Spatiotemporal expression patterns of N-syndecan, a transmembrane heparan sulfate proteoglycan, in developing retina.

PURPOSE: N-syndecan is a transmembrane heparan sulfate proteoglycan, that is highly expressed in neural tissues. In the current study, changes in N-syndecan expression during retinal development were examined.
METHODS: Localization of N-syndecan in developing rat retina was examined by immunohistochemistry and in situ hybridization. The amount of the core protein was evaluated by immunoblot analysis, using retinal homogenates at various developmental stages. In addition, mRNA expression was semiquantified by reverse transcription-polymerase chain reaction (RT-PCR). To understand better the localization of N-syndecan in retinal neuronal cells, we performed immunocytochemistry using retinal ganglion cells in culture.
RESULTS: N-syndecan is highly expressed in nerve fiber-rich layers of the retina at early postnatal stages (between postnatal day [P]0 and P14). In contrast, immunoreactivity was faint during embryonic stages and late postnatal stages. In addition, in retinal flatmounted sections, N-syndecan immunoreactivity was observed on the axons of retinal ganglion cells. Intense signals were observed in the ganglion cell layer during in situ hybridization. Immunoblot analyses demonstrated that the amount of N-syndecan core protein reached a peak at approximately P14. The RT-PCR analyses using N-syndecan primers showed that an intense amplified band was observed in the cDNA derived from P14 retinas, whereas only faint bands were detected in the embryonic day (E)16 and P42 retinas. In retinal ganglion cells in culture, N-syndecan was located on the long, extended neurites.
CONCLUSIONS: The data show that N-syndecan is transiently expressed, primarily in retinal neural fibers, during retinal development, indicating that it may be involved in formation of the retinal neural network.