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

Role of the protein tyrosine phosphatase Shp2 in homeostasis of the intestinal epithelium

Protein tyrosine phosphorylation is thought to be important for regulation of the proliferation, differentiation, and rapid turnover of intestinal epithelial cells (IECs). The role of protein tyrosine phosphatases in such homeostatic regulation of IECs has remained largely unknown, however. Src homology 2-containing protein tyrosine phosphatase (Shp2) is a ubiquitously expressed cytoplasmic protein tyrosine phosphatase that functions as a positive regulator of the Ras-mitogen-activated protein kinase (MAPK) signaling pathway operative downstream of the receptors for various growth factors and cytokines, and it is thereby thought to contribute to the regulation of cell proliferation and differentiation. We now show that mice lacking Shp2 specifically in IECs (Shp2 CKO mice) develop severe colitis and die as early as 3 to 4 weeks after birth. The number of goblet cells in both the small intestine and colon of Shp2 CKO mice was markedly reduced compared with that for control mice. Furthermore, Shp2 CKO mice showed marked impairment of both IEC migration along the crypt-villus axis in the small intestine and the development of intestinal organoids from isolated crypts. The colitis as well as the reduction in the number of goblet cells apparent in Shp2 CKO mice were normalized by expression of an activated form of K-Ras in IECs. Our results thus suggest that Shp2 regulates IEC homeostasis through activation of Ras and thereby protects against the development of colitis.

Ephrin-B2 governs morphogenesis of endolymphatic sac and duct epithelia in the mouse inner ear

Control over ionic composition and volume of the inner ear luminal fluid endolymph is essential for normal hearing and balance. Mice deficient in either the EphB2 receptor tyrosine kinase or the cognate transmembrane ligand ephrin-B2 (Efnb2) exhibit background strain-specific vestibular-behavioral dysfunction and signs of abnormal endolymph homeostasis. Using various loss-of-function mouse models, we found that Efnb2 is required for growth and morphogenesis of the embryonic endolymphatic epithelium, a precursor of the endolymphatic sac (ES) and duct (ED), which mediate endolymph homeostasis. Conditional inactivation of Efnb2 in early-stage embryonic ear tissues disrupted cell proliferation, cell survival, and epithelial folding at the origin of the endolymphatic epithelium. This correlated with apparent absence of an ED, mis-localization of ES ion transport cells relative to inner ear sensory organs, dysplasia of the endolymph fluid space, and abnormally formed otoconia (extracellular calcite-protein composites) at later stages of embryonic development. A comparison of Efnb2 and Notch signaling-deficient mutant phenotypes indicated that these two signaling systems have distinct and non-overlapping roles in ES/ED development. Homozygous deletion of the Efnb2 C-terminus caused abnormalities similar to those found in the conditional Efnb2 null homozygote. Analyses of fetal Efnb2 C-terminus deletion heterozygotes found mis-localized ES ion transport cells only in the genetic background exhibiting vestibular dysfunction. We propose that developmental dysplasias described here are a gene dose-sensitive cause of the vestibular dysfunction observed in EphB-Efnb2 signaling-deficient mice.

Eph receptors and ephrins as targets for cancer therapy

Eph receptor tyrosine kinases and their ephrin ligands are involved in various signalling pathways and mediate critical steps of a wide variety of physiological and pathological processes. Increasing experimental evidence demonstrates that both Eph receptor and ephrin ligands are overexpressed in a number of human tumours, and are associated with tumour growth, invasiveness and metastasis. In this regard, the Eph/ephrin system provides the foundation for potentially exciting new targets for anticancer therapies for Eph-expressing tumours. The purpose of this review is to outline current advances in the role of Eph receptors and ephrin ligands in cancer, and to discuss novel therapeutic approaches of anticancer therapies.

New pharmacotherapy options for chemotherapy-induced alimentary mucositis

INTRODUCTION

Chemotherapy-induced alimentary mucositis is an extremely common condition that is caused by a breakdown of the mucosal barrier. It occurs in between 40 - 100% of cancer patients depending on the treatment regimen. Symptoms typically include pain from oral ulceration, vomiting and diarrhoea. Alimentary mucositis often necessitates chemotherapy reductions or treatment breaks, overall potentially compromising survival outcomes. Consequently, alimentary mucositis creates a burden not only on patients' quality of life but also on healthcare costs. Despite this, currently, there is no clinically effective localised/pharmacological therapy intervention strategy to prevent alimentary mucositis.

AREAS COVERED

Over recent years, a number of novel pharmacotherapy agents have been trialed in various preclinical and clinical settings. This critical review will therefore provide an overview of emerging pharmacotherapies for the treatment of alimentary mucositis following chemotherapy with particular emphasis on studies published in the last 2 years. A Pubmed literature search was conducted to identify eligible articles published before 30 November 2013 and each article was reviewed by all authors. All articles were written in English.

EXPERT OPINION

Currently, there is no clinically effective localised therapeutic intervention strategy to prevent the condition. New emerging areas of research have recently been proposed to play key roles in the development of alimentary mucositis and these areas may provide researchers and clinicians with new research directions. Hopefully this will continue, and evidence-based informed guidelines can be produced to improve clinical practice management of this condition.

Functional zonation of the rat adrenal cortex: the development and maintenance

The adrenal cortex of mammals consists of three concentric zones, i.e., the zona glomerulosa (zG), the zona fasciculata (zF), and the zona reticularis (zR), which secrete mineralocorticoids, glucocorticoids, and adrenal androgens, respectively. In 1994, we identified immunohistochemically a new zone between zG and zF of the rat adrenal gland. The zone appeared to be devoid of any significant endocrine functions specific to adrenocortical zones, therefore, we designated the zone as "undifferentiated cell zone (zU)". Further, BrdU (5-bromo-2'-deoxyuridine)-incorporating cells (cells in S-phase) were concentrated at the outer region and the inner region of zU, and these cells proliferated and migrated bidirectionally: toward zG centrifugally and toward zF centripetally. We proposed that cells in and around zU are stem/progenitor cells of the rat adrenal cortex, maintaining functional zonation of the adrenal cortex. The view is consistent with observations reported recently that Sonic hedgehog (Shh), an important factor in embryonic development and adult stem cell maintenance, exists in zU of the rat adrenal gland and the Shh-containing cells seem to migrate bidirectionally.

Effect of reduced EPHB4 expression in thymic epithelial cells on thymocyte development and peripheral T cell function

The Eph kinase (EPH) and ephrin (EFN) families are involved in a broad range of developmental processes. Increasing evidence is demonstrating the important roles of EPHBs and EphrinBs in the immune system. In this study on epithelial cell-specific Ephb4 knockout (KO) mice, we investigated T-cell development and function after EPHB4 deletion. KO mice presented normal thymic weight and cellularity. Their thymocyte subpopulation percentages were in the normal range. KO mice had normal T-cell numbers and percentages in the spleen, and T cells were activated and proliferated normally upon TCR ligation. Furthermore, naïve spleen CD4 cells from KO and wild type mice were capable of differentiating, in a comparable manner, into Th1, Th17 and Treg cells. In vivo, KO mice mounted effective delayed type hypersensitivity responses, indicating that thymocytes develop normally in the absence of TEC EPHB4, and T cells derived from EPHB4-deleted thymic epithelian cells (TEC) have normal function. Our data suggest that heavy redundancy and promiscuous interaction between EPHs and EFNs compensate for the missing EPHB4 in TECs, and TEC EPHB4's role in T cell development might only be revealed if multiple EPHs are ablated simultaneously. We cannot exclude the possibility that (1) some immunological parameters not examined in this study are affected by the deletion; (2) the deletion is not complete due to the leaky Cre-LoxP system, and the remaining EPHB4 in TEC is sufficient for thymocyte development; or (3) EPHB4 expression in TEC is not required for T cell development and function.

Role of the EphB2 receptor in autophagy, apoptosis and invasion in human breast cancer cells

The Eph and Ephrin proteins, which constitute the largest family of receptor tyrosine kinases, are involved in normal tissue development and cancer progression. Here, we examined the expression and role of the B-type Eph receptor EphB2 in breast cancers. By immunohistochemistry using a progression tissue microarray of human clinical samples, we found EphB2 to be expressed in benign tissues, but strongly increased in cancers particularly in invasive and metastatic carcinomas. Subsequently, we found evidence that EphB2, whose expression varies in established cell breast lines, possesses multiple functions. First, the use of a DOX-inducible system to restore EphB2 function to low expressers resulted in decreased tumor growth in vitro and in vivo, while its siRNA-mediated silencing in high expressers increased growth. This function involves the onset of apoptotic death paralleled by caspases 3 and 9 activation. Second, EphB2 was also found to induce autophagy, as assessed by immunofluorescence and/or immunoblotting examination of the LC3, ATG5 and ATG12 markers. Third, EphB2 also has a pro-invasive function in breast cancer cells that involves the regulation of MMP2 and MMP9 metalloproteases and can be blocked by treatment with respective neutralizing antibodies. Furthermore, EphB2-induced invasion is kinase-dependent and is impeded in cells expressing a kinase-dead mutant EphB2. In summary, we identified a mechanism involving a triple role for EphB2 in breast cancer progression, whereby it regulates apoptosis, autophagy, and invasion.

Age-associated defects in EphA2 signaling impair the migration of human cardiac progenitor cells

BACKGROUND

Aging negatively impacts on the function of resident human cardiac progenitor cells (hCPCs). Effective regeneration of the injured heart requires mobilization of hCPCs to the sites of damage. In the young heart, signaling by the guidance receptor EphA2 in response to the ephrin A1 ligand promotes hCPC motility and improves cardiac recovery after infarction.

METHODS AND RESULTS

We report that old hCPCs are characterized by cell-autonomous inhibition of their migratory ability ex vivo and impaired translocation in vivo in the damaged heart. EphA2 expression was not decreased in old hCPCs; however, the elevated level of reactive oxygen species in aged cells induced post-translational modifications of the EphA2 protein. EphA2 oxidation interfered with ephrin A1-stimulated receptor auto-phosphorylation, activation of Src family kinases, and caveolin-1-mediated internalization of the receptor. Cellular aging altered the EphA2 endocytic route, affecting the maturation of EphA2-containing endosomes and causing premature signal termination. Overexpression of functionally intact EphA2 in old hCPCs corrected the defects in endocytosis and downstream signaling, enhancing cell motility. Based on the ability of phenotypically young hCPCs to respond efficiently to ephrin A1, we developed a novel methodology for the prospective isolation of live hCPCs with preserved migratory capacity and growth reserve.

CONCLUSIONS

Our data demonstrate that the ephrin A1/EphA2 pathway may serve as a target to facilitate trafficking of hCPCs in the senescent myocardium. Importantly, EphA2 receptor function can be implemented for the selection of hCPCs with high therapeutic potential, a clinically relevant strategy that does not require genetic manipulation of stem cells.

Development of intestinal organoids as tissue surrogates: cell composition and the epigenetic control of differentiation

Intestinal organoids are multicellular crypt-like structures that can be derived from adult intestinal stem cells (ISCs), embryonic stem cells (ESCs) or induced pluripotent stem cells (IPSCs). Here we show that intestinal organoids generated from mouse ESCs were enriched in ISCs and early progenitors. Treatment of these organoids with a γ-secretase inhibitor increased Math1 and decreased Hes1 expression, indicating Notch signaling regulates ISC differentiation in these organoids. Lgr5 and Tert positive ISCs constituted approximately 10% and 20% of the organoids. As found in native tissue, Lgr5 and Tert expressing cells resolved into two discreet populations, which were stable over time. Intestinal organoids derived from cancer-prone Apc(Min/+) mice showed similar numbers of ISCs, but had reduced Math1 expression, indicating a suppressed secretory cell differentiation potential (as found in intestinal tissue). Apc(Min/+) organoids were used to screen epigenetically active compounds for those that increased Math1 expression and organoid differentiation (including HDAC inhibitors, Sirtuin (SIRT) modulators and methyltransferase inhibitors). Broad-spectrum HDAC inhibitors increased both Math1 and Muc2 expression, indicating an ability to promote the suppressed secretory cell differentiation pathway. Other epigenetic compounds had a diverse impact on cell differentiation, with a strong negative correlation between those that activated the secretory marker Muc2 and those that activated the absorptive cell marker Fabp2. These data show that ESC-derived intestinal organoids can be derived in large numbers, contain distinct ISC types and can be used to screen for agents that promote cell differentiation through different lineage pathways.

3q26.31-q29 duplication and 9q34.3 microdeletion associated with omphalocele, ventricular septal defect, abnormal first-trimester maternal serum screening and increased nuchal translucency: prenatal diagnosis and aCGH characterization

We present prenatal diagnosis and array comparative genomic hybridization characterization of 3q26.31-q29 duplication and 9q34.3 microdeletion in a fetus with omphalocele, ventricular septal defect, increased nuchal translucency, abnormal first-trimester maternal screening and facial dysmorphism with distinct features of the 3q duplication syndrome and Kleefstra syndrome. The 26.61-Mb duplication of 3q26.31-q29 encompasses EPHB3, CLDN1 and CLDN16, and the 972-kb deletion of 9q34.3 encompasses EHMT1. We review the literature of partial trisomy 3q associated with omphalocele and discuss the genotype-phenotype correlation in this case.

Neuron glia-related cell adhesion molecule (NrCAM) promotes topographic retinocollicular mapping

NrCAM (Neuron-glial related cell adhesion molecule), a member of the L1 family of cell adhesion molecules, reversibly binds ankyrin and regulates axon growth, but it has not been studied for a role in retinotopic mapping. During development of retino-collicular topography, NrCAM was expressed uniformly in retinal ganglion cells (RGCs) along both mediolateral and anteroposterior retinal axes, and was localized on RGC axons within the optic tract and superior colliculus (SC). Anterograde tracing of RGC axons in NrCAM null mutant mice at P10, when the map resembles its mature form, revealed laterally displaced ectopic termination zones (eTZs) of axons from the temporal retina, indicating defective mediolateral topography, which is governed by ephrinB/EphBs. Axon tracing at P2 revealed that interstitial branch orientation of ventral-temporal RGC axons in NrCAM null mice was compromised in the medial direction, likely accounting for displacement of eTZs. A similar retinocollicular targeting defect in EphB mutant mice suggested that NrCAM and EphB interact to regulate mediolateral retino-collicular targeting. We found that EphB2 tyrosine kinase but not an EphB2 kinase dead mutant, phosphorylated NrCAM at a conserved tyrosine residue in the FIGQY ankyrin binding motif, perturbing ankyrin recruitment in NrCAM transfected HEK293 cells. Furthermore, the phosphorylation of NrCAM at FIGQY in SC was decreased in EphB1/3 and EphB1/2/3 null mice compared to WT, while phospho-FIGQY of NrCAM in SC was increased in EphB2 constitutively active (F620D/F620D) mice. These results demonstrate that NrCAM contributes to mediolateral retinocollicular axon targeting by regulating RGC branch orientation through a likely mechanism in which ephrinB/EphB phosphorylates NrCAM to modulate linkage to the actin cytoskeleton.

Colorectal cancer defeating? Challenge accepted!

Colorectal tumours are actually considered as aberrant organs, within it is possible to notice a different stage of cell growth and differentiation. Their origin is reported to arise from a subpopulation of tumour cells endowed with, just like the healthy stem cells, self-renewal and aberrant multi-lineage differentiation capacity likely to be called colorectal cancer stem cells (CCSCs). Cancer stem cells (CSCs) fate, since their origin, reflects the influences from their microenvironment (or niche) both in the maintenance of stemness, in promoting their differentiation, and in inducing epithelial-mesenchymal transition, responsible of CSCs dissemination and subsequent formation of metastatic lesions. The tumour cells heterogeneity and their immuno-response resistance nowadays probably responsible of the failure of the conventional therapies, make this research field an open issue. Even more importantly, our increasing understanding of the cellular and molecular mechanisms that regulate CSC quiescence and cell cycle regulation, self-renewal, chemotaxis and resistance to cytotoxic agents, is expected to eventually result in tailor-made therapies with a significant impact on the morbidity and overall survival of colorectal cancer patients.

Transgenic overexpression of ephrin b1 in bone cells promotes bone formation and an anabolic response to mechanical loading in mice

To test if ephrin B1 overexpression enhances bone mass, we generated transgenic mice overexpressing ephrin B1 under the control of a 3.6 kb rat collagen 1A1 promoter (Col3.6-Tg^efnb1). Col3.6-Tg^efnb1 mice express 6-, 12- and 14-fold greater levels of full-length ephrin B1 protein in bone marrow stromal cells, calvarial osteoblasts, and osteoclasts, respectively. The long bones of both genders of Col3.6-Tg^efnb1 mice have increased trabecular bone volume, trabecular number, and trabecular thickness and decreased trabecular separation. Enhanced bone formation and decreased bone resorption contributed to this increase in trabecular bone mass in Col3.6-Tg^efnb1 mice. Consistent with these findings, our in vitro studies showed that overexpression of ephrin B1 increased osteoblast differentiation and mineralization, osterix and collagen 1A1 expression in bone marrow stromal cells. Interaction of ephrin B1 with soluble clustered EphB2-Fc decreased osteoclast precursor differentiation into multinucleated cells. Furthermore, we demonstrated that the mechanical loading-induced increase in EphB2 expression and newly formed bone were significantly greater in the Col3.6-Tg^efnb1 mice than in WT littermate controls. Our findings that overexpression of ephrin B1 in bone cells enhances bone mass and promotes a skeletal anabolic response to mechanical loading suggest that manipulation of ephrin B1 actions in bone may provide a means to sensitize the skeleton to mechanical strain to stimulate new bone formation.

Random chromosome segregation in mouse intestinal epithelial stem cells

The mammalian intestinal epithelium is endowed with a high cell turnover sustained by a few stem cells located in the bottoms of millions of crypts. Until recently, it was generally assumed that the extreme sensitivity to DNA damaging agents leading to cell death and the asymmetric mode of chromosome segregation of intestinal epithelial stem cells prevented the illicit survival of mutated stem cells and guarded against mistakes leading to aneuploidy and neoplastic transformation. Recent evidence points instead to a pool of mutipotent self-renewing stem cells capable of repairing DNA by homologous recombination significantly more efficiently than other crypt cells. Furthermore, the equilibrium between cell division and differentiation is achieved at the level of the cell population obeying to a random mode of chromosome segregation and a predominantly symmetric mode of cell division. This review summarizes the experimental findings on the mode of cell division adopted by intestinal epithelial stem cells.

Developmental mechanisms of topographic map formation and alignment

Brain connections are organized into topographic maps that are precisely aligned both within and across modalities. This alignment facilitates coherent integration of different categories of sensory inputs and allows for proper sensorimotor transformations. Topographic maps are established and aligned by multistep processes during development, including interactions of molecular guidance cues expressed in gradients; spontaneous activity-dependent axonal and dendritic remodeling; and sensory-evoked plasticity driven by experience. By focusing on the superior colliculus, a major site of topographic map alignment for different sensory modalities, this review summarizes current understanding of topographic map development in the mammalian visual system and highlights recent advances in map alignment studies. A major goal looking forward is to reveal the molecular and synaptic mechanisms underlying map alignment and to understand the physiological and behavioral consequences when these mechanisms are disrupted at various scales.

Contact repulsion controls the dispersion and final distribution of Cajal-Retzius cells

Cajal-Retzius (CR) cells play a fundamental role in the development of the mammalian cerebral cortex. They control the formation of cortical layers by regulating the migration of pyramidal cells through the release of Reelin. The function of CR cells critically depends on their regular distribution throughout the surface of the cortex, but little is known about the events controlling this phenomenon. Using time-lapse video microscopy in vivo and in vitro, we found that movement of CR cells is regulated by repulsive interactions, which leads to their random dispersion throughout the cortical surface. Mathematical modeling reveals that contact repulsion is both necessary and sufficient for this process, which demonstrates that complex neuronal assemblies may emerge during development through stochastic events. At the molecular level, we found that contact repulsion is mediated by Eph/ephrin interactions. Our observations reveal a mechanism that controls the even distribution of neurons in the developing brain.

EphB2 isolates a human marrow stromal cell subpopulation with enhanced ability to contribute to the resident intestinal cellular pool

To identify human bone marrow stromal cell (BMSC) subsets with enhanced ability to engraft/contribute to the resident intestinal cellular pool, we transplanted clonally derived BMSCs into fetal sheep. Analysis at 75 d post-transplantation showed 2 of the 6 clones engrafting the intestine at 4- to 5-fold higher levels (5.03±0.089 and 5.04±0.15%, respectively) than the other clones (P<0.01), correlating with the percentage of donor-derived Musashi-1(+) (12.01-14.17 vs. 1.2-3.8%; P<0.01) or leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5)(+) cells within the intestinal stem cell (ISC) region. Phenotypic and transcriptome analysis determined that the clones with enhanced intestinal contribution expressed high levels of Ephrin type B receptor 2 (EphB2). Intestinal explants demonstrated proliferation of the engrafted cells and ability to generate crypt-like structures in vitro still expressing EphB2. Additional transplants based on BMSC EphB2 expression demonstrated that, at 7 d post-transplant, the EphB2(high) BMSCs engrafted in the ISC region at levels of 2.1 ± 0.2%, while control EphB2(low) BMSCs engrafted at 0.3 ± 0.1% (P<0.01). Therefore we identified a marker for isolating and culturing an expandable subpopulation of BMSCs with enhanced intestinal homing and contribution to the ISC region.

EphA3 maintains tumorigenicity and is a therapeutic target in glioblastoma multiforme

Significant endeavor has been applied to identify functional therapeutic targets in glioblastoma (GBM) to halt the growth of this aggressive cancer. We show that the receptor tyrosine kinase EphA3 is frequently overexpressed in GBM and, in particular, in the most aggressive mesenchymal subtype. Importantly, EphA3 is highly expressed on the tumor-initiating cell population in glioma and appears critically involved in maintaining tumor cells in a less differentiated state by modulating mitogen-activated protein kinase signaling. EphA3 knockdown or depletion of EphA3-positive tumor cells reduced tumorigenic potential to a degree comparable to treatment with a therapeutic radiolabelled EphA3-specific monoclonal antibody. These results identify EphA3 as a functional, targetable receptor in GBM.

Loss of miR-204 expression enhances glioma migration and stem cell-like phenotype

Phenotypic similarities have long been recognized between subpopulations of glioma and neural stem cells. Many of these similar properties, including the robust abilities to self-renew, migrate, and invade, are hallmarks of glioma cells that render them extremely aggressive. However, the molecular mechanisms underlying this character, particularly in glioma stem-like cells that drive this disease, remain poorly understood. Here, we report the results of a differential miRNA expression screen that compared glioma and neural stem cells, where we found that miR-204 was markedly downregulated in both types of cells. Mechanistic investigations revealed that miR-204 simultaneously suppressed self-renewal, stem cell-associated phenotype, and migration of glioma cells by targeting the stemness-governing transcriptional factor SOX4 and the migration-promoting receptor EphB2. Restoring miR-204 expression in glioma cells suppressed tumorigenesis and invasiveness in vivo and increased overall host survival. Further evaluation revealed that the miR-204 promoter was hypermethylated and that attenuating promoter methylation was sufficient to upregulate miR-204 in glioma cells. Together, our findings reveal miR-204 as a pivotal regulator of the development of stem cell-like phenotypes and cell motility in malignant glioma cells.

Eph/ephrinB signalling is involved in the survival of thymic epithelial cells

The signals that determine the survival/death of the thymic epithelial cells (TECs) component during embryonic development of the thymus are largely unknown. In this study, we combine different in vivo and in vitro experimental approaches to define the role played by the tyrosine kinase receptors EphB2 and EphB3 and their ligands, ephrinsB, in the survival of embryonic and newborn (NB) TECs. Our results conclude that EphB2 and EphB3 are involved in the control of TEC survival and that the absence of these molecules causes increased apoptotic TEC proportions that result in decreased numbers of thymic cells and a smaller-sized gland. Furthermore, in vitro studies using either EphB2-Fc or ephrinB1-Fc fusion proteins demonstrate that the blockade of Eph/ephrinB signalling increases TEC apoptosis, whereas its activation rescues TECs from cell death. In these assays, both heterotypic thymocyte-TEC and homotypic TEC-TEC interactions are important for Eph/ephrinB-mediated TEC survival.

Ephrin-B stimulation of calvarial bone formation

INTRODUCTION

Ephrin-B2 on osteoclasts was reported to promote bone formation as part of homeostasis by activating the EphB4 tyrosine kinase receptor on osteoblasts. Little is known about the role of ephrin-B signaling to EphBs in developmental bone formation.

RESULTS

We observed expression of an ephrin-B2 LacZ chimeric allele in the periosteum, sutural bone fronts, and dura mater of embryonic and neonatal mice. Expression in the adult skull was confined to sutures, but was heavily upregulated at sites of bone injury. Culture of embryonic calvariae with soluble recombinant ephrin-B2/Fc doubled their bone content without altering suture width or overall skull morphology. Ephrin-B2/Fc also stimulated osteoblast marker gene expression in cultured MC3T3 preosteoblastic cells without the need for type 1 collagen-induced differentiation. EphB4 was absent in embryonic and adult skulls. However, EphB1 and EphB2, both physiological receptors for ephrin-Bs, were expressed at sites of osteogenesis, and EphB1 knockout mice displayed a reduction in calvarial bone content compared to controls.

CONCLUSIONS

These data support a role for ephrin-B2 in the development and healing of bone through activation of osteoblast-specific gene expression. EphB1 and EphB2 are likely candidates receptors for the ephrin-B2 in bone.

Ephrin regulation of palate development

Studies of palate development are motivated by the all too common incidence of cleft palate, a birth defect that imposes a tremendous health burden and can leave lasting disfigurement. Although, mechanistic studies of palate growth and fusion have focused on growth factors such as Transforming Growth Factor ß-3 (Tgfß3), recent studies have revealed that the ephrin family of membrane bound ligands and their receptors, the Ephs, play central roles in palatal morphogenesis, growth, and fusion. In this mini-review, we will discuss the recent findings by our group and others on the functions of ephrins in palatal development.

The Eph/Ephrin family in cancer metastasis: communication at the service of invasion

Cancer cells rely on intercellular communication throughout the different stages of their transformation and progression into metastasis. They do so by co-opting different processes such as cell-cell junctions, growth factors, receptors, and vesicular release. Initially characterized in neuronal and vascular tissues, Ephs and Ephrins, the largest family of receptor tyrosine kinases, comprised of two classes (i.e., A and B types), is increasingly scrutinized by cancer researchers. These proteins possess the particular features of both the receptors and ligands being membrane-bound which, via mandatory direct cell-cell interactions, undergo a bidirectional signal transduction initiated from both the receptor and the ligand. Following cell-cell interactions, Ephs/Ephrins behave as guidance molecules which trigger both repulsive and attractive signals, so as to direct the movement of cells through their immediate microenvironment. They also direct processes which include sorting and positioning and cytoskeleton rearrangements, thus making them perfect candidates for the control of the metastatic process. In fact, the role of Ephs and Ephrins in cancer progression has been demonstrated for many of the family members and they, surprisingly, have both tumor promoter and suppressor functions in different cellular contexts. They are also able to coordinate between multiple processes including cell survival, proliferation, differentiation, adhesion, motility, and invasion. This review is an attempt to summarize the data available on these Ephs/Ephrins' biological functions which contribute to the onset of aggressive cancers. I will also provide an overview of the factors which could explain the functional differences demonstrated by Ephs and Ephrins at different stages of tumor progression and whose elucidation is warranted for any future therapeutic targeting of this signaling pathway in cancer metastasis.

Major signaling pathways in intestinal stem cells

BACKGROUND

The discovery of markers to identify the intestinal stem cell population and the generation of powerful transgenic mouse models to study stem cell physiology have led to seminal discoveries in stem cell biology.

SCOPE OF REVIEW

In this review we give an overview of the current knowledge in the field of intestinal stem cells (ISCs) highlighting the most recent progress on markers defining the ISC population and pathways governing intestinal stem cell maintenance and differentiation. Furthermore we review their interaction with other stem cell related pathways. Finally we give an overview of alteration of these pathways in human inflammatory gastrointestinal diseases.

MAJOR CONCLUSIONS

We highlight the complex network of interactions occurring among different pathways and put in perspective the many layers of regulation that occur in maintaining the intestinal homeostasis.

GENERAL SIGNIFICANCE

Understanding the involvement of ISCs in inflammatory diseases can potentially lead to new therapeutic approaches to treat inflammatory GI pathologies such as IBD and celiac disease and could reveal the molecular mechanisms leading to the pathogenesis of dysplasia and cancer in inflammatory chronic conditions. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

CD24 can be used to isolate Lgr5+ putative colonic epithelial stem cells in mice

A growing body of evidence has implicated CD24, a cell-surface protein, as a marker of colorectal cancer stem cells and target for antitumor therapy, although its presence in normal colonic epithelium has not been fully characterized. Previously, our group showed that CD24-based cell sorting can be used to isolate a fraction of murine small intestinal epithelial cells enriched in actively cycling stem cells. Similarly, we hypothesized that CD24-based isolation of colonic epithelial cells would generate a fraction enriched in actively cycling colonic epithelial stem cells (CESCs). Immunohistochemistry performed on mouse colonic tissue showed CD24 expression in the bottom half of proximal colon crypts and the crypt base in the distal colon. This pattern of distribution was similar to enhanced green fluorescent protein (EGFP) expression in Lgr5-EGFP mice. Areas expressing CD24 contained actively proliferating cells as determined by ethynyl deoxyuridine (EdU) incorporation, with a distinct difference between the proximal colon, where EdU-labeled cells were most frequent in the midcrypt, and the distal colon, where they were primarily at the crypt base. Flow cytometric analyses of single epithelial cells, identified by epithelial cell adhesion molecule (EpCAM) positivity, from mouse colon revealed an actively cycling CD24(+) fraction that contained the majority of Lgr5-EGFP(+) putative CESCs. Transcript analysis by quantitative RT-PCR confirmed enrichment of active CESC markers [leucine-rich-repeat-containing G protein-coupled receptor 5 (Lgr5), ephrin type B receptor 2 (EphB2), and CD166] in the CD24(+)EpCAM(+) fraction but also showed enrichment of quiescent CESC markers [leucine-rich repeats and immunoglobin domains (Lrig), doublecortin and calmodulin kinase-like 1 (DCAMKL-1), and murine telomerase reverse transcriptase (mTert)]. We conclude that CD24-based sorting in wild-type mice isolates a colonic epithelial fraction highly enriched in actively cycling and quiescent putative CESCs. Furthermore, the presence of CD24 expression in normal colonic epithelium may have important implications for the use of anti-CD24-based colorectal cancer therapies.

Alteration of colonic stem cell gene signatures during the regenerative response to injury

Since aberrant wound healing and chronic inflammation can promote malignant transformation, we determined whether dietary bioactive fish oil (FO)-derived n-3 polyunsaturated fatty acids (n-3 PUFA) modulate stem cell kinetics in a colitis-wounding model. Lgr5-LacZ and Lgr5-EGFP-IRES-creER(T2) mice were fed diets enriched with n-3 PUFA vs n-6 PUFA (control) and exposed to dextran sodium sulfate (DSS) for 5days in order to induce crypt damage and colitis throughout the colon. Stem cell number, cell proliferation, apoptosis, expression of stem cell (Lgr5, Sox9, Bmi1, Hopx, mTert, Ascl2, and DCAMKL-1) and inflammation (STAT3) markers were quantified. DSS treatment resulted in the ablation of Lgr5(+) stem cells in the distal colon, concurrent with the loss of distal crypt structure and proliferating cells. Lgr5, Ascl2 and Hopx mRNA expression levels were decreased in damaged colonic mucosa. Lgr5(+) stem cells reappeared at day 5 of DSS recovery, with normal levels attained by day 6 of recovery. There was no effect of diet on the recovery of stem cells. FO fed animals exhibited higher levels of phospho-STAT3 at all time points, consistent with a higher wounding by DSS in FO feeding. n-3 PUFA-fed mice exhibited a reduction in stem cell associated factors, Ascl2, Axin2 and EphB3. These results indicate that rapidly cycling Lgr5(+) stem cells residing at position 1 in the colon epithelium are highly susceptible to DSS-induced damage and that dietary cues can impact stem cell regulatory networks.

Nm23-H1 regulates contact inhibition of locomotion, which is affected by ephrin-B1

Contact inhibition of locomotion (CIL) is the process by which cells stop the continual migration in the same direction after collision with another cell. Highly invasive malignant cells exhibit diminished CIL when they contact stromal cells, which allows invasion of the tissue by tumors. We show that Nm23-H1 is essential for the suppression of Rac1 through inactivation of Tiam1 at the sites of cell-cell contact, which plays a pivotal role in CIL. U87MG cells show CIL when they contact normal glia. In spheroid confrontation assays U87MG cells showed only limited invasion of the glial population, but reduction of Nm23-H1 expression in U87MG cells abrogated CIL resulting in invasion. In U87MG cells, Nm23-H1 is translocated to the sites of contact with glia through association with α-catenin and N-cadherin. Mutants of Nm23-H1, which lacked the binding ability with Tiam1, or α-catenin did not restore CIL. Moreover, the expression of ephrin-B1 in tumor cells disrupted CIL and promoted invasion. As one mechanism, ephrin-B1 inhibits the association of Nm23-H1 with Tiam1, which contributes for activation of Rac1. These results indicate a novel function of Nm23-H1 to control CIL, and its negative regulation by ephrin-B1.

Activation of two distinct Sox9-EGFP-expressing intestinal stem cell populations during crypt regeneration after irradiation

Recent identification of intestinal epithelial stem cell (ISC) markers and development of ISC reporter mice permit visualization and isolation of regenerating ISCs after radiation to define their functional and molecular phenotypes. Previous studies in uninjured intestine of Sox9-EGFP reporter mice demonstrate that ISCs express low levels of Sox9-EGFP (Sox9-EGFP Low), whereas enteroendocrine cells (EEC) express high levels of Sox9-EGFP (Sox9-EGFP High). We hypothesized that Sox9-EGFP Low ISCs would expand after radiation, exhibit enhanced proliferative capacities, and adopt a distinct gene expression profile associated with rapid proliferation. Sox9-EGFP mice were given 14 Gy abdominal radiation and studied between days 3 and 9 postradiation. Radiation-induced changes in number, growth, and transcriptome of the different Sox9-EGFP cell populations were determined by histology, flow cytometry, in vitro culture assays, and microarray. Microarray confirmed that nonirradiated Sox9-EGFP Low cells are enriched for Lgr5 mRNA and mRNAs enriched in Lgr5-ISCs and identified additional putative ISC markers. Sox9-EGFP High cells were enriched for EEC markers, as well as Bmi1 and Hopx, which are putative markers of quiescent ISCs. Irradiation caused complete crypt loss, followed by expansion and hyperproliferation of Sox9-EGFP Low cells. From nonirradiated intestine, only Sox9-EGFP Low cells exhibited ISC characteristics of forming organoids in culture, whereas during regeneration both Sox9-EGFP Low and High cells formed organoids. Microarray demonstrated that regenerating Sox9-EGFP High cells exhibited transcriptomic changes linked to p53-signaling and ISC-like functions including DNA repair and reduced oxidative metabolism. These findings support a model in which Sox9-EGFP Low cells represent active ISCs, Sox9-EGFP High cells contain radiation-activatable cells with ISC characteristics, and both participate in crypt regeneration.

The simultaneous expression of both ephrin B3 receptor and E-cadherin in Barrett`s adenocarcinoma is associated with favorable clinical staging

Background

In intestinal epithelium, tyrosine kinase receptor Ephrin B3 (Eph B3) maintains the architecture of the crypt-villus axis by repulsive interaction with its ligand ephrin-B1. While loss of Eph B3 is linked to colorectal cancer initiation, overexpression of Eph B3 in cancer cell lines inhibits growth and induces functional changes with decreased mesenchymal and increased epithelial markers. In order to study this tumor suppressor activity of Eph B3 in esophageal adenocarcinoma we analyzed the simultaneous expression of Eph B3 and E-cadherin in both the healthy esophagus and in Barrett’s carcinoma.

Methods

Simultaneous expression of Eph B3 and E-cadherin was investigated in samples from 141 patients with Barrett’s carcinoma and from 20 healthy esophagi using immunhistology and quantitative PCR. Results from healthy squamous epithelium, Barrett’s metaplasia and staging-specific esophageal adenocarcinoma were correlated.

Results

A significantly reduced E-cadherin mRNA expression could be detected in adenocarcinoma compared to dysplasia. The immunhistological activity of E-cadherin and Eph B3 was reduced in adenocarcinoma compared to dysplasia or healthy esophageal mucosa. The intracellular E-cadherin distribution changed significantly from the cytoplasm to the membrane, when the Eph receptor was simultaneously expressed. Simultaneous expression of E-cadherin and Eph B3 showed a significant inverse correlation to tumor stage.

Conclusions

We present novel evidence of the tumor suppressor activity of Eph B3 in esophageal adenocarcinoma possibly due to the impact on redistribution of cellular E-cadherin to the membrane. Our results suggest that this effect might play a role in the dysplasia-adenocarcinoma sequence, the infiltrative growth pattern and the development of lymph node metastases.

A review of spatial computational models for multi-cellular systems, with regard to intestinal crypts and colorectal cancer development

Colon rectal cancers (CRC) are the result of sequences of mutations which lead the intestinal tissue to develop in a carcinoma following a "progression" of observable phenotypes. The actual modeling and simulation of the key biological structures involved in this process is of interest to biologists and physicians and, at the same time, it poses significant challenges from the mathematics and computer science viewpoints. In this report we give an overview of some mathematical models for cell sorting (a basic phenomenon that underlies several dynamical processes in an organism), intestinal crypt dynamics and related problems and open questions. In particular, major attention is devoted to the survey of so-called in-lattice (or grid) models and off-lattice (off-grid) models. The current work is the groundwork for future research on semi-automated hypotheses formation and testing about the behavior of the various actors taking part in the adenoma-carcinoma progression, from regulatory processes to cell-cell signaling pathways.

A review of spatial computational models for multi-cellular systems, with regard to intestinal crypts and colorectal cancer development

Colon rectal cancers (CRC) are the result of sequences of mutations which lead the intestinal tissue to develop in a carcinoma following a "progression" of observable phenotypes. The actual modeling and simulation of the key biological structures involved in this process is of interest to biologists and physicians and, at the same time, it poses significant challenges from the mathematics and computer science viewpoints. In this report we give an overview of some mathematical models for cell sorting (a basic phenomenon that underlies several dynamical processes in an organism), intestinal crypt dynamics and related problems and open questions. In particular, major attention is devoted to the survey of so-called in-lattice (or grid) models and off-lattice (off-grid) models. The current work is the groundwork for future research on semi-automated hypotheses formation and testing about the behavior of the various actors taking part in the adenoma-carcinoma progression, from regulatory processes to cell-cell signaling pathways.

Generating intestinal tissue from stem cells: potential for research and therapy

Intestinal resection and malformations in adult and pediatric patients result in devastating consequences. Unfortunately, allogeneic transplantation of intestinal tissue into patients has not been met with the same measure of success as the transplantation of other organs. Attempts to engineer intestinal tissue in vitro include disaggregation of adult rat intestine into subunits called organoids, harvesting native adult stem cells from mouse intestine and spontaneous generation of intestinal tissue from embryoid bodies. Recently, by utilizing principles gained from the study of developmental biology, human pluripotent stem cells have been demonstrated to be capable of directed differentiation into intestinal tissue in vitro. Pluripotent stem cells offer a unique and promising means to generate intestinal tissue for the purposes of modeling intestinal disease, understanding embryonic development and providing a source of material for therapeutic transplantation.

SDF-1 activates papillary label-retaining cells during kidney repair from injury

The adult kidney contains a population of low-cycling cells that resides in the papilla. These cells retain for long periods S-phase markers given as a short pulse early in life; i.e., they are label-retaining cells (LRC). In previous studies in adult rat and mice, we found that shortly after acute kidney injury many of the quiescent papillary LRC started proliferating (Oliver JA, Klinakis A, Cheema FH, Friedlander J, Sampogna RV, Martens TP, Liu C, Efstratiadis A, Al-Awqati Q. J Am Soc Nephrol 20: 2315-2327, 2009; Oliver JA, Maarouf O, Cheema FH, Martens TP, Al-Awqati Q. J Clin Invest 114: 795-804, 2004) and, with cell-tracking experiments, we found upward migration of some papillary cells including LRC (Oliver JA, Klinakis A, Cheema FH, Friedlander J, Sampogna RV, Martens TP, Liu C, Efstratiadis A, Al-Awqati Q. J Am Soc Nephrol 20: 2315-2327, 2009). To identify molecular cues involved in the activation (i.e., proliferation and/or migration) of the papillary LRC that follows injury, we isolated these cells from the H2B-GFP mice and found that they migrated and proliferated in response to the cytokine stromal cell-derived factor-1 (SDF-1). Moreover, in a papillary organ culture assay, the cell growth out of the upper papilla was dependent on the interaction of SDF-1 with its receptor Cxcr4. Interestingly, location of these two proteins in the kidney revealed a complementary location, with SDF-1 being preferentially expressed in the medulla and Cxcr4 more abundant in the papilla. Blockade of Cxcr4 in vivo prevented mobilization of papillary LRC after transient kidney ischemic injury and worsened its functional consequences. The data indicate that the SDF-1/Cxcr4 axis is a critical regulator of papillary LRC activation following transient kidney injury and during organ repair.

Targeted disruption of ephrin B1 in cells of myeloid lineage increases osteoclast differentiation and bone resorption in mice

Disruption of ephrin B1 in collagen I producing cells in mice results in severe skull defects and reduced bone formation. Because ephrin B1 is also expressed during osteoclast differentiation and because little is known on the role of ephrin B1 reverse signaling in bone resorption, we examined the bone phenotypes in ephrin B1 conditional knockout mice, and studied the function of ephrin B1 reverse signaling on osteoclast differentiation and resorptive activity. Targeted deletion of ephrin B1 gene in myeloid lineage cells resulted in reduced trabecular bone volume, trabecular number and trabecular thickness caused by increased TRAP positive osteoclasts and bone resorption. Histomorphometric analyses found bone formation parameters were not changed in ephrin B1 knockout mice. Treatment of wild-type precursors with clustered soluble EphB2-Fc inhibited RANKL induced formation of multinucleated osteoclasts, and bone resorption pits. The same treatment of ephrin B1 deficient precursors had little effect on osteoclast differentiation and pit formation. Similarly, activation of ephrin B1 reverse signaling by EphB2-Fc treatment led to inhibition of TRAP, cathepsin K and NFATc1 mRNA expression in osteoclasts derived from wild-type mice but not conditional knockout mice. Immunoprecipitation with NHERF1 antibody revealed ephrin B1 interacted with NHERF1 in differentiated osteoclasts. Treatment of osteoclasts with exogenous EphB2-Fc resulted in reduced phosphorylation of ezrin/radixin/moesin. We conclude that myeloid lineage produced ephrin B1 is a negative regulator of bone resorption in vivo, and that activation of ephrin B1 reverse signaling inhibits osteoclast differentiation in vitro in part via a mechanism that involves inhibition of NFATc1 expression and modulation of phosphorylation status of ezrin/radixin/moesin.

Recent progress in histochemistry and cell biology

Studies published in Histochemistry and Cell Biology in the year 2011 represent once more a manifest of established and newly sophisticated techniques being exploited to put tissue- and cell type-specific molecules into a functional context. The review is therefore the Histochemistry and Cell Biology's yearly intention to provide interested readers appropriate summaries of investigations touching the areas of tissue biology, developmental biology, the biology of the immune system, stem cell research, the biology of subcellular compartments, in order to put the message of such studies into natural scientific-/human- and also pathological-relevant correlations.

Eph and ephrins in epithelial stem cell niches and cancer

The family of Eph tyrosine kinase receptors is an important part of signaling pathways involved in development, tissue homeostasis and tumorigenesis. Binding and activation of the receptors by their ligands, the ephrins, result in bidirectional signaling into both receptor and ligand expressing cells. Adult stem cell niches and tumors frequently express receptors and ligands, although their function is only beginning to be understood. Thus, Eph receptors and ephrins have become important molecules for understanding basic biological processes as well as tumorigenesis, and are promising targets for potential therapeutic intervention in human disease.

EphB2 receptor controls proliferation/migration dichotomy of glioblastoma by interacting with focal adhesion kinase

Glioblastoma multiforme (GBM) are the most frequent and aggressive primary brain tumors in adults. Uncontrolled proliferation and abnormal cell migration are two prominent spatially and temporally disassociated characteristics of GBMs. In this study, we investigated the role of the receptor tyrosine kinase EphB2 in controlling the proliferation/migration dichotomy of GBM. We studied EphB2 gain-of-function and loss-of function in glioblastoma-derived stem-like neurospheres (GBM-SCs), whose in vivo growth pattern closely replicates human GBM. EphB2 expression stimulated GBM neurosphere cell migration and invasion, and inhibited neurosphere cell proliferation in vitro. In parallel, EphB2 silencing increased tumor cell proliferation and decreased tumor cell migration. EphB2 was found to increase tumor cell invasion in vivo using an internally controlled dual-fluorescent xenograft model. Xenografts derived from EphB2 overexpressing GBM neurospheres also showed decreased cellular proliferation. The non-receptor tyrosine kinase focal adhesion kinase (FAK) was found to be co-associated with and highly activated by EphB2 expression and FAK activation facilitated focal adhesion formation, cytoskeleton structure change and cell migration in EphB2-expression GBM neurosphere cells. Taken together, our findings indicate that EphB2 has pro-invasive and anti-proliferative actions in GBM stem-like neurospheres mediated, in part, by interactions between EphB2 receptors and FAK. These novel findings suggest that tumor cell invasion can be therapeutically targeted by inhibiting EphB2 signaling and that optimal anti-tumor responses to EphB2 targeting may require the concurrent use of anti-proliferative agents.

Eph/ephrin signaling: genetic, phosphoproteomic, and transcriptomic approaches

The Eph receptor tyrosine kinases and their ephrin partners compose a large and complex family of signaling molecules involved in a wide variety of processes in development, homeostasis, and disease. The complexity inherent to Eph/ephrin signaling derives from several characteristics of the family. First, the large size and functional redundancy/compensation by family members presents a challenge in defining their in vivo roles. Second, the capacity for bidirectional signaling doubles the potential complexity, since every member has the ability to act both as a ligand and a receptor. Third, Ephs and ephrins can utilize a wide array of signal transduction pathways with a tremendous diversity of cell biological effect. The daunting complexity of Eph/ephrin signaling has increasingly prompted investigators to resort to multiple technological approaches to gain mechanistic insight. Here we review recent progress in the use of advanced mouse genetics in combination with proteomic and transcriptomic approaches to gain a more complete understanding of signaling mechanism in vivo. Integrating insights from such disparate approaches provides advantages in continuing to advance our understanding of how this multifarious group of signaling molecules functions in a diverse array of biological contexts.

Expansion of Paneth cell population in response to enteric Salmonella enterica serovar Typhimurium infection

Paneth cells residing at the base of the small intestinal crypts contribute to the mucosal intestinal first line defense by secreting granules filled with antimicrobial polypeptides including lysozyme. These cells derive from the columnar intestinal stem cell located at position 0 and the transit amplifying cell located at position +4 in the crypts. We have previously shown that Salmonella enterica serovar Typhimurium (ST), a leading cause of gastrointestinal infections in humans, effects an overall reduction of lysozyme in the small intestine. To extend this work, we examined small-intestinal tissue sections at various time points after ST infection to quantify and localize expression of lysozyme and assess Paneth cell abundance, apoptosis, and the expression of Paneth cell differentiation markers. In response to infection with ST, the intestinal Paneth cell-specific lysozyme content, the number of lysozyme-positive Paneth cells, and the number of granules per Paneth cell decreased. However, this was accompanied by increases in the total number of Paneth cells and the frequency of mitotic events in crypts, by increased staining for the proliferation marker PCNA, primarily at the crypt side walls where the transit amplifying cell resides and not at the crypt base, and by apoptotic events in villi. Furthermore, we found a time-dependent upregulation of first β-catenin, followed by EphB3, and lastly Sox9 in response to ST, which was not observed after infection with a Salmonella pathogenicity island 1 mutant deficient in type III secretion. Our data strongly suggest that, in response to ST infection, a Paneth cell differentiation program is initiated that leads to an expansion of the Paneth cell population and that the transit amplifying cell is likely the main progenitor responder. Infection-induced expansion of the Paneth cell population may represent an acute intestinal inflammatory response similar to neutrophilia in systemic infection.

EphB2 tyrosine kinase-dependent forward signaling in migration of neuronal progenitors that populate and form a distinct region of the dentate niche

The dentate gyrus (DG) is one of two areas in the mature brain where stem cells reside to continuously produce new neurons throughout adulthood. While much research has focused on the DG for its roles in adult neurogenesis, little is known regarding how this key region of the brain initially develops to form its distinct architecture. We show here that the murine EphB2 receptor tyrosine kinase is critical for embryonic/postnatal development of a specific region of the DG known as the lateral suprapyramidal blade (LSB). Intracellular truncation and point mutants demonstrate that EphB2 catalytic activity is essential for LSB formation. This is consistent with expression of EphB2 in nestin-positive neural progenitor cells that migrate medially from the lateral ventricle dentate notch neuroepithelium to populate the tertiary matrix and form the DG near the midline of the brain. Animals lacking ephrin-B1 recapitulate loss of the receptor and show that this molecule acts as the ligand to stimulate EphB2 forward signaling and direct migration of the neural progenitors into the dorsal compartment of the tertiary matrix and form the LSB. Immunoreactivity against the extracellular matrix protein Reelin in a region directly above the developing LSB is dramatically reduced when EphB2 forward signaling is disrupted. Together, these results indicate ephrin-B1 interacting with EphB2 controls the migration of dentate progenitor cells into the dorsal half of the developing DG, perhaps in part by affecting Reelin expression in a key compartment directly above the LSB.

Krüppel-like factor 5 is important for maintenance of crypt architecture and barrier function in mouse intestine

BACKGROUND & AIMS

Krüppel-like factor 5 (KLF5) is transcription factor that is expressed by dividing epithelial cells of the intestinal epithelium. KLF5 promotes proliferation in vitro and in vivo and is induced by mitogens and various stress stimuli. To study the role of KLF5 in intestinal epithelial homeostasis, we examined the phenotype of mice with conditional deletion of Klf5 in the gut.

METHODS

Mice were generated with intestinal-specific deletion of Klf5 (Vil-Cre;Klf5fl/fl). Morphologic changes in the small intestine and colon were examined by immunohistochemistry, immunoblotting, and real-time polymerase chain reaction.

RESULTS

Klf5 mutant mice were born at a normal Mendelian ratio but had high mortality compared with controls. Complete deletion of Klf5 from the intestinal mucosa resulted in neonatal lethality that corresponded with an absence of epithelial proliferation. Variegated intestinal-specific deletion of Klf5 in adult mice resulted in morphologic changes that included a regenerative phenotype, impaired barrier function, and inflammation. Adult mutant mice exhibited defects in epithelial differentiation and migration. These changes were associated with reduced expression of Caudal type homeobox (Cdx) 1, Cdx2, and Eph and ephrin signaling proteins. Concomitantly, Wnt signaling to β-catenin was reduced. Proliferation in regenerative crypts was associated with increased expression of the progenitor cell marker Sox9.

CONCLUSIONS

Deletion of Klf5 in the gut epithelium of mice demonstrated that KLF5 maintains epithelial proliferation, differentiation, and cell positioning along the crypt radial axis. Morphologic changes that occur with deletion of Klf5 are associated with disruption of canonical Wnt signaling and increased expression of Sox9.

Complementary expression and repulsive signaling suggest that EphB receptors and ephrin-B ligands control cell positioning in the gastric epithelium

Eph receptors and ephrin ligands are membrane-bound cell-cell communication molecules with well-defined roles in development. However, their expression and functions in the gastric epithelium are virtually unknown. We detected several EphB receptors and ephrin-Bs in the gastric corpus mucosa of the adult rodent stomach by RT-PCR amplification. Immunostaining showed complementary expression patterns, with EphB receptors preferentially expressed in the deeper regions and ephrin-Bs in the superficial regions of the gastric units. EphB1, EphB2 and EphB3 are expressed in mucous neck, chief and parietal cells, respectively. In contrast, ephrin-B1 is in pit cells and proliferating cells of the isthmus. In a mouse ulcer model, EphB2 expression was upregulated in the regenerating epithelium and expanded into the isthmus. Thus, EphB/ephrin-B signaling likely occurs preferentially in the isthmus, where receptor-ligand overlap is highest. We show that EphB signaling in primary gastric epithelial cells promotes cell retraction and repulsion at least in part through RhoA activation. Based on these findings, we propose that the EphB-positive progeny of gastric stem cells migrates from the isthmus toward the bottom of the gastric glands due to repulsive signals arising from contact with ephrin-Bs, which are preferentially expressed in the more superficial regions of the isthmus and gastric pits.

Critical roles for EphB and ephrin-B bidirectional signalling in retinocollicular mapping

Graded expression of EphB and ephrin-B along the dorsoventral axis of the retina indicates a role for these bidirectional signaling molecules in dorsoventral-mediolateral retinocollicular mapping. While previous studies have implicated EphB2 forward signaling in mice, the intracellular component of EphB2 essential for retinocollicular mapping is unknown as are the roles for EphB1, ephrin-B1, and ephrin-B2. Here we show that EphB2 tyrosine kinase catalytic activity and EphB1 intracellular signaling are key mediators of ventral-temporal retinal ganglion cell axon retinocollicular mapping, by likely interacting with ephrin-B1 in the superior colliculus. We further elucidate roles for the ephrin-B2 intracellular domain in retinocollicular mapping and present the unexpected finding that both dorsal and ventral-temporal retinal ganglion cell axons utilize reverse signaling for topographic mapping. These data demonstrate that both forward and reverse signaling initiated by EphB:ephrin-B interactions play a major role in dorsoventral retinal ganglion cell axon termination along the mediolateral axis of the superior colliculus.

Complementary expression of EphB receptors and ephrin-B ligand in the pyloric and duodenal epithelium of adult mice

Eph receptors and ephrin ligands are membrane-bound cell-cell communication molecules that regulate the spatial organisation of cells in various tissues by repulsive or adhesive signals arising from contact between EphB- and ephrin-bearing cells. However, the expression and functions of Eph receptors in the gastric epithelium and Brunner's glands are virtually unknown. We detected several EphB receptors and ephrin-B ligands in the pyloric and duodenal mucosa of the adult mouse by RT-PCR amplification. Immunostaining showed complementary expression patterns, with ephrin-B1 being preferentially expressed in the superficial part and EphB receptors in the deeper part of both epithelia. In the gastric pylorus, ephrin-B1 was expressed in pit cells and proliferating cells of the isthmus. In contrast, EphB2, EphB3, and EphB4 were expressed in pyloric glandular cells and proliferating cells of the isthmus. In the duodenum, ephrin-B1 was expressed in cells lining the ducts of Brunner's glands as well as those covering villi and the upper portion of the crypts of Lieberkühn. In contrast, EphB2 and EphB3 were expressed in the gland segment of Brunner's glands and the lower portion of the crypts and EphB4, in the crypts. In both mucosae, EphB2, EphB3, and EphB4 were found to be tyrosine phosphorylated, suggesting that EphB/ephrin-B signalling might occur preferentially in the isthmus, crypts, and duct-gland transition of Brunner's glands, where the receptor and ligand expression overlaps. Based on these findings, we propose that EphB/ephrin-B signalling may regulate cell positioning within the pyloric and duodenal epithelium.

Control of cell adhesion and compartmentalization in the intestinal epithelium

Continuous cell renewal in the intestinal mucosa occurs without disrupting the integrity of the epithelial layer. Despite the restrictions imposed by strong cell-to-cell adhesions, epithelial intestinal cells migrate constantly between tissue compartments. Alterations in cell adhesion and compartmentalization play key roles in diseases of the intestine. In particular, decreased E-cadherin-mediated adhesion during inflammatory bowel disease and loss of EphB/ephrin-B-mediated compartmentalization in colorectal cancer have recently emerged as key players of these prevalent pathologies. Here we will review our current knowledge on how cell-to-cell adhesion, migration and cell positioning are coordinated in the intestinal epithelium. We will highlight what the in vivo genetic analysis of intestinal epithelium has taught us about the complex regulation of cell adhesion and migration in homeostasis and disease.

Dancing with the dead: Eph receptors and their kinase-null partners

Eph receptor tyrosine kinases and their ligands, ephrins, are membrane proteins coordinating a wide range of biological functions both in developing embryos and in adult multicellular organisms. Numerous studies have implicated Eph receptors in the induction of opposing responses, including cell adhesion or repulsion, support or inhibition of cell proliferation and cell migration, and progression or suppression of multiple malignancies. Similar to other receptor tyrosine kinases, Eph receptors rely on their ability to catalyze tyrosine phosphorylation for signal transduction. Interestingly, however, Eph receptors also actively utilize three kinase-deficient receptor tyrosine kinases, EphB6, EphA10, and Ryk, in their signaling network. The accumulating evidence suggests that the unusual flexibility of the Eph family, allowing it to initiate antagonistic responses, might be partially explained by the influence of the kinase-dead participants and that the exact outcome of an Eph-mediated action is likely to be defined by the balance between the signaling of catalytically potent and catalytically null receptors. We discuss in this minireview the emerging functions of the kinase-dead EphB6, EphA10, and Ryk receptors both in normal biological responses and in malignancy, and analyze currently available information related to the molecular mechanisms of their action in the context of the Eph family.