The photoreceptor outer segment is the site of phototransduction. The phototransductive disk membranes of each outer segment are continually renewed, resulting in a large amount of membrane trafficking from the photoreceptor inner segment to the photoreceptor outer segment, and, eventually, to the retinal pigmented epithelial cells. The formation of outer segment disk membranes is a major process of membrane remodeling, and the renewal is central to photoreceptor cell biology and disease. Competing hypotheses, resulting from differing EM observations, have been presented in the literature to account for how these disk membranes are formed. It has been argued that the different results are due to different methods of tissue fixation. However, in addition to differen methods of tissue preservation, the different studies have focused on different species, and, moreover, time of day has not been considered (yet, there is evidence of a daily cycle in disk membrane growth). The proposed research will advance our knowledge of the organization of nascent rod outer segment disks, and thus mechanisms of disk morphogenesis, by addressing the gaps in published work, and by applying novel technologies to this problem. We will study mouse and monkey retinas. With mouse, we will take the method of preservation of the basal disk membranes to a higher level by using high-pressure freezing/freeze substitution, and thus obviate potential artifacts introduced by chemical primary fixation. Further, we will perform EM serial tomography of the basal rod disks in mouse and monkey, in order to obtain nano-scale, 3D resolution of their organization. The superior resolution afforded by this method, together with the 3D imagery, will enable a complete analysis of membrane connections and continuities that has been unavailable by the methods used to date. This novel approach, will allow us to focus on defining the fundamentally important organization of newly formed basal disks in rod outer segments. Following the studies on WT mouse, we will perform comparable analyses, using three lines of mutant mice that possess defective disk morphogenesis. EM tomographic analyses of the aberrant disks in these mice will provide insight into the normal process, as well as increase our understanding of mechanisms underlying the forms of retinitis pigmentosa, cone-rod dystrophy, and macular degeneration that these mice model. Overall, this proposal will apply state-of-the-art EM technology and 3D image analyses that will provide a major advance in one of the most essential cell biological problems in photoreceptor biology and disease.

Public Health Relevance

The proposed research will provide a fundamental mechanistic understanding of the way disk membranes of the photoreceptor outer segment are formed. It will apply novel 3-D image analyses to resolve nano-level structures of nascent disk membranes, and thus take the field of photoreceptor cell biology a major step forward. The research will include studies of mouse models retinal degeneration, specifically retinitis pigmentosa, cone-rod dystrophy, and macular degeneration, and thus will provide a basis for understanding the pathogenesis of these forms of blindness.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY024667-03
Application #
9248370
Study Section
Biology of the Visual System Study Section (BVS)
Program Officer
Neuhold, Lisa
Project Start
2015-04-01
Project End
2019-03-31
Budget Start
2017-04-01
Budget End
2018-03-31
Support Year
3
Fiscal Year
2017
Total Cost
$345,937
Indirect Cost
$60,187
Name
University of California Santa Barbara
Department
Type
Organized Research Units
DUNS #
094878394
City
Santa Barbara
State
CA
Country
United States
Zip Code
93106
Volland, Stefanie; Williams, David S (2018) Preservation of Photoreceptor Nanostructure for Electron Tomography Using Transcardiac Perfusion Followed by High-Pressure Freezing and Freeze-Substitution. Adv Exp Med Biol 1074:603-607
Goldberg, Andrew F X; Moritz, Orson L; Williams, David S (2016) Molecular basis for photoreceptor outer segment architecture. Prog Retin Eye Res 55:52-81
Volland, Stefanie; Hughes, Louise C; Kong, Christina et al. (2015) Three-dimensional organization of nascent rod outer segment disk membranes. Proc Natl Acad Sci U S A 112:14870-5