Foxp1 suppresses cortical angiogenesis and attenuates HIF-1alpha signaling to promote neural progenitor cell maintenance

Neural progenitor cells within the cerebral cortex undergo a characteristic switch between symmetric self-renewing cell divisions early in development and asymmetric neurogenic divisions later. Yet, the mechanisms controlling this transition remain unclear. Previous work has shown that early but not late neural progenitor cells (NPCs) endogenously express the autism-linked transcription factor Foxp1, and both loss and gain of Foxp1 function can alter NPC activity and fate choices. Here, we show that premature loss of Foxp1 upregulates transcriptional programs regulating angiogenesis, glycolysis, and cellular responses to hypoxia. These changes coincide with a premature destabilization of HIF-1α, an elevation in HIF-1α target genes, including Vegfa in NPCs, and precocious vascular network development. In vitro experiments demonstrate that stabilization of HIF-1α in Foxp1-deficient NPCs rescues the premature differentiation phenotype and restores NPC maintenance. Our data indicate that the endogenous decline in Foxp1 expression activates the HIF-1α transcriptional program leading to changes in the tissue environment adjacent to NPCs, which, in turn, might alter their self-renewal and neurogenic capacities.

Foxp1 Regulates Neural Stem Cell Self-Renewal and Bias Toward Deep Layer Cortical Fates

The laminar architecture of the mammalian neocortex depends on the orderly generation of distinct neuronal subtypes by apical radial glia (aRG) during embryogenesis. Here, we identify critical roles for the autism risk gene Foxp1 in maintaining aRG identity and gating the temporal competency for deep-layer neurogenesis. Early in development, aRG express high levels of Foxp1 mRNA and protein, which promote self-renewing cell divisions and deep-layer neuron production. Foxp1 levels subsequently decline during the transition to superficial-layer neurogenesis. Sustained Foxp1 expression impedes this transition, preserving a population of cells with aRG identity throughout development and extending the early neurogenic period into postnatal life. FOXP1 expression is further associated with the initial formation and expansion of basal RG (bRG) during human corticogenesis and can promote the formation of cells exhibiting characteristics of bRG when misexpressed in the mouse cortex. Together, these findings reveal broad functions for Foxp1 in cortical neurogenesis.

Direct and indirect roles of Fgf3 and Fgf10 in innervation and vascularisation of the vertebrate hypothalamic neurohypophysis

The neurohypophysis is a crucial component of the hypothalamo-pituitary axis, serving as the site of release of hypothalamic neurohormones into a plexus of hypophyseal capillaries. The growth of hypothalamic axons and capillaries to the forming neurohypophysis in embryogenesis is therefore crucial to future adult homeostasis. Using ex vivo analyses in chick and in vivo analyses in mutant and transgenic zebrafish, we show that Fgf10 and Fgf3 secreted from the forming neurohypophysis exert direct guidance effects on hypothalamic neurosecretory axons. Simultaneously, they promote hypophyseal vascularisation, exerting early direct effects on endothelial cells that are subsequently complemented by indirect effects. Together, our studies suggest a model for the integrated neurohemal wiring of the hypothalamo-neurohypophyseal axis.

Foxp-mediated suppression of N-cadherin regulates neuroepithelial character and progenitor maintenance in the CNS

Neuroepithelial attachments at adherens junctions are essential for the self-renewal of neural stem and progenitor cells and the polarized organization of the developing central nervous system. The balance between stem cell maintenance and differentiation depends on the precise assembly and disassembly of these adhesive contacts, but the gene regulatory mechanisms orchestrating this process are not known. Here, we demonstrate that two Forkhead transcription factors, Foxp2 and Foxp4, are progressively expressed upon neural differentiation in the spinal cord. Elevated expression of either Foxp represses the expression of a key component of adherens junctions, N-cadherin, and promotes the detachment of differentiating neurons from the neuroepithelium. Conversely, inactivation of Foxp2 and Foxp4 function in both chick and mouse results in a spectrum of neural tube defects associated with neuroepithelial disorganization and enhanced progenitor maintenance. Together, these data reveal a Foxp-based transcriptional mechanism that regulates the integrity and cytoarchitecture of neuroepithelial progenitors.

FGF-dependent midline-derived progenitor cells in hypothalamic infundibular development

The infundibulum links the nervous and endocrine systems, serving as a crucial integrating centre for body homeostasis. Here we describe that the chick infundibulum derives from two subsets of anterior ventral midline cells. One set remains at the ventral midline and forms the posterior-ventral infundibulum. A second set migrates laterally, forming a collar around the midline. We show that collar cells are composed of Fgf3(+) SOX3(+) proliferating progenitors, the induction of which is SHH dependent, but the maintenance of which requires FGF signalling. Collar cells proliferate late into embryogenesis, can generate neurospheres that passage extensively, and differentiate to distinct fates, including hypothalamic neuronal fates and Fgf10(+) anterior-dorsal infundibular cells. Together, our study shows that a subset of anterior floor plate-like cells gives rise to Fgf3(+) SOX3(+) progenitor cells, demonstrates a dual origin of infundibular cells and reveals a crucial role for FGF signalling in governing extended infundibular growth.

E-Cadherin, beta -Catenin and cadmium carcinogenesis

Cadmium (Cd(2+)) is an important industrial and environmental pollutant that has been classified as a human carcinogen. Studies reported in the literature indicate that cadmium may play a role in both the initiation of cancer, by activating oncogenes, and in the progression of cancer, by increasing the metastatic potential of existing cancer cells. However, the mechanisms underlying these effects have yet to be elucidated. Recent studies from our laboratory have shown that cadmium can disrupt the tight junctions between many types of epithelial cells by interfering with the normal function of E-cadherin, a Ca(2+)-dependent cell adhesion molecule that plays a key role in epithelial cell-cell adhesion. This finding may be especially significant because a large volume of evidence indicates that the disruption of E-cadherin-mediated cell adhesion can trigger the beta-catenin-mediated activation of oncogenes in epithelial cells and increase the invasive potential of existing epithelial-derived cancers. The hypothesis that we are proposing is that the cadmium-induced disruption of E-cadherin dependent cell-cell junctions may represent a pivotal step in both the initiation of cancer by cadmium and in the tumor promoting actions of cadmium.

The role of district hospitals and the action in international medicine network

As the first-referral hospitals for the primary health care (PHC) services, district hospitals providing secondary health care (SHC) have a peculiar importance in the developing world. The World Health Organization has led the way in defining their functions and adopting the concept of the district health system linking PHC and SHC in a vital relationship. The author's personal experience in this area over many years in Nigeria is presented in this article. The need for postgraduate training programs to encourage physicians to pursue a career at the district level is becoming widely recognized as an extension of the discipline of general practice/family medicine.

Function associated with IL-2 receptor-beta on human neutrophils. Mechanism of activation of antifungal activity against Candida albicans by IL-2

Polymorphonuclear neutrophils (PMN) are essential components of the host defense system against a wide variety of pathogens. We report here the novel finding that freshly isolated human PMN constitutively express detectable surface levels of IL-2R beta, but not IL-2R alpha, as analyzed by flow cytometry. Northern blot analysis confirmed the constitutive expression of mRNA for IL-2R beta in PMN. Scatchard analysis using 125I-labeled IL-2 demonstrated the presence of approximately 600 intermediate binding IL-2R per PMN, with a dissociation constant of 1.1 x 10(-9) M, similar to that of IL-2 binding to YT-1 tumor cells that specifically express IL-2R beta. More importantly, PMN were able to respond functionally to IL-2 by enhanced growth-inhibitory activity against an opportunistic fungal pathogen, Candida albicans. IL-2 activation of antifungal activity was dose-dependent, with some functional activation detected at 1 U/ml of rIL-2 and maximal activation at 1000 U/ml. The action of IL-2 was rapid, with maximal PMN activation after 30-min incubation with IL-2. The IL-2 enhancement of antifungal activity could be blocked by a specific antibody against IL-2R beta, but not by anti-IL-2R alpha. Analysis of the mechanism of IL-2 activation of PMN indicated that oxidative metabolism, as measured by superoxide anion production, was not involved. Instead, PMN release of lactoferrin appeared to be responsible for the heightened activity against C. albicans in IL-2-treated PMN. Not only was lactoferrin detected in the supernatants of IL-2-treated PMN, but also the antifungal activity of PMN activated by IL-2 could be blocked in the presence of antilactoferrin. These results, taken together, indicate that normal PMN are capable of functionally responding to IL-2 via expression of the IL-2R beta chain.

Function associated with IL-2 receptor-beta on human neutrophils. Mechanism of activation of antifungal activity against Candida albicans by IL-2

Polymorphonuclear neutrophils (PMN) are essential components of the host defense system against a wide variety of pathogens. We report here the novel finding that freshly isolated human PMN constitutively express detectable surface levels of IL-2R beta, but not IL-2R alpha, as analyzed by flow cytometry. Northern blot analysis confirmed the constitutive expression of mRNA for IL-2R beta in PMN. Scatchard analysis using 125I-labeled IL-2 demonstrated the presence of approximately 600 intermediate binding IL-2R per PMN, with a dissociation constant of 1.1 x 10(-9) M, similar to that of IL-2 binding to YT-1 tumor cells that specifically express IL-2R beta. More importantly, PMN were able to respond functionally to IL-2 by enhanced growth-inhibitory activity against an opportunistic fungal pathogen, Candida albicans. IL-2 activation of antifungal activity was dose-dependent, with some functional activation detected at 1 U/ml of rIL-2 and maximal activation at 1000 U/ml. The action of IL-2 was rapid, with maximal PMN activation after 30-min incubation with IL-2. The IL-2 enhancement of antifungal activity could be blocked by a specific antibody against IL-2R beta, but not by anti-IL-2R alpha. Analysis of the mechanism of IL-2 activation of PMN indicated that oxidative metabolism, as measured by superoxide anion production, was not involved. Instead, PMN release of lactoferrin appeared to be responsible for the heightened activity against C. albicans in IL-2-treated PMN. Not only was lactoferrin detected in the supernatants of IL-2-treated PMN, but also the antifungal activity of PMN activated by IL-2 could be blocked in the presence of antilactoferrin. These results, taken together, indicate that normal PMN are capable of functionally responding to IL-2 via expression of the IL-2R beta chain.

Lactoferrin release and interleukin-1, interleukin-6, and tumor necrosis factor production by human polymorphonuclear cells stimulated by various lipopolysaccharides: relationship to growth inhibition of Candida albicans

Lipopolysaccharides (LPSs) from Escherichia coli, Serratia marcescens, and Salmonella typhimurium, at doses from 1 to 100 ng/ml, strongly enhanced growth inhibition of Candida albicans by human polymorphonuclear leukocytes (PMN) in vitro. Flow cytometry analysis demonstrated that LPS markedly augmented phagocytosis of Candida cells by increasing the number of yeasts ingested per neutrophil as well as the number of neutrophils capable of ingesting fungal cells. LPS activation caused augmented release of lactoferrin, an iron-binding protein which itself could inhibit the growth of C. albicans in vitro. Antibodies against lactoferrin effectively and specifically reduced the anti-C. albicans activity of both LPS-stimulated and unstimulated PMN. Northern (RNA blot) analysis showed enhanced production of mRNAs for interleukin-1 beta, tumor necrosis factor alpha, and interleukin-6 and in neutrophils within 1 h of stimulation with LPS. The cytokines were also detected in the supernatant of the activated PMN, and their synthesis was prevented by pretreatment of LPS-stimulated PMN with protein synthesis inhibitors, such as emetine and cycloheximide. These inhibitors, however, did not block either lactoferrin release or the anti-Candida activity of LPS-stimulated PMN. These results demonstrate the ability of various bacterial LPSs to augment neutrophil function against C. albicans and suggest that the release of a candidastatic, iron-binding protein, lactoferrin, may contribute to the antifungal effect of PMN. Moreover, the ability to produce cytokines upon stimulation by ubiquitous microbial products such as the endotoxins points to an extraphagocytic, immunomodulatory role of PMN during infection.

Differential release of interleukin (IL)-1 alpha, IL-1 beta, and IL-6 from normal human monocytes stimulated with a virulent and an avirulent isogenic variant of Mycobacterium avium-intracellulare complex

Members of the Mycobacterium avium-intracellulare complex (MAC) can exist in a transparent or opaque colonial morphology when cultured on synthetic medium. An opaque variant was developed from a transparent strain of a clinical MAC isolate. Comparison of the two variants showed a greater ability of the transparent colonial variant to infect normal human monocytes as measured by growth in monocyte-bacteria cocultures. Further analyses indicated diminished ability of the transparent variant to induce extracellular secretion of interleukin (IL)-1 and IL-6, as well as membrane-associated IL-1 when compared with the opaque isotype. At the molecular level, induction of specific IL-1 alpha, IL-1 beta, and IL-6 mRNAs was consistent with the protein results. These results suggest that the virulent transparent MAC, as opposed to the avirulent opaque type, may escape host defenses by failing to induce IL-1 and IL-6, key factors in the initiation of a normal immune response.

Production of granulocyte-macrophage colony-stimulating factor (GM-CSF) by monocytes and large granular lymphocytes stimulated with Mycobacterium avium-M. intracellulare: activation of bactericidal activity by GM-CSF

Treatment of monocytes with recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) was shown to enhance their antimycobacterial activity in an in vitro assay. Furthermore, Mycobacterium avium-M. intracellulare was found to induce the production of this hemopoietic growth factor. Human peripheral blood mononuclear cells were fractionated by plastic adherence and Percoll density centrifugation, and each population of cells was stimulated with mycobacteria. GM-CSF was produced by both monocytes and large granular lymphocytes (LGL) but not T lymphocytes. The phenotype of the GM-CSF-producing LGL was found to be CD2+, CD16+, and HLA-DR+ but negative for T-cell and monocyte markers. Kinetic studies demonstrated that GM-CSF appeared in the supernatant fluids within 2 days of culture of either monocytes or LGL and continued to be produced up to 7 days of incubation. Northern (RNA) blot analysis of RNA from both cell types demonstrated the expression of GM-CSF message within 24 h of stimulation. From these studies, LGL and monocytes are capable of responding to M. avium-M. intracellulare by producing factors that augment normal immune functions, including the antibacterial capability of monocytes.

Mycobacterium avium-intracellulare induces interleukin-6 from human monocytes and large granular lymphocytes

Mycobacterium avium-intracellulare (MAI) is an opportunistic pathogen commonly found in acquired immunodeficiency syndrome patients, whose immune systems are severely compromised. However, normal responses to this bacterium are apparently sufficient to prevent disseminated infection because disease is rarely found unless an immunocompromised state is present. Because interleukin-6 (IL-6) is an inflammatory cytokine with a multitude of activities, we investigated the potential of MAI to induce IL-6 from normal human leukocytes. Peripheral blood mononuclear cells were fractionated into monocytes (Mo), large granular lymphocytes (LGL), and T cells and stimulated with bacteria. Culture supernatants were collected and assayed for IL-6 activity by bioassay. Mo and LGL, but not T cells, were found to release IL-6 within 12 hours of stimulation, with optimal production occurring by 2 days of culture. Production of IL-6 from human leukocyte subsets was confirmed by Northern blot analysis and by neutralization of biologic function of the culture supernatants with specific antisera. Taken together, these results indicate that production of IL-6 is a key response of Mo and LGL to MAI. The role of IL-6 in MAI infection, therefore, needs to be further investigated.

Participation of tenascin and transforming growth factor-beta in reciprocal epithelial-mesenchymal interactions of MCF7 cells and fibroblasts

The tumor stroma is essential for the development of the tumor epithelium. Tenascin is an extracellular matrix protein highly expressed in the stroma of malignant mammary tumors. We therefore tested whether in vitro MCF7 cells were able to induce fibroblasts to synthesize tenascin. Indeed MCF7 cell-conditioned medium contained tenascin-inducing activity. This activity was shown to be transforming growth factor-beta. The morphology of the MCF7 cells was in turn affected by the addition of tenascin to the culture medium. The cells partially detached from the substratum and lost their cell-cell contracts.

Establishment of Heterodera glycines in Three Soil Types

The establishment ofHeterodera glycines race 3, from soil plugs infested with population densities ranging from 0 to 10 eggs and second-stage juveniles per 10 cm(3) soil, was compared in three soils (Haynie sandy loam, Eudora silt loam, and Chase silty clay loam) that were either pasteurized or unpasteurized. Final population densities of H. glycines in soil and on soybean (Glycine max cv. Williams 82) roots were affected by soil type but not by soil pasteurization (P = 0.05). Higher numbers of H. glycines females and cysts were recovered from the sandy loam than from the silty loams after 8 weeks. The relationships between initial populations in infested soil plugs and the levels of recovery in the previously uninfested soils were described by sigmoidal Gompertz growth models. Estimated threshold levels for establishment were approximately 75% lower in the sandy loam than in the silty loams.

Tenascin: cDNA cloning and induction by TGF-beta

cDNA clones coding for tenascin, an extracellular matrix glycoprotein with a restricted tissue distribution, were isolated from a chicken fibroblast cDNA expression library using a specific tenascin antiserum. Antibodies eluted from the cDNA-encoded fusion proteins reacted exclusively with tenascin. Limited trypsin treatment of purified tenascin resulted in a peptide which confirmed the deduced protein sequences. The largest clone encoding 632 amino acids showed a cysteine-rich region containing 13 consecutive epidermal growth factor-like repeats of unusual uniformity. Northern blot analysis revealed 8- to 9-kb messages. Tenascin is shown to be induced in vitro by fetal calf serum as well as by transforming growth factor beta (TGF-beta). A 4-fold increase in tenascin secretion by chick embryo fibroblasts was seen after TGF-beta treatment. The induction of tenascin protein synthesis was preceded by an increase of tenascin mRNA as determined by Northern blot analysis. The induction of tenascin was compared with fibronectin. The accumulation of the two extracellular matrix proteins in the medium was differentially affected by fetal calf serum and TGF-beta and the increase was in both cases higher for tenascin.

Epithelial induction of stromal tenascin in the mouse mammary gland: from embryogenesis to carcinogenesis

The distribution of the extracellular matrix glycoprotein tenascin was studied by immunofluorescence in the developmental history of the mouse mammary gland from embryogenesis to carcinogenesis. Tenascin appeared only in the mesenchyme immediately surrounding the epithelia just starting morphogenesis, that is, in embryonic mammary glands from 13th to 16th day of gestation, in mammary endbuds which are a characteristic structure starting development during maturation of the mammary gland, and in the stroma of malignant mammary tumors. However, tenascin was absent in the elongating ducts of embryonic, adult, proliferating, and involuting mammary glands and preneoplastic hyperplastic alveolar nodules. The transplantation of embryonic submandibular mesenchyme into adult mammary glands induces the development of duct-alveolus nodules, which morphologically resemble developing endbuds. Tenascin reappeared around those nodules during the initial stages of their development. Tenascin expression could be induced experimentally in several ways. First, tenascin was detected at the site where the first mammary tumor cells GMT-L metastasized. Second, tenascin was detected in the connective tissue in the tumors derived from the injected C3H mammary tumor cell line CMT315 into Balb/c nude mouse. Cross-strain marker anti-CSA antiserum clearly showed that the tenascin-positive fibroblasts were of Balb/c origin. Third, when embryonic mammary epithelium was explanted on to embryonic mammary fat pad cultures, the mesenchymal cells condensed immediately surrounding the epithelium. Tenascin was detected in these condensed cells. From these three observations we conclude that both embryonic and neoplastic epithelium induced tenascin synthesis in their surrounding mesenchyme.

Tenascin interferes with fibronectin action

Primary chick embryo fibroblasts attach to a tenascin substrate, but remain rounded and do not spread out. The proportion between tenascin and fibronectin in mixtures used to coat the substrate determines the shape of the cells. Tenascin inhibits integrin-mediated chick fibroblast attachment to fibronectin, laminin, and the GRGDS peptide. Rat fibroblast attachment to fibronectin, but not to laminin, is inhibited by tenascin. A monoclonal antibody against tenascin, as well as its Fab fragments, is able to neutralize the inhibitory activity on cell attachment and is therefore assumed to mask the cell-binding site of tenascin. On electron micrographs showing this monoclonal antibody bound to tenascin, its epitope can be localized to the terminal knob at the distal ends of the tenascin arms.

Effect of Heterodera glycines on Charcoal Rot Severity in Soybean Cultivars Resistant and Susceptible to Soybean Cyst Nematode

Field experiments were conducted in two soil types in northeastern Kansas to evaluate the influence of Heterodera glycines on the severity of charcoal rot in group III soybean cultivars resistant and susceptible to soybean cyst nematode race 3. Resistant cultivars Asgrow 3307 and Fayette and susceptible cultivars Asgrow 3127, Harper, Pella, Sprite, and Williams 82 were planted in carbofuran-treated and nontreated plots. Heterodera glycines and the charcoal rot fungus, Macrophomina phaseolina, were suppressed by carbofuran treatment in loamy sand, but not loam soil, and by nematode-resistant cultivars in both soils. Root densities of the fungus were positively correlated with nematode densities and negatively correlated with seed yield at both locations. Results indicate that H. glycines infection can increase colonization of soybean roots by M. phaseolina which may increase losses due to charcoal rot.

Tenascin is a stromal marker for epithelial malignancy in the mammary gland

Tenascin is an extracellular matrix glycoprotein that is not present in the normal mature rat mammary gland. The distribution of tenascin was examined by immunohistochemistry in mammary tumors from carcinogen-treated and untreated rats, in virus-induced mammary tumors from mice, and in a variety of mammary gland lesions from humans. Tenascin was detectable in the stroma of the malignant but not of the benign tumors from all species. An inhibition ELISA, testing homogenates of rat tumors, confirmed that tenascin was present in malignant but not in benign tumors. Thus, tenascin was consistently found to be a stromal marker for epithelial malignancy in the mammary gland. It is concluded that tenascin may be involved in the interactions between the epithelial and mesenchyme-derived (stromal) components of the mammary gland, which are known to influence epithelial carcinogenesis in this organ.

Tenascin: an extracellular matrix protein involved in tissue interactions during fetal development and oncogenesis

The extracellular matrix protein tenascin (previously described as myotendinous antigen) is selectively present in the mesenchyme surrounding fetal rat mammary glands, hair follicles, and teeth, three organ anlagen where the mesenchyme is essential for development. No tenascin is detectable in the normal adult mammary gland. Carcinogen-induced mammary tumors contained tenascin in their fibrous tissue. As reported for the molecule described as a "hexabrachion," tenascin contaminates so-called "cell-surface fibronectin," where it accounts for most of the detectable hemagglutinating activity. Of the extracellular matrix proteins compared, tenascin is the least effective substrate for attachment of primary mammary tumor cells, but the most effective in promoting cell growth after serum is removed from the culture medium.