Biosensor
Medaka for Monitoring Intersex Caused by
Estrogenic Chemicals
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Abstract
Estrogenic
chemicals can induce intersex in fish species leading
to disturbance of spermatogenesis and impairment of reproductive success.
To overcome the shortcomings of conventional histopathological observation
on intersex (low sensitivity, relatively poor accuracy, long experimental
periods, as well as laborious and time-consuming), we generated a
pMOSP1-EGFP transgenic medaka fish model. In this transgenic fish,
the green fluorescence protein (GFP) reporter gene was derived by
the regulatory elements of the OSP1 gene, which is a specific and
sensitive molecular biomarker for indicating intersex occurrence in
male medaka fish exposed to estrogenic chemicals. The transgenic GFP
was faithfully expressed in ovaries and in testes with intersex, perfectly
mimicking the expression pattern of endogenous OSP1. In intersex testis,
the diameters of primary oocytes which could be distinguished by GFP
fluorescence observation were as small as 10 μm, lower than
that (more than 20 μm) which is observable by histopathology.
Using the novel transgenic medaka fish, intersex was observed after
90-day exposure to 0.75 ng/L 17α-ethinyloestradiol (EE<sub>2</sub>) (0–90 dph), but only at concentrations of at least 1.38
ng/L EE<sub>2</sub> by histopathology. An effectiveness of a short-term
in vivo assay for screening estrogenic chemicals that can monitor
intersex appearance at early sex developmental stage (about 30 dph)
in male medaka fish was also demonstrated by assessing the intersex
induction of EE<sub>2</sub>, 17β-estradiol and 4-nonylphenol.
This newly developed assay provides an enhanced ability for screening
and testing estrogenic chemicals with the potential to induce intersex
and studying their biological impacts