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Retinal degeneration in the pcd/pcd mutant mouse: accumulation of spherules in the interphotoreceptor space
1Department of Ophthalmology, University of Southern California School of Medicine, Los Angeles.
Insights
The Purkinje cell degeneration (pcd) mouse model exhibits retinal photoreceptor cell loss. Ultrastructural analysis reveals extracellular vesicles in the retina, potentially linked to this degeneration.
Area of Science:
- Neuroscience
- Cell Biology
- Ophthalmology
Background:
- The Purkinje cell degeneration (pcd) mutant mouse model is characterized by progressive loss of cerebellar Purkinje cells and retinal photoreceptor cells.
- Photoreceptor degeneration in pcd/pcd mice occurs in distinct phases, with significant loss by 5 weeks of age and continued loss throughout the first year.
Purpose of the Study:
- To investigate the ultrastructure of developing photoreceptor cells in pcd/pcd mutant mice.
- To further characterize the previously reported retinal vesicles associated with the pcd mutation using advanced microscopy techniques.
Main Methods:
- Transmission electron microscopy (TEM) was employed to examine the morphology and distribution of extracellular vesicles.
- Scanning electron microscopy (SEM) was used to elucidate the origin and three-dimensional structure of these vesicles.
- The study focused on photoreceptor cells in the retina of pcd/pcd mice at specific post-natal developmental stages (P25 and P40).
Main Results:
- TEM revealed abundant, membrane-bound, amorphous extracellular vesicles (125-370 nm) in the inner segment region of photoreceptor cells at post-natal day 25.
- SEM suggested these vesicles originate from outpocketing and pinching off of the plasma membrane in the mitochondria-rich region of the rod inner segment, forming spherules.
- At P25, spherules were concentrated in the interphotoreceptor space; by P40, they were displaced to the level of rod outer segments and the subretinal space.
Conclusions:
- The study characterizes novel extracellular spherules in the pcd/pcd mouse retina, originating from rod inner segments.
- These findings provide ultrastructural insights into the cellular mechanisms underlying photoreceptor degeneration in the pcd mutant.
- Further research is warranted to determine the precise role of these spherules in photoreceptor cell death and retinal dysfunction.
Abstract:
The Purkinje cell degeneration (pcd) mutant mouse rapidly loses cerebellar Purkinje cells and about 50% of its retinal photoreceptor cells at between 3 and 5 weeks of age, and thereafter slowly loses the remaining photoreceptor cells during the first year of life. An ultrastructural study of the developing photoreceptor cells of the pcd/pcd retina was undertaken using both transmission and scanning electron microscopy to characterize further the previously reported retinal vesicles associated with this mutation. Transmission electron microscopy (TEM) revealed an abundance of 'bead-like' vesicles or excrescences in the extracellular matrix surrounding the inner segment region at post-natal day (P) 25. The vesicles are membrane bound, amorphous in appearance and vary in size from 125 to 370 nm. Scanning electron microscopy suggests that the vesicles seen with TEM are actually spherules formed from outpocketing and pinching off of the plasma membrane in the mitochondria-rich region of the rod inner segment. At P25, the spherules are concentrated in the interphotoreceptor space at the level of rod inner segments; at P40, however, they are displaced from their origin and appear mostly at the level of rod outer segments and in the subretinal space.