Abstract
Purpose: :
Retinal ganglion cells (RGCs) lose their regenerative capacity through early postnatal development. Mitochondria are key players in RGC survival and potentially in axon regeneration. In order to further understand how mitochondria regulate survival and regeneration, we investigated the differences in mitochondrial size and mass throughout specific developmental stages.
Methods: :
Retinal wholemounts and optic nerves were obtained from transgenic Thy1/cox8A-mtCFP mice at embryonic (E) and postnatal (P) days, E18 through adult. Samples were perfused or fixed by immersion for 2-3 hours with 4% PFA at room temperature and then mounted and imaged by confocal microscopy, examining RGC axons in the nerve fiber layer and optic nerve. Images were analyzed using ImageJ. A limited age range was also examined using electron microscopy (EM) and analyzed in Axiovision.
Results: :
Mitochondria were detected in RGC axons in the nerve fiber layer and optic nerve using both fluorescence and EM. Mitochondrial size (per mitochondria) and mass (per axon area) in the nerve fiber layer and optic nerve increased significantly from P9 until adulthood, with a particularly abrupt increase from P13-P15.
Conclusions: :
Mitochondrial size and mass in RGC axons in the retina and optic nerve increase significantly during a short postnatal window coincident with eye opening. This increase may be light- or activity-dependent, and further experiments manipulating light and activity are planned to investigate this phenomenon. Determining mitochondrial dynamics and distribution may lead to new approaches to enhance RGCs’ survival and regeneration.
Keywords: ganglion cells • mitochondria • development