Cross-Talk Between Estrogen and Thyroid Hormones During Amphibian Development

It is generally thought that in amphibians, thyroid hormones (THs) regulate metamorphosis, while sex steroids (estrogens and androgens) regulate gonadal differentiation. However, inhibition of TH synthesis in frogs alters gonadal differentiation, suggesting instead that these two endocrine axes int...

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Main Author: Duarte Guterman, Paula
Other Authors: Trudeau, Vance
Format: Others
Language:en
Published: Université d'Ottawa / University of Ottawa 2011
Subjects:
Online Access:http://hdl.handle.net/10393/19967
http://dx.doi.org/10.20381/ruor-4581
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spelling ndltd-uottawa.ca-oai-ruor.uottawa.ca-10393-199672021-06-29T05:29:48Z Cross-Talk Between Estrogen and Thyroid Hormones During Amphibian Development Duarte Guterman, Paula Trudeau, Vance Metamorphosis Sexual development Brain Sex steroids Gonad Intersex Triiodothyronine Aromatase inhibitor Silurana tropicalis Engystomops pustulosus Gene expression Comparative endocrinology It is generally thought that in amphibians, thyroid hormones (THs) regulate metamorphosis, while sex steroids (estrogens and androgens) regulate gonadal differentiation. However, inhibition of TH synthesis in frogs alters gonadal differentiation, suggesting instead that these two endocrine axes interact during development. Specifically, THs may be involved in male development, while estrogens may inhibit tadpole metamorphosis. However, we do not currently know the mechanisms that account for these interactions, let alone how such mechanisms may differ between species. To develop and test new hypotheses on the roles of sex steroids and THs, I first examined transcriptional profiles (mRNA) of enzymes and receptors related to sex steroids and THs during embryogenesis and metamorphosis in Silurana tropicalis. Tadpoles were exposed to either an estrogen synthesis inhibitor (fadrozole) or TH (triiodothyronine, T3) during early larval or tadpole development. Acute exposures of S. tropicalis to fadrozole or T3 during early development resulted in increased expression of androgen- and TH-related genes in whole body larvae, while chronic exposure to fadrozole during metamorphosis affected gonadal differentiation but did not affect tadpole development. On the other hand, acute exposure to T3 during metamorphosis increased the expression of androgen-related transcripts both in the brain and gonad. In S. tropicalis, the results suggested that cross-talk is primarily in one direction (i.e., effect of THs on the reproductive axis) with a strong relationship between TH and androgen status. Lastly, I established developmental transcript profiles and investigated T3 regulation of brain and gonad transcripts in Engystomops pustulosus. I then compared these results with S. tropicalis and an earlier study in Lithobates pipiens. While each species developed with similar profiles, they differed in their response to T3. Exposure to T3 resulted in either an increase in androgen-related genes (S. tropicalis) or a decrease in estrogen-related genes (E. pustulosus and L. pipiens). In conclusion, these data demonstrated that cross-talk mechanisms differ among these three evolutionary separate species, but in all cases, T3 appears to affect the balance of sex steroids, stimulating the androgen system and providing potential mechanisms of the masculinising effects of THs. These results will contribute to understanding the mechanisms of hormone interactions and their evolutionary basis in frogs. 2011-05-09T17:44:04Z 2011-05-09T17:44:04Z 2011 2011 Thesis http://hdl.handle.net/10393/19967 http://dx.doi.org/10.20381/ruor-4581 en application/pdf Université d'Ottawa / University of Ottawa
collection NDLTD
language en
format Others
sources NDLTD
topic Metamorphosis
Sexual development
Brain
Sex steroids
Gonad
Intersex
Triiodothyronine
Aromatase inhibitor
Silurana tropicalis
Engystomops pustulosus
Gene expression
Comparative endocrinology
spellingShingle Metamorphosis
Sexual development
Brain
Sex steroids
Gonad
Intersex
Triiodothyronine
Aromatase inhibitor
Silurana tropicalis
Engystomops pustulosus
Gene expression
Comparative endocrinology
Duarte Guterman, Paula
Cross-Talk Between Estrogen and Thyroid Hormones During Amphibian Development
description It is generally thought that in amphibians, thyroid hormones (THs) regulate metamorphosis, while sex steroids (estrogens and androgens) regulate gonadal differentiation. However, inhibition of TH synthesis in frogs alters gonadal differentiation, suggesting instead that these two endocrine axes interact during development. Specifically, THs may be involved in male development, while estrogens may inhibit tadpole metamorphosis. However, we do not currently know the mechanisms that account for these interactions, let alone how such mechanisms may differ between species. To develop and test new hypotheses on the roles of sex steroids and THs, I first examined transcriptional profiles (mRNA) of enzymes and receptors related to sex steroids and THs during embryogenesis and metamorphosis in Silurana tropicalis. Tadpoles were exposed to either an estrogen synthesis inhibitor (fadrozole) or TH (triiodothyronine, T3) during early larval or tadpole development. Acute exposures of S. tropicalis to fadrozole or T3 during early development resulted in increased expression of androgen- and TH-related genes in whole body larvae, while chronic exposure to fadrozole during metamorphosis affected gonadal differentiation but did not affect tadpole development. On the other hand, acute exposure to T3 during metamorphosis increased the expression of androgen-related transcripts both in the brain and gonad. In S. tropicalis, the results suggested that cross-talk is primarily in one direction (i.e., effect of THs on the reproductive axis) with a strong relationship between TH and androgen status. Lastly, I established developmental transcript profiles and investigated T3 regulation of brain and gonad transcripts in Engystomops pustulosus. I then compared these results with S. tropicalis and an earlier study in Lithobates pipiens. While each species developed with similar profiles, they differed in their response to T3. Exposure to T3 resulted in either an increase in androgen-related genes (S. tropicalis) or a decrease in estrogen-related genes (E. pustulosus and L. pipiens). In conclusion, these data demonstrated that cross-talk mechanisms differ among these three evolutionary separate species, but in all cases, T3 appears to affect the balance of sex steroids, stimulating the androgen system and providing potential mechanisms of the masculinising effects of THs. These results will contribute to understanding the mechanisms of hormone interactions and their evolutionary basis in frogs.
author2 Trudeau, Vance
author_facet Trudeau, Vance
Duarte Guterman, Paula
author Duarte Guterman, Paula
author_sort Duarte Guterman, Paula
title Cross-Talk Between Estrogen and Thyroid Hormones During Amphibian Development
title_short Cross-Talk Between Estrogen and Thyroid Hormones During Amphibian Development
title_full Cross-Talk Between Estrogen and Thyroid Hormones During Amphibian Development
title_fullStr Cross-Talk Between Estrogen and Thyroid Hormones During Amphibian Development
title_full_unstemmed Cross-Talk Between Estrogen and Thyroid Hormones During Amphibian Development
title_sort cross-talk between estrogen and thyroid hormones during amphibian development
publisher Université d'Ottawa / University of Ottawa
publishDate 2011
url http://hdl.handle.net/10393/19967
http://dx.doi.org/10.20381/ruor-4581
work_keys_str_mv AT duartegutermanpaula crosstalkbetweenestrogenandthyroidhormonesduringamphibiandevelopment
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