Role of Purpurin as a Retinol-Binding Protein in Goldfish Retina during the Early Stage of Optic Nerve Regeneration: Its Priming Action on Neurite Outgrowth

Abstract

Unlike mammals, the fish optic nerve can regenerate after injury. So far, many growth or trophic factors have been shown as an axon-regenerating molecule. However, it is totally unknown what substance regulates or triggers the activity of these factors on axonal elongation. Therefore, we constructed a goldfish retina cDNA library prepared from the retina treated with optic nerve transection 5 d previously, when it was just before regrowing optic axons after injury. A cDNA clone for goldfish purpurin for which expression was upregulated during the early stage of optic nerve regeneration was isolated from the retina cDNA library. Purpurin was discovered as a secretory retinol-binding protein in developing chicken retinas. Levels of purpurin mRNA and protein transiently increased and rapidly decreased 2-5 d and 10 d after axotomy, respectively. Purpurin mRNA was localized to the photoreceptor cells, whereas the protein was diffusely found in all of the retinal layers. A recombinant purpurin alone did not affect any change of neurite outgrowth in explant culture of the control retina, whereas a concomitant addition of the recombinant purpurin and retinol first induced a drastic enhancement of neurite outgrowth. Furthermore, the action of retinol-bound purpurin was effective only in the control (untreated) retinas but not in those primed (treated) with a previous optic nerve transection. Thus, purpurin with retinol is the first candidate molecule of priming neurite outgrowth in the early stage of optic nerve regeneration in fish.

A distinct effect of transient and sustained upregulation of cellular factor XIII in the goldfish retina and optic nerve on optic nerve regeneration

“…Therefore, during the recent decade we have been searching for regeneration-associated genes involved in fish optic nerve regeneration using fish visual systems (Liu et al, 2002;Matsukawa et al, 2004;Sugitani et al, 2006;Koriyama et al, 2007;Nagashima et al, 2011). We succeeded in cloning a tissue type transglutaminase (TG), a cross-linking enzyme from axotomized goldfish retina (Sugitani et al, 2006).…”

Upregulation of anti-apoptotic factors in upper motor neurons after spinal cord injury in adult zebrafish

“…Immunohistochemistry was performed as described previously (Matsukawa et al, 2004;Nagashima et al, 2009). In brief, antigen retrieval was performed by autoclaving sections at 121 °C for 20 min in 0.01 M citrate buffer (pH 6.0) for Bcl-2, p-Akt and GAP43 immunohistochemistry, or 9 incubating sections with 2 M HCl at 37 °C for 30 min for BrdU immunohistochemistry.…”

“…In optic nerve regeneration, we previously identified a variety of regeneration-associated genes and pathways involved in axonal elongation, such as retinoic acid signaling, retinal transglutaminase, and nitric oxide synthetase/NO signaling (Matsukawa et al, 2004;Sugitani et al, 2006;Koriyama et al, 2009;Nagashima et al, 2009;Sugitani et al, 2012). The next goal is to determine such regeneration-associated genes enabling upper motor neurons to regenerate their axons.…”

Upregulation of IGF-I in the goldfish retinal ganglion cells during the early stage of optic nerve regeneration

“…The retinal explant culture was performed as described previously (Matsukawa et al, 2004a). Briefly, intact (unprimed) or injured (primed) retinas with ON crush 1 or 5 days previously were isolated under sterile condition.…”

“…Furthermore, biochemical and genetic approaches for identifying molecules involved in ON regeneration in fish have recently accumulated (Schwalb et al, 1996;Liu et al, 2002;Matsukawa et al, 2004a;Fisher et al, 2004;Sugitani et al, 2006). However, there are few reports clarifying the reason why fish can regenerate optic axons after injury.…”