Glial cell differentiation in neuron-free and neuron-rich regions. I. Selective appearance of S-100 protein in radial glial cells of the hippocampal fimbria in human fetuses

S100B actions on glial and neuronal cells in the developing brain: an overview

The S100B is a member of the S100 family of "E" helix-loop- "F" helix structure (EF) hand calcium-binding proteins expressed in diverse glial, selected neuronal, and various peripheral cells, exerting differential effects. In particular, this review compiles descriptions of the detection of S100B in different brain cells localized in specific regions during the development of humans, mice, and rats. Then, it summarizes S100B's actions on the differentiation, growth, and maturation of glial and neuronal cells in humans and rodents. Particular emphasis is placed on S100B regulation of the differentiation and maturation of astrocytes, oligodendrocytes (OL), and the stimulation of dendritic development in serotoninergic and cerebellar neurons during embryogenesis. We also summarized reports that associate morphological alterations (impaired neurite outgrowth, neuronal migration, altered radial glial cell morphology) of specific neural cell groups during neurodevelopment and functional disturbances (slower rate of weight gain, impaired spatial learning) with changes in the expression of S100B caused by different conditions and stimuli as exposure to stress, ethanol, cocaine and congenital conditions such as Down's Syndrome. Taken together, this evidence highlights the impact of the expression and early actions of S100B in astrocytes, OL, and neurons during brain development, which is reflected in the alterations in differentiation, growth, and maturation of these cells. This allows the integration of a spatiotemporal panorama of S100B actions in glial and neuronal cells in the developing brain.

The HOPX and BLBP landscape and gliogenic regions in developing human brain

Outer radial glial cells (oRGs) give rise to neurons and glial cells and contribute to cell migration and expansion in developing neocortex. HOPX has been described as a marker of oRGs and possible actor in glioblastomas. Recent years' evidence points to spatiotemporal differences in brain development which may have implications for the classification of cell types in the central nervous system and understanding of a range of neurological diseases. Using the Human Embryonic/Fetal Biobank, Institute of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark, HOPX and BLBP immunoexpression was investigated in developing frontal, parietal, temporal and occipital human neocortex, other cortical areas and brain stem regions to interrogate oRG and HOPX regional heterogeneity. Furthermore, usage of high-plex spatial profiling (Nanostring GeoMx® DSP) was tested on the same material. HOPX marked oRGs in several human developing brain regions as well as cells in known gliogenic areas but did not completely overlap with BLBP or GFAP. Interestingly, limbic structures (e.g. olfactory bulb, indusium griseum, entorhinal cortex, fimbria) showed more intense HOPX immunoreactivity than adjacent neocortex and in cerebellum and brain stem, HOPX and BLBP seemed to stain different cell populations in cerebellar cortex and corpus pontobulbare. DSP screening of corresponding regions indicated differences in cell type composition, vessel density and presence of apolipoproteins within and across regions and thereby confirming the importance of acknowledging time and place in developmental neuroscience.

Astrocyte-Neuron Signaling in Synaptogenesis

Astrocytes are the key component of the central nervous system (CNS), serving as pivotal regulators of neuronal synapse formation and maturation through their ability to dynamically and bidirectionally communicate with synapses throughout life. In the past 20 years, numerous astrocyte-derived molecules promoting synaptogenesis have been discovered. However, our understanding of the cell biological basis underlying intra-neuron processes and astrocyte-mediated synaptogenesis is still in its infancy. Here, we provide a comprehensive overview of the various ways astrocytes talk to neurons, and highlight astrocytes’ heterogeneity that allow them to displays regional-specific capabilities in boosting synaptogenesis. Finally, we conclude with promises and future directions on how organoids generated from human induced pluripotent stem cells (hiPSCs) effectively address the signaling pathways astrocytes employ in synaptic development.

Astrogliogenesis in human fetal brain: complex spatiotemporal immunoreactivity patterns of GFAP, S100, AQP4 and YKL-40

The astroglial lineage consists of heterogeneous cells instrumental for normal brain development, function and repair. Unfortunately, this heterogeneity complicates research in the field, which suffers from lack of truly specific and sensitive astroglial markers. Nevertheless, single astroglial markers are often used to describe astrocytes in different settings. We therefore investigated and compared spatiotemporal patterns of immunoreactivity in developing human brain from 12 to 21 weeks post conception and publicly available RNA expression data for four established and potential astroglial markers - GFAP, S100, AQP4 and YKL-40. In the hippocampal region, we also screened for C3, a complement component highly expressed in A1-reactive astrocytes. We found diverging partly overlapping patterns of the established astroglial markers GFAP, S100 and AQP4, confirming that none of these markers can fully describe and discriminate different developmental forms and subpopulations of astrocytes in human developing brain, although AQP4 seems to be the most sensitive and specific marker for the astroglial lineage at midgestation. AQP4 characterizes a brain-wide water transport system in cerebral cortex with regional differences in immunoreactivity at midgestation. AQP4 distinguishes a vast proportion of astrocytes and subpopulations of radial glial cells destined for the astroglial lineage, including astrocytes determined for the future glia limitans and apical truncated radial glial cells in ganglionic eminences, devoid of GFAP and S100. YKL-40 and C3d, previously found in reactive astrocytes, stain different subpopulations of astrocytes/astroglial progenitors in developing hippocampus at midgestation and may characterize specific subpopulations of 'developmental astrocytes'. Our results clearly reflect that lack of pan-astrocytic markers necessitates the consideration of time, region, context and aim when choosing appropriate astroglial markers.

Brain barriers and a subpopulation of astroglial progenitors of developing human forebrain are immunostained for the glycoprotein YKL-40

YKL-40, a glycoprotein involved in cell differentiation, has been associated with neurodevelopmental disorders, angiogenesis, neuroinflammation and glioblastomas. We evaluated YKL-40 protein distribution in the early human forebrain using double-labeling immunofluorescence and immunohistochemistry. Immunoreactivity was detected in neuroepithelial cells, radial glial end feet, leptomeningeal cells and choroid plexus epithelial cells. The subpial marginal zone was YKL-40-positive, particularly in the hippocampus, from an early beginning stage in its development. Blood vessels in the intermediate and subventricular zones showed specific YKL-40 reactivity confined to pericytes. Furthermore, a population of YKL-40-positive, small, rounded cells was identified in the ventricular and subventricular zones. Real-time quantitative RT-PCR analysis showed strong YKL-40 mRNA expression in the leptomeninges and the choroid plexuses, and weaker expression in the telencephalic wall. Immunohistochemistry revealed a differential distribution of YKL-40 across the zones of the developing telencephalic wall. We show that YKL-40 is associated with sites of the brain barrier systems and propose that it is involved in controlling local angiogenesis and access of peripheral cells to the forebrain via secretion from leptomeningeal cells, choroid plexus epithelium and pericytes. Furthermore, we suggest that the small, rounded, YKL-40-positive cells represent a subpopulation of astroglial progenitors, and that YKL-40 could be involved in the differentiation of a particular astrocytic lineage.

Zbtb20 defines a hippocampal neuronal identity through direct repression of genes that control projection neuron development in the isocortex

Hippocampal pyramidal neurons are important for encoding and retrieval of spatial maps and episodic memories. While previous work has shown that Zbtb20 is a cell fate determinant for CA1 pyramidal neurons, the regulatory mechanisms governing this process are not known. In this study, we demonstrate that Zbtb20 binds to genes that control neuronal subtype specification in the developing isocortex, including Cux1, Cux2, Fezf2, Foxp2, Mef2c, Rorb, Satb2, Sox5, Tbr1, Tle4, and Zfpm2. We show that Zbtb20 represses these genes during ectopic CA1 pyramidal neuron development in transgenic mice. These data reveal a novel regulatory mechanism by which Zbtb20 suppresses the acquisition of an isocortical fate during archicortical neurogenesis to ensure commitment to a CA1 pyramidal neuron fate. We further show that the expression pattern of Zbtb20 is evolutionary conserved in the fetal human hippocampus, where it is complementary to the expression pattern of the Zbtb20 target gene Tbr1. Therefore, the disclosed Zbtb20-mediated transcriptional repressor mechanism may be involved in development of the human archicortex.

Immunolocalization of S100-like protein in the brain of an emerging model organism: Nothobranchius furzeri

The S100 protein in nervous tissue appears to play important roles in regulating neuronal differentiation, glial proliferation, plasticity, development, axonal growth, and in neurogenetic processes. In fish, the adult neurogenic activity is much higher than in mammals. In this study, the localization of S100 protein was investigated in the brain of annual teleost fish, Nothobranchius furzeri, which is an emerging model organism for aging research. By immunohistochemical techniques, S100 immunoreactivity (IR) was detected in glial cells, small neurons, and fibers throughout all regions of central nervous system (CNS) with different pattern of distribution. In the telencephalon, S100 IR was seen in the olfactory bulbs and in different areas of the telencephalic hemispheres. In the diencephalon, S100 positivity was observed in the habenular nuclei of the epithalamus, in the cortical thalamic nucleus, in the dorsal, ventral and caudal portions, the latter with the posterior recessus nucleus, and in the diffuse inferior lobe of the hypothalamus, along the diencephalic ventricle and in the dorsal optic tract. In the mesencephalon, S100 IR was observed in the longitudinal tori, in the optic tectum, and along the mesencephalic ventricle. In the rhombencephalon, S100 IR was shown in valvula and body of the cerebellum, and in some nuclei of the medulla oblongata. The results suggest that S100 may play a key role in the maintenance of the CNS and in neurogenesis processes in the adulthood.

Expression and distribution of S100 protein in the nervous system of the adult zebrafish (Danio rerio)

S100 proteins are EF-hand calcium-binding protein highly preserved during evolution present in both neuronal and non-neuronal tissues of the higher vertebrates. Data about the expression of S100 protein in fishes are scarce, and no data are available on zebrafish, a common model used in biology to study development but also human diseases. In this study, we have investigated the expression of S100 protein in the central nervous system of adult zebrafish using PCR, Western blot, and immunohistochemistry. The central nervous system of the adult zebrafish express S100 protein mRNA, and contain a protein of approximately 10 kDa identified as S100 protein. S100 protein immunoreactivity was detected widespread distributed in the central nervous system, labeling the cytoplasm of both neuronal and non-neuronal cells. In fact, S100 protein immunoreactivity was primarily found in glial and ependymal cells, whereas the only neurons displaying S100 immunoreactivity were the Purkinje's neurons of the cerebellar cortex and those forming the deep cerebellar nuclei. Outside the central nervous system, S100 protein immunoreactivity was observed in a subpopulation of sensory and sympathetic neurons, and it was absent from the enteric nervous system. The functional role of S100 protein in both neurons and non-neuronal cells of the zebrafish central nervous system remains to be elucidated, but present results might serve as baseline for future experimental studies using this teleost as a model.

Fetuin and fetuin messenger RNA in granulosa cells of the rat ovary

The hardening reaction that occurs in the zona pellucida to block polyspermy can be overcome in oocyte cultures in the presence of fetal serum or the serum component fetuin. Fetuin may also prevent precocious zona hardening by inhibiting a ZP2 proteinase released spontaneously by cortical granules during maturation of the oocyte. We demonstrated fetuin mRNA in the rat ovary by reverse transcriptase-polymerase chain reaction and localized it by in situ hybridization. Fetuin mRNA was present in all granulosa cells of growing and large follicles. Immunohistochemical analysis revealed that the fetuin protein was only present in some of the small, growing follicles. In large, healthy follicles, fetuin protein was confined to cumulus cells and granulosa cells bordering the antrum. Fetuin was present in atretic follicles, but the staining pattern differed from that of healthy follicles. The follicular antrum contained a substantial amount of fetuin, but whether granulosa cells secreted it or it originated in the ovarian blood supply could not be confirmed. We concluded that at least a portion of the fetuin is produced by granulosa cells of growing and large follicles, suggesting that fetuin may function in a paracrine manner to maintain the zona pellucida in a penetrable state for fertilization.

Oligodendrocyte apoptosis and primary demyelination induced by local TNF/p55TNF receptor signaling in the central nervous system of transgenic mice: models for multiple sclerosis with primary oligodendrogliopathy

The scientific dogma that multiple sclerosis (MS) is a disease caused by a single pathogenic mechanism has been challenged recently by the heterogeneity observed in MS lesions and the realization that not all patterns of demyelination can be modeled by autoimmune-triggered mechanisms. To evaluate the contribution of local tumor necrosis factor (TNF) ligand/receptor signaling pathways to MS immunopathogenesis we have analyzed disease pathology in central nervous system-expressing TNF transgenic mice, with or without p55 or p75TNF receptors, using combined in situ terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling and cell identification techniques. We demonstrate that local production of TNF by central nervous system glia potently and selectively induces oligodendrocyte apoptosis and myelin vacuolation in the context of an intact blood-brain barrier and absence of immune cell infiltration into the central nervous system parenchyma. Interestingly, primary demyelination then develops in a classical manner in the presence of large numbers of recruited phagocytic macrophages, possibly the result of concomitant pro-inflammatory effects of TNF in the central nervous system, and lesions progress into acute or chronic MS-type plaques with axonal damage, focal blood-brain barrier disruption, and considerable oligodendrocyte loss. Both the cytotoxic and inflammatory effects of TNF were abrogated in mice genetically deficient for the p55TNF receptor demonstrating a dominant role for p55TNF receptor-signaling pathways in TNF-mediated pathology. These results demonstrate that aberrant local TNF/p55TNF receptor signaling in the central nervous system can have a potentially major role in the aetiopathogenesis of MS demyelination, particularly in MS subtypes in which oligodendrocyte death is a primary pathological feature, and provide new models for studying the basic mechanisms underlying oligodendrocyte and myelin loss.

S-100-positive glial cells are involved in the regeneration of the visual pathway of teleosts

Glial cells in the normal and regenerating visual pathways of Tinca tinca (Cyprinid, Teleost) were studied by labelling with anti-S-100 antibody. In normal fish, S-100-positive bipolar cells were found in the optic nerve, optic tract, and in the diencephalic visual pathways. After crushing the left optic nerve, the distribution and the number of S-100-immunoreactive cells were modified. In the injured nerve, 7 to 15 days after crushing no immunoreactive cell bodies were found in the crushed area, but a greater number of S-100-positive cells were found on both sides of the injured area. Sixty days after crushing, positive cells penetrating the crushed area were observed; the normal pattern was almost restored 200 days after crushing. In the diencephalon, 25 days after crushing, the number of S-100-positive cells increased remarkably and the most intense immunostaining of glial processes was observed 60 days after crushing. The density of S-100-labelled cells decreased after 4 months postcrushing. However, in the optic tectum no changes were observed. The increase of glial cells in the lesioned visual pathway suggests that they could play an important role in axonal regeneration after crushing.

Distribution of S100 immunoreactivity in the retina and optic nerve head of the teleost Tinca tinca L

The distribution of S100 immunoreactivity within the normal and regenerating retina and optic nerve head of the teleost Tinca tinca L. has been investigated using the avidin-biotin complex (ABC) method and a polyclonal antibody against S100. Astrocytes and Müller cells were labeled with this antibody. This represents the first description of astrocytes localized in the optic nerve head and in the nerve fiber layer of the fish retina displaying a typical bipolar morphology. Horizontal cells in the inner nuclear layer were immunolabeled; we also observed species-specific S100 labeling of horizontal cells of the H1 subtype. No significant changes were seen in the S100 immunoreactive Müller cells, astrocytes, or horizontal cells in the tench retina after optic nerve crushing and during regeneration. These results might help to understand the function of glial cells in the normal and experimentally induced regenerating fish visual system.

Human fetal hippocampal development: II. The neuronal cytoskeleton

In this study of the developing human hippocampus, we monitor the timing of onset and the sequential patterns of expression of 11 developmentally regulated proteins that are important components of the neuronal cytoskeleton. Immunohistochemistry using well-characterized antibodies was conducted with fixed paraffin-embedded sections from hippocampi at various stages of fetal and postnatal development. At 9 weeks gestational age, immunoreactivity was evident for the microtubule-associated proteins (MAPs), MAP2 and MAP5, low molecular weight (Mr) neurofilament (NF) protein (NF-L), poorly phosphorylated mid-Mr NF protein (NF-M/P-), vimentin, and alpha-and beta-tubulins within the somatodendritic domain of neurons of the hippocampal plate. Weak immunoreactivity for moderately phosphorylated, high Mr NF protein (NF-H/P + + +), tau, and nestin was observed. Highly phosphorylated mid-Mr NF protein (NF-M/P + + +) and alpha-internexin were first detected at 15 weeks and highly phosphorylated, high Mr NF protein (NF-H/P+3) at 20 weeks. At 15 weeks, MAP2, MAP5, and tubulins were expressed in an "inside-out" gradient and in a gradient between hippocampal subfields with subiculum > ammonic subfields > dentate gyrus. These gradients paralleled the maturational gradients seen in cytoarchitectural and neuronal morphologic studies. The adult pattern of neuronal cytoskeletal protein expression in the hippocampus was attained by the second postnatal year for all proteins. Our findings demonstrate an elaborate orchestration of cytoskeletal protein expression within the hippocampus that is qualitatively similar to what is seen in other brain regions and in nonhuman species but which also has some important differences in timing and pattern. The differences in the developmentally regulated expression of neuronal cytoskeletal proteins in separate regions of the central nervous system (CNS) suggest that there are region-specific differences in composition and function of the neuronal cytoskeleton. These observations have implications for understanding the role of the neuronal cytoskeleton in the developing, mature, and diseased CNS.

Age-dependent changes in the proliferative response of S-100 protein-positive glial cells to injury in the rat brain

A mechanical injury was inflicted to the left cerebral hemisphere in rats of four age groups: newborns, 6, 14 and 30 days old. The injury was followed by [3H]thymidine injections at different time intervals. Brain sections were immunostained for S-100 protein and subjected to autoradiography. During microscopic observations of the injury region, locations and numbers of the autoradiographically labeled astrocytes expressing S-100 protein were recorded. On the basis of the observations, injury-induced changes in the total number of proliferating astrocytes, as well as in their distribution, were analysed quantitatively. In rats injured neonatally, as well as those injured on postnatal days 6 and 14, the reactive increase in the number of proliferating astrocytes began on the first post-traumatic day. In 30-day-old rats the increase was slower and appeared on day 2. The maximal increase in the astrocyte proliferative activity occurred in 6-day-old rats as early as day 1 after injury and was about eight times higher than that recorded in newborns, and nearly twice as high as that recorded in brains of 30-day-old rats. The results suggest that the intensity of astrocyte proliferative response to injury cannot be regarded as simply being proportional to the developmental progress of the brain tissue. Rather, these results indicate that changes in glial proliferative responses to injury follow a developmental time course, with a peak around the end of the first postnatal week.

Post-embedding tem signal-to-noise ratio of S-100

We assessed the reactivity of purified S-100 antiserum in immuno-electron microscopy by counting the number of gold particles per microns 2 over inner ear tissues embedded in different media. Sections containing predominantly Schwann's cell cytoplasm and nucleus, afferent fiber axoplasm and myelin sheath of chick cochleae were reacted with anti-S-100 IgG, an antibody to a calcium binding protein of neuronal tissues, then labeled with anti-IgG-gold conjugate. This investigation was conducted because previously published procedures, unmodified, did not yield acceptable results. Preparation of all specimens was identical. Only the medium (PolyBed 812, Araldite or Spurr epoxies; and LR White, LR Gold or Lowicryl plastics) was changed. The medium was made the changing variable because antigens available in post-embedding immuno-electron microscopy are decreased by heat, either used and/or released during polymerization of the embedding medium. The results indicate that: (a) none of the embedding media above provided optimal signal-to-noise ratio for all parts of the nerve stained in the same section; (b) aggregation of gold particles over cells was highest in embedding media with high background labeling over areas devoid of tissue (noise); (c) aggregation occurred randomly throughout both cellular and acellular regions; and (d) particles aggregated less and were distributed more evenly in tissues from media yielding good ultrastructural integrity.

Glial cell differentiation in neuron-free and neuron-rich regions. II. Early appearance of S-100 protein positive astrocytes in human fetal hippocampus

The development of the human fetal hippocampus and dentate gyrus has been studied immunocytochemically. The first glial cells to appear are vimentin-positive radial glial cells. A gradual transition from vimentin to glial fibrillary acidic protein (GFAP) reactivity in the radial glial cells occurs at week 8. The GFAP-positive radial glial cells transform into astrocytes from week 14. A population of small S-100-positive somata which morphologically and spatially are distinct from GFAP-positive radial glial cells and their transformed progeny, are found as early as week 9.5 in the hippocampus during the period of peak neurogenesis. The well-defined immunoreactivity of the morphologically homogenous cell subpopulation for S-100 protein, which has been used as an astrocytic marker in the adult hippocampus, indicates that astrocytes may differentiate at very early gestational ages in human fetuses. The S-100-positive astrocytes are thought to be derived from ventricular zone cells, which at the time of their appearance do not express any of the applied astrocytic markers (S-100, GFAP, vimentin). It is suggested that the S-100-positive astrocytic cell population interacts with the first incoming projection fibers, so modulating the pattern of connectivity.