uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Persistent sex-reversal and oviducal agenesis in adult Xenopus (Silurana) tropicalis frogs following larval exposure to the environmental pollutant ethynylestradiol
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Physiology and Developmental Biology, Environmental Toxicology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Physiology and Developmental Biology, Environmental Toxicology.
Show others and affiliations
2006 (English)In: Aquatic Toxicology, ISSN 0166-445X, E-ISSN 1879-1514, Vol. 79, no 4, 356-365 p.Article in journal (Refereed) Published
Abstract [en]

It is known that estrogen-like environmental pollutants can feminise gonadal differentiation in frogs resulting in female-biased sex-ratios at metamorphosis. The long-term effects on reproductive function in frogs following larval exposure to pollutants are less known. Amphibian test systems which allow life-cycle studies are therefore needed. The aim of the present study was to characterise long-term estrogenic effects on the reproductive system of the emerging model species Xenopus (Silurana) tropicalis following larval exposure to ethynylestradiol (EE2). EE2 is a synthetic estrogen that has been detected in sewage effluents and in surface waters. Newly hatched tadpoles (Niewkoop Faber (NF) stage 48) were exposed to the nominal EE2 concentrations 0 (control), 1, 10, and 100 nM (with analytical chemistry support) until complete metamorphosis (NF stage 66). Effects on the reproductive organs were determined in juveniles (I month after metamorphosis) and in 9-month-old frogs. Larval exposure to EE2 caused female-biased phenotypic sex-ratios in both juvenile and adult frogs, which is in agreement with previous work on other frog species. Nearly all (97%) of the 63 EE2-exposed 9-month-old frogs had ovaries. Histological evaluation of the gonads of the 9-month-old frogs showed that they were sexually mature. Among the adult frogs with ovaries there was a dose-dependent increase in the frequency of individuals lacking oviducts. Adult frogs exposed to 100 nM EE2 that had ovaries but no oviducts had lower levels of estrogen receptor alpha (ER alpha) mRNA in the brain than control animals and those exposed to 100 nM EE2 that had ovaries as well as oviducts. EE2 exposure did not cause any significant changes in ER alpha mRNA levels in the ovaries of the adult frogs. The reduced level of ER alpha mRNA in the brain of individuals with ovaries lacking oviducts suggests an organizing effect of EE2 on the central nervous system. The results show that transient early life-stage exposure to an environmental pollutant can induce effects on the reproductive organs and the central nervous system that persist into adulthood. Overall, our data suggest that X. tropicalis, which has a shorter generation time than the well-established model species Xenopus laevis, is a suitable model organism for research on developmental reproductive toxicity in anuran species.

Place, publisher, year, edition, pages
2006. Vol. 79, no 4, 356-365 p.
Keyword [en]
amphibia, Xenopus (Silurana) tropicalis, test system, sex differentiation, estrogen receptor, gonad, oviduct
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:uu:diva-97445DOI: 10.1016/j.aquatox.2006.07.004ISI: 000241090300005PubMedID: 16942807OAI: oai:DiVA.org:uu-97445DiVA: diva2:172400
Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Endocrine Disruption in Amphibians: Developmental Effects of Ethynylestradiol and Clotrimazole on the Reproductive System
Open this publication in new window or tab >>Endocrine Disruption in Amphibians: Developmental Effects of Ethynylestradiol and Clotrimazole on the Reproductive System
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Amphibian populations are declining world-wide and one of the suggested reasons is environmental pollutants. Studies of long-term effects on the reproductive system in frogs following larval exposure to environmental pollutants are scarce. It is therefore important to develop methods to study developmental reproductive toxicity in amphibians. In this thesis the usefulness of Xenopus tropicalis (the West African clawed frog) as a model species for a test system was investigated. Effects on the reproductive system after larval exposure to the pharmaceuticals ethynylestradiol (EE2) and clotrimazole were evaluated. The susceptibility to EE2 exposure was compared between the model species and a wild species, the European common frog (Rana temporaria). Larval exposure to EE2 caused female-biased sex ratios in both examined frog species, indicating male-to-female sex-reversal. In adult Xenopus tropicalis, male frogs that were not sex-reversed had reduced fertility and decreased amount of mature spermatozoa in the seminiferous tubules. The proportion of frogs with ovaries but lacking oviducts increased with increasing EE2-concentrations. A female frog without oviducts is sterile. The development of ovaries in sex-reversed male frogs was implied to be similar to control females. The combination of a reduced number of males, due to sex-reversal, and impaired fertility could have severe effects on frog populations. Larval exposure to clotrimazole modulated aromatase activity in gonads and brain in Xenopus tropicalis. Brain aromatase activity was decreased at the time for gonadal differentiation and gonadal aromatase activity was increased at metamorphosis. The findings in this thesis indicate that reproduction in wild frogs might be impaired by estrogenic compounds in the environment. The results combined with the short generation time supports the use of Xenopus tropicalis as a model species when evaluating long term effects of endocrine disruptors on the reproductive system in amphibians.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 57 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 545
Keyword
Test system, Xenopus tropicalis, Rana temporaria, sex ratio, sex differentiation, fertility, aromatase, ovary, testis, oviduct
National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-9209 (URN)978-91-554-7260-3 (ISBN)
Public defence
2008-09-26, Lindahlsalen, Evolutionsbiologisk centrum (EBC), Norbyvägen 18A, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2013-09-06Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textPubMed

Authority records BETA

Pettersson, IrinaLundstedt-Enkel, KatrinBerg, Cecilia

Search in DiVA

By author/editor
Pettersson, IrinaLundstedt-Enkel, KatrinBerg, Cecilia
By organisation
Environmental Toxicology
In the same journal
Aquatic Toxicology
Biological Sciences

Search outside of DiVA

GoogleGoogle Scholar

doi
pubmed
urn-nbn

Altmetric score

doi
pubmed
urn-nbn
Total: 580 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf