Cone survival despite rod degeneration in XOPS-mCFP transgenic zebrafish.
OBJECTIVE
In animal models of retinitis pigmentosa, rod photoreceptor degeneration eventually leads to loss of cone photoreceptors. The purpose of this study was to characterize a transgenic model of rod degeneration in zebrafish.


METHODS
Zebrafish transgenic for XOPS-mCFP, a membrane-targeted form of cyan fluorescent protein driven by the Xenopus rhodopsin promoter, were generated by plasmid injection. Immunohistochemistry was used to detect cell type, proliferation, and TUNEL markers in larval and adult retinas. Rod- and cone-specific transcripts were detected by RT-PCR. Visual responses in transgenic adults were measured by electroretinogram.


RESULTS
The XOPS promoter directed specific expression of mCFP in rods by 55 hours post fertilization (hpf). Rods in XOPS-mCFP heterozygotes began dying at 3.5 days post fertilization (dpf) and were almost completely absent by 5 dpf. A few rods were observed at the retinal margin, and numerous immature rods were observed in the outer nuclear layer (ONL) of transgenic adults. Apoptosis was increased in the ONL of larval and adult transgenic animals, and an elevation of rod precursor proliferation in adults was observed. ERG analysis confirmed that rod responses were absent in this line. Cone morphology and electrophysiology appeared normal in transgenic animals up to 7 months of age.


CONCLUSIONS
The XOPS-mCFP transgene causes selective degeneration of rods without secondary loss of cones in animals up to 7 months of age. This raises important questions about the significance of rod-cone interactions in zebrafish and their potential as a model of human inherited retinal degenerations.
Morris
Ann C
AC
Biomedical Research Facility, Department of Biological Science and Program in Neuroscience, Florida State University, Tallahassee, Florida 32306, USA. amorris@bio.fsu.edu
Schroeter
Eric H
EH
Bilotta
Joseph
J
Wong
Rachel O L
RO
Fadool
James M
JM
D000818:Animals; D030801:Animals, Genetically Modified; D017209:Apoptosis; D002470:Cell Survival / Q000502:physiology; D004195:Disease Models, Animal; D004596:Electroretinography; D019084:Fluorescent Antibody Technique, Indirect; D049452:Green Fluorescent Proteins / Q000235:genetics*; D020287:In Situ Nick-End Labeling; D018613:Microscopy, Confocal; D010957:Plasmids; D011993:Recombinant Fusion Proteins / Q000235:genetics*; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology* / Q000502:physiology; D012162:Retinal Degeneration / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism / Q000473:pathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012243:Rhodopsin / Q000235:genetics*; D019076:Transgenes; D015027:Zebrafish / Q000235:genetics*
C485182:Cyan Fluorescent Protein; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D012243:Rhodopsin