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dc.contributor.advisorNunez, B. Scotten
dc.creatorApplebaum, Scott Lee, 1974-en
dc.date.accessioned2012-08-31T17:37:31Zen
dc.date.available2012-08-31T17:37:31Zen
dc.date.issued2008-08en
dc.identifier.urihttp://hdl.handle.net/2152/17730en
dc.descriptiontexten
dc.description.abstractSurvival of teleost larvae requires growth and development which depend upon endocrine processes. In this dissertation I have examined the ontogeny of elements of the thyroid hormone (TH) and corticosteroid (CS) systems in red drum (Sciaenops ocellatus). Basal cortisol production was first detected 3 days post-hatch (DPH) and a cortisol stress response was present from 6 DPH forward. Changes in steroidogenic enzyme mRNA (CYP11B and CYP21) levels did not correlate with these events. The time necessary to reach peak cortisol levels as well as return to basal levels declined as larvae developed. A second set of studies examined ontogenetic patterns in levels of mRNAs encoding thyroid (soTR[alpha] and soTR[beta]) and corticosteroid (soGR) hormone receptors and assessed the regulation of these mRNAs by exogenous triiodothyronine (T3) and cortisol. soTR[alpha], soTR[beta] and soGR were expressed in all stages of red drum examined. soTR[alpha] levels increased during the time when surging TH levels have been reported. soTR[beta] levels did not differ significantly during development. soGR levels were strongly correlated with those of soTR[alpha]. T3 up-regulated soTR[alpha] and soTR[beta] levels in 7 DPH, but not older larvae. Cross-regulation of receptor mRNAs by exogenous treatment with T3 or cortisol was not observed. Finally, I assessed the influence of a common herbicide, atrazine, on receptor mRNA, TH levels and growth of red drum. In two experiments, red drum exposed to environmentally relevant levels of atrazine did not alter hormone receptor mRNA levels, or TH content. However, atrazine did depress growth in some instances. In conclusion, the expression patterns of hormone receptor mRNA in embryos suggests receptor proteins could be activated by maternal hormones prior to the onset of endogenous hormone production. A correlation between soTR[alpha] and soGR mRNA levels suggests coordinated function of TH and CS systems, although regulatory interactions between these systems were not evident under the conditions in this study. Patterns in soTR[alpha] and soTR[beta] mRNA levels support an important role for TH in the larval to juvenile transformation of red drum larvae. The results also support growing evidence indicating atrazine exposure effects larval growth and may impact their survival in the wild.en
dc.format.mediumelectronicen
dc.language.isoengen
dc.rightsCopyright is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en
dc.subject.lcshRed drum--Larvae--Endocrinologyen
dc.subject.lcshThyroid hormones--Receptorsen
dc.subject.lcshGlucocorticoids--Receptorsen
dc.subject.lcshAtrazine--Physiological effecten
dc.subject.lcshRed drum--Larvae--Effect of stress onen
dc.subject.lcshStress (Physiology)--Endocrine aspectsen
dc.subject.lcshMessenger RNAen
dc.titleRegulation of elements of the thyroid hormone and corticosteroid systems by stress, hormone treatment, and atrazine during ontogeny of red drum (Sciaenops ocellatus)en
dc.description.departmentMarine Scienceen
thesis.degree.departmentMarine Scienceen
thesis.degree.disciplineMarine Scienceen
thesis.degree.grantorThe University of Texas at Austinen
thesis.degree.levelDoctoralen
thesis.degree.nameDoctor of Philosophyen


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