Retinoid level dynamics during gonad recycling in the limpet Patella vulgata.

Germ cell commitment and meiosis initiation are among the multitude of physiological roles of retinoic acid (RA) in vertebrates. Acting via receptor-mediated transcription, RA induces the expression of meiotic factors, triggering meiosis. Contrasting with vertebrates, invertebrate RA metabolism is scarcely understood. Still, some physiological processes appear to be conserved. Here we set to evaluate the role of retinoids in the gonad maturation process of the marine gastropod Patella vulgata. We found that retinoid concentration in gonadal tissue, namely RA, varies between breeding and resting specimens, with maxima attained in the latter. Additionally, we isolated and quantified the expression of both the retinoic acid receptor (RAR) and the retinoid X receptor (RXR) in gonads. In view of the stability of retinoid receptor expression, we suggest that the balance of RA levels operates through the enzymatic control of synthetic and catabolic processes. Overall, the reported data are supportive for a developmental role of RA during gonadal maturation in P. vulgata, which should be addressed in other protostome lineages.

The inhibitory effect of environmental ammonia on Danio rerio LPS induced acute phase response.

Ammonia is a toxic by-product of amino acid catabolism and a common environmental pollutant that has been associated with increased disease susceptibility in fish although the mechanism is not well understood. We addressed the hypothesis that elevated environmental ammonia acts by impairing the acute phase response (APR). Specifically, we determined the impact of sub-lethal acute (24 h) and chronic (14 d) ammonia exposure on acute phase protein gene expression in zebrafish (Danio rerio) in response to a challenge with bacterial lipopolysaccharide (LPS: i.p. 10 µg/g after 24h). A panel of LPS-responsive genes (SAA, HAMP, LECT2, Hp and IL1ß) were identified and evaluated by real-time quantitative PCR. Ammonia was found to impair induction of SAA, HAMP and LECT2 by 50-90%. Both short (15 min, 1h and 24h) and long-term (14 days) exposure to high environmental ammonia concentrations significantly elevated whole-body cortisol levels compared with control fish. Our results reveal for the first time that exposure to high environmental levels of ammonia suppresses the innate immune response in fish. We hypothesize that high environmental ammonia-mediated elevation of cortisol levels in zebrafish may be playing a key role in this immunosuppression, while the mechanisms involved remains to be elucidated.