Selective upregulation of RB3/stathmin4 by ciliary neurotrophic factor following optic nerve axotomy

In this study, we examined the cellular responses of stathmin-related proteins in the rat retina following optic nerve (ON) axotomy. To examine the distribution of stathmin-related gene products, we performed semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), in situ hybridization (ISH) and immunohistochemical analyses. Retrograde labeling using a fluorescein tracer, fluorogold (FG), was used for the identification of retinal ganglion cells (RGCs). RT-PCR and ISH analyses indicated that the expression of RB3 was specifically increased in the ganglion cell layer (GCL) comparing to other members of stathmin-related gene family examined 3 days following the ON axotomy. When brain-derived neurotrophic factor was administrated intravitreously, the induction of RB3 mRNA sustained up to 7 days after axotomy, although the peak induction level was unchanged. In contrast, ciliary neurotrophic factor (CNTF) administration increased the peak level of RB3 mRNA induction significantly at 3 days after axotomy. Immunohistochemistry in combination with the retrograde labeling of axotomized cells by FG revealed that RB3 was increased following axotomy in FG-labeled RGCs. These data suggest that RB3 is the unique response protein in the stathmin-related proteins following ON axotomy and the induced RB3 may play a critical role in the CNTF-induced response on the axotomized RGCs, e.g. axonal regeneration and/or neuroprotection.