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M. Parrilla-Monge, C. Lillo, E. Cid, J. Herrero, J. Lara, J. Aijon, A. Velasco; Pax2 in a Continuous Growth and Regeneration Model of the Visual System. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4363. doi: https://doi.org/.
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Pax2 is a transcription factor involved in axonal guidance and glial differentiation in optic nerve (ON) development. We study the role of Pax2 in the visual system of adult goldfish which is continuously adding new axons and is capable of regenerate and restore vision after a lesion.
We used 12 controls and 15 goldfish injured by cryo-lesion of the retina periphery which were sacrificed 2, 7, 15, 30 and 60 days post-injury. Using Western Blot (WB) we checked IgG anti-Pax2 immunospecificity. To analyse the Pax2+ cells, we used electron and optic immunohistochemistry using double labelling with astrocyte (GFAP, GS and S100), dividing cells (PCNA and BrdU) and growing axon (Zn8) markers. The variations in Pax2 expression were studied by PCR.
We demonstrate by WB the presence of Pax2 in the adult goldfish ON. Pax2+ cells are only situated in the ON. Moreover, they are mostly located in the optic nerve head (ONH), increase their number along the pre-chiasmatic segment and start to decrease from the optic chiasm to the optic tract. By electron microscopy, we found that there were two astrocyte populations in the ON: Pax2+ and Pax2- cells. In the ONH, Pax2+ cells showed a different organization from the rest of the ON. There are astrocytes Pax2+/GFAP+ situated limiting the retina, the vitreous humour and the central artery with the ON. In the optic disc they are closely associated with the vitreal processes of the Müller cells labelled with both GFAP+ and GS+. Some Pax2+ cells can also divide (Pax2+/PCNA+) and others are situated longitudinally to the growing axons (Zn8+) and intimately associated with them. With immunohistochemistry and PCR techniques, we found that Pax2 expression falls in the absence of growing axons.
The maintenance of Pax2 in the ON, especially in the ONH, could be related to the continuous growth capacity of the visual system of goldfish. Pax2 could take part in both the new arriving axon guidance and packing, and in the continuous new glial cells forming and their correct differentiation.
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