Purchase this article with an account.
Stephanie Sloat, Connor Jankowski, Rachel Hutto, Michelle Giarmarco, Whitney M Cleghorn, Van Tran, Gayatri Shandar, Susan E Brockerhoff, James Hurley; Quantification of Mitochondrial Structure in Photoreceptors. Invest. Ophthalmol. Vis. Sci. 2016;57(12):566. doi: https://doi.org/.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Rods and cones have unique energetic demands that change in light and darkness. Mitochondria in other cell types can undergo fission and fusion in response to changing metabolic demands. We hypothesized that photoreceptor mitochondria have a specialized morphology that accommodates the unique metabolic needs of photoreceptor neurons.
We used Serial Block-Face Scanning Electron Microscopy (SBEM) to collect images of photoreceptor inner segments (IS) containing mitochondria. We used TrakEM2 software from ImageJ to follow structures through image stacks and render three dimensional structures. Samples were collected from wild-type mice and zebrafish under light and dark conditions.
Light adapted mice have 8.0±3.1 mitochondria per rod IS compared to 36.3±3.1 mitochondria per cone IS, a 4.5-fold difference. Rod mitochondria are long, thin, and oriented lengthwise along the edge of the plasma membrane of the IS, leaving a void in the middle (Figure 1). Mouse cones are also oriented lengthwise, but are less ordered. We found no difference between light and dark adapted mouse rods and cones. Light adapted zebrafish rods have 17.3±2.1 mitochondria per IS, whereas single cones have approximately 80 mitochondria (n=1), also reflecting 4.5-fold difference between rods and cones. Mitochondria in zebrafish rods are also oriented lengthwise, but form tight clusters that reach the edge of the cell. Zebrafish cone mitochondria are globular in shape and form tight clusters in the distal portion of the IS (Figure 2). In zebrafish rods, total mitochondria quantity and morphology do not change in darkness, but total mitochondrial volume increases 340%. In zebrafish single cones, darkness increases the number of mitochondria 15-fold and mitochondrial volume 20-fold.
Photoreceptors exhibit a wide array of mitochondrial shape, size and quantity. Mitochondria in mouse rods and cones have a fixed morphology in light and darkness, whereas there are differences in the numbers of mitochondria in zebrafish rods and cones in light and darkness. Our results are consistent with our hypothesis that photoreceptors with different metabolic demands will exhibit unique mitochondrial morphology.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Figure 1: 3D reconstruction of mitochondria from the inner segment of light adapted mouse rod.
Figure 2: 3D reconstruction of mitochondria from the inner segment of light adapted zebrafish single cone.
This PDF is available to Subscribers Only