Abstract
Purpose:
The optic nerve lamina (ONL) is a unique optic nerve structure bordering the retina and optic nerve. The ONL has a rich vasculature supply compared with rest of the optic nerve, and plays an important role in many optic nerve diseases. We recently found that there are abundant Sox2+ cells in the adult lamina. Sox2 is a nuclear transcription factor, essential for the pluripotency of adult neural stem cells (NSC) in central nervous system (CNS). We wanted to characterize these Sox2+ cells in order to have a better understanding of this unique region.
Methods:
6 wild type mice (C57BL/6J) at age postnatal day 30-36 were utilized in the study. Mice were perfused with 4% paraformaldehyde. The optic laminae with approximately 0.5mm optic nerve were dissected and post fixed in PFA over night, and transferred to PBS, then 30% sucrose, and embedded in OCT and quickly frozen in dry ice. Ten micron thick frozen sections were prepared for immunohistochemical analysis. We performed immunohistochemistry using antibodies to Sox2, Nestin, GFAP, Ki67, Ng2, NeuN, Laminin. Slides were examined on an Olympus 900 laser confocal microscope.
Results:
Sox2+ cells are abundant in the ONL and fewer in the distal ON. In the retina, Sox2+ cells are located in the inner nuclear and ganglion cell layers. Sox2+ cells in ONL and ON are strongly associated with GFAP (glial astrocyte and neural stem cell marker), as well as nestin (neural stem cell marker). Some Sox2+ cells in the ONL are Ki67 positive. The Sox2 expressing cells in the ONL and their association with the other cell markers are very similar to those seen in the CNS subgranular zone (SGZ) in mice of same age. No association of Sox2+ and iba1 (macrophage marker) was seen, nor were Ng2 (oligodendrocyte precursor) or laminin (blood vessel). In the retina, Sox2+ cells are not clearly associated with GFAP, or nestin. They do not co-localize with NeuN (neuron marker) or Ki67.
Conclusions:
Sox2+ cells are abundantly expressed in the adult mouse ONL. Their expression pattern and their associations with other stem cell markers such as nestin, and mitotic markers such as KI67, are similar to what have seen in SGZ. Sox2+ cells in the retina do not associate with GFAP, implying that these cells may be of a different type. Collectively, these findings suggest that similar to the pluripotent neural stem cells seen in the SGZ, ONL Sox2+ cells may possess the ability to develop into other cell types.