Presumptive common precursor for neuronal and glial cell lineages in mouse hypothalamus

Progressions on the Coexistence of Neuronal and Glial Precursor Cells in the Cerebral Ventricular Zone

Heterogeneity is defined as the quality or state of being diverse in character or content. This article summarizes the natural progression from my studies, reported in the first issue of the Journal of Neuroscience, that identified molecular heterogeneity in precursor cells of the developing primate cerebral cortex to the current state in which differences defined at the molecular, cellular, circuit, and systems levels are building data encyclopedias. The emphasis on heterogeneity has impacted many contributors in the field of developmental neuroscience, who have led a quest to determine the extent to which there is diversity, when it appears developmentally, and what heritable and nonheritable factors mediate nervous system assembly and function. Since the appearance of the article on progenitor cell heterogeneity in the inaugural issue of the Journal of Neuroscience, there have been continuous advances in technologies and data analytics that are contributing to a much better understanding of the origins of neurobiological and behavioral heterogeneity.

S100 proteins: An emerging cynosure in pregnancy & adverse reproductive outcome

S100 proteins are calcium (Ca²⁺)-binding proteins and these have an important function in progression, manifestation and therapeutic aspects of various inflammatory, metabolic and neurodegenerative disorders. Based on their involvement in intracellular or extracellular regulatory effects, S100 proteins are classified into three subgroups: one subgroup is specialized in exerting only intracellular effects, other performs both intracellular and extracellular functions and the third subgroup members only display extracellular regulatory effects. S100 proteins are expressed particularly in vertebrates and have cell-specific expression. Functionally, S100 proteins act through their surface receptors and regulate cell functions in autocrine or paracrine mode. Receptor for advanced glycation end products (RAGEs) and toll-like receptor 4 are the main surface receptors. S100 proteins participate in the regulation of cellular differentiation, proliferation, apoptosis and inflammation along with Ca²⁺ homeostasis, energy metabolism and cellular migration, and perform the respective functions through their interaction with transcription factors, nucleic acids, enzymes, receptors, cytoskeleton system, etc. Currently, their role in adverse pregnancy outcomes and compromised reproductive health is being explored. These proteins are present in amniotic fluid, endometrium tissue and foetal brain; therefore, it is quite likely that alterations in the expression levels of S100 family members will be affecting the particular function they are involved in and ultimately affecting the pregnancy in adverse manner. The current review discusses about an association of S100 proteins in pregnancy disorders such as endometriosis, intrauterine growth retardation and miscarriage.

Hypothalamic tanycytes-masters and servants of metabolic, neuroendocrine, and neurogenic functions

There is a resurgent interest in tanycytes, a radial glial-like cell population occupying the floor and ventro-lateral walls of the third ventricle (3V). Tanycytes reside in close proximity to hypothalamic neuronal nuclei that regulate appetite and energy expenditure, with a subset sending projections into these nuclei. Moreover, tanycytes are exposed to 3V cerebrospinal fluid and have privileged access to plasma metabolites and hormones, through fenestrated capillaries. Indeed, some tanycytes act as conduits for trafficking of these molecules into the brain parenchyma. Tanycytes can also act as neural stem/progenitor cells, supplying the postnatal and adult hypothalamus with new neurons. Collectively, these findings suggest that tanycytes regulate and integrate important trophic and metabolic processes and possibly endow functional malleability to neuronal circuits of the hypothalamus. Hence, manipulation of tanycyte biology could provide a valuable tool for modulating hypothalamic functions such as energy uptake and expenditure in order to tackle prevalent eating disorders such as obesity and anorexia.

Developmental changes in hypothalamic leptin receptor: relationship with the postnatal leptin surge and energy balance neuropeptides in the postnatal rat

In the adult brain, leptin regulates energy homeostasis primarily via hypothalamic circuitry that affects food intake and energy expenditure. Evidence from rodent models has demonstrated that during early postnatal life, leptin is relatively ineffective in modulating these pathways, despite the high circulating levels and the presence of leptin receptors within the central nervous system. Furthermore, in recent years, a neurotrophic role for leptin in the establishment of energy balance circuits has emerged. The precise way in which leptin exerts these effects, and the site of leptin action, is unclear. To provide a detailed description of the development of energy balance systems in the postnatal rat in relation to leptin concentrations during this time, endogenous leptin levels were measured, along with gene expression of leptin receptors and energy balance neuropeptides in the medial basal hypothalamus, using in situ hybridization. Expression of leptin receptors and both orexigenic and anorexigenic neuropeptides increased in the arcuate nucleus during the early postnatal period. At postnatal day 4 (P4), we detected dense leptin receptor expression in ependymal cells of the third ventricle (3V), which showed a dramatic reduction over the first postnatal weeks, coinciding with marked morphological changes in this region. An acute leptin challenge robustly induced suppressor of cytokine signaling-3 expression in the 3V of P4 but not P14 animals, revealing a clear change in the location of leptin action over this period. These findings suggest that the neurotrophic actions of leptin may involve signaling at the 3V during a restricted period of postnatal development.

Early developmental expression of leptin receptor gene and [125I]leptin binding in the rat forebrain

Leptin, via leptin receptors (Ob-R), regulates appetite and energy balance. Of the six isoforms of the receptor identified, so far, only the long form (Ob-Rb) can fully activate downstream signal transduction pathways. Although the expression and function of leptin receptors is well described in the adult brain, little is known about the ontogeny of leptin receptor system around the time of birth. In this study, the mRNA expression patterns of total leptin receptor, Ob-R, and the long signalling form of the receptor, Ob-Rb, were investigated in the brain of embryonic and newborn rats using in situ hybridisation and [125I]leptin binding. On embryonic day 18 (E18), Ob-R mRNA was detected in the choroid plexus and the ependymal layer of the third ventricle by in situ hybridisation. At E21, Ob-Rb mRNA was first observed in the arcuate and the ventral premammillary hypothalamic nuclei while at P3, receptor expression was also found in the dorsomedial nucleus. Other leptin target areas identified were the trigeminal ganglion, the thalamus and the hippocampus. Using quantitative receptor autoradiography specific [125I]leptin binding sites on the choroid plexus were found to increase with age in contrast to the ependymal layer of the third ventricle where levels decreased with age. Together these findings demonstrate that the leptin receptor system is differentially regulated during late gestation and early postnatal life in the rat.

Neurogenesis in the ependymal layer of the adult rat 3rd ventricle

Neurogenesis has been described in limited regions of the adult mammalian brain. In this study, we showed that the ependymal layer of the 3rd ventricle is a neurogenic region in the adult rat brain. DiI labeling of the 3rd ventricle revealed that neural progenitor cells were derived from cells at the ependymal layer of the adult 3rd ventricle. The mitosis of these progenitor cells at the ependymal layer was promoted by bFGF administration. Combination of BrdU administration, nestin/GFAP immunohistochemistry, and labeling by GFP-recombinant adenoviral infection (vGFP) indicated that at least some tanycytes might be neural progenitor cells in the ependymal layer of the 3rd ventricle. Tracing by vGFP indicated that neural progenitor cells may have migrated from the 3rd ventricle to the hypothalamic parenchyma, where they were integrated into neural networks by forming synapses. In addition, some BrdU(+) neurons had immunoreactivity for orexin A in the hypothalamus. These results indicate that neural progenitor cells exist in the ependymal layer of the adult rat 3rd ventricle and that they may differentiate into neurons functioning in the hypothalamus.

Visualization of S100B-positive neurons and glia in the central nervous system of EGFP transgenic mice

S100B, the EF-hand Ca(++)-binding protein with gliotrophic and neurotrophic properties implicated in the pathogenesis of Alzheimer's disease, is coined as a glial marker, despite its documented presence in rodent brain neurons. We have generated a transgenic mouse whose EGFP reporter, controlled by the -1,669/+3,106 sequence of the murine S100B gene, allows the direct microscopic observation of most S100B-expressing cells in the central nervous system (CNS). From embryonic day 13 onward, EGFP expression was targeted to selected neuroepithelial, glial, and neuronal cells, indicating that cell-specific expression of S100B is regulated at the transcriptional level during development. In adult mice, the highest level of EGFP expression was found in ependymocytes; astrocytes; and spinal, medullar, pontine, and deep cerebellar S100B neurons. Our results, thus, agree with earlier reports suggesting that S100B is not a CNS glial-specific marker. In addition, we detected EGFP and S100B in forebrain neurons previously thought not to express S100B in the mouse, including neurons of primary motor and somatosensory neocortical areas, the ventral pallidum and prerubral field. Another interesting finding was the selected EGFP targeting to neonatal S100B oligodendrocytes and adult NG2 progenitors as opposed to mature S100B oligodendrocytes. This finding suggests that, except for oligodendrocytes at the last stage of myelin maturation, the -1,669/+3,106 sequence of the S100B gene is a useful reagent for driving expression of transgenes in most S100B-expressing cells of mouse brain.

Ependymal and choroidal cells in culture: characterization and functional differentiation

During the past 10 years, our teams developed long-term primary cultures of ependymal cells derived from ventricular walls of telencephalon and hypothalamus or choroidal cells (modified ependymal cells) derived from plexuses dissected out of fetal or newborn mouse or rat brains. Cultures were established in serum-supplemented or chemically defined media after seeding on serum-, fibronectin-, or collagen-laminin-coated plastic dishes or semipermeable inserts. To identify and characterize cell types growing in our cultures, we used morphological features provided by phase contrast, scanning, and transmission electron microscopy. We used antibodies against intermediate filament proteins (vimentin, glial fibrillary acidic protein, cytokeratin, desmin, neurofilament proteins), actin, myosin, ciliary rootlets, laminin, and fibronectin in single or double immunostaining, and monoclonal antibodies against epitopes of ependymal or endothelial cells, to recognize ventricular wall cell types with immunological criteria. Ciliated or nonciliated ependymal cells in telencephalic cultures, tanycytes and ciliated and nonciliated ependymal cells in hypothalamic cultures always exceeded 75% of the cultured cells under the conditions used. These cells were characterized by their cell shape and epithelial organization, by their apical differentiations observed by scanning and transmission electron microscopy, and by specific markers (e.g., glial fibrillary acidic protein, ciliary rootlet proteins, DARPP 32) detected by immunofluorescence. All these cultured ependymal cell types remarkably resembled in vivo ependymocytes in terms of molecular markers and ultrastructural features. Choroidal cells were also maintained for several weeks in culture, and abundantly expressed markers were detected in both choroidal tissue and culture (Na+-K+-dependent ATPase, DARPP 32, G proteins, ANP receptors). In this review, the culture models we developed (defined in terms of biological material, media, substrates, duration, and subculturing) are also compared with those developed by other investigators during the last 10 years. Focusing on morphological and functional approaches, we have shown that these culture models were suitable to investigate and provide new insights on (1) the gap junctional communication of ependymal, choroidal, and astroglial cells in long-term primary cultures by freeze-fracture or dye transfer of Lucifer Yellow CH after intracellular microinjection; (2) some ionic channels; (3) the hormone receptors to tri-iodothyronine or atrial natriuretic peptides; (4) the regulatory effect of tri-iodothyronine on glutamine synthetase expression; (5) the endocytosis and transcytosis of proteins; and (6) the morphogenetic effects of galactosyl-ceramide. We also discuss new insights provided by recent results reported on in vitro ependymal and choroidal expressions of neuropeptide-processing enzymes and neurosecretory proteins or choroidal expression of transferrin regulated through serotoninergic activation.

Ependymal development, proliferation, and functions: a review

A survey of the literature shows that proliferation of ependyma occurs largely during the embryonic and early postnatal periods of development in most species. Differentiation of these cells proceeds along particular regional and temporal gradients as does the expression of various cytoskeletal (vimentin, cytokeratins, glial fibrillary acidic protein) and secretory proteins (S-100). Turnover declines significantly postnatally, and only low levels of residual activity persist into adulthood under normal conditions. Although the reported response of ependyma to injury is somewhat equivocal, only limited regenerative capacity appears to exist and to varying degrees in different regions of the neuraxis. Proliferation has been most often observed in response to spinal cord injury. Indeed, the ependyma plays a significant role in the initiation and maintenance of the regenerative processes in the spinal cord of inframammalian vertebrates. In the human, however, ependyma appears never to regenerate at any age nor re-express cytoskeletal proteins characteristic of immature cells. The functions of ependyma including tanycytes, a specialized form of ependymal cell that persists into adulthood within circumscribed regions of the nervous system, are still largely speculative. Fetal unlike mature ependyma is believed to be secretory and is believed to play a role in neurogenesis, neuronal differentiation/axonal guidance, transport, and support. In the adult brain, mature ependyma is not merely an inert lining but may regulate the transport of ions, small molecules, and water between the cerebrospinal fluid and neuropil and serve an important barrier function that protects neural tissue from potentially harmful substances by mechanisms that are still incompletely understood.

Differentiation of mesencephalic progenitor cells into dopaminergic neurons by cytokines

Rat progenitor cells from the germinal region of the fetal mesencephalon were isolated and expanded in media containing the mitogen epidermal growth factor. These cells remained mitotically active (up to 8 months), were immunoreactive for the progenitor cell marker nestin, and were readily infected with the BAG alpha retrovirus. When incubated in complete media containing serum in poly-L-lysine-coated plates, these cells spontaneously converted to neurons and glia but rarely expressed the dopamine (DA) neuron phenotype. Nineteen different cytokines were screened for their ability to induce the DA phenotype and only interleukin (IL)-1 was found to induce the expression of the DA neuron marker tyrosine hydroxylase (TH). The addition of IL-1, IL-11, leukemia inhibitory factor (LIF), and glial cell line-derived neurotrophic factor (GDNF) were found to further increase the number of TH immunoreactive (TH-ir) cells. The addition of mesencephalic membrane fragments and striatal culture-conditioned media along with the cytokine mixture induced the expression of morphologically mature TH-ir cells that were also immunoreactive for dopa-decarboxylase, the DA transporter, and DA itself. The DA neuron cell counts were approximately 20-25% of the overall cell population and 50% of the neurofilament population. Astrocytes and oligodendrocytes were also present. These data suggest that hematopoietic cytokines participate in the development of the DA neuron phenotype. Parallels between the function of hematopoietic cytokines in bone marrow and the central nervous system may exist and be useful in understanding the factors which regulate the differentiation of neurons in the brain.

In vitro cell density-dependent clonal growth of EGF-responsive murine neural progenitor cells under serum-free conditions

Neural progenitor cell populations responsive to epidermal growth factor (EGF) have been shown to have proliferative potential and give rise to neurons, astrocytes, and oligodendrocytes. We have characterized EGF-responsive neural progenitor cells that give rise to bilineage neuronal/glial colonies (colony-forming unit neuron-glia; CFU-NeGl) and unilineage neuronal colonies (CFU-Ne). Clonality was confirmed utilizing mixtures of brain cells from Balb/c and ROSA26 (transgenic for beta-galactosidase) mice. With a few exceptions, colonies showed either all blue cells or all clear cells after staining with X-Gal. Clonal growth was analyzed after 10-11 days in relation to cell density by determining colony size and plating efficiency. Growth was density dependent (no growth below 10,000 cell/ml) and thus single cell cloning was not accomplished. An average plating efficiency of 4% was found for EGF-responsive neural cells derived from day 15-18 murine embryos when cultured at 12,500 to 200,000 cells/ml. Similar results were obtained with 1-day-old postnatal neural cells. When colonies were categorized by size, the relative number of colonies over 50 cells appeared to be maximum at 50,000 plated cells/ml. After 11 days in culture, 94, 96, and 78% of the colonies contained cells that expressed nestin, neurofilament, and GFAP, respectively. Double-label experiments revealed that > 62% of the colonies contained both GFAP and neurofilament expressing cells. These studies establish the existence of at least two populations of clonal neural progenitors: CFU-Ne and CFU-NeGl in fetal and postnatal murine brain.

Regulation of the rat S100 beta gene expression: the role of the 2 kb 5'-upstream sequence in glial specific expression

We have studied the role of the 2047 bp 5'-upstream region and 232 bp first exon sequence of the rat S100 beta gene in glial specific expression. S100 beta luciferase expression vectors carrying serial deletions of the S100 beta 5' upstream sequence were constructed and transiently transfected into the peripheral nervous system (PNS) glial-type cell line RT4-D6, the PNS neuronal-type cell line RT4-E5, and the central nervous system (CNS) glial-type cell line C6. The hepatoma cell line HTC was also transfected as a nonneural control. From this functional analysis, we found a glial-specific positive regulatory sequence(s) mapped between -583 and -106 relative to the transcriptional start site. This region confers a significantly higher level of luciferase expression in the glial-type cell lines RT4-D6 and C6 than in the neuronal cell line RT4-E5 and the hepatoma cell line HTC. Also, a non-cell type specific positive regulatory element was identified in the first exon sequence between +78 and +232. Though non-cell type-specific, it was found to have a predominant effect in glial cells. From these observations, we have concluded that the 2047 bp 5'-upstream region and 232 bp of the first exon sequence confers the high levels of S100 beta expression in glial cells through these two positive elements.

Ependyma: phylogenetic evolution of glial fibrillary acidic protein (GFAP) and vimentin expression in vertebrate spinal cord

The phylogenetic evolution was studied of both glial fibrillary acidic protein (GFAP) and vimentin expression in the ependyma of the adult vertebrate spinal cord. Eleven species from different vertebrate groups were examined using different fixatives and fixation procedures to demonstrate any differences in immunoreactivity. GFAP expression in the ependymal cells showed a clear inverse relation with phylogenetic evolution because it was more elevated in lower than in higher vertebrates. GFAP positive cells can be ependymocytes and tanycytes, although depending on their structural characteristics and distribution, the scarce GFAP positive ependymal cells in higher vertebrates may be tanycytes. Ependymal vimentin expression showed a species-dependent pattern instead of a phylogenetic pattern of expression. Vimentin positive ependymal cells were only found in fish and rats; in fish, they were tanycytes and were quite scarce, with only one or two cells per section being immunostained. However, in the rat spinal cord, all the ependymocytes showed positive immunostaining for vimentin. The importance of the immunohistochemical procedure, the cellular nature of GFAP positive ependymal cells and the relationship between tanycytes and ependymocytes are discussed, as well as GFAP and vimentin expression.

Tissue-specific versus cell type-specific expression of the glial fibrillary acidic protein

Expression of the glial cell-specific gene encoding glial fibrillary acidic protein (GFAP) is regulated in a tissue-specific (neural tissue versus other tissues) as well as a cell type-specific (glial cell versus neuron) manner. Using a family of rat neurotumor RT4 cell lines in which neuronal/glial differentiation occurs in vitro, along with cell lines of different tissue origins, we identified by transient- and permanent-transfection assays two negative regulatory regions, GFAP downstream regulators 1 and 2 (GDR1 and GDR2). Both regions lie 3' of the transcription start site; GDR1 is in a 2.7-kb region extending from the first intron through the fifth exon, and GDR2 is within 1.7 kb 3' of the polyadenylylation site. GDR1 alone is responsible for tissue-specific expression (suppression in nonneural tissues), while both GDR1 and GDR2 are necessary for cell type-specific expression (suppression in neuronal cells).

Plasticity of astroglial glutamate and gamma-aminobutyric acid uptake in cell cultures derived from postnatal mouse cerebellum

The plasticity of astroglial glutamate and gamma-aminobutyric acid (GABA) uptakes was investigated using mouse cerebellar cell cultures. The influence of external factors, such as different sera and/or the presence of neurons, was examined. Control autoradiography experiments showed that after short-term exposure to radioactive amino acids, granule cells took up neither glutamate nor GABA, and beta-alanine predominantly inhibited astroglial GABA uptake. Astroglial uptake was quantified by measuring the radioactivity taken up by the cells in the culture and relating this measurement to the number of glial fibrillary acidic protein-positive cells present. Glutamate uptake was investigated in astroglial cultures and subcultures and in neuronal-astroglial cultures derived from postnatal day 4 mouse cerebella. In the absence of neurons, glutamate uptake increased during the first 9 days after plating and then leveled off. At 14 days in vitro in horse serum, which favors the differentiation of fibrous-like astrocytes, glutamate uptake related to astrocyte number was twice as high as in fetal calf serum. In the presence of cerebellar neurons, this rate was even higher. The specificity of the responsiveness of astrocytes to neurons with respect to glutamate uptake was investigated by comparing GABA uptake in the different culture conditions. Neurons also increased the rate of GABA uptake by astrocytes. Another component of the astroglial plasma membrane, the density of beta-adrenergic receptors, was, however, not markedly affected by the presence of neurons. Hence, these results showed that in astrocytes plated from postnatal day 4 mouse cerebella, the level of neurotransmitter uptake can be regulated in vitro by factors present in sera and by cerebellar neurons in the culture. However, this plasticity declined during development because astrocytes plated from postnatal day 8 cerebella and cultured under identical conditions were less active in glutamate uptake and were insensitive to the presence of horse serum. The latter observation suggested that the metabolic plasticity of astrocytes is restricted to a period defined early in cerebellar development and is no longer evident by postnatal day 8.

Differentiation and heterogeneity in T-antigen immortalized precursor cell lines from mouse cerebellum

Recently, various techniques have been developed to transfer oncogenes into brain cells in order to generate immortalized neural cell lines. It is of interest to establish how well such cell lines reflect their cellular origin. Here we report the characterization of sixteen cell lines from mouse cerebellum and, as a control, six cell lines from skin. Lines were established by immortalizing postnatal primary cell cultures with a retrovirus carrying a modified temperature-sensitive variant of SV40 large T antigen. The cell lines reflect many properties of the cell type from which they were derived. All of the sixteen cerebellar lines expressed one or more markers of the neural precursor cells, namely, nestin and epitopes for NG2 and A2B5. In contrast, none of the six skin lines expressed neural precursor markers. Both types of cell lines expressed vimentin and fibronectin. Differentiation occurred in some of the cerebellar lines and was enhanced in defined medium. A small percentage of cerebellar cells, usually less than 5%, was positive for a marker of differentiation, e.g., glial fibrillary acidic protein (GFAP), galactocerebroside (GalC), or L1. Expression of GFAP colocalized with that of nestin at varying levels of intensity, indicating a gradual replacement of nestin by GFAP in the cytoskeleton. Both the cells positive for precursor markers and those positive for differentiation markers tended to be located in clusters, suggesting that stochastic processes or cell-cell interactions are important for the determination of the fate of cells within a clonal cell line in vitro. The degree of differentiation seemed to correlate with a shift from serum-containing to defined medium, but not with a shift from the permissive to the nonpermissive temperature for T antigen expression. The immortalization approach described here thus allows the establishment of cell lines which are "captured" in the precursor state of the developing mouse neuroepithelium.

Immunohistochemical localization of glutamine synthetase in mesencephalon and telencephalon of the lizard Gallotia galloti during ontogeny

The immunohistochemical localization of glutamine synthetase, an astrocyte marker in mammals, was determined in the telencephalon and mesencephalon of the lizard Gallotia galloti during development by using an antiserum raised against chicken brain glutamine synthetase. Ependymal glial cells and their radial processes were glutamine synthetase immunoreactive, and they were present also in the adult. Immunoreactivity was also detected in two populations of scattered cell bodies, each preferentially localized in different zones: star-shaped cells morphologically similar to mammalian astrocytes, and ovoid or pear-shaped cell bodies, the processes of which were aligned with radial fibers and formed perivascular end-feet. Both populations displayed ultrastructural characteristics of astrocytes even though a comparison with our previous results (Monzon-Mayor et al., 1989; Yanes et al., 1989) indicated that many of these cells did not react with antibodies directed against the astrocyte-specific glial fibrillary acidic protein. During ontogeny, glutamine synthetase immunoreactivity appeared in radial glial processes and in ependymal glial cells of midbrain at embryonic stage 35 (E35) and of telencephalon at E37; in both regions, immunoreactivity in the radial glia increased until hatching and then decreased until adulthood, but it did not disappear. Labelled scattered cells became progressively more numerous and more immunoreactive. A comparative analysis of the distribution of these cells at different ages tends to suggest that some of the "ovoid" astrocytes originate in, and migrate out from, the proliferative zone of the different sulci, whereas the star-shaped cells appear directly in situ, probably because they begin to express glutamine synthetase after they have reached their final location.

Division and differentiation of isolated CNS blast cells in microculture

The mechanism of transformation of the overtly similar cells of the neural plate into the numerous and diverse cell types of the mature vertebrate central nervous system (CNS) can better be understood by studying the clonal development of isolated CNS precursor cells. Here I describe a culture system in which blast cells (cells capable of division) isolated from embryonic day 13.5-14.5 rat forebrain can divide and differentiate into a variety of clonal types. Most clones contain only neurons or glia; 22% contain both neurons and non-neuronal cells. For the division of blast cells, live conditioning cells need to be present indicating that environmental signals influence proliferation. Heterogeneous clones develop in homogeneous culture conditions, so factors intrinsic to the blast cells are probably important in determining the number and type of clonal progeny.

Comparative marker analysis of the ependymocytes of the subcommissural organ in four different mammalian species

The subcommissural organ (SCO), classified as one of the circumventricular organs, is composed mainly of modified ependymal cells, attributable to a glial lineage. Nevertheless, in the rat, these cells do not possess glial markers such as glial fibrillary acidic protein (GFAP), protein S100, or the enzyme glutamine synthetase (GS). They receive a synaptic 5-HT input and show pharmacological properties for uptake of GABA resembling the uptake mechanism of neurons. In this study, we examine the phenotype of several mammalian SCO (cat, mouse, rabbit) and compare them with the corresponding features of the rat SCO. In all these species, the SCO ependymocytes possess vimentin as an intermediate filament, but never express GFAP or neurofilament proteins. They do not contain GS as do glial cells involved in GABA metabolism, and when they contain protein S100 (rabbit, mouse), its rate is low in comparison to classical glial or ependymal cells. Thus, these ependymocytes display characteristics that differentiate them from other types of glial cells (astrocytes, epithelial ependymocytes and tanycytes). Striking interspecies differences in the capacity of SCO-ependymocytes for uptake of GABA might be related to their innervation and suggest a species-dependent plasticity in their function.

Expression of carbonic anhydrase II gene in early brain cells as revealed by in situ hybridization and immunohistochemistry

A mouse carbonic anhydrase (CA II) complementary(c) DNA probe was used for in situ hybridization on mouse brain cultured cells in order to follow CA II gene expression during brain development. An improved method was established using biotinated probes that resulted in a high sensitivity and an absence of background; this method could be combined with immunohistochemistry. Hypothalamic cells of embryonic day (ED) 12-14 mice were cultured for various periods. Chronologic appearance of CA II messenger(m)RNA and protein was studied. The CA II gene transcripts are detectable as early as ED 12-13, although the protein they encode is not detectable until ED 17-18. Gene expression is restricted to 0.1% of the total population. Northern blot analysis confirmed the presence of CA II transcripts in embryonic hypothalamus. At postnatal stage, the majority of glial cells express both the CA II mRNA and the protein. Our results favour the early appearance of a glial lineage in a precise area of the developing CNS. The precocity of CA II gene transcription makes in situ hybridization an invaluable approach in defining the onset of nerve cell lineages during embryonic development.

Growth promoting effects of IGF-I on fetal hypothalamic cell lines under serum-free culture conditions

Recent evidence indicates that the insulin-like family of peptides may act as endogenous trophic factors in the central nervous system. To further examine this possibility we have investigated the effects of three insulin-like peptides on the in vitro growth of fetal hypothalamic cell lines. Two virally transformed rat hypothalamic cell lines which have been developed in our laboratory (A-6 and F-12) were used. Cells were plated at varying densities and cultured in the presence or absence of either insulin-like growth factor I (IGF-I), insulin, or multiplication stimulating activity (MSA or IGF-II), in serum-free medium for 1 wk. Cell growth was assessed by counting or by measuring cellular incorporation of 3H-thymidine. Of the three peptides tested IGF-I was the most potent in eliciting cell growth. Insulin also stimulated growth of both cell lines, but was 100 times less potent for A-6 cells while it was equipotent with IGF-I in F-12 cells. MSA had no effect on either cell line. Both IGF-I and insulin showed dose-response effects in increasing cell growth. We also found that the two cell lines had the greatest response to IGF-I at low cell densities. Finally, time-course experiments suggested that a continued presence of the peptide is essential for the growth-promoting effects. We conclude that IGF-I is a potent growth factor for virally transformed cell lines derived from the rat fetal hypothalamus. Since both IGF-I immunoreactivity and IGF-I receptors have been located in this diencephalic area these results suggest that IGF-I may constitute a mitogenic signal for hypothalamic cells during neurogenesis.

Developmental and functional studies of parvalbumin and calbindin D28K in hypothalamic neurons grown in serum-free medium

The Ca2+-binding proteins parvalbumin (Mr = 12K) and calbindin D28K [previously designated vitamin D-dependent Ca2+-binding protein (Mr = 28K)] are neuronal markers, but their functional roles in mammalian brain are unknown. The expression of these two proteins was studied by immunocytochemical methods in serum-free cultures of hypothalamic cells from 16-day-old fetal mice. Parvalbumin is first detected in all immature neurons, but during differentiation, the number of parvalbumin-immunoreactive neurons greatly declines to a level reminiscent of that observed in vivo, where only a subpopulation of neurons stains for parvalbumin. In contrast, calbindin D28K was expressed throughout the period investigated only in a distinct subpopulation of neurons. Depolarization of fully differentiated hypothalamic neurons in culture resulted in a dramatic decrease of parvalbumin immunoreactivity but not of calbindin D28K immunoreactivity. The parvalbumin staining was restored on repolarization. Because the anti-parvalbumin serum seems to recognize only the metal-bound form of parvalbumin, the loss of immunoreactivity may signal a release of Ca2+ from intracellular parvalbumin during depolarization of the cells. We suggest that parvalbumin might be involved in Ca2+-dependent processes associated with neurotransmitter release.

Gradient isolation of glial cells: evidence that flat epithelial cells are astroglial cell precursors

Discontinuous gradients of metrizamide were used to separate the cell components of monolayers of primary cultures of embryonic rat brains. These primary cell cultures were of two types: long-term cultures (more than a year) of embryonic rat brain, which contained several glial cell types, and monolayers of cell cultures (several weeks old), which contained a complex population of cells, including neuronal elements. The gradient separation produces fractions of pure flat epithelial cells that are able to survive and proliferate. After a few days, all flat epithelial cells become confluent and show a positive reaction to glial fibrillary acidic protein (GFAP); this indicates that these cells astroglial precursor cells. Following their maintenance in vitro for several months, all cultures give rise to a pure population of astrocytes identified not only by their characteristic morphology, but also by their content of GFAP. It is proposed that the differentiation controls are dependent on cell interactions that are influenced by the composition of the cell population and/or the molecular growth and differentiation factors released by these cells into the medium.

Cell-type-specific responses of RT4 neural cell lines to dibutyryl-cAMP: branch determination versus maturation

This report describes the induction of cell-type-specific maturation, by dibutyryl-cAMP and testololactone, of neuronal and glial properties in a family of cell lines derived from a rat peripheral neurotumor, RT4. This maturation allows further understanding of the process of determination because of the close lineage relationship between the cell types of the RT4 family. The RT4 family is characterized by the spontaneous conversion of one of the cell types, RT4-AC (stem-cell type), to any of three derivative cell types, RT4-B, RT4-D, or RT4-E, with a frequency of about 10(-5). The RT4-AC cells express some properties characteristic of both neuronal and glial cells. Of these neural properties expressed by RT4-AC cells, only the neuronal properties are expressed by the RT4-B and RT4-E cells, and only the glial properties are expressed by the RT4-D cells. This in vitro cell-type conversion of RT4-AC to three derivative cell types is a branch point for the coordinate regulation of several properties and seems to resemble determination in vivo. In our standard culture conditions, several other neuronal and glial properties are not expressed by these cell types. However, addition of dibutyryl-cAMP induces expression of additional properties, in a cell-type-specific manner: formation of long cellular processes in the RT4-B8 and RT4-E5 cell lines and expression of high-affinity uptake of gamma-aminobutyric acid, by a glial-cell-specific mechanism, in the RT4-D6-2 cell line. These new properties are maximally expressed 2-3 days after addition of dibutyryl-cAMP. This indicates that conversion of RT4-AC to the derivative cell types is also a branch point for the regulation of cell-type-specific properties whose expression is responsive to cAMP. Thus, the potential for maturation in response to increased cAMP is a property that segregates in a cell-type-specific manner and is activated at the determinational level in this system.

Serotonin initiates and autoamplifies its own synthesis during mouse central nervous system development

Some cells from cultured embryonic mouse hypothalamus were found to express aromatic-L-amino acid decarboxylase (EC 4.1.1.28) activity and serotonin uptake and storage. These neuron-like cells differed from serotoninergic neurons in cultured embryonic mouse brain stem since they did not contain tryptophan hydroxylase. We studied the effect of the serotonin agonist 8-hydroxy-2-[di-(n-propyl)amino]tetralin on neuronal differentiation of hypothalamic cells from 12- to 15-day embryos. Repeated treatment of cultures with the serotonin agonist for 10 days resulted in an increased number of serotonin cells containing high levels of decarboxylase activity. Both the increase in cell numbers and the elevated decarboxylase activity could be suppressed by the addition of the serotonin antagonist metergoline to the culture medium. These data show that serotonin (or an agonist), acting on specific receptors, can initiate and amplify its own synthesis in embryonic hypothalamic neurons, as observed in the primitive hypothalamic nerve cell line F7 [De Vitry, F., Catelon, J., Dubois, M., Thibault, J., Barritault, D., Courty, J., Bourgoin, S. & Hamon, M. (1986) Neurochem. Int. 9, 43-53]. Such an autocrine-like mechanism may be active during nervous system development and may represent an example of learning at the cellular level.

Differential immunocytochemical staining for glial fibrillary acidic (GFA) protein, S-100 protein and glutamine synthetase in the rat subcommissural organ, nonspecialized ventricular ependyma and adjacent neuropil

Antibodies raised against glial fibrillary acidic protein (GFA), S-100 protein (S100) and glutamine synthetase (GS) are currently used as glial markers. The distribution of GFA, S100 and GS in the ependyma of the rat subcommissural organ (SCO), as well as in the adjacent nonspecialized ventricular ependyma and neuropil of the periaqueductal grey matter, was studied by use of the immunocytochemical peroxidase-antiperoxidase technique. In the neuropil, GFA, S100 and GS were found in glial elements, i.e., in fibrous (GFA, S100) and protoplasmic astrocytes (S100, GS). The presence of S100 in the majority of the ventricular ependymal cells and tanycytes, and the presence of GFA in a limited number of ventricular ependymal cells and tanycytes confirm the glial nature of these cells. The absence of S100, GFA and GS from the ependymocytes of the SCO, which are considered to be modified ependymal cells, suggests either a non-astrocytic lineage of these cells or an extreme specialization of the SCO-cells as glycoprotein-synthesizing and secreting elements, a process that may have led to the disappearance of the glial markers.

Differentiation of human retinoblastoma in vitro into cell types with characteristics observed in embryonal or mature retina

The capacity of a primitive human retinoblastoma cell line (Y-79) to differentiate into several cell types of normal human retina was investigated. Cells were studied in suspension and monolayer cultures, in serum-free or serum-supplemented medium, and in the presence or absence of differentiating agents such as N6O12-dibutyryl adenosine 3',5'-cyclic monophosphate (dbc-AMP) and sodium butyrate (Nabut). Electron microscopy, immunohistochemistry for detection of myelin basic protein (MBP), and formaldehyde-induced fluorescence (FIF) for catecholamines were performed. Treated cells exhibited morphologic characteristics supportive of differentiation toward photoreceptors, conventional neurons and glial cells, increased FIF reactivity, and MBP expression. Growth in serum-free medium without differentiating agents led to a similar but less enhanced morphologic differentiation. These results confirm the concept that human retinoblastoma originates from a primitive neuroectodermal multipotential cell.

Ontogeny of electrically excitable cells in cultured olfactory epithelium

A primary system has been developed in which it is possible to study the production of electrically excitable neuron-like cells from a precursor population of olfactory epithelial cells. Rat nasal epithelium was dissociated and placed in culture. The initial surviving cells are flat and ciliated and contain glial fibrillary acidic protein (GFAP). After 3-5 days electrically excitable cells appear that contain neuron-specific enolase but not GFAP. These round cells originate by means of the differentiation of the GFAP-positive flat cell to a round cell, followed by the division of the round cell. Therefore, neuron-like cells can be derived from cells that synthesize GFAP.

Immunocytochemical localization of S-100 protein in stellate cells (folliculo-stellate cells) of the anterior lobe of the normal human pituitary

With the use of an anti-human S-100 protein antibody, it was possible to reveal a characteristic cell type in the anterior lobe of the normal human pituitary. These cells, so-called folliculo-stellate cells, were present in all pituitaries studied but their number varied from one gland to another. Immunoreactive cells, isolated or grouped, were arranged close to various secretory granulated cells. Especially by use of double immunoenzymatic labeling, it was evident that these cells are spatially related either to somatotropes, prolactin cells and "corticotropes", or to glycoprotein-containing cells. Such immunoreactive cells were rare or absent in pseudo-follicular arrangements of secretory granulated cells. Since it is now possible to identify this cell type by light microscopy and since no reliable functional significance is known, it seems more advisable to term this cell type "stellate cell" instead of "folliculo-stellate cell".

Immunocytochemical characterization of pulmonary histiocytosis X cells in lung biopsies

Morphologic and immunohistochemical studies were made of open lung biopsies from 9 patients with pulmonary histiocytosis X (HX) and 12 patients with other conditions, and of skin biopsies from patients with cutaneous sarcoidosis, Chester-Erdheim disease, and eruptive histiocytoma. The monoclonal antibody OKT6 was detected with the use of goat anti-mouse IgG labeled with fluorescein (FITC) for light microscopy, and sheep antimouse Fab'2 fragment of IgG labeled with horseradish peroxidase (HRP) for immunoelectron microscopy. The presence of S-100 protein was revealed by an antibody prepared against bovine S-100 protein, using sheep anti-rabbit IgG labeled with FITC for light microscopy and with HRP for immunoelectron microscopy. OKT6 antibody and S-100 protein were detected simultaneously by double labeling with FITC and rhodamine. In all patients with pulmonary HX, the major cellular components (HX cells) of the granulomas showed labeling of the plasma membranes by OKT6 and of the cytoplasm by the anti S-100 protein antibody. The double-labeling technique demonstrated that the same cells carried both reactivities. Immunoelectron microscopy showed that the reactive cells had all the structural characteristics of Langerhans cells, including Langerhans cell granules. Cells reacting with OKT6 showed discrete internal labeling in some of the Langerhans granules, especially those in continuity with the plasma membranes. However, internal labeling of Langerhans granules was not demonstrated in preparations for the localization of S-100 protein. Control samples of sarcoid lesions and other pulmonary lesions unrelated to HX did not show any reactivity except in Langerhans cells; a skin lesion from a patient with eruptive histiocytoma contained OKT6-positive cells which did not have Langerhans granules.

Cyclic morphological changes of glial cells in long-term cultures of rat brain

Brain cells from embryonic rats were dissociated with trypsin, cultivated under constant conditions in Falcon flasks, and studied for periods of one year or more. Antisera against glial fibrillary acidic protein (GFA) and myelin basic protein (MBP) were used to identify glial cell types. For scanning electron microscopical (SEM) observation an embedding method in resin was developed that allows good preservation of the fine ultrastructural features of the cultivated cells and precise characterization of the cell types. Under our culture conditions, after four subcultures and 8-10 weeks of cultivation, the following cell types can be distinguished. (a) Flat epitheloid cells. From an immunocytological point of view these cells form a heterogeneous population composed of GFA- and MBP-positive and negative cells. They are the precursors of the following cell types. (b) Astroglial cells. SEM observations show a characteristic network of radially orientated prolongations. 92% of these cells are GFA-positive. (c) Oligodendroglial cells with characteristic dichotomously dividing branches. Secondary and tertiary branches end in flat amoeboid prolongations. These cells are MBP-positive. After approximately six weeks the most prominent cells are the flat epitheloid cells. The astroglial cells originate continuously from the epitheloid cells during the whole cultivation time. The formation of oligodendroglial cells, on the other hand, takes place at relatively precise intervals of time (approximately every 20-30 days) over the entire cultivation period (of more than one year).

Induction of muscle genes in neural cells

The regulation of skeletal muscle genes was examined in heterokaryons formed by fusing differentiated chick skeletal myocytes to four different rat neural cell lines. Highly enriched populations of heterokaryons isolated using irreversible biochemical inhibitors were labeled with [35S]methionine and analyzed on two-dimensional gels. Rat skeletal myosin light chains were induced in three of the four cell combinations. The one exception, the S-20 cholinergic cell line, not only failed to synthesize rat muscle proteins but also suppressed chick myogenic functions. Experiments with heterokaryons between chick myocytes and cells from whole embryonic rat brain cultures demonstrated that rat skeletal myosin light chains are inducible in normal diploid neural cells as well as in established neural cell lines. In contrast, dividing cell hybrids between rat myoblasts and rat glial cells were nonmyogenic. These results demonstrate that although neural cells may contain factors that prevent the decision to differentiate along myogenic lines in cell hybrids, most neural cell lines do not dominantly suppress the expression of muscle structural genes in heterokaryons. Furthermore, the skeletal myosin light chain genes in most neural cell lines are regulated by a mechanism that permits them to respond to putative chick skeletal myocyte-inducing factors. The "open" state of these myogenic genes may explain many of the reports of apparent "transdifferentiation" to muscle in neural cultures and neural tumors.

Production and characterization of monoclonal antibodies against the "brain-specific" proteins 14-3-2 and S-100

We have raised mouse hybridomas that secrete monoclonal antibodies against bovine brain-specific proteins 14-3-2 and S-100, and we have characterized the antibodies by immunoperoxidase and immunofluorescence methods in sections and in tissue cultures of rat brain. One monoclonal antibody to 14-3-2 (E8.F9) has been found to react strongly with bovine 14-3-2 and with rat neuron-specific enolase in an enzyme-linked immunosorbent assay (ELISA) and to react weakly with rat nonneuronal enolase. This pattern of specificity is reflected in strong neuronal labeling and occasional weak glial labeling in immunocytochemical preparations. After appropriate tissue fixation, E8.F9 could be shown to be localized primarily to the cytoplasm of neurons; with less adequate fixation nuclear labeling was also seen. A monoclonal antibody to the calcium binding protein S-100 (G12.B8) reacted strongly with bovine S-100 in an ELISA and with the major protein bands in electrophoretically separated S-100. In immunocytochemical preparations G12.B8 labeled the cytoplasm of astrocytes. Both antibodies are of the IgG1 subclass. Because of its specificity, the antibody against the S-100 protein promises to be useful as an immunological marker for astrocytes in the adult animal and in mature tissue cultures of brain cells. Although it has been thought that the generally low levels and relatively late appearance of S-100 during ontogeny may restrict its usefulness as a marker for developing astrocytes, preliminary immunocytochemical evidence indicates that G12.B8 selectively labels radial glial cells and astrocytes or astrocyte precursors as early as, or even earlier than, antibodies against the glial fibrillary acidic protein. The antibody against neuron-specific enolase is likely to be of limited use as a neuronal marker because of its crossreactivity with nonneuronal enolase.