Ontogeny of thyroid hormones, cortisol, hsp70 and hsp90 during silver sea bream larval development.

We studied the profiles of silver sea bream (Sparus sarba) thyroxine (T(4)), triiodothyronine (T(3)), cortisol and the heat shock protein (hsp) families hsp70 and hsp90 during larval development. Eggs from sexually mature female sea bream were fertilized and larvae were collected at incremental time intervals between 1-46 days post hatch (dph). Both T(4) and T(3) were detected in 1 dph larvae and it was found that both increased as development progressed with a distinct surge in amounts between 21-35 dph, a time associated with direct development of larvae to juveniles. Cortisol increased from 1 dph reaching a maximum and constant level from 35 dph onwards. Using RT-PCR coupled with radioisotope hybridization of immobilized cDNA we assessed the transcript levels of hsp70 and it was found that transcript remained unaltered between 1-14 dph before progressively increasing. Immunoblotting was used to study the larval concentrations of hsp70 and hsp90 and it was found that hsp70 was not significantly changed between 1-14 dph whereas hsp90 increased from 1 dph onwards. These findings suggest an important role for hsp90 in the corticosteroid receptor complex during silver sea bream larval development.