The carbohydrate epitope 3-fucosyl-N-acetyllactosamine is region-specifically expressed in astrocytes of the rat brain. Light- and electron-microscopical observations

Identification and validation of a Lewis x glycomimetic peptide

Glycans play important roles in regulating cell recognition and interactions to fine tune development, and synaptic plasticity and regeneration in the adult nervous system. The spatial and temporal expression pattern of Lewis(x) (a terminal trisaccharide epitope characterized by alpha1,3-fucosyl-N-acetyl-lactosamine) in the nervous system indicates an important role of this epitope in neurogenesis and brain development. Localization of Lewis(x) in the proliferative subventricular zone of the developing nervous system and also its expression on stem cells of the adult nervous system suggests a role in neurogenesis and hence regeneration. To provide an alternative tool to elucidate the functional roles of Lewis(x), we screened a random peptide phage library against a Lewis(x)-specific antibody to identify a Lewis(x) glycomimetic peptide. We identified a peptide that specifically bound to the Lewis(x)-specific antibody and this binding could be competed by the Lewis(x) glycan. Different aspects of the Lewis(x) glycomimetic peptide were investigated by introducing it in in vitro assays measuring neurite outgrowth and in in vivo assays to determine its efficacy in regeneration of peripheral nerve and spinal cord after injury in adult mice. In vitro, neurite outgrowth triggered by the Lewis(x-)carrying adhesion molecule CD24 was abolished alike by the Lewis(x) glycan and the glycomimetic peptide, while no influence of the glycomimetic peptide was seen in regeneration. Our results validate the use of Lewis(x) glycomimetic peptide as a functionally equivalent structure to the Lewis(x) glycan.

Brain development, environment and sex: what can we learn from studying graviperception, gravitransduction and the gravireaction of the developing CNS to altered gravity?

As man embarks on space exploration and contemplates space habitation, there is a critical need for basic understanding of the impact of the environmental factors of space, and in particular gravity, on human survival, health, reproduction and development. This review summarizes our present knowledge on the effect of altered gravity on the developing CNS with respect to the response of the developing CNS to altered gravity (gravireaction), the physiological changes associated with altered gravity that could contribute to this effect (gravitransduction), and the possible mechanisms involved in the detection of altered gravity (graviperception). Some of these findings transcend gravitational research and are relevant to our understanding of the impact of environmental factors on CNS development on Earth.

Impact of thyroid hormone deficiency on the developing CNS: cerebellar glial and neuronal protein expression in rat neonates exposed to antithyroid drug propylthiouracil

The developing rat cerebellum is vulnerable to thyroid hormone (TH) deficiency. The present study addresses the molecular mechanisms involved in this response. Specifically, the study focuses on the expression of selected cerebellar proteins that are known to be directly [protein expressing 3-fucosyl-N-acetyl-lactosamine antigen (CD15), neuronal cell adhesion molecule (L1)] or indirectly [glial fibrillary acidic protein (GFAP)], involved in glial-neuronal interactions and thus regulation of cell proliferation and granule cell migration. Cerebellar mass, structure, and protein expression in rat neonates exposed to antithyroid drug propylthiouracil (PTU) from the embryonic day (E) 16 to postnatal day (P) 21 were compared against rat neonates that received replacement of thyroxin (T4) starting on day P1 or untreated controls. Cerebellar proteins were analyzed by quantitative Western blots. PTU-treated rats lagged in growth and showed reduction in cerebellar mass and alterations in cerebellar structure on P15. Daily treatment of neonates with T4 restored normal cerebellum-to-body-mass ratio, cerebellar structure, and cerebellar protein expression. Densitometric analysis of Western blots revealed altered expression of selected proteins in the cerebella of hypothyroid neonates. A decrease of CD15 (46%, p = 0.031) was observed on P10 and was accompanied by a decrease in GFAP expression (64%, p = 0.039). Furthermore, a shift in the developmental GFAP profile was observed in the PTU-treated cerebellum. L1 expression was not significantly affected in the hypothyroid cerebellum. Altered expression of cerebellar proteins is likely to affect cell-cell interactions and consequently cell proliferation and migration and contribute to structural and functional alterations seen in the hypothyroid rat neonates.

Synaptic connectivity of the diffuse bipolar cell type DB6 in the inner plexiform layer of primate retina

Diffuse bipolar cells in primate retina receive synaptic input from multiple cones and provide output to ganglion cells. Diffuse bipolar cells can be subdivided into six types (DB1-DB6) according to the stratification of their axon terminals in the inner plexiform layer, but their synaptic connectivity in the inner plexiform layer is not well understood. Here the stratification and synaptic connectivity of DB6 axon terminals were studied in the retinae of New World (marmoset) and Old World (macaque) monkeys. Immunohistochemical markers were applied to retinal sections. The sections were analyzed by confocal and deconvolution light microscopy as well as electron microscopy. The DB6 cells were identified with antibodies against CD15; rod bipolar cells were identified with antibodies against protein kinase Calpha (PKCalpha); and AII amacrine cells were identified with antibodies against calretinin. The axons of DB6 and rod bipolar cells occupy distinct regions in stratum 5 of the inner plexiform layer. The distal processes of calretinin-labeled AII cells are usually closely associated with rod bipolar axons but sometimes also with DB6 axons. Pre-embedding immunoelectron microscopy showed that the vast majority (over 86%) of the synaptic output of DB6 cells is onto amacrine cell processes, whereas less than 14% goes to ganglion cell processes. In double-labeled preparations DB6 axons occasionally made output onto calretinin-labeled amacrine processes. Thus it is possible that AII cells receive some input from DB6 cells.

Environmental impacts on the developing CNS: CD15, NCAM-L1, and GFAP expression in rat neonates exposed to hypergravity

We have previously reported that the developing rat cerebellum is affected by hypergravity exposure. The effect is observed during a period of both granule and glial cell proliferation and neuronal migration in the cerebellum and coincides with changes in thyroid hormone levels. The present study begins to address the molecular mechanisms involved in the cerebellar response to hypergravity. Specifically, the study focuses on the expression of cerebellar proteins that are known to be directly involved in cell-cell interactions [protein expressing 3-fucosyl-N-acetyl-lactosamine antigen (CD15), neuronal cell adhesion molecule (NCAM-L1)] and those that affect cell-cell interactions indirectly [glial fibrillary acidic protein (GFAP)] in rat neonates exposed to centrifuge-produced hypergravity. Cerebellar mass and protein expression in rat neonates exposed to hypergravity (1.5 G) from gestational day (G) 11 to postnatal day (P) 30 were compared at one of six time points between P6 and P30 against rat neonates developing under normal gravity. Proteins were analyzed by quantitative western blots of cerebellar homogenates prepared from male or female neonates. Cerebellar size was most clearly reduced in male neonates on P6 and in female neonates on P9, with a significant gender difference; differences in cerebellar mass remained significant even when change in total body mass was factored in. Densitometric analysis of western blots revealed both quantitative and temporal changes in the expression of selected cerebellar proteins that coincided with changes in cerebellar mass and were gender-specific. In fact, our data indicated certain significant differences even between male and female control animals. A maximal decrease in expression of CD15 was observed in HG females on P9, coinciding with maximal change in their cerebellar mass. A shift in the time-course of NCAM-L1 expression resulted in a significant increase in NCAM-L1 in HG males on P18, an isolated time at which cerebellar mass does not significantly differ between HG and SC neonates. A maximal decrease in expression of GFAP was observed in HG males on P6, coinciding with maximal change in their cerebellar mass. Altered expression of cerebellar proteins is likely to affect a number of developmental processes and contribute to the structural and functional alterations seen in the CNS developing under altered gravity. Our data suggest that both cerebellar development and its response to gravitational manipulations differ in males and females.

Molecular cloning of rat alpha1,3-fucosyltransferase IX (Fuc-TIX) and comparison of the expression of Fuc-TIV and Fuc-TIX genes during rat postnatal cerebellum development

Fucosylated glycoconjugates play an essential role in central nervous system development, but the regulation of expression of these molecules is not well understood. The final biosynthetic step for a major group of cerebellar fucosylated glycoconjugates (those bearing the developmentally regulated epitope 3-fucosyl-N-acetyllactosamine, CD15, and related fucosylated epitopes) is catalyzed by an alpha-1,3-fucosyltransferase (FucT). The major FucT activity in postnatal rat cerebellum has a specificity consistent with that encoded by either a Fuc-TIV- or Fuc-TIX-like gene, and thus the expression of these genes was investigated during postnatal rat cerebellar development. A rFuc-TIX cDNA was cloned and a comparison of its enzymatic activity with rFuc-TIV revealed similar results on oligosaccharides, but strikingly higher activity on lipid acceptors, suggesting a greater role for rFuc-TIX than rFuc-TIV in the synthesis of CD15 glycolipids. rFuc-TIX mRNA levels were much higher than those of rFuc-TIV in neonatal cerebellum. Whereas rFuc-TIX mRNA levels remained relatively constant, rFuc-TIV mRNA levels declined during postnatal cerebellar development. In situ hybridization of postnatal rat cerebella also revealed different patterns of expression for these two genes. The rFuc-TIV gene was expressed predominantly in Purkinje cells and the deep cerebellar nuclei throughout postnatal development, but was expressed in granule neurons only in the neonatal, and not the adult, rat. In contrast, the rFuc-TIX gene was expressed in cells in the granule cell layers in both neonatal and in the adult rat. The potential implications of the different enzymatic activities and cell localization of rFuc-TIV and rFuc-TIX expression for the regulation of fucosylated glycoconjugates during cerebellar development are discussed.

Restriction of high CD15 expression to a subset of rat cerebellar astroglial cells can be overcome by transduction with adenoviral vectors expressing the rat alpha 1,3-fucosyltransferase IV gene

Glycoconjugates bearing the epitope 3-fucosyl-N-acetyllactosamine (CD15) are believed to be involved in cell-cell interactions and are temporally and spatially regulated in the brain. In the rat postnatal cerebellum, CD15 is predominantly expressed in the molecular layer by Bergmann glial cells, but little CD15 expression is seen in other astroglia, and the basis for this restricted expression is not known. Adenoviral vectors were shown to efficiently deliver transgenes to cerebellar glial cells and were used to determine whether manipulation of glycosyltransferase activities could enhance the expression of CD15 in these cells. In dissociated cerebellar cell cultures, few glial cells normally express CD15. However, transduction of these cells with an adenoviral vector (AdGFPCMVFucT) that expressed both green fluorescent protein (GFP) and FLAG-tagged rat alpha 1, 3-fucosyltransferase IV (rFuc-TIV) resulted in high CD15 expression on the surface of all transduced glial cells. Likewise, infection of cerebellar slice cultures caused the appearance of CD15-positive transduced cells of glial cell morphology in the internal granule cell layer. Thus, enhancement of Fuc-T activity caused robust CD15 expression in cerebellar glial cells that normally show little expression of CD15, suggesting a role for Fuc-T levels in regulating CD15 expression in this cell type. The manipulation of levels of glycosyltransferases using adenoviral vectors may prove a useful tool to investigate questions of glycoconjugate regulation in glial cells in the developing rodent cerebellum.