Controlled rod cell ablation in transgenic Xenopus laevis.
OBJECTIVE
Because of their high cone/rod ratio, Xenopus laevis may be a useful system for examining rod-cone interactions during retinal degeneration and mechanisms that underlie secondary cone degeneration. The authors developed an inducible model of retinitis pigmentosa (RP) in X. laevis to investigate these issues.


METHODS
The authors generated transgenic X. laevis that express a modified caspase-9 (iCasp9) under the control of the X. laevis rod opsin promoter. iCasp9 is activated by the compound AP20187, resulting in an apoptotic cascade. Confocal microscopy, Western blot analysis, and electroretinography (ERG) were used to determine the effects of AP20187 on transgenic retinas.


RESULTS
AP20187 induced rod cell apoptosis in transgenic tadpoles and postmetamorphic frogs. Longitudinal results indicate rod cell death led to cone cell dysfunction within 3 months; however, cone function was reinstated after 6 months. Returning cone function may be associated with increased numbers of morphologically normal cone cells and thickening of the inner nuclear layer.


CONCLUSIONS
These studies indicate that X. laevis may be a useful system for examining cone dysfunction associated with rod death in RP and longer term regeneration of cone responses. This inducible model of RP is unique in that rod death proceeds through a well-understood mechanism, rod death can be carefully controlled to occur at any stage of development, and the stimulus for rod death can be removed at any time.
Hamm
Lisa M
LM
Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, Canada.
Tam
Beatrice M
BM
Moritz
Orson L
OL
D000818:Animals; D030801:Animals, Genetically Modified; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D004596:Electroretinography; D004789:Enzyme Activation; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D055355:Opsins / Q000235:genetics; D011401:Promoter Regions, Genetic; D012160:Retina / Q000201:enzymology / Q000503:physiopathology*; D017949:Retinal Cone Photoreceptor Cells / Q000201:enzymology / Q000473:pathology*; D017948:Retinal Rod Photoreceptor Cells / Q000201:enzymology / Q000473:pathology*; D012174:Retinitis Pigmentosa / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D016559:Tacrolimus / Q000031:analogs & derivatives* / Q000494:pharmacology; D014982:Xenopus laevis / Q000235:genetics
C463061:AP20187; D055355:Opsins; D049452:Green Fluorescent Proteins; D053453:Caspase 9; D016559:Tacrolimus