Effects of Exposure to 17α-Ethynylestradiol
during Sexual Differentiation on the Transcriptome of the African
Clawed Frog (<i>Xenopus laevis</i>)
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Abstract
Exposure to estrogens during the
period of sexual differentiation
is known to adversely affect the development of testes in African
clawed frogs (<i>Xenopus</i> laevis), but little is known
about molecular changes that coincide with the development of altered
phenotypes. Therefore, the transcriptome-level effects of exposure
to 17α-ethynylestradiol (EE2) during sexual differentiation
of <i>X. laevis</i> were evaluated by use of <i>Illumina</i> sequencing coupled with RNA-Seq expression analysis. Overall, a
number of processes were affected by 17α-ethynylestradiol, including
steroid biosynthesis, thyroid hormone signaling and metabolism, testicular
development, and spermatogenesis. Some of the altered pathways, such
as thyroid hormone signaling and testicular development, could be
linked with biological effects on metamorphosis and gonadal phenotypes,
respectively, that were observed in frogs that were exposed to 17α-ethynylestradiol
throughout metamorphosis and the early postmetamorphic period. Thus,
early changes at the transcriptome-level were predictive of pathologies
that did not manifest until later in development. To validate the
quantitative capacity of RNA-Seq, a subset of transcripts identified
to have altered abundances in individuals exposed to 17α-ethynylestradiol
was also evaluated by use of quantitative polymerase chain reaction
(qPCR). While small sample sizes (<i>n</i> = 3) limited
the ability to draw conclusions pertaining to differences in qPCR-derived
abundances of transcripts between control and exposed tadpoles, there
was a significant relationship (<i>r</i><sup>2</sup> = 0.78)
between fold-changes for RNA-Seq and qPCR