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S. Bolz, S. Kustermann, H. Hildebrandt, K.L. Kohler; Polysialylated NCAM Is Expressed in Photoreceptors of Zebrafish . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5331.
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Purpose: Polysialic acid (PSA) on the neural cell adhesion molecule (NCAM) has been shown to play a key role in the formation and activity–dependent remodelling of neuronal circuits. The fish retina retains a high degree of synaptic plasticity and remodelling even in its adult stages and throughout its lifetime. We therefore examined a possible involvement of PSA in these processes in the developing and adult zebrafish retina. Methods: PSA expression was examined with an antibody specific for polysialylated NCAM. Immunohistochemistry was carried out on sections of the zebrafish retina and brain at 2, 3, 4, 7, 9, 14, and 21 days post fertilisation (dpf) and in adult fertile animals. PSA colocalization was assessed with antibodies against recoverin and glutamine synthetase, respectively. Dividing cells in the adult retina were marked by BrdU. Post–embedding techniques with 10nm gold were used for electron microscopic localization of PSA. For controls, PSA was enzymatically removed from the retina by intra–vitreal injections of endoneuraminidase NE. Results: First PSA labelling was observed at 9 dpf in the retina whereas a positive PSA staining was already present at 2 dpf in the brain. Immunoreactivity was found in the outer nuclear layer (ONL), the region of the photoreceptor terminals, and in those parts of the outer plexiform layer located between the horizontal cell bodies and the inner nuclear layer. In contrast to mammals (Bartsch, Kirchhoff, et al. 1990) PSA expression was never observed in the inner parts of the zebrafish retina. In addition, no PSA expression was present in the marginal zone of the zebrafish retina. This pattern remained constant during all further stages of development. PSA immunoreactivity in the ONL was colocalized with recoverin but not with glutamine synthetase. Electron microscopy revealed PSA expression along the cell membrane of photoreceptors and in the terminals of rods. In the adult fish retina new rods form from precursor cells which can be labelled by BrdU; all of the BrdU–positive cells were negative for PSA. Conclusions:Restriction of the PSA expression to the ONL is in accordance with the high cellular plasticity in this part of the retina. PSA expression correlates with the first appearance of rod photoreceptors during eye development and their functional differentiation in the adult zebrafish.
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