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

Abstract

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.

Müller glia: Stem cells for generation and regeneration of retinal neurons in teleost fish

“…This has not been described in other teleost species, and its significance for retinal histogenesis or visual function is not known. The Müller glial processes in the ONL of adult zebrafish retina express abundant amounts of a modified form of NCAM (neural cell adhesion molecule), polysialic acid–NCAM (PSA–NCAM), associated with embryonic and adult neurogenesis, and this may provide microenvironment cues necessary for continued rod photoreceptor generation (Kustermann et al, 2010). …”

“…NCAM is expressed in Müller glia in the unlesioned adult zebrafish retina, but only on the Müller glial processes in the ONL, where it has been suggested to provide directional migratory cues and a microenvironment for undifferentiated rod precursors (Kustermann et al, 2010). Transcription of ncam is decreased in Müller glia through 36 h after acute light lesion (Qin et al, 2009), but transcription levels increase slowly during a chronic light lesion, as measured by microarray analysis of whole retina homogenates (Kassen et al, 2007).…”

“…Although the characteristics of the ECM in and around the neurogenic clusters in the regenerating fish retina have not been examined, in the intact retina the permissive version of NCAM, PSA–NCAM, is expressed on the apical processes of Müller glia associated with on-going production of rod photoreceptors (Kustermann et al, 2010). The addition of PSA to NCAM can disrupt cell adhesion, and it has been proposed that the balance between PSA–NCAM, NCAM, and N-cadherin regulates the neurogenic niche in the brain (Gascon et al, 2010).…”

Mapping the Expressed Glycome and Glycosyltransferases of Zebrafish Liver Cells as a Relevant Model System for Glycosylation Studies

“…O -mannosylation is necessary for normal embryonic development, since the inhibition of protein O -mannosyltranferase activities induces severe phenotypes in embryos . Terminal polysialylation of the N -glycans of the neural cell adhesion molecule is required for a wide range of processes in developing animals including axon fasciculation and commissural axonal guidance, myotome formation, genesis of retina , and neuronal migration not only in embryos but also in adult fishes . Similarly, core fucosylation of N -glycans appears to be required for proper midline patterning during embryogenesis .…”

Stemming vision loss with stem cells

“…The retinal (41,42) and subretinal (43) tissue microenvironments can modulate the functionality of injected autologous or allogeneic cells by inducing differentiation to several different cell types.…”