Expression variations of two retinoid signaling pathway receptors in the rotifer Brachionus calyciflorus exposed to three endocrine disruptors

Endocrine disruption compounds (EDC) are known to affect reproduction,
development, and growth of exposed organisms. Although in vertebrates, EDCs mainly
act through steroid receptors (e.g. androgen and estrogen receptors), their absence in
many invertebrates suggests the involvement of another biological pathway in
endocrine disruption effects. As retinoid signalling pathway is present in almost all
Metazoa and its involvement in the endocrine disruption of gastropods (i.e. imposex)
has been demonstrated, the present work was devoted to investigating the relative
mRNA variations of two retinoid receptors genes, retinoid X receptor (RXR) and
retinoid acid receptor (RAR), in the freshwater rotifer Brachionus calyciflorus exposed
for 6, 12 and 24 hours to flutamide, fenitrothion and cyproterone acetate, three antiandrogens
known to disrupt sexual reproduction of Brachionus sp.
Results revealed that fenitrothion did not affect the relative mRNA levels RXR and RAR
in B. calyciflorus, whereas RXR and RAR mRNA levels could be significantly increased
by 2 to 4.5-fold and from 2 to 7-fold after exposure to flutamide and cyproterone
acetate, respectively. Moreover, the effects of flutamide and cyproterone acetate were
measured from 6 and 12 hours of exposure, respectively. Cyproterone acetate caused
the highest increase of RXR and RAR mRNA levels, probably due to its progestin
activity in addition to its anti-androgenic activity and the potential presence of a
membrane-associated progesterone receptor as reported in Brachionus manjavacas.
Consequently, although it is still difficult to evaluate the hormonal pathways involved in
the endocrine disruption in Brachionus sp., this work suggests that the retinoid
signaling pathway appears to be a good starting point to try to elucidate the molecular
mechanisms involved in sexual reproductive dysfunction in Brachionidae.