Thyroid Hormone Induces a Time-Dependent Opsin Switch in the Retina of Salmonid Fishes
Bibliographic record
Abstract
PURPOSE: To determine the role of thyroid hormone in inducing the UV (SWS1)-to-blue (SWS2) opsin switch in the retina of two salmonid fishes, the coho salmon (Oncorhynchus kisutch) and the rainbow trout (O. mykiss). METHODS: Fish were treated with thyroid hormone (T(4)) or the vehicle solution (0.1 M NaOH, control), exogenously or by intraocular injection, at different life history stages. Microspectrophotometry and in situ hybridization with riboprobes against the SWS1 and SWS2 opsins were used to reveal the dynamics of opsin expression in treated and control animals. To assess whether thyroid hormone induced differentiation of retinal progenitor cells into cones, treated and control fish were injected intraocularly with bromodeoxyuridine (BrdU) and the number of proliferating cells in the outer nuclear layer (ONL) determined. These observations were accompanied by histologic counts of cone densities. RESULTS: Thyroid hormone induced a reversible UV-to-blue opsin switch in differentiated single cones of juvenile salmonids (alevin and parr stages), but failed to exert any effect in the retina of older fish (smolt stage). The switch progressed from the ventral to the dorsal retina in clockwise fashion. Thyroid hormone did not induce cone density changes or alterations in the number of BrdU-labeled cells, which were the same in control and treated animals. CONCLUSIONS: Thyroid hormone induces a UV (SWS1)-to-blue (SWS2) opsin switch in the retina of young salmonid fishes that is identical with that occurring during natural development. The switch occurs in differentiated photoreceptors, is reversible (maintained by thyroid hormone exposure), and can be induced only before its natural onset. Thyroid hormone did not cause changes in the number of proliferating cells in the ONL. These results conform to the dynamics of thyroid hormone-induced opsin expression in the mouse and are consistent with the opsin plasticity found in differentiated photoreceptors of the fruit fly, Drosophila melanogaster. This work establishes a role for thyroid hormone in triggering opsin switches in the vertebrate retina.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".