Neural Cell Adhesion Molecule NCAM Research Articles

Neural Signature Expressed by Cells from Ovarian Carcinoma (A Case Report)

Aim: To demonstrate the presence of differentiated cells in ovarian carcinomatosis nodules after chemotherapy. Patient and method: A patient of 85 years, who presented a pelvic mass of 10 cm. The anatomo-pathological study was performed on the biopsies (before treatment) and post operational samples (after treatment by Carbotaxol). Histological samples were analyzed with ovarian cancer markers for diagnosis. The immune cells (CD3, CD4, CD8 and CD20) and neural markers such as anti: neurofilament (NF), neural cell adhesion molecules NCAM (CD56), chromogranin A, neuronal specific enolase (NSE), S100 protein and synaptophysine were used for demonstrating the neuronal differentiation tendencies of carcinomatosis cells. Proliferation activities were studied by using proliferative index and Ki67 antibody. Results: The histological result of biopsies of bilateral ovarian carcinomatosis showed the poorly differentiated monomorphic cell serous carcinoma (cytokeratin+, estrogen receptor+, protein S100+, anti-wilms tumor-1+ with proliferative index (31%) and high Ki67 marker (45%). Semi-quantitative histological evaluations of post operational samples presented two cellular quotas. One was composed of monomorphic cells with high proliferative index (19%) and ki67 marker (30%). In another quota, large size polymorphic cells with no proliferative index and Ki67 marker were distinguished. Before treatment, all neuronal markers except NSE and S100 protein were found negative in primary tumors. In the proliferative zone of post-operative samples, NSE and S100 protein markers persist with any other neuronal markers. These zones were highly infiltrated by CD3, CD4 and CD20 immune cells. In contrast, in degenerative non-proliferative zone, all primary tumor markers except Ki67, all neuronal markers except synaptophysine, and dramatically decreased infiltrated immune cells. Conclusion: These results are in favors of differentiation of poorly differentiated ovarian cancer cells with high proliferative index to other tissue with no proliferation potential. Targeting of differentiation of cancer cells by differencing inductors may be a new way for cancer therapy.

Investigation of recombinant therapeutic genes expression in umbilical cord blood mononuclear cells transduced with three adenoviral vectors encoding neurotrophic factors GDNF, VEGF and neural cell adhesion molecule NCAM

Investigation of recombinant therapeutic genes expression in umbilical cord blood mononuclear cells transduced with three adenoviral vectors encoding neurotrophic factors GDNF, VEGF and neural cell adhesion molecule NCAM

A crucial role for polysialic acid in developmental interneuron migration and the establishment of interneuron densities in the mouse prefrontal cortex.

Polysialic acid (polySia) is a unique glycan modification of the neural cell adhesion molecule NCAM and a major determinant of brain development. Polysialylation of NCAM is implemented by the two polysialyltransferases (polySTs) ST8SIA2 and ST8SIA4. Dysregulation of the polySia-NCAM system and variation in ST8SIA2 has been linked to schizophrenia and other psychiatric disorders. Here, we show reduced interneuron densities in the medial prefrontal cortex (mPFC) of mice with either partial or complete loss of polySia synthesizing capacity by ablation of St8sia2, St8sia4, or both. Cells positive for parvalbumin and perineuronal nets as well as somatostatin-positive cells were reduced in the mPFC of all polyST-deficient lines, whereas calretinin-positive cells and the parvalbumin-negative fraction of calbindin-positive cells were unaffected. Reduced interneuron numbers were corroborated by analyzing polyST-deficient GAD67-GFP knock-in mice. The accumulation of precursors in the ganglionic eminences and reduced numbers of tangentially migrating interneurons in the pallium were observed in polyST-deficient embryos. Removal of polySia by endosialidase treatment of organotypic slice cultures led to decreased entry of GAD67-GFP-positive interneurons from the ganglionic eminences into the pallium. Moreover, the acute loss of polySia caused significant reductions in interneuron velocity and leading process length. Thus, attenuation of polySia interferes with the developmental migration of cortical interneurons and causes pathological changes in specific interneuron subtypes. This provides a possible link between genetic variation in polyST genes, neurodevelopmental alterations and interneuron dysfunction in neuropsychiatric disease.

Cytoplasmic domain of NCAM140 interacts with ubiquitin-fold modifier-conjugating enzyme-1 (Ufc1)

The neural cell adhesion molecule NCAM is implicated in different neurodevelopmental processes and in synaptic plasticity in adult brain. The cytoplasmic domain of NCAM interacts with several cytoskeletal proteins and signaling molecules. To identify novel interaction partners of the cytosolic domain of NCAM a protein macroarray has been performed. We identified the ubiquitin-fold modifier-conjugating enzyme-1 (Ufc1) as an interaction partner of NCAM140. Ufc1 is one of the enzymes involved in modification of proteins with the ubiquitin-like molecule ubiquitin-fold modifier-1 (Ufm1). We also observed a partial co-localization of NCAM140 with Ufc1 and Ufm1 and increased endocytosis of NCAM140 in the presence of Ufm1 suggesting a possible ufmylation of NCAM140 and a potential novel function of Ufm1 for cell surface proteins.

3-Methylcholanthrene Induces Neurotoxicity in Developing Neurons Derived from Human CD34+Thy1+ Stem Cells by Activation of Aryl Hydrocarbon Receptor

Developing neurons, derived from the human umbilical cord blood stem cells (hUCBSCs), were investigated for their stage-specific responses against 3-methylcholanthrene (MC), a well-known polycyclic aromatic hydrocarbon. Three-dimensional (3D) molecular docking demonstrates the strong hydrogen bonding and hydrophobic interactions of MC with amino acids of aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator (ARNT) within 4 Å and subsequent inhibition of cAMP response element-binding protein (CREB), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors. Protein-protein docking also confirms that induced levels of AHR inhibit the neurogenesis-related transcription factor (CREB) with maximum docking scores. In concurrence with in silico data, MC exposure significantly up regulates the expression and activity of AHR, CYP1A1 and glutathione S-transferase P1-1 (GSTP1-1) and down regulates the expression of CREB, AMPA and NMDA receptors in hUCBSC-derived neuronal cells at various maturity (0, 2, 4, 8 days of differentiation). MC-mediated significant down regulation in the expression of stage-specific neuronal markers (Nestin, neural cell adhesion molecule-NCAM, synaptophysin-SYP, CREB, AMPA and N-methyl-D-aspartate receptor subunit 2A-NR2A) was also noticed in cells all through the differentiation. Data identify the possible interference of MC in neuronal transmission and neurogenesis.

Polysialic Acid Is Present in Mammalian Semen as a Post-translational Modification of the Neural Cell Adhesion Molecule NCAM and the Polysialyltransferase ST8SiaII

Fertilization in animals is a complex sequence of several biochemical events beginning with the insemination into the female reproductive tract and, finally, leading to embryogenesis. Studies by Kitajima and co-workers (Miyata, S., Sato, C., and Kitajima, K. (2007) Trends Glycosci. Glyc, 19, 85-98) demonstrated the presence of polysialic acid (polySia) on sea urchin sperm. Based on these results, we became interested in the potential involvement of sialic acid polymers in mammalian fertilization. Therefore, we isolated human sperm and performed analyses, including Western blotting and mild 1,2-diamino-4,5-methylenedioxybenzene-HPLC, that revealed the presence α2,8-linked polySia chains. Further analysis by a glyco-proteomics approach led to the identification of two polySia carriers. Interestingly, besides the neural cell adhesion molecule, the polysialyltransferase ST8SiaII has also been found to be a target for polysialylation. Further analysis of testis and epididymis tissue sections demonstrated that only epithelial cells of the caput were polySia-positive. During the epididymal transit, polySia carriers were partially integrated into the sperm membrane of the postacrosomal region. Because polySia is known to counteract histone as well as neutrophil extracellular trap-mediated cytotoxicity against host cells, which plays a role after insemination, we propose that polySia in semen represents a cytoprotective element to increase the number of vital sperm.

The Polysialyltransferases Interact with Sequences in Two Domains of the Neural Cell Adhesion Molecule to Allow Its Polysialylation

The neural cell adhesion molecule (NCAM) is the major substrate for the polysialyltransferases (polySTs), ST8SiaII/STX and ST8SiaIV/PST. The polysialylation of NCAM N-glycans decreases cell adhesion and alters signaling. Previous work demonstrated that the first fibronectin type III repeat (FN1) of NCAM is required for polyST recognition and the polysialylation of the N-glycans on the adjacent Ig5 domain. In this work, we highlight the importance of an FN1 acidic patch in polyST recognition and also reveal that the polySTs are required to interact with sequences in the Ig5 domain for polysialylation to occur. We find that features of the Ig5 domain of the olfactory cell adhesion molecule (OCAM) are responsible for its lack of polysialylation. Specifically, two basic OCAM Ig5 residues (Lys and Arg) found near asparagines equivalent to those carrying the polysialylated N-glycans in NCAM substantially decrease or eliminate polysialylation when used to replace the smaller and more neutral residues (Ser and Asn) in analogous positions in NCAM Ig5. This decrease in polysialylation does not reflect altered glycosylation but instead is correlated with a decrease in polyST-NCAM binding. In addition, inserting non-conserved OCAM sequences into NCAM Ig5, including an "extra" N-glycosylation site, decreases or completely blocks NCAM polysialylation. Taken together, these results indicate that the polySTs not only recognize an acidic patch in the FN1 domain of NCAM but also must contact sequences in the Ig5 domain for polysialylation of Ig5 N-glycans to occur.

Polysialic Acid: Versatile Modification of NCAM, SynCAM 1 and Neuropilin-2

The glycan polysialic acid is well-known as a unique posttranslational modification of the neural cell adhesion molecule NCAM. Despite remarkable acceptor specificity, however, a few other proteins can be targets of polysialylation. Here, we recapitulate the biosynthesis of polysialic acid by the two polysialyltransferases ST8SIA2 and ST8SIA4 and highlight the increasing evidence that variation in the human ST8SIA2 gene is linked to schizophrenia and possibly other neuropsychiatric disorders. Moreover, we summarize the knowledge on the role of NCAM polysialylation in brain development gained by the analysis of NCAM- and polysialyltransferase-deficient mouse models. The last part of this review is focused on recent advances in identifying SynCAM 1 and neuropilin-2 as novel acceptors of polysialic acid in NG2 cells of the perinatal brain and in dendritic cells of the immune system, respectively.

Polysialinsäure — ein Zucker reguliert die Hirnentwicklung

Modification with polysialic acid controls functions of the neural cell adhesion molecule NCAM during ontogenic processes. This cooperation between a protein and its posttranslational modification provides an outstanding example of how glycans amplify the genomic information and create the functional diversity required to build complex structures like the human brain.

Homeostatic regulation of NCAM polysialylation is critical for correct synaptic targeting.

During development, axonal projections have a remarkable ability to innervate correct dendritic subcompartments of their target neurons and to form regular neuronal circuits. Altered axonal targeting with formation of synapses on inappropriate neurons may result in neurodevelopmental sequelae, leading to psychiatric disorders. Here we show that altering the expression level of the polysialic acid moiety, which is a developmentally regulated, posttranslational modification of the neural cell adhesion molecule NCAM, critically affects correct circuit formation. Using a chemically modified sialic acid precursor (N-propyl-D: -mannosamine), we inhibited the polysialyltransferase ST8SiaII, the principal enzyme involved in polysialylation during development, at selected developmental time-points. This treatment altered NCAM polysialylation while NCAM expression was not affected. Altered polysialylation resulted in an aberrant mossy fiber projection that formed glutamatergic terminals on pyramidal neurons of the CA1 region in organotypic slice cultures and in vivo. Electrophysiological recordings revealed that the ectopic terminals on CA1 pyramids were functional and displayed characteristics of mossy fiber synapses. Moreover, ultrastructural examination indicated a "mossy fiber synapse"-like morphology. We thus conclude that homeostatic regulation of the amount of synthesized polysialic acid at specific developmental stages is essential for correct synaptic targeting and circuit formation during hippocampal development.

Polysialic acid controls NCAM signals at cell–cell contacts to regulate focal adhesion independent from FGF receptor activity

The polysialic acid (polySia) modification of the neural cell adhesion molecule NCAM is a key regulator of cell migration. Yet its role in NCAM-dependent or NCAM-independent modulation of motility and cell-matrix adhesion is largely unresolved. Here, we demonstrate that loss of polySia attenuates tumour cell migration and augments the number of focal adhesions in a cell-cell contact- and NCAM-dependent manner. In the presence or absence of polySia, NCAM never colocalised with focal adhesions but was enriched at cell-cell contacts. Focal adhesion of polySia- and NCAM-negative cells was enhanced by incubation with soluble NCAM or by removing polySia from heterotypic contacts with polySia-NCAM-positive cells. Focal adhesion was compromised by the src-family kinase inhibitor PP2, whereas loss of polySia or exposure to NCAM promoted the association of p59(Fyn) with the focal adhesion scaffolding protein paxillin. Unlike other NCAM responses, NCAM-induced focal adhesion was not prevented by inhibiting FGF receptor activity and could be evoked by NCAM fragments comprising immunoglobulin domains three and four but not by the NCAM fibronectin domains alone or by an NCAM-derived peptide known to interact with and activate FGF receptors. Together, these data indicate that polySia regulates cell motility through NCAM-induced but FGF-receptor-independent signalling to focal adhesions.

Synapsin I Is an Oligomannose-Carrying Glycoprotein, Acts As an Oligomannose-Binding Lectin, and Promotes Neurite Outgrowth and Neuronal Survival When Released via Glia-Derived Exosomes

Oligomannosidic glycans play important roles in nervous system development and function. By performing a phage display screening with oligomannose-specific antibodies, we identified an oligomannose-mimicking peptide that was functionally active in modulating neurite outgrowth and neuron-astrocyte adhesion. Using the oligomannose-mimicking peptide in crosslinking experiments, synapsin I was identified as a novel oligomannose-binding protein in mouse brain. Further analyses not only verified that synapsin I is an oligomannose-binding lectin, but also indicated that it is a glycoprotein carrying oligomannose and Lewis(x). We also found that synapsin I is expressed in glia-enriched cultures and is released from glial cells via exosomes. Incubation of glial-derived exosomes in the presence of high KCl concentrations or subjecting glial cell cultures to either oxygen/glucose deprivation or hydrogen peroxide resulted in release of synapsin I from exosomes. Application of synapsin I promoted neurite outgrowth from hippocampal neurons and increased survival of cortical neurons upon hydrogen peroxide treatment or oxygen/glucose deprivation. Coculture experiments using wild-type hippocampal neurons and wild-type or synapsin-deficient glial cells showed enhanced neurite outgrowth when synapsin was expressed by glial cells. Synapsin-induced neurite outgrowth was dependent on oligomannose on synapsin I and the neural cell adhesion molecule NCAM at the neuronal cell surface. The data indicate that, under conditions of high neuronal activity and/or oxidative stress, synapsin can be released from glial-derived exosomes and promotes neurite outgrowth and neuronal survival by modulating the interactions between glia and neurons.

Expression of the neural cell adhesion molecule and polysialic acid in human neuroblastoma cell lines

The neural cell adhesion molecule NCAM is a cell surface glycoprotein of the immunoglobulin superfamily and is widely expressed in tumours of neuroectodermal origin such as neuroblastoma. NCAM can be decorated by the carbohydrate polymer polysialic acid (polySia), which attenuates NCAM-mediated cell adhesion and increases cellular motility. The key enzymes in the biosynthesis of polySia are the two polysialyltransferases ST8SiaII and ST8SiaIV. In the present study, expression of NCAM, polySia-NCAM, ST8SiaII and ST8SiaIV was investigated in five human neuroblastoma cell lines before and after xenografting into SCID mice by immunohistochemistry, Western blot analysis and real-time PCR. Results were correlated with the metastatic potential. In vitro, three cell lines (LAN-1, LAN-5 and SH-SY5Y) were positive for polySia attached to the transmembrane isoforms NCAM-140 and NCAM-180, whereas Kelly and SK-N-SH cells were negative for NCAM and polySia. In the presence of NCAM, the level of polySia correlated with the amount of polysialyltransferase transcripts, which were highest in LAN-1, LAN‑5 and SH-SY5Y cells. In the respective primary tumours grown in SCID mice, the expression patterns of NCAM, polySia and polysialyl-transferases were similar to those observed in vitro. After subcutaneous engraftment, polySia-NCAM-positive neuroblastoma developed disseminated micrometastases, a metastatic pattern that was not observed for tumours derived from NCAM-negative cell lines. Together, this indicates that the presence of polySia reduces the adhesiveness of tumour cells and promotes dissemination.

The GTPase-activating protein Rap1GAP: A new player to modulate Ret signaling

Glial cell line-derived neurotrophic factor (GDNF) plays a critical role in orchestrating the development and maintenance of different populations of central and peripheral neurons. GDNF was initially discovered by its ability to promote the survival of ventral midbrain dopaminergic neurons 1. In addition, GDNF promotes the survival and control the differentiation of motor neurons and many peripheral neurons, including sensory and sympathetic neurons. Moreover, it is required to induce proliferation, migration and survival of enteric neurons. GDNF promotes these trophic effects through the activation of the receptor tyrosine kinase (RTK) Ret. A distinctive feature of the receptor complex for GDNF is the requirement of two types of receptors, one specialized in GDNF binding, represented by the glycosyl-phosphatidyl inositol (GPI)-linked co-receptor GFRα1, and another involved in transmembrane signaling, represented by the RTK Ret or the neural cell adhesion molecule NCAM 1, 2. Following homodimeric GDNF binding to GFRα1, Ret becomes dimerized and tyrosine phosphorylated, and triggers many different signaling pathways, including the Ras-Raf-MAPK (ERK1/2) cascade, the phosphatidylinositol-3-kinase (PI3K)-Akt, the PLC-γ and the Src signaling pathways 3.

Differentiated Parkinson patient-derived induced pluripotent stem cells grow in the adult rodent brain and reduce motor asymmetry in Parkinsonian rats

Recent advances in deriving induced pluripotent stem (iPS) cells from patients offer new possibilities for biomedical research and clinical applications, as these cells could be used for autologous transplantation. We differentiated iPS cells from patients with Parkinson's disease (PD) into dopaminergic (DA) neurons and show that these DA neurons can be transplanted without signs of neurodegeneration into the adult rodent striatum. The PD patient iPS (PDiPS) cell-derived DA neurons survived at high numbers, showed arborization, and mediated functional effects in an animal model of PD as determined by reduction of amphetamine- and apomorphine-induced rotational asymmetry, but only a few DA neurons projected into the host striatum at 16 wk after transplantation. We next applied FACS for the neural cell adhesion molecule NCAM on differentiated PDiPS cells before transplantation, which resulted in surviving DA neurons with functional effects on amphetamine-induced rotational asymmetry in a 6-OHDA animal model of PD. Morphologically, we found that PDiPS cell-derived non-DA neurons send axons along white matter tracts into specific close and remote gray matter target areas in the adult brain. Such findings establish the transplantation of human PDiPS cell-derived neurons as a long-term in vivo method to analyze potential disease-related changes in a physiological context. Our data also demonstrate proof of principle of survival and functional effects of PDiPS cell-derived DA neurons in an animal model of PD and encourage further development of differentiation protocols to enhance growth and function of implanted PDiPS cell-derived DA neurons in regard to potential therapeutic applications.

NCAM-Induced Neurite Outgrowth Depends on Binding of Calmodulin to NCAM and on Nuclear Import of NCAM and fak Fragments

The neural cell adhesion molecule NCAM plays important functional roles not only during nervous system development, but also in the adult after injury and in synaptic plasticity. Homophilic binding of NCAM triggers intracellular signaling events resulting in cellular responses such as neurite outgrowth that require NCAM palmitoylation-dependent raft localization and activation of the nonreceptor tyrosine kinases fyn and fak. In this study, we show that stimulation of NCAM by a function-triggering NCAM antibody results in proteolytic processing of NCAM and fak. The C-terminal fragment of NCAM, consisting of the intracellular domain, the transmembrane domain, and a stub of the extracellular domain, and the N-terminal fragment of fak are imported into the nucleus. NCAM-stimulated fak activation, generation, and nuclear import of NCAM and fak fragments as well as neurite outgrowth are abolished by mutation of the calmodulin binding motif in the intracellular domain of NCAM that is responsible for the calcium-dependent binding of calmodulin to NCAM. This mutation interferes neither with NCAM cell surface expression, palmitoylation, and raft localization nor with fyn activation. The way by which the transmembrane NCAM fragment reaches the nucleus in a calmodulin- and calcium-dependent manner is by endocytotic transport via the endoplasmic reticulum and the cytoplasm. The generation and nuclear import of NCAM and phosphorylated fak fragments resulting from NCAM stimulation may represent a signal pathway activating cellular responses in parallel or in association with classical kinase- and phosphorylation-dependent signaling cascades.

Binding of αII spectrin to 14-3-3β is involved in NCAM-dependent neurite outgrowth

Members of the 14-3-3 protein family have been implicated in neuronal migration, synaptic plasticity and learning. Using affinity chromatography followed by mass spectrometry analysis, we show here that the cytoskeletal protein αII spectrin is a novel ligand of 14-3-3β. We found that 14-3-3β interacts with αII spectrin via the mode 2 14-3-3 binding motif RLIQS1302HP. Binding required phosphorylation of Ser1302 by casein kinase II and was enhanced in the presence of calmodulin. Co-immunoprecipitation of αII spectrin and 14-3-3β with the neural cell adhesion molecule NCAM suggested that the 14-3-3-spectrin-interaction affects NCAM function. Indeed, disruption of the 14-3-3β/αII spectrin interaction by mutating Ser1302 to Ala enhanced NCAM-dependent neurite outgrowth. Our results indicate that the phosphorylation-dependent interaction between 14-3-3β and αII spectrin acts as a switch between positive and negative regulation of neurite outgrowth stimulated by NCAM, representing a novel and acute mechanism preventing uncontrolled elongation of neuronal processes.

Synaptic cell adhesion molecule SynCAM 1 is a target for polysialylation in postnatal mouse brain

Among the large set of cell surface glycan structures, the carbohydrate polymer polysialic acid (polySia) plays an important role in vertebrate brain development and synaptic plasticity. The main carrier of polySia in the nervous system is the neural cell adhesion molecule NCAM. As polySia with chain lengths of more than 40 sialic acid residues was still observed in brain of newborn Ncam(-/-) mice, we performed a glycoproteomics approach to identify the underlying protein scaffolds. Affinity purification of polysialylated molecules from Ncam(-/-) brain followed by peptide mass fingerprinting led to the identification of the synaptic cell adhesion molecule SynCAM 1 as a so far unknown polySia carrier. SynCAM 1 belongs to the Ig superfamily and is a powerful inducer of synapse formation. Importantly, the appearance of polysialylated SynCAM 1 was not restricted to the Ncam(-/-) background but was found to the same extent in perinatal brain of WT mice. PolySia was located on N-glycans of the first Ig domain, which is known to be involved in homo- and heterophilic SynCAM 1 interactions. Both polysialyltransferases, ST8SiaII and ST8SiaIV, were able to polysialylate SynCAM 1 in vitro, and polysialylation of SynCAM 1 completely abolished homophilic binding. Analysis of serial sections of perinatal Ncam(-/-) brain revealed that polySia-SynCAM 1 is expressed exclusively by NG2 cells, a multifunctional glia population that can receive glutamatergic input via unique neuron-NG2 cell synapses. Our findings sug-gest that polySia may act as a dynamic modulator of SynCAM 1 functions during integration of NG2 cells into neural networks.

Divergent impact of the polysialyltransferases ST8SiaII and ST8SiaIV on polysialic acid expression in immature neurons and interneurons of the adult cerebral cortex

Polysialic acid (PSA) is a negatively charged carbohydrate polymer, which confers antiadhesive properties to the neural cell adhesion molecule NCAM and facilitates cellular plasticity during brain development. In mice, PSA expression decreases drastically during the first postnatal weeks and it gets confined to immature neurons and regions displaying structural plasticity during adulthood. In the brain, PSA is exclusively synthesized by the two polysialyltransferases ST8SiaII and ST8SiaIV. To study their individual contribution to polysialylation in the adult, we analyzed PSA expression in mice deficient for either polysialyltransferase. Focusing on the cerebral cortex, our results indicate that ST8SiaIV is solely responsible for PSA expression in mature interneurons and in most regions of cortical neuropil. By contrast, ST8SiaII is the major polysialyltransferase in immature neurons of the paleocortex layer II and the hippocampal subgranular zone. The numbers of cells expressing PSA or doublecortin, another marker of immature neurons, were increased in the paleocortex layer II of ST8SiaIV-deficient mice, indicating altered differentiation of these cells. Analysis of doublecortin expression also indicated that the production of new granule neurons in the subgranular zone of ST8SiaII-deficient mice is not affected. However, many of the immature granule neurons showed aberrant locations and morphology, suggesting a role of ST8SiaII in their terminal differentiation.

Genesis of rods in the zebrafish retina occurs in a microenvironment provided by polysialic acid‐expressing Müller glia

Polysialic acid (polySia) is a posttranslational modification of the neural cell adhesion molecule NCAM, which in the vertebrate brain is dynamically regulated during development and crucially involved in developmental and adult neurogenesis. In the fish retina, new neurons are persistently generated, but the possible contribution of polySia has not yet been addressed. Here we used immunohistochemistry with NCAM- and polySia-specific antibodies to study spatiotemporal expression patterns of NCAM and polySia in the developing and mature zebrafish retina. As early as 2.3 days postfertilization (dpf), NCAM but not polySia was detected on cell somata and fibers of the developing retina. At 4.3 dpf polySia immunoreactivity first appeared in the ventral retina and was localized to the nascent outer nuclear layer (ONL). In mature zebrafish, polySia immunoreactivity in the ONL extended to the entire retina. Colocalization with rhodopsin-EGFP in transgenic zebrafish or the Müller glia-specific protein cellular retinaldehyde-binding protein (CRALBP) revealed that polySia immunoreactivity was confined to the compartment of radial Müller glia processes crossing the ONL and to a small band of processes positioned proximal to the horizontal cell layer of the mature retina. As shown by 5-bromo-2-deoxyuridine (BrdU) labeling, both newly generated rod precursors within the mature ONL and precursors of the marginal zone were polySia-negative. Thus, polySia-negative rod precursors of the mature zebrafish retina face a polySia-NCAM-positive microenvironment presented by radial Müller glia. In view of the prominent role of polySia in other neurogenic systems, this pattern indicates that polySia provides environmental cues that are relevant for the generation of new rods.