If
the rhodopsin-GFP construct lacks the C-terminal sequence (D334-348),
the fusion protein still is transported to the outer segment. In contrast
to the fusion protein with the C-terminal attached, however (see
prior page), the truncated protein also goes to the lateral plasma
membrane and synaptic terminal, i.e. it is delocalized. Delocalized distribution
is also a characteristic of mutated rhodopsins and is correlated with
subsequent death of the rods by apoptosis.
This truncated protein induces retinal degeneration of the rods in our
transgenic frogs. Click on the image to see
that retina. 
Rab8
helps transport rhodopsin to the rod outer segment (ROS). Rab8 is a small
protein that binds GTP. In this form it binds to membranes and helps them
move towards their destination. Rab8 can also hydrolyze GTP to GDP. With
GDP bound, it is inactive, i.e., it acts like a switch. Expression
of rab8 linked to the C-terminal of GFP changes the distribution of the
GFP. Whereas GFP distributes throughout the cytoplasm and enters the nucleus,
the GFP-rab8 fusion protein is excluded from the nucleus. If images of less
saturation are obtained, the GFP-rab8 is found in the Golgi, post-Golgi
vesicles, synapse and on the vesicles clustered below the connecting cilium
that joins the inner to the outer segment. The rab8 constructs were provided
to us by our collaborator Dr. Johan Peranen at the University of Helsinki,
Finland. The experiments are being conducted in collaboration with Dr. Dusanka
Deretic at the University of New Mexico Medical center . Click
on the image to see an enlarged view.
Expression
of mutant rab8 induces a profound loss of rod photoreceptors. These two
models of retinal degeneration offer us the possibility to study cell fratricide
in a cone-rich retina. Click
on the image for access.
