, bacterial toxicity assays suggest that "crest" mutations in both species severely impact kinase activity. We conclude that head crests are associated with different mutations in the same functional domain of the same gene in two different columbid species, thereby representing striking evolutionary convergence in morphology and molecules.

Oleic acid enhances the motility of umbilical cord blood derived mesenchymal stem cells through EphB2-dependent F-actin formation

The role of unsaturated fatty acids (UFAs) is essential for determining stem cell functions. Eph/Ephrin interactions are important for regulation of stem cell fate and localization within their niche, which is significant for a wide range of stem cell behavior. Although oleic acid (OA) and Ephrin receptors (Ephs) have critical roles in the maintenance of stem cell functions, interrelation between Ephs and OA has not been explored. Therefore, the present study investigated the effect of OA-pretreated UCB-MSCs in skin wound-healing and underlying mechanism of Eph expression. OA promoted the motility of UCB-MSCs via EphB2 expression. OA-mediated GPR40 activation leads to Gαq-dependent PKCα phosphorylation. In addition, OA-induced phosphorylation of GSK3β was followed by β-catenin nuclear translocation in UCB-MSCs. Activation of β-catenin was blocked by PKC inhibitors, and OA-induced EphB2 expression was suppressed by β-cateninsiRNA transfection. Of those Rho-GTPases, Rac1 was activated in an EphB2-dependent manner. Accordingly, knocking down EphB2 suppressed F-actin expression. In vivo skin wound-healing assay revealed that OA-treated UCB-MSCs enhanced skin wound repair compared to UCB-MSCs pretreated with EphB2siRNA and OA. In conclusion, we showed that OA enhances UCB-MSC motility through EphB2-dependent F-actin formation involving PKCα/GSK3β/β-catenin and Rac1 signaling pathways.

An EphB-Abl signaling pathway is associated with intestinal tumor initiation and growth

EphB receptors regulate the proliferation and positioning of intestinal stem and progenitor cells. In addition, they can act as tumor promoters for adenoma development but suppress progression to invasive carcinoma. We used imatinib to abrogate Abl kinase activity in Apc(Min/+) mice and in mice with LGR5(+) stem cells that were genetically engineered to develop adenomatous polyposis coli. Imatinib treatment inhibited the tumor-promoting effects of EphB signaling without attenuating EphB-mediated tumor suppression, demonstrating a role for EphB signaling in the initiation of intestinal tumors. The imatinib treatment regimen extended the life span of Apc(Min/+) mice and reduced cell proliferation in cultured slices of adenomas from patients with familial adenomatous polyposis. These findings connect the EphB signaling pathway to the regulation of intestinal adenoma initiation via Abl kinase. Our findings may have clinical implications for pharmacological therapy against adenoma formation and cancer progression in patients predisposed to develop colorectal cancer.

Control of cortical neuronal migration by glutamate and GABA

Neuronal migration in the cortex is controlled by the paracrine action of the classical neurotransmitters glutamate and GABA. Glutamate controls radial migration of pyramidal neurons by acting primarily on NMDA receptors and regulates tangential migration of inhibitory interneurons by activating non-NMDA and NMDA receptors. GABA, acting on ionotropic GABAA-rho and GABAA receptors, has a dichotomic action on radially migrating neurons by acting as a GO signal in lower layers and as a STOP signal in upper cortical plate (CP), respectively. Metabotropic GABAB receptors promote radial migration into the CP and tangential migration of interneurons. Besides GABA, the endogenous GABAergic agonist taurine is a relevant agonist controlling radial migration. To a smaller extent glycine receptor activation can also influence radial and tangential migration. Activation of glutamate and GABA receptors causes increases in intracellular Ca(2+) transients, which promote neuronal migration by acting on the cytoskeleton. Pharmacological or genetic manipulation of glutamate or GABA receptors during early corticogenesis induce heterotopic cell clusters in upper layers and loss of cortical lamination, i.e., neuronal migration disorders which can be associated with neurological or neuropsychiatric diseases. The pivotal role of NMDA and ionotropic GABA receptors in cortical neuronal migration is of major clinical relevance, since a number of drugs acting on these receptors (e.g., anti-epileptics, anesthetics, alcohol) may disturb the normal migration pattern when present during early corticogenesis.

Localization of juxtacrine factor ephrin-B2 in pituitary stem/progenitor cell niches throughout life

We have recently reported that Sox2-expressing pituitary stem/progenitor cells contact each other via a tight-junction protein CAR to form stem/progenitor cell niches in the marginal cell layer facing the lumen and in the clusters scattered in the parenchyma of the anterior lobe. However, the microenvironment of the niche for the maintenance of stem cell function in the pituitary remains obscure. In this study of pituitary stem/progenitor cell niches, we have attempted to identify the expression of juxtacrine factor ephrin and its receptor. We have found that ephrin-B2 is expressed in the pituitary throughout development but changes its localization pattern. Notably, in the adult pituitary, ephrin-B2 immuno-signals occur in SOX2-, E-cadherin-, and CAR-triple-positive stem/progenitor cells in the niches. Our data suggest that ephrin-B2 signaling has an important role in the formation of pituitary stem/progenitor cell niches and in pituitary organogenesis.

Pou3f4-mediated regulation of ephrin-b2 controls temporal bone development in the mouse

The temporal bone encases conductive and sensorineural elements of the ear. Mutations of POU3F4 are associated with unique temporal bone abnormalities and X-linked mixed deafness (DFNX2/DFN3). However, the target genes and developmental processes controlled by POU3F4 transcription factor activity have remained largely uncharacterized. Ephrin-B2 (Efnb2) is a signaling molecule with well-documented effects on cell adhesion, proliferation, and migration. Our analyses of targeted mouse mutants revealed that Efnb2 loss-of-function phenocopies temporal bone abnormalities of Pou3f4 hemizygous null neonates: qualitatively identical malformations of the stapes, styloid process, internal auditory canal, and cochlear capsule were present in both mutants. Using failed/insufficient separation of the stapes and styloid process as a quantitative trait, we found that single gene Efnb2 loss-of-function and compound Pou3f4/Efnb2 loss-of-function caused a more severe phenotype than single gene Pou3f4 loss-of-function. Pou3f4 and Efnb2 gene expression domains overlapped at the site of impending stapes-styloid process separation and at subcapsular mesenchyme surrounding the cochlea; at both these sites, Efnb2 expression was attenuated in Pou3f4 hemizygous null mutants relative to control. Results of immunoprecipitation experiments using chromatin isolated from nascent middle ear mesenchyme supported the hypothesis of a physical association between Pou3f4 and specific non-coding sequence of Efnb2. We propose that Efnb2 is a target of Pou3f4 transcription factor activity and an effector of mesenchymal patterning during temporal bone development.

Eph- and ephrin-dependent mechanisms in tumor and stem cell dynamics

The erythropoietin-producing hepatocellular (Eph) receptors comprise the largest family of receptor tyrosine kinases (RTKs). Initially regarded as axon-guidance and tissue-patterning molecules, Eph receptors have now been attributed with various functions during development, tissue homeostasis, and disease pathogenesis. Their ligands, ephrins, are synthesized as membrane-associated molecules. At least two properties make this signaling system unique: (1) the signal can be simultaneously transduced in the receptor- and the ligand-expressing cell, (2) the signaling outcome through the same molecules can be opposite depending on cellular context. Moreover, shedding of Eph and ephrin ectodomains as well as ligand-dependent and -independent receptor crosstalk with other RTKs, proteases, and adhesion molecules broadens the repertoire of Eph/ephrin functions. These integrated pathways provide plasticity to cell-microenvironment communication in varying tissue contexts. The complex molecular networks and dynamic cellular outcomes connected to the Eph/ephrin signaling in tumor-host communication and stem cell niche are the main focus of this review.

Endothelial progenitor cells as a possible component of stem cell niche to promote self-renewal of mesenchymal stem cells

Stem cells dwell at the "stem cell niche" to accomplish a series of biological processes. The composition of the niche should be determined because the insufficient understanding of this feature limits the development in the study of stem cells. We showed in our study on mesenchymal stem cells (MSCs) that the MSCs first neighbored to CD31(+) cells, which proved to be endothelial progenitor cells (EPCs), and formed a group of cell colony before they exerted their biological functions. It was further proved that EPCs have close interactions with MSCs and promoted the self-renewal of the MSCs in vitro and in vivo. Together with these achievements, we hypothesized that EPCs may be a possible biological component of the MSC stem cell niche and affect the biological processes of MSCs.

SNAIL1 combines competitive displacement of ASCL2 and epigenetic mechanisms to rapidly silence the EPHB3 tumor suppressor in colorectal cancer

EPHB3 is a critical cellular guidance factor in the intestinal epithelium and an important tumor suppressor in colorectal cancer (CRC) whose expression is frequently lost at the adenoma-carcinoma transition when tumor cells become invasive. The molecular mechanisms underlying EPHB3 silencing are incompletely understood. Here we show that EPHB3 expression is anti-correlated with inducers of epithelial-mesenchymal transition (EMT) in primary tumors and CRC cells. In vitro, SNAIL1 and SNAIL2, but not ZEB1, repress EPHB3 reporter constructs and compete with the stem cell factor ASCL2 for binding to an E-box motif. At the endogenous EPHB3 locus, SNAIL1 triggers the displacement of ASCL2, p300 and the Wnt pathway effector TCF7L2 and engages corepressor complexes containing HDACs and the histone demethylase LSD1 to collapse active chromatin structure, resulting in rapid downregulation of EPHB3. Beyond its impact on EPHB3, SNAIL1 deregulates markers of intestinal identity and stemness and in vitro forces CRC cells to undergo EMT with altered morphology, increased motility and invasiveness. In xenotransplants, SNAIL1 expression abrogated tumor cell palisading and led to focal loss of tumor encapsulation and the appearance of areas with tumor cells displaying a migratory phenotype. These changes were accompanied by loss of EPHB3 and CDH1 expression. Intriguingly, SNAIL1-induced phenotypic changes of CRC cells are significantly impaired by sustained EPHB3 expression both in vitro and in vivo. Altogether, our results identify EPHB3 as a novel target of SNAIL1 and suggest that disabling EPHB3 signaling is an important aspect to eliminate a roadblock at the onset of EMT processes.

Defining hierarchies of stemness in the intestine: evidence from biomarkers and regulatory pathways

For decades, the rapid proliferation and well-defined cellular lineages of the small intestinal epithelium have driven an interest in the biology of the intestinal stem cells (ISCs) and progenitors that produce the functional cells of the epithelium. Recent and significant advances in ISC biomarker discovery have established the small intestinal epithelium as a powerful model system for studying general paradigms in somatic stem cell biology and facilitated elegant genetic and functional studies of stemness in the intestine. However, this newfound wealth of ISC biomarkers raises important questions of marker specificity. Furthermore, the ISC field must now begin to reconcile biomarker status with functional stemness, a challenge that is made more complex by emerging evidence that cellular hierarchies in the intestinal epithelium are more plastic than previously imagined, with some progenitor populations capable of dedifferentiating and functioning as ISCs following damage. In this review, we discuss the state of the ISC field in terms of biomarkers, tissue dynamics, and cellular hierarchies, and how these processes might be informed by earlier studies into signaling networks in the small intestine.

Regenerative medicine: prospects for the treatment of inflammatory bowel disease

This article reviews the current understanding of the processes driving the development and progression of inflammatory bowel disease (IBD), discusses how the dynamic crosstalk between resident microorganisms, host cells and the immune system is required in order to maintain immune homeostasis, and considers innovative strategies that allow the modification or modulation of the intestinal microorganismal community as a potential approach for treating IBD. This article next rationalizes the use of cell-based regenerative medicine as treatment for IBD, discusses the obstacles hindering its success, summarizes some of the results of recent clinical trials employing these therapies, and discusses ongoing work to enhance mesenchymal stem/stromal cells, making them better suited to the task of repairing the damage within the IBD gut.

Intestinal stem cells and celiac disease

Stem cells (SCs) are the key to tissue genesis and regeneration. Given their central role in homeostasis, dysfunctions of the SC compartment play a pivotal role in the development of cancers, degenerative disorders, chronic inflammatory pathologies and organ failure. The gastrointestinal tract is constantly exposed to harsh mechanical and chemical conditions and most of the epithelial cells are replaced every 3 to 5 d. According to the so-called Unitarian hypothesis, this renewal is driven by a common intestinal stem cell (ISC) residing within the crypt base at the origin of the crypt-to-villus hierarchical migratory pattern. Celiac disease (CD) can be defined as a chronic immune-mediated disease that is triggered and maintained by dietary proteins (gluten) in genetically predisposed individuals. Many advances have been achieved over the last years in understanding of the pathogenic interactions among genetic, immunological and environmental factors in CD, with a particular emphasis on intestinal barrier and gut microbiota. Conversely, little is known about ISC modulation and deregulation in active celiac disease and upon a gluten-free diet. Nonetheless, bone marrow-derived SC transplantation has become an option for celiac patients with complicated or refractory disease. This manuscript summarizes the “state of the art” regarding CD and ISCs, their niche and potential role in the development and treatment of the disease.