The effect of elevated oocyte triiodothyronine content on development of rainbow trout embryos and expression of mRNA encoding for thyroid hormone receptors
Bibliographic record
Abstract
The ability of developing rainbow trout Oncorhynchus mykiss embryos to compensate for elevated oocyte triiodothyronine (T3) content and whether elevation of oocyte T3 content within a physiologically meaningful range affects growth rates of the embryo or the expression of genes encoding for thyroid hormone receptors α(TRα) and β(TRβ) were examined. Oocytes were immersed in ovarian fluid alone (control) or T3‐enriched ovarian fluid prior to fertilization and water hardening, to induce a dose‐dependant increase in oocyte T3 content of c. 3 (control), c. 30 (LT3) or c. 110 ng egg−1(HT3). To examine the interaction of embryo somatic growth with altered thyroid state more effectively, the embryos were reared at two ambient temperatures (8·5 and 5·5°C ) to induce different growth rates. A significant decline in whole embryo T3 content was measured in the T3‐treatment groups reared at both water temperatures by 3 weeks post‐fertilization (dpf), and may have reflected the action of outer ring monodeiodinase, which was present in microsomes prepared from embryos 23 dpf. Whole embryo T3 levels in the HT3 group, however, remained higher than controls until phase 2 of development [the onset of endogenous thyroid hormone (TH) release]. This suggested that the embryos exerted some control over their response to exogenous TH, but that there was a limit to the level of control exerted by the embryonic tissues. Reverse transcriptase‐polymerase chain reaction (RT‐PCR) revealed the presence of mRNA encoding for the two TR isoforms as early as 26 dpf, and quantitative real‐time RT‐PCR (qPCR) was used to examine the effect of elevated oocyte T3 content on the expression of these TR genes in embryos raised at 8·5 and 5·5° C, and sampled at similar developmental stages prior to the onset of embryonic TH synthesis, to ensure that the oocyte T3 was the only source of TH exposure to the embryo. There was a suppression of the TRα gene expression in the control 5·5° C group relative to the control 8·5° C group. In addition, both TRα and TRβ mRNA accumulation was lower, relative to the controls, in the LT3 treatment group reared at 8·5° C suggesting a suppressive effect of the lower level of T3 treatment on the TR gene expression. Conversely, there were no differences from controls in the HT3 treatment group, possibly indicating that this level of exposure overrides the down‐regulating capacity of the embryo. Similar patterns were seen for TRα and TRβ mRNA accumulation in embryos reared at 5·5° C, but because of the temperature suppressed level of TRα mRNA in the controls, significant affects of the LT3 treatment were only found for TRβ. There were no measurable effects of T3 treatment on oocyte fertility or embryo somatic growth for either temperature treatment group, nor was somatic growth hormone content (measured only in the 8·5° C treatment group) apparently related to in ovo T3 levels. The results suggest that altered in ovo T3 levels, within the ranges used here, do not induce marked affects on embryo development, probably because of the ability of the embryo to maintain the integrity of its TH milieu.
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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 | 0.001 |
| 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".