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mRNAs coding for proteins of the cGMP cascade in the degenerative retina of the rd mouse
1Jules Stein Eye Institute, UCLA School of Medicine 90024.
Abstract:
A lesion in cGMP metabolism has been hypothesized to cause retinal degeneration in rd mice. Available cloned cDNAs coding for proteins involved in the cGMP cascade have been used to compare the corresponding retinal RNAs in the degenerative (rd/rd) mouse at 8-11 days with those in the 8-11-day-old morphologically normal (rd/+) and adult normal (+/+) mice. Northern analysis of these RNAs hybridized to the specific 32P-labeled cDNA probes for G-protein, 48,000 MW protein and opsin, indicates in each case, that the corresponding transcripts are made in the rd/rd mouse retina and that there are no overt differences in their size compared to the transcripts hybridized in the rd/+ or +/+ mouse retinas. Although a defect in the phosphorylation of opsin has been described in rd mice, no difference was found in the transcripts hybridized by a cDNA probe corresponding to the region of the opsin molecule on which phosphorylation occurs. We do find, however, that labeled bovine-derived opsin cDNA recognizes five different RNA size classes in mouse and bovine retinas. Control experiments were performed to confirm that the RNA hybridized by opsin cDNA was not due to non-specific hybridization to unrelated RNAs.
Insights
Researchers investigated retinal degeneration in rd mice, finding that key cGMP cascade protein transcripts are present and normal in affected retinas. This suggests the defect lies elsewhere, not in the basic production of these essential proteins.
Area of Science:
- Molecular Biology
- Genetics
- Neuroscience
Background:
- Retinal degeneration in rd mice is linked to cGMP metabolism.
- Understanding the molecular basis of this degeneration is crucial for potential therapies.
Purpose of the Study:
- To investigate the expression levels and sizes of transcripts for proteins in the cGMP cascade in rd mice.
- To determine if altered gene expression contributes to retinal degeneration in rd mice.
Main Methods:
- Northern blot analysis was used to compare retinal RNA from degenerative (rd/rd) mice with normal (rd/+) and (+/+) mice.
- Specific cDNA probes for G-protein, 48,000 MW protein, and opsin were employed.
Main Results:
- Transcripts for G-protein, 48,000 MW protein, and opsin were detected in rd/rd mouse retinas.
- No significant differences in transcript size or presence were observed between rd/rd and normal mouse retinas.
- While opsin phosphorylation defects are known, the corresponding opsin transcripts showed no differences.
Conclusions:
- The study indicates that the basic production of key cGMP cascade proteins is not the cause of retinal degeneration in rd mice.
- The findings suggest that the defect in rd mice may lie in post-transcriptional regulation or other cellular processes, rather than transcript abundance or size.