Insulin-like growth factor II mRNA is expressed in neurones of the brain of the bony fish Oreochromis mossambicus,the tilapia

The physiological meaning of insulin-like growth factor II (IGF-II) is still enigmatic. IGF-II occurs in the adult mammalian brain where it is expressed in the mesodermal portion of the choroid plexus and the meninges, but results on its presence in cells of neuroepithelial origin are controversial. However, IGF-II mRNA is transiently expressed in neurones during mammalian early development. In bony fish, IGF-II mRNA is also present in the adult brain but nothing is known about its synthesis sites. Thus, the present study using in situ hybridization with digoxigenin-labelled RNA species-specific probes investigates the cellular distribution of IGF-II mRNA in the adult brain of a bony fish, the tilapia (Oreochromis mossambicus). As in mammals, IGF-II mRNA was strongly expressed in the choroid plexus and meninges. Thus, IGF-II synthesis by choroid plexus and meninges seems to have a long evolutionary history and may be common to all vertebrates. However, as shown by the detailed investigation of landmark nuclei and regions, IGF-II mRNA occurred also in numerous neurones at all levels of the tilapia brain. The distinct localization of IGF-II mRNA in neurones might indicate that neuronal IGF-II acts as transmitter or modulator. However, the widespread occurrence of the IGF-II-producing neurones argues against this assumption and most probably suggests that IGF-II plays a role in the differentiation, maintenance and regeneration of neurones. It is further assumed that the sustained neuronal IGF-II expression in the brain of the adult tilapia correlates with continued post-embryonic up to life-long brain growth as has been shown in many teleost fishes.     

Immunohistochemical study of insulin-like growth factor II (IGF-II) and insulin-like growth factor binding protein-2 (IGFBP-2) in choroid plexus papilloma.

Insulin-like growth factor-II (IGF-II), a mitogen for various kinds of cells, has been shown to be secreted from the choroid plexus in animals. Insulin-like growth factor binding protein-2 (IGFBP-2), one of the six carrier proteins for IGFs, is also thought to be released from the choroid plexus, bind to IGF-II in the cerebrospinal fluid (CSF) and modulate the action of this growth factor. Little is known about the expression and localization of these substances in human choroid plexus and choroid plexus papillomas. The present immunohistochemical study demonstrated all six choroid plexus papillomas were positive for IGF-II, whereas normal choroid plexuses were negative for IGF-II. On the other hand, IGFBP-2 was positive in the endothelium and vascular media in the normal choroid plexus, while it was weakly positive in four and negative in two out of six choroid plexus papillomas. These results suggest that the alterations in the IGF-II/IGFBP-2 axis might be involved in the tumorigenesis of choroid plexus papilloma.     

Immunohistochemical study of insulin-like growth factor II (IGF-II) and insulin-like growth factor binding protein-2 (IGFBP-2) in choroid plexus papilloma

Abstract

Insulin-like growth factor-ll (IGF-II), a mitogen for various kinds of cells, has been shown to be secreted from the choroid plexus in animals. Insulin-like growth factor binding protein-2 (IGFBP-2), one of the six carrier proteins for IGFs, is also thought to be released from the choroid plexus, bind to IGF-II in the cerebrospinal fluid (CSF) and modulate the action of this growth factor. Little is known about the expression and localization of these substances in human choroid plexus and choroid plexus papillomas. The present immunohistochemical study demonstrated all six choroid plexus papillomas were positive for IGF-II, whereas normal choroid plexuses were negative for IGF-II. On the other hand, IGFBP-2 was positive in the endothelium and vascular media in the normal choroid plexus, while it was weakly positive in four and negative in two out of six choroid plexus papillomas. These results suggest that the alterations in the IGF-II/ IGFBP-2 axis might be involved in the tumorigenesis of choroid plexus papilloma. [Neurol Res 1999; 21: 339-344]     

Autocrine Role of Insulin-like Growth Factor II Secretion by the Rat Choroid Plexus

Insulin-like growth factor II (IGF-II) is expressed and secreted by the choroid plexus and has been suggested to act as a trophic factor in the adult mammalian central nervous system. The aim of the present study was to investigate whether IGF-II has an autocrine role in the choroid plexus. Using in situ hybridization we demonstrate that IGF-II is primarily expressed in the epithelium of adult rat choroid plexus. Conditioned medium from primary cultures of purified rat choroid plexus epithelial cells, intact choroid plexus tissue, as well as rat CSF, displaced IGF-II binding to a 23 HMM melanoma cell line in an IGF-II radioreceptor assay. The presence of IGF-II and IGF binding protein-2 in conditioned medium was shown by Western immunoblot. The mitotic activity in choroid plexus epithelial cell cultures was quantified by immunohistochemical staining of bromodeoxyuridine incorporated into cell nuclei. A monoclonal antibody towards IGF-II inhibited cell division by 35%, while IGF-I increased the number of stained nuclei by 75%. Basic fibroblast growth factor stimulated cell division at low concentrations, but had no effect at high concentrations. Growth hormone had no effect. We conclude that IGF-II in the choroid plexus could have an autocrine role in the regulation of choroid plexus epithelial cell growth.     

Immunocytochemical detection of insulin-like growth factor II (IGF-II) in choroid plexus papilloma: a possible marker for differential diagnosis

BACKGROUND: Insulin-like growth factor II (IGF-II) has been detected in the choroid plexus of animals by means of immunohistochemistry and in situ hybridization, and this factor is thought to play an important role in the central nervous system (CNS). Little is known, however, about the presence and localization of this substance in the choroid plexus and in choroid plexus papilloma in humans. MATERIALS AND METHODS: 5 normal choroid plexus and 10 choroid plexus papillomas were examined for IGF-II by immunocytochemistry. IGF-II was not detected in normal human choroid plexus, whereas it was found in choroid plexus papilloma. Furthermore, to assess the possibility that IGF-II could serve as an immunohistological marker of choroid plexus papilloma, we used the same technique to examine paraffin-embedded samples from various kinds of brain tumors. RESULTS AND CONCLUSION: Our results suggest that IGF-II may be a useful marker for choroid plexus papilloma in differential diagnosis.     

Neuroendocrine regulatory mechanisms in the choroid plexus-cerebrospinal fluid system

The CSF is often regarded as merely a mechanical support for the brain, as well as an unspecific sink for waste products from the CNS. New methodology in receptor autoradiography, immunohistochemistry and molecular biology has revealed the presence of many different neuroendocrine substances or their corresponding receptors in the main CSF-forming structure, the choroid plexus. Both older research on the sympathetic nerves and recent studies of peptide neurotransmitters in the choroid plexus support a neurogenic regulation of choroid plexus CSF production and other transport functions. Among the endocrine substances present in blood and CSF, 5-HT, ANP, vasopressin and the IGFs have high receptor concentrations in the choroid plexus and have been shown to influence choroid plexus function. Finally, the choroid plexus produces the growth factor IGF-II and a number of transport proteins, most importantly transthyretin, that might regulate hormone transport from blood to brain. These studies suggest that the choroid plexus-CSF system could constitute an important pathway for neuroendocrine signalling in the brain, although clearcut evidence for such a role is still largely lacking.     

Plasma membrane Ca(2+)-ATPase isoforms: distribution of mRNAs in rat brain by in situ hybridization.

Several mRNAs which encode for isoforms of the plasma membrane Ca(2+)-transport ATPase (PMCA) are present in adult rat brain. Using in situ hybridization with antisense oligonucleotide probes we found complex patterns of specific hybridization for three isoforms (PMCA1-3). Each rat brain region studied exhibited a distinct pattern of expression of isoforms. PMCA1 mRNA, which is widely distributed in rat tissues, was highest in CA1 pyramidal cells of hippocampus and very low in hypothalamic nuclei, cerebellum and choroid plexus. PMCA2 mRNA was highest in Purkinje cells of cerebellum and low in caudate-putamen, hypothalamic nuclei, habenula and choroid plexus. The highest levels of PMCA3 mRNA were found in habenula and choroid plexus. The PMCA1-3 isoforms appeared to be expressed primarily in neurons since hybridization was detected neither in white matter nor in regions rich in astrocytes. In different regions, different levels of expression of each PMCA mRNA may underlie specialized requirements for calcium homeostasis in specific neurons.     

Transferrin gene expression in choroid plexus of the adult rat brain

Transferrin immunoreactivity and transferrin messenger RNA (mRNA) were recently found to be present in oligodendrocytes of the adult rat brain by using immunohistochemistry and in situ hybridization procedure. The present study demonstrates, in the same way, that epithelial cells of the choroid plexus also contain transferrin together with transferrin mRNA. Choroid plexus of the lateral and the third ventricle are rich in transferrin mRNA, while choroid plexus of the fourth ventricle contain few if any transferrin mRNA. These results demonstrate that epithelial cells of the choroid plexus as well as oligodendrocytes express the transferrin gene in the adult rat brain.     

Constitutive expression of cyclooxygenase-2 (COX-2) in developing brain. A. Choroid plexus in human fetuses

It is believed that prostanoids produced by COX-1 activity are essential for the physiological functions of tissues while those produced by COX-2 lead to various pathological changes in these tissues. Brain is an exceptional organ where in some neurons COX-2 mRNA and its protein are constitutively expressed. Since some prostaglandins may play an important role in the control of blood-brain barrier and cerebral blood flow the purpose of the present study was to examine the COX-2 expression in choroid plexus, which participate in the nutrition of brain parenchyma of human fetuses. Study was performed on 25 brains of human fetuses from 12 to 38 weeks of gestation. In light and electron microscopy characteristic developmental transformation of choroid morphology was observed. In young fetuses from 12 to 20 week of gestation epithelial cells of choroid plexus are cuboidal, contain large amount of glycogen storage and their nuclei are COX-2 immunopositive. From 25 week of gestation until term the amount of glycogen in the choroid plexus diminishes, some apical nuclei are shifted toward central parts of the cells and number of cytoplasm organelles increases. In these cells expression of COX-2 protein is located in cytoplasm but epithelial nuclei are immunonegative. Our results provided evidence that COX-2 is constitutively expressed in the developing human choroid plexus. Different localization of COX-2 in choroid epithelial cells suggests that this enzyme may play a different role in various periods of the choroid plexus development.     

Kynurenine aminotransferase I (KATI) isoform gene expression in the rat brain: an in situ hybridization study

Kynurenine aminotransferase I (KATI) converts kynurenine into kynurenic acid (KYNA), a broadspectrum antagonist at ionotropic excitatory amino acid receptors. The main interest in KYNA centers on its potential neuroprotective action in physiological and pathological conditions. We show here by in situ hybridization that KATI mRNA is widely expressed throughout the adult rat brain. A strong autoradiographic signal was detected in the hippocampus, piriform cortex, and choroid plexus. Microscopic evaluation suggested that KATI mRNA was expressed not only in astrocytes but also in hippocampal neurons and in choroid plexus epithelial cells. Neuronal expression of KATI mRNA was further confirmed by RT-PCR and in a model of transient cerebral ischemia. The expression pattern of the mitochondrial form (mKATI) of the enzyme was almost comparable to that of KATI. The major difference was observed in the choroid plexus where mKATI mRNA signal was very low.     

Transthyretin: a choroid plexus-specific transport protein in human brain. The 1986 S. Weir Mitchell award

Plasma transthyretin (TTR, formerly called prealbumin) is a 55-kd protein that participates in the plasma transport of both thyroxine and retinol (vitamin A). TTR concentrations are disproportionately high in human ventricular CSF, suggesting that TTR is either selectively transported across or synthesized de novo within the blood-CSF barrier. To address this question, we adopted a molecular genetic approach; after isolating a cDNA clone encoding human TTR, we previously demonstrated specific TTR messenger RNA (mRNA) synthesis in rat choroid plexus. We have now extended these investigations to the human brain. Northern analysis of postmortem brain homogenates revealed abundant TTR mRNA in choroid plexus, but not in cerebellum or cerebral cortex. Choroid plexus mRNA was readily translated into TTR preprotein in an in vitro translation system. An immunocytochemical survey of human postmortem brain sections revealed the presence of TTR protein specifically and uniquely in the cytoplasm of choroid plexus epithelial cells; these results were corroborated at the mRNA level by an extensive survey of whole rat-brain sections by in situ hybridization. Therefore, within the mammalian CNS, TTR is the first known protein synthesized solely by the choroid plexus, suggesting a special role for TTR in the brain or CSF. Whether this function differs from its established plasma transport functions is presently unknown.     

Differential expression of cell adhesion molecules (CAM), neural CAM and epithelial cadherin in ependymomas and choroid plexus tumors

A series of frozen specimens of 18 ependymomas and 7 choroid plexus tumors were examined for their expression of cell adhesion molecules, such as neural cell adhesion molecule (NCAM), its polysialylated isoforms (PSA NCAM), and epithelial (E-) cadherin, and of intermediate filament proteins, such as glial fibrillary acidic protein (GFAP) and cytokeratin, using various monoclonal and polyclonal antibodies. Normal choroid plexus and ependyma were taken as controls. Anti-E-cadherin immunoreactivity was observed on the basolateral part of most adult choroid plexus and benign choroid plexus papilloma cells. However, a small number of atypical papillomas and carcinoma cells showed anti- E-cadherin immunoreactivity throughout their cell surface membrane. NCAM were not expressed by adult choroid plexus and benign papilloma cells. Only a few cells expressed NCAM and PSA NCAM in developing choroid plexus, atypical papillomas and carcinomas. Cytokeratin expression was always observed in choroid plexus and their tumors; GFAP expression was variable from case to case. In contrast, ependymal cells and their tumors never expressed E-cadherin but strongly expressed NCAM. PSA NCAM was found in ependymomas exhibiting anaplastic features. All ependymomas strongly expressed GFAP and a few demonstrated slight expression of cytokeratin. These data suggest that, besides GFAP and cytokeratin, NCAM and E-cadherin are of potential diagnostic value in distinguishing choroid plexus tumors from ependymomas. E-cadherin and NCAM may play a role in the functional organization of normal choroid plexus and ependyma, respectively. In particular, incomplete or irregular anti-E-cadherin expression in choroid plexus tumors and PSA NCAM immunoreativity in ependymomas and choroid plexus tumors correlates with the emergence of anaplastic histological features.     

Immunohistochemical study on distribution of transthyretin in normal human brain tissue and tumors

Immunohistochemical examination of transthyretin (TTR), which is known to be synthesized in the epithelial cells of the choroid plexus as well as in the liver cells, was carried out on normal brain tissues and 84 human brain tumors, using a peroxidase-antiperoxidase (PAP) technique. TTR was demonstrated diffusely and strongly in the cytoplasm of normal choroid plexus cells, but not in ependyma and other tissues of normal brain. In all of 10 choroid plexus papillomas, TTR was found within the cytoplasm of tumor cells. In contrast, neither the two papillary ependymomas nor any other brain tumors contained TTR. Among the choroid plexus papillomas, some cases showed clear positive reactions in almost all tumor cells, while others had only a few TTR-positive cells. With these immunohistochemical findings, TTR proved a very useful marker of normal choroid plexus and choroid plexus papilloma.     

Comprehensive lectin histochemistry of normal and neoplastic human choroid plexus cells: alternation of lectin-binding patterns through neoplastic transformation

Summary Lectin histochemistry of the normal and neoplastic human choroid plexus cells [six choroid plexus papillomas (CPPs) and three choroid plexus carcinomas (CPCs)] was performed using eight representative lectins to study the development of sugar chain structures and also to determine whether lectins were useful for a histopathological diagnosis of choroid plexus neoplasms (CPNs). The normal choroid plexus cells reacted with Ricinus communis (RCA-I), Canavalia ensiformis (Con A), Limax flavus (LFA) and Triticum vulgaris (WGA), while Arachis hypoaea (PNA) stained them only after the removal of sialic acid. Human fetal choroid plexus cells at 8 weeks gestation already showed the same lectin-binding patterns as adult ones. All CPNs were stained by RCA-I and Con A in a similar manner as the normal choroid plexus cells. Although seven CPNs were positive for LFA, two CPCs were not stained by LFA, which bound to sialic acid. Two LFA-positive CPPs were stained by PNA before the removal of sialic acid. Moreover, unlike the normal choroid plexus cells, Ulex europaeus-, Glycine maximus- and Dolichos biflorus- binding sites often appeared, and WGA-binding sites of three CPNs remained even after sialic acid removal. In conclusion, the glycosialylation in normal choroid plexus cells was completed during the early embryonic stage. The lectin-binding patterns of CPNs were heterogenous in each case. The alternation of the glycosialylation and/or acquisition of binding sites for some lectins was sometimes observed through a neoplastic transformation.