Mitochondrial response and resilience to anthropogenic chemicals during embryonic development.

Mitochondria are integral to maintaining cellular homeostasis. Optimum mitochondrial function is critical during embryonic development, as they play a key role in early signaling cascades and epigenetic programming, in addition to sustaining an adequate energy production. Mitochondria are sensitive targets of environmental toxins, potentially even at levels considered safe under current regulatory limits. Most mitochondrial analyses have focused only on chemical exposure effects in vitro or in isolated mitochondria. However, comparatively little is known about mitochondrial effects of chemical exposure during vertebrate embryogenesis, especially during the recovery phase following a chemical insult. Here, we used the zebrafish (Danio rerio), in a 96-well plate system, to examine mitochondrial effects of 24 chemicals including pharmaceuticals, industrial chemicals, and agrochemicals. We used oxygen consumption rate (OCR) during embryogenesis as a proxy for mitochondrial function. Embryonic OCR (eOCR) was measured in clean egg water immediately following 24 h of chemical exposure and subsequently for an additional 8 h. Each chemical, dependent upon the concentration, resulted in a unique eOCR response profile. While some eOCR effects were persistent or recoverable over time, some effects were only detected several hours after being removed from the exposure. Non-monotonic dose response effects as well as mitochondrial hormesis were also detected following exposure to some chemicals. Collectively, our study shows that mitochondrial response to chemicals are highly dynamic and warrant careful consideration when determining mitochondrial toxicity of a given chemical.

The influence of thermal signals during embryonic development on intrasexual and sexually dimorphic gene expression and circulating steroid hormones in American alligator hatchlings (Alligator mississippiensis).

Incubation temperatures experienced by developing embryos exert powerful influences over gonadal sex determination and differentiation in many species. However, the molecular mechanisms controlling these impacts remain largely unknown. We utilize the American alligator to investigate the sensitivity of the reproductive system to thermal signals experienced during development and ask specifically whether individuals of the same sex, yet derived from different incubation temperatures display persistent variation in the expression patterns of sex biased transcripts and plasma sex hormones. Our analysis focuses on assessments of circulating sex steroids and transcript abundance in brain and gonad, two tissues that display sexually dimorphic gene expression and directly contribute to diverse sexually dimorphic phenotypes. Whereas our results identify sexually dimorphic patterns for several target gonadal genes in postnatal alligators, sex linked variation in circulating 17ß-estradiol, testosterone, and expression of two brain transcripts (aromatase and gonadotropin releasing hormone) was not observed. Regarding intrasexual variation, we found that AMH transcript abundance in hatchling testes is positively correlated with temperatures experienced during sexual differentiation. We also describe highly variable patterns of gene expression and circulating hormones within each sex that are not explained by the intensity of embryonic incubation temperatures. The magnitude of sexually dimorphic gene expression, however, is directly associated with temperature for SOX9 and AMH, two transcripts with upstream roles in Sertoli cell differentiation. Collectively, our findings regarding temperature linked variation provide new insights regarding the connections between embryonic environment and persistent impacts on sexual differentiation in a reptile species that displays temperature dependent sex determination.