Temperature induced variation in gene expression of thyroid hormone receptors and deiodinases of European eel (Anguilla anguilla) larvae.

Thyroid hormones (THs) are key regulators of growth, development, and metabolism in vertebrates and influence early life development of fish. TH is produced in the thyroid gland (or thyroid follicles) mainly as T4 (thyroxine), which is metabolized to T3 (3,5,3'-triiodothyronine) and T2 (3,5-diiodothyronine) by deiodinase (DIO) enzymes in peripheral tissues. The action of these hormones is mostly exerted by binding to a specific nuclear thyroid hormone receptor (THR). In this study, we i) cloned and characterized thr sequences, ii) investigated the expression pattern of the different subtypes of thrs and dios, and iii) studied how temperature affects the expression of those genes in artificially produced early life history stages of European eel (Anguilla anguilla), reared in different thermal regimes (16, 18, 20 and 22 °C) from hatch until first-feeding. We identified 2 subtypes of thr (thrα and thrß) with 2 isoforms each (thrαA, thrαB, thrßA, thrßB) and 3 subtypes of deiodinases (dio1, dio2, dio3). All thr genes identified showed high similarity to the closely related Japanese eel (Anguilla japonica). We found that all genes investigated in this study were affected by larval age (in real time or at specific developmental stages), temperature, and/or their interaction. More specifically, the warmer the temperature the earlier the expression response of a specific target gene. In real time, the expression profiles appeared very similar and only shifted with temperature. In developmental time, gene expression of all genes differed across selected developmental stages, such as at hatch, during teeth formation or at first-feeding. Thus, we demonstrate that thrs and dios show sensitivity to temperature and are involved in and during early life development of European eel.

Time and concentration dependency of MacroGard® induced apoptosis.

In previous studies an effect of ß-glucan on apoptosis in fish was noted and in this investigation we determine the time and concentration dependency of this effect. Primary cell cultures of pronephric carp cells were incubated for 6, 24, 48 h with various concentrations ranging from 0 to 1000 µg/ml of MacroGard(®) ß-glucan. Apoptosis was monitored via acridine orange staining. Results indicate a clear effect of time and concentration on the induction of apoptosis in vitro, with only concentration ≥500 µg/ml causing significantly higher percentages of apoptotic cells. Apoptosis was detected after 6 h. This concentration dependent effect has to be considered when studying apoptosis in relation to immunostimulation.

The influence of dietary ß-glucan, PAMP exposure and Aeromonas salmonicida on apoptosis modulation in common carp (Cyprinus carpio).

The association between ß-glucan (MacroGard®) supplemented feed and apoptosis in immune-related organs of common carp (Cyprinus carpio) was studied using fluorescence microscopy and real-time PCR. In addition the effect of Aeromonas salmonicida, LPS and Poly(I:C) injections on this relationship was evaluated. Whilst acridine orange staining revealed that apoptosis levels were independent of MacroGard® and LPS/Poly(I:C) administration or their combination, it was shown that injection with A. salmonicida increased the percentage of apoptotic cells irrespective of the feeding regime. It was apparent that in all the treatments gene expression profiles displayed organ and time dependency. For example no effect was observed at 7 days of MacroGard® administration while 25 days of feeding led to increased iNOS expression and differential up-regulation of anti- or pro-apoptotic genes depending on organ. This may indicate differences in NO sensitivity. MacroGard® also led to an elevation of pro- as well as anti-apoptotic genes in LPS or Poly(I:C) injected fish, while LPS/Poly(I:C) alone had little effect. A. salmonicida caused enhanced iNOS expression and it is possible that the type of apoptosis pathway induced is organ dependent as Caspase 9 is induced in mid-gut but not in pronephros. These results indicate that MacroGard® feeding alone or in combination with other pathogenic factors did not induce significant apoptosis in immune organs.