Involvement of the retinoic acid signaling pathway in sex differentiation and pubertal development in the European sea bass Dicentrarchus labrax

Estrogenic and retinoid-like activity in stagnant waters with mass occurrence of water blooms

Stagnant freshwaters can be affected by anthropogenic pollution and eutrophication that leads to massive growth of cyanobacteria and microalgae forming complex water blooms. These can produce various types of bioactive compounds, some of which may cause embryotoxicity, teratogenicity, endocrine disruption and impair animal or human health. This study focused on potential co-occurrence of estrogenic and retinoid-like activities in diverse stagnant freshwaters affected by phytoplankton blooms with varying taxonomic composition. Samples of phytoplankton bloom biomass and its surrounding water were collected from 17 independent stagnant water bodies in the Czech Republic and Hungary. Total estrogenic equivalents (EEQ) of the most potent samples reached up to 4.9 ng·g^-1 dry mass (dm) of biomass extract and 2.99 ng·L^-1 in surrounding water. Retinoic acid equivalent (REQ) measured by in vitro assay reached up to 3043 ng·g^-1 dm in phytoplankton biomass and 1202 ng·L^-1in surrounding water. Retinoid-like and estrogenic activities at some sites exceeded their PNEC and effect-based trigger values, respectively. The observed effects were not associated with any particular species of cyanobacteria or algae dominating the water blooms nor related to phytoplankton density. We found that taxonomically diverse phytoplankton communities can produce and release retinoid-like compounds to surrounding water, while estrogenic potency is likely related to estrogens of anthropogenic origin adsorbed to phytoplankton biomass. Retinoids occurring in water blooms are ubiquitous signalling molecules, which can affect development and neurogenesis. Selected water bloom samples (both water and biomass extracts) with retinoid-like activity caused effects on neurodifferentiation in vitro corresponding to those of equivalent all-trans-retinoic acid concentrations. Co-occurrence of estrogenic and retinoid-like activities in stagnant water bodies as well as the potential of compounds produced by water blooms to interfere with neural differentiation should be considered in the assessment of risks associated with water blooms, which can comprise complex mixtures of natural and anthropogenic bioactive compounds.

Developmental changes in gene expression and gonad morphology during sex differentiation in Atlantic salmon (Salmo salar)

The Atlantic salmon (Salmo salar) is a globally important species for its value in fisheries and aquaculture, and as a research model. In order to characterise aspects of sex differentiation at the morphological and mRNA level in this species, the present study examined developmental changes in gonad morphology and gene expression in males and females between 0 and 79 days post hatch (dph). Morphological differentiation of the ovary (indicated by the formation of germ cell cysts) became apparent from 52 dph. By 79 dph, ovarian phenotype was evident in 100% of genotypic females. Testes remained in an undifferentiated-like state throughout the experiment, containing germ cells dispersed singularly within the gonadal region distal to the mesentery. There were no significant sex-related differences in gonad cross-section size, germ cell number or germ cell diameter during the experiment. The expression of genes involved in teleost sex differentiation (anti-müllerian hormone (amh), cytochrome P450, family 19, subfamily A, polypeptide 1a (cyp19a1a), forkhead box L2a (foxl2a), gonadal soma-derived factor (gsdf), r-spondin 1 (rspo1), sexually dimorphic on the Y chromosome (sdY)), retinoic acid-signalling (aldehyde dehydrogenase 1a2 (aldh1a2), cytochrome P450 family 26 a1 (cyp26a1), cytochrome P450 family 26 b1 (cyp26b1), t-box transcription factor 1 (tbx1a)) and neuroestrogen production (cytochrome P450, family 19, subfamily A, polypeptide 1b (cyp19a1b)) was investigated. Significant sex-related differences were observed only for the expression of amh, cyp19a1a, gsdf and sdY. In males, amh, gsdf and sdY were upregulated from 34, 59 and 44 dph respectively. In females, cyp19a1a was upregulated from 66 dph. Independent of sex, foxl2a expression was highest at 0 dph and had reduced ∼ 47-fold by the time of morphological sex differentiation at 52 dph. This study provides new insights into the timing and sequence of some physiological changes associated with sex differentiation in Atlantic salmon. These findings also reveal that some aspects of the mRNA sex differentiation pathways in Atlantic salmon are unique compared to other teleost fishes, including other salmonids.

Effects of endocrine disrupting chemicals on gonad development: Mechanistic insights from fish and mammals

Over the past century, evidence has emerged that endocrine disrupting chemicals (EDCs) have an impact on reproductive health. An increased frequency of reproductive disorders has been observed worldwide in both wildlife and humans that is correlated with accidental exposures to EDCs and their increased production. Epidemiological and experimental studies have highlighted the consequences of early exposures and the existence of key windows of sensitivity during development. Such early in life exposures can have an immediate impact on gonadal and reproductive tract development, as well as on long-term reproductive health in both males and females. Traditionally, EDCs were thought to exert their effects by modifying the endocrine pathways controlling reproduction. Advances in knowledge of the mechanisms regulating sex determination, differentiation and gonadal development in fish and rodents have led to a better understanding of the molecular mechanisms underlying the effects of early exposure to EDCs on reproduction. In this manuscript, we review the key developmental stages sensitive to EDCs and the state of knowledge on the mechanisms by which model EDCs affect these processes, based on the roadmap of gonad development specific to fish and mammals.