Abstract
Purpose: :
Rab GTPases regulate vesicular trafficking in eukaryotic cells. Recent studies highlight the importance of Rab6 and other family members in maintenance of adult photoreceptor outer segments. We investigated the distribution of Rab6 during development in the wild type (wt) mouse retina and the rd1 mouse retina, where photoreceptors degenerate prior to outer segment formation.
Methods: :
Eyecups were harvested at various developmental ages between birth and postnatal day 21 from wt and rd1 littermates. Tissue was fixed, cryoprotected, and processed for immunohistochemistry using a primary antibody against Rab6. Statistical analysis was done using ImageJ software.
Results: :
In the P4 wt retina, Rab6-like immunoreactivity (LIR) appears as punctate staining throughout the IPL and in bordering cells in both the ganglion cell and neuroblast layers. By P8, Rab6-LIR is seen in both plexiform layers, with intense labeling of processes in distinct sublamina in the IPL. Staining is also apparent throughout the GCL, INL, and more sparsely in the ONL. Some Rab6-LIR is seen at the ONL outer margin. By P12, all layers of the retina are labeled, including punctate Rab6-LIR in the developing inner segments (IS). The overall pattern of Rab6-LIR in the rd1 retina is similar to the wt, although at most time points the developing IS contain brighter and larger Rab6-positive punctae. Surprisingly, the inner plexiform layer is more intensely stained in the rd1 retina at early time points.
Conclusions: :
Our results suggest Rab6 plays an important role in vesicular transport throughout the retina during early postnatal development. Differences seen in the developing IS of the rd1 retina compared to wt are of particular interest. These observations are consistent with previous findings from EM studies demonstrating abnormal vesicular trafficking by P5 in rd1 photoreceptors.
Keywords: retinal degenerations: cell biology • photoreceptors • retinal development