Ontogeny of hypophyseal-thyroid axis during temperature sex determination/differentiation period in pejerrey Odontesthes bonariensis

CHALDE T; MIRANDA LA

JOURNAL OF FISH BIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2017

0022-1112

Themorphological development of the thyroid gland of pejerrey O. bonariensis during larvae-juvenile transition period was studiedand related to the the whole-body concentrations of thyroxine (T4)and triiodothyronine (T3). A cDNA fragmentof the thyroid stimulating hormone β-subunit (tshb) was sequenced and its transcript levels were quantified duringthis period. Follicles with eosinophilic and T4-immunoreactivecolloids were detected at hatching together with tshb transcript levels and whole-body concentrations of T4and T3 hormones. Thyroid follicles were located in thesubpharyngeal region associated with the ventral aorta below the hyoid bone. Folliclesstructure switched from a rounded form at hatching to an oval form at juvenilestage. Significant increase of follicle number per larva, mean colloidal areaand total colloidal area were observed throughout development recording maximumvalues at the end of the larvae-juvenile transition period. A significant decreaseof tshb expression together with asignificant increase in T4 and T3 whole-body concentrationswas observed prior to achieving the juvenile phenotype. These results are inaccordance with (1) a negative feedback regulation of tshb expression by thyroid hormones and (2) a possible association betweenthe thyroid hormones levels with the acceleration of metabolic processesnecessary to complete metamorphosis. All this information was related toseveral behavioural, morphological and physiological changes during thistransition period.