Extracellular matrix-inducing Sox9 promotes both basal progenitor proliferation and gliogenesis in developing neocortex

Neocortex expansion is largely based on the proliferative capacity of basal progenitors (BPs), which is increased by extracellular matrix (ECM) components via integrin signaling. Here we show that the transcription factor Sox9 drives expression of ECM components and that laminin 211 increases BP proliferation in embryonic mouse neocortex. We show that Sox9 is expressed in human and ferret BPs and is required for BP proliferation in embryonic ferret neocortex. Conditional Sox9 expression in the mouse BP lineage, where it normally is not expressed, increases BP proliferation, reduces Tbr2 levels and induces Olig2 expression, indicative of premature gliogenesis. Conditional Sox9 expression also results in cell-non-autonomous stimulation of BP proliferation followed by increased upper-layer neuron production. Our findings demonstrate that Sox9 exerts concerted effects on transcription, BP proliferation, neuron production, and neurogenic vs. gliogenic BP cell fate, suggesting that Sox9 may have contributed to promote neocortical expansion.

Integrin αvβ3 and thyroid hormones promote expansion of progenitors in embryonic neocortex

Neocortex expansion during evolution is associated with the enlargement of the embryonic subventricular zone, which reflects an increased self-renewal and proliferation of basal progenitors. In contrast to human, the vast majority of mouse basal progenitors lack self-renewal capacity, possibly due to lack of a basal process contacting the basal lamina and downregulation of cell-autonomous production of extracellular matrix (ECM) constituents. Here we show that targeted activation of the ECM receptor integrin αvβ3 on basal progenitors in embryonic mouse neocortex promotes their expansion. Specifically, integrin αvβ3 activation causes an increased cell cycle re-entry of Pax6-negative, Tbr2-positive intermediate progenitors, rather than basal radial glia, and a decrease in the proportion of intermediate progenitors committed to neurogenic division. Interestingly, integrin αvβ3 is the only known cell surface receptor for thyroid hormones. Remarkably, tetrac, a thyroid hormone analog that inhibits the binding of thyroid hormones to integrin αvβ3, completely abolishes the intermediate progenitor expansion observed upon targeted integrin αvβ3 activation, indicating that this expansion requires the binding of thyroid hormones to integrin αvβ3. Convergence of ECM and thyroid hormones on integrin αvβ3 thus appears to be crucial for cortical progenitor proliferation and self-renewal, and hence for normal brain development and the evolutionary expansion of the neocortex.

Role of maternal thyroid hormones in the developing neocortex and during human evolution

The importance of thyroid hormones during brain development has been appreciated for many decades. In humans, low levels of circulating maternal thyroid hormones, e.g., caused by maternal hypothyroidism or lack of iodine in diet, results in a wide spectrum of severe neurological defects, including neurological cretinism characterized by profound neurologic impairment and mental retardation, underlining the importance of the maternal thyroid hormone contribution. In fact, iodine intake, which is essential for thyroid hormone production in the thyroid gland, has been related to the expansion of the brain, associated with the increased cognitive capacities during human evolution. Because thyroid hormones regulate transcriptional activity of target genes via their nuclear thyroid hormone receptors (THRs), even mild and transient changes in maternal thyroid hormone levels can directly affect and alter the gene expression profile, and thus disturb fetal brain development. Here we summarize how thyroid hormones may have influenced human brain evolution through the adaptation to new habitats, concomitant with changes in diet and, therefore, iodine intake. Further, we review the current picture we gained from experimental studies in rodents on the function of maternal thyroid hormones during developmental neurogenesis. We aim to evaluate the effects of maternal thyroid hormone deficiency as well as lack of THRs and transporters on brain development and function, shedding light on the cellular behavior conducted by thyroid hormones.

Abundant occurrence of basal radial glia in the subventricular zone of embryonic neocortex of a lissencephalic primate, the common marmoset Callithrix jacchus

Subventricular zone (SVZ) progenitors are a hallmark of the developing neocortex. Recent studies described a novel type of SVZ progenitor that retains a basal process at mitosis, sustains expression of radial glial markers, and is capable of self-renewal. These progenitors, referred to here as basal radial glia (bRG), occur at high relative abundance in the SVZ of gyrencephalic primates (human) and nonprimates (ferret) but not lissencephalic rodents (mouse). Here, we analyzed the occurrence of bRG cells in the embryonic neocortex of the common marmoset Callithrix jacchus, a near-lissencephalic primate. bRG cells, expressing Pax6, Sox2 (but not Tbr2), glutamate aspartate transporter, and glial fibrillary acidic protein and retaining a basal process at mitosis, occur at similar relative abundance in the marmoset SVZ as in human and ferret. The proportion of progenitors in M-phase was lower in embryonic marmoset than developing ferret neocortex, raising the possibility of a longer cell cycle. Fitting the gyrification indices of 26 anthropoid species to an evolutionary model suggested that the marmoset evolved from a gyrencephalic ancestor. Our results suggest that a high relative abundance of bRG cells may be necessary, but is not sufficient, for gyrencephaly and that the marmoset's lissencephaly evolved secondarily by changing progenitor parameters other than progenitor type.

Endothelial basement membrane limits tip cell formation by inducing Dll4/Notch signalling in vivo

How individual components of the vascular basement membrane influence endothelial cell behaviour remains unclear. Here we show that laminin α4 (Lama4) regulates tip cell numbers and vascular density by inducing endothelial Dll4/Notch signalling in vivo. Lama4 deficiency leads to reduced Dll4 expression, excessive filopodia and tip cell formation in the mouse retina, phenocopying the effects of Dll4/Notch inhibition. Lama4-mediated Dll4 expression requires a combination of integrins in vitro and integrin β1 in vivo. We conclude that appropriate laminin/integrin-induced signalling is necessary to induce physiologically functional levels of Dll4 expression and regulate branching frequency during sprouting angiogenesis in vivo.

Integrin-dependent and -independent functions of astrocytic fibronectin in retinal angiogenesis

Fibronectin (FN) is a major component of the extracellular matrix and functions in cell adhesion, cell spreading and cell migration. In the retina, FN is transiently expressed and assembled on astrocytes (ACs), which guide sprouting tip cells and deposit a provisional matrix for sprouting angiogenesis. The precise function of FN in retinal angiogenesis is largely unknown. Using genetic tools, we show that astrocytes are the major source of cellular FN during angiogenesis in the mouse retina. Deletion of astrocytic FN reduces radial endothelial migration during vascular plexus formation in a gene dose-dependent manner. This effect correlates with reduced VEGF receptor 2 and PI3K/AKT signalling, and can be mimicked by selectively inhibiting VEGF-A binding to FN through intraocular injection of blocking peptides. By contrast, AC-specific replacement of the integrin-binding RGD sequence with FN-RGE or endothelial deletion of itga5 shows little effect on migration and PI3K/AKT signalling, but impairs filopodial alignment along AC processes, suggesting that FN-integrin α5β1 interaction is involved in filopodial adhesion to the astrocytic matrix. AC FN shares its VEGF-binding function and cell-surface distribution with heparan-sulfate (HS), and genetic deletion of both FN and HS together greatly enhances the migration defect, indicating a synergistic function of FN and HS in VEGF binding. We propose that in vivo the VEGF-binding properties of FN and HS promote directional tip cell migration, whereas FN integrin-binding functions to support filopodia adhesion to the astrocytic migration template.

OSVZ progenitors of human and ferret neocortex are epithelial-like and expand by integrin signaling

A major cause of the cerebral cortex expansion that occurred during evolution is the increase in subventricular zone (SVZ) progenitors. We found that progenitors in the outer SVZ (OSVZ) of developing human neocortex retain features of radial glia, in contrast to rodent SVZ progenitors, which have limited proliferation potential. Although delaminating from apical adherens junctions, OSVZ progenitors maintained a basal process contacting the basal lamina, a canonical epithelial property. OSVZ progenitor divisions resulted in asymmetric inheritance of their basal process. Notably, OSVZ progenitors are also found in the ferret, a gyrencephalic nonprimate. Functional disruption of integrins, expressed on the basal process of ferret OSVZ progenitors, markedly decreased the OSVZ progenitor population size, but not that of other, process-lacking SVZ progenitors, in slice cultures of ferret neocortex. Our findings suggest that maintenance of this epithelial property allows integrin-mediated, repeated asymmetric divisions of OSVZ progenitors, providing a basis for neocortical expansion.

Defective N-sulfation of heparan sulfate proteoglycans limits PDGF-BB binding and pericyte recruitment in vascular development

During vascular development, endothelial platelet-derived growth factor B (PDGF-B) is critical for pericyte recruitment. Deletion of the conserved C-terminal heparin-binding motif impairs PDGF-BB retention and pericyte recruitment in vivo, suggesting a potential role for heparan sulfate (HS) in PDGF-BB function during vascular development. We studied the participation of HS chains in pericyte recruitment using two mouse models with altered HS biosynthesis. Reduction of N-sulfation due to deficiency in N-deacetylase/N-sulfotransferase-1 attenuated PDGF-BB binding in vitro, and led to pericyte detachment and delayed pericyte migration in vivo. Reduced N-sulfation also impaired PDGF-BB signaling and directed cell migration, but not proliferation. In contrast, HS from glucuronyl C5-epimerase mutants, which is extensively N- and 6-O-sulfated, but lacks 2-O-sulfated L-iduronic acid residues, retained PDGF-BB in vitro, and pericyte recruitment in vivo was only transiently delayed. These observations were supported by in vitro characterization of the structural features in HS important for PDGF-BB binding. We conclude that pericyte recruitment requires HS with sufficiently extended and appropriately spaced N-sulfated domains to retain PDGF-BB and activate PDGF receptor beta (PDGFRbeta) signaling, whereas the detailed sequence of monosaccharide and sulfate residues does not appear to be important for this interaction.

Prevalence of environmental Aeromonas in South East Queensland, Australia: a study of their interactions with human monolayer Caco-2 cells

AIMS

To investigate the prevalence of Aeromonas in a major waterway in South East Queensland, Australia, and their interactions with a gut epithelial model using Caco-2 cells.

METHODS AND RESULTS

A total of 81 Aeromonas isolates, collected from a major waterway in South East Queensland, Australia, were typed using a metabolic fingerprinting method, and tested for their adhesion to HEp-2 and Caco-2 cells and for cytotoxin production on Vero cells and Caco-2 cells. Aeromonas hydrophila had the highest (43%) and Aeromonas veronii biovar sobria had the lowest (25%) prevalence. Four patterns of adhesion were observed on both HEp-2 and Caco-2 cell lines. Representative isolates having different phenopathotypes (nine strains) together with two clinical isolates were tested for their translocation ability and for the presence of virulence genes associated with pathogenic Escherichia coli. The rate and degree of translocation across Caco-2 monolayers varied among strains and was more pronounced with LogA pattern. Translocation was associated with the adherence of strains to Caco-2 cells microvilli, followed by internalization into Caco-2 cells. Two Aer. veronii biovar sobria strains were positive for the presence of heat-labile toxin genes, with one strain also positive for Shiga-like toxin gene.

CONCLUSIONS

Pathogenic strains of Aeromonas carrying one or more virulence characteristics are highly prevalent in the waterways studied and are capable of translocating across a human enterocyte cell model.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study indicates that Aeromonas strains carrying one or more virulence properties are prevalent in local waterways and are capable of translocating in a human enterocyte cell culture model. However, their importance in human gastrointestinal disease has yet to be verified under competitive conditions of the gut.

Ultrastructural study of Chlamydia pneumoniae in a continuous-infection model

We have established an in vitro model of long-term continuous Chlamydia pneumoniae infection in HEp-2 cells. Using transmission electron microscopy, we demonstrated the presence of spontaneous abnormal chlamydial inclusions similar in appearance to the persistent chlamydial forms induced in vitro by treatment with cytokines or antibiotics or by nutrient deprivation.

Differential expression of ompA, ompB, pyk, nlpD and Cpn0585 genes between normal and interferon-gamma treated cultures of Chlamydia pneumoniae

A common feature of many chlamydial infections is that they are often asymptomatic and may persist for long periods of time if left untreated. In addition to the well recognized lytic stage of the chlamydial developmental cycle, evidence is now emerging to support a persistent phase in the cycle in which the reticulate bodies are morphologically abnormal, viable but non-infectious and presumably also have altered gene expression patterns. We used an RT-PCR approach to study the differential levels of gene transcription for 14 genes (16SrRNA, ompA, ompB, omcB, 76 kDa, gseA, pmp1, gltX, hsp60, yaeT, pyk, nlpD, Cpn0585, Cpn1046) between normal and IFN-gamma treated Chlamydia pneumoniae cell cultures. Even though the level of morphologically abnormal reticulate bodies in our IFN-gamma treated cultures was low (approximately 10% morphologically discernible, although presumably a larger percentage were in the persistent state but not yet morphologically altered) we identified five genes (ompA, ompB, pyk, nlpD, Cpn0585) that were clearly upregulated when compared to normal cultures. This gene transcript profile may be characteristic of a general stress state in Chlamydia, induced by IFN-gamma treatment in this case, but perhaps more widely induced in other in vitro and in vivo situations.

Plesiomonas shigelloides enters polarized human intestinal Caco-2 cells in an in vitro model system

This study provides the first definitive evidence that the gram-negative bacterium Plesiomonas shigelloides adheres to and enters eukaryotic intestinal host cells in vitro. P. shigelloides is increasingly regarded as an emerging enteric pathogen and has been implicated in intestinal and extraintestinal infections in humans. However, the establishment of its true role in enteric disease has been hindered by inadequacies in experimental design, deficiencies in clinical diagnosis, and the lack of an appropriate animal model. In this investigation, an in vitro system was used to evaluate plesiomonad pathogenesis. Differentiated epithelium-derived Caco-2 cell monolayers inoculated apically with 12 isolates of P. shigelloides from clinical (intestinal) origins were examined at high resolution using transmission electron microscopy. Bacterial cells were observed adhering to intact microvilli and to the plasma membrane on both the apical and the basal surfaces of the monolayer. The bacteria entered the Caco-2 cells and were observed enclosed in single and multiple membrane-bound vacuoles within the host cell cytoplasm. This observation suggests that initial uptake may occur through a phagocytic-like process, as has been documented for many other enteropathogens. P. shigelloides also was noted free in the cytosol of Caco-2 cells, suggesting escape from cytoplasmic vacuoles. Differences in invasion phenotypes were revealed, suggesting the possibility that, like Escherichia coli, P. shigelloides comprises different pathogenic phenotypes.

Bacterial Contamination Of Cracks In Symptomatic Vital Teeth

As part of an ongoing study on the initiation of cracks in teeth, 20 teeth exhibiting symptoms consistent with the presence of dentinal cracks were examined. The presence of a cracked cusp was confirmed by the selective application of pressure either with a mirror handle or Fracfinder (Svenoka, Dental Instruments, Vasby, Sweden). Cracked cusps were fractured from the teeth after the removal of all existing restorations and were immediately placed into ten percent formalin. Subsequently, specimens were dehydrated, sputter-coated and examined under the scanning electron microscope (SEM). All the cracked cusps exhibited complete fracture of the dentine to the level of the dentino-enamel junction. No partial fractures were seen. Numerous bacteria of many morphological forms were present on the dentinal surfaces, of all fractured cusps, in all teeth. Cocci, bacilli and filamentous forms were consistently found. Many bacteria were in the process of division. While bacterial contamination of dentinal cracks has been described in histological studies, the nature and distribution of these bacterial and fungal forms has not been shown previously in any detail. Prior SEM studies investigating the nature and mechanisms of fracture have not revealed bacterial contamination of the fractured surface. This paper draws attention to the fact that all symptomatic cracks in teeth appear to 1. extend right through the dentine to the dentino-enamel junction, and 2. appear to be extensively contaminated by bacteria.

Cellular localisation of the ataxia-telangiectasia (ATM) gene product and discrimination between mutated and normal forms

The recently cloned gene (ATM) mutated in the human genetic disorder ataxia-telangiectasia (A-T) is involved in DNA damage response at different cell cycle checkpoints and also appears to have a wider role in signal transduction. Antibodies prepared against peptides from the predicted protein sequence detected a approximately 350 kDa protein corresponding to the open reading frame, which was absent in 13/23 A-T homozygotes. Subcellular fractionation, immunoelectronmicroscopy and immunofluorescence showed that the ATM protein is present in the nucleus and cytoplasmic vesicles. This distribution did not change after irradiation. We also provide evidence that ATM protein binds to p53 and this association is defective in A-T cells compatible with the defective p53 response in these cells. These results provide further support for a role for the ATM protein as a sensor of DNA damage and in a more general role in cell signalling, compatible with the broader phenotype of the syndrome.

The endocytic pathway for H-ferritin established in live MOLT-4 cells by laser scanning confocal microscopy

We have established the intracellular destination of the putative immunoregulatory protein, human recombinant H (heavy)-ferritin, in the transformed T-cell line MOLT-4, by laser scanning confocal microscopy of live cells. A series of confocal images was collected over a 60 min time course using indirect immunofluorescence of H-ferritin and transferrin, their respective monoclonal antibodies, and fluorescein isothiocyanate (FITC)-labelled IgG. A marked drop in FITC fluorescence after 40 min of H-ferritin internalization, indicative of an acidic environment, and co-localization with tetramethylrhodamine isothiocyanate-labelled-dextran strongly suggests that H-ferritin is transferred to the lysosome. In contrast, transferrin was observed to return to the cell surface. Electron microscopy confirmed that H-ferritin was transferred to the lysosome. The receptor-mediated endocytosis and lysosomal delivery of H-ferritin may thus potentiate its putative immunoregulatory activity.

Immune response to a synthetic peptide corresponding to an epitope of a parasitophorous vacuole membrane antigen from Plasmodium falciparum

The parasitophorous vacuole membrane antigen QF 116 from Plasmodium falciparum contains a defined epitope, DNNLVSGP, proximal to the carboxyl-terminus which binds to the inhibitory monoclonal antibody 8E7/55. A synthetic peptide containing this epitope was constructed and coupled to diphtheria toxoid as carrier. Mice and rabbits were inoculated with this conjugate using CFA, SAF-1, or aluminum phosphate as adjuvants. The peptide conjugate was highly immunogenic in both animal species, giving rise to polyclonal antibodies with a similar epitope specificity as the original mAb. Antibody titers were dependent on the route of immunization. Rabbit antibodies produced in sufficient quantity for biologic assays inhibited parasite growth in vitro. This synthetic peptide thus shows promise as an immunogen for use in synthetic vaccine design.

Immune response to a synthetic peptide corresponding to an epitope of a parasitophorous vacuole membrane antigen from Plasmodium falciparum

The parasitophorous vacuole membrane antigen QF 116 from Plasmodium falciparum contains a defined epitope, DNNLVSGP, proximal to the carboxyl-terminus which binds to the inhibitory monoclonal antibody 8E7/55. A synthetic peptide containing this epitope was constructed and coupled to diphtheria toxoid as carrier. Mice and rabbits were inoculated with this conjugate using CFA, SAF-1, or aluminum phosphate as adjuvants. The peptide conjugate was highly immunogenic in both animal species, giving rise to polyclonal antibodies with a similar epitope specificity as the original mAb. Antibody titers were dependent on the route of immunization. Rabbit antibodies produced in sufficient quantity for biologic assays inhibited parasite growth in vitro. This synthetic peptide thus shows promise as an immunogen for use in synthetic vaccine design.

Monoclonal antibody against a melanosomal protein in melanotic and amelanotic human melanoma cells

BALB/c mice were immunized with tyrosinase, partially purified in two stages from a human melanoma cell line. A hybridoma was obtained which produced monoclonal antibody (MoAb 1C11) reactive with 8/10 melanoma cell lines and 10/10 primary cultures of human melanocytes, neval cells, and melanomas. Immunoreactivity correlated to a certain extent with tyrosinase activity but not with melanin content. No crossreactivity was obtained with neuroblastoma, medulloblastoma, fibroblasts, keratinocytes, lymphoid cells, or murine melanomas. Purification of the antigen directly from cell lysates with a MoAb 1C11 CNBr-Sepharose affinity column gave a green-brown protein of 56 kDa with no detectable tyrosinase activity. This protein was therefore different from 60 kDa active tyrosinase, identified by enzyme activity and Western blotting with a MoAb derived previously (MoAb 5C12). Unlike 5C12, 1C11 reactivity was not destroyed by pretreatment of the antigen with periodate. Immunogold labelling showed that the 1C11-reactive antigen was associated with melanosomes, and there was close correlation between 5C12 and 1C11 reactivity in resistance to trypsin and in staining various melanocytic cell populations. MoAb 1C11 may therefore recognise a polypeptide epitope in a molecule closely linked to melanin biosynthesis.

The 140/130/105 kilodalton protein complex in the rhoptries of Plasmodium falciparum consists of discrete polypeptides

Four monoclonal antibodies (MAbs) recognise an antigen localised in the rhoptries of Plasmodium falciparum merozoites using both indirect immunofluorescence assay and immunoelectron microscopy with immunogold labeling. All MAbs immunoprecipitated bands at 140, 130 and 105 kDa from [35S]methionine-labeled parasites; however, one MAb immunoblotted only the 130 kDa protein and another MAb immunoblotted the 105 kDa protein. The affinity purified antigen complex consisted of proteins of 140, 130, 105 and 98 kDa. The individual proteins were subjected to peptide mapping with Staphylococcus aureus V8 protease; the 98 kDa protein was a degradation product of the 105 kDa protein and the 140, 130, and 105 kDa proteins were found to be unrelated. The antigen complex was synthesised at the mid trophozoite stage and was considered to be soluble as judged by release from mature schizonts by freeze/thaw lysis. One of the MAbs inhibited parasite growth and/or merozoite invasion of erythrocytes, in vitro, to a small but significant extent.

The role of reactive oxygen metabolites in lymphocyte-mediated cytolysis

To examine the possible role of reactive oxygen metabolites in lymphocyte-mediated cytolysis, the morphology of cell death following the exposure of cells to reactive oxygen metabolites in vitro was compared with the morphology of cell-mediated killing in vitro of tumour cells by natural killer (NK) cells. Ultrastructural examination of human tumour cells that were dying following incubation for 60 min with the oxygen metabolite generating systems, xanthine-xanthine oxidase or t-butylhydroperoxide, showed that cell death in both instances was exclusively by necrosis. It was unclear which oxygen metabolites were involved in killing. Cell death was not decreased by the addition of superoxide dismutase, a scavenger of the superoxide anion, to the xanthine-xanthine oxidase mixture. Although the cells were not killed by incubation with 1 mM-hydrogen peroxide, the addition of catalase, a scavenger of hydrogen peroxide, to the xanthine-xanthine oxidase mixture significantly reduced cell death. The addition of scavengers for the hydroxyl radical to either the xanthine-xanthine oxidase mixture or t-butylhydroperoxide gave inconsistent protection. In contrast, tumour cell killing mediated by natural killer cells was by apoptosis, a morphologically distinct mode of cell death with a different basic mechanism, indicating that reactive oxygen metabolites are not directly involved in lymphocyte-mediated cytolysis.