Molecular responses to 17β-estradiol in early life stage salmonids.
Environmental estrogens (EE) are ubiquitous in many aquatic environments and biological responses to EEs in early developmental stages of salmonids are poorly understood compared to juvenile and adult stages. Using 17β-estradiol (E2) as a model estrogen, waterborne exposures were conducted on early life stage rainbow trout (Oncorhynchus mykiss; egg, alevin, swim-up fry) and both molecular and physiological endpoints were measured to quantify the effects of E2. To investigate developmental stage-specific effects, laboratory exposures of 1 μg/L E2 were initiated pre-hatching as eyed embryos or post-hatching upon entering the alevin stage. High mortality (∼90%) was observed when E2 exposures were initiated at the eyed embryo stage compared to the alevin stage (∼35% mortality), demonstrating stage-specific sensitivity. Gene expression analyses revealed that vitellogenin was detectable in the liver of swim-up fry, and was highly inducible by 1 μg/L E2 (>200-fold higher levels compared to control animals). Experiments also confirmed the induction of vitellogenin protein levels in protein extracts isolated from head and tail regions of swim-up fry after E2 exposure. These findings suggest that induction of vitellogenin, a well-characterized biomarker for estrogenic exposure, can be informative measured at this early life stage. Several other genes of the reproductive endocrine axis (e.g. estrogen receptors and androgen receptors) exhibited decreased expression levels compared to control animals. In addition, chronic exposure to E2 during the eyed embryo and alevin stages resulted in suppressive effects on growth related genes (growth hormone receptors, insulin-like growth factor 1) as well as premature hatching, suggesting that the somatotropic axis is a key target for E2-mediated developmental and growth disruptions. Combining molecular biomarkers with morphological and physiological changes in early life stage salmonids holds considerable promise for further defining estrogen action during development, and for assessing the impacts of endocrine disrupting chemicals in vivo in teleosts.
Nautilus Environmental, 8664 Commerce Court, Burnaby, British Columbia V5A 4N71, Canada. Electronic address: vicki.marlatt@ufv.ca.
Vicki L
VL
Marlatt
Canadian Rivers Institute and Department of Biology, University of New Brunswick, Saint John, New Brunswick, Canada.
Jinying
J
Sun
Nautilus Environmental, 8664 Commerce Court, Burnaby, British Columbia V5A 4N71, Canada.
Cat A
CA
Curran
Nautilus Environmental, 8664 Commerce Court, Burnaby, British Columbia V5A 4N71, Canada.
Howard C
HC
Bailey
Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, Canada.
Chris K
CK
Kennedy
Nautilus Environmental, 8664 Commerce Court, Burnaby, British Columbia V5A 4N71, Canada.
James R
JR
Elphick
Canadian Rivers Institute and Department of Biology, University of New Brunswick, Saint John, New Brunswick, Canada.
Christopher J
CJ
Martyniuk
D000818:Animals; D004625:Embryo, Nonmammalian / Q000187:drug effects*; D052244:Endocrine Disruptors / Q000494:pharmacology*; D004958:Estradiol / Q000494:pharmacology*; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D017686:Oncorhynchus mykiss / Q000254:growth & development / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism; D012098:Reproduction / Q000187:drug effects*; D014819:Vitellogenins / Q000378:metabolism; D014873:Water Pollutants / Q000494:pharmacology
D052244:Endocrine Disruptors; D004967:Estrogens; D011960:Receptors, Estrogen; D014819:Vitellogenins; D014873:Water Pollutants; D004958:Estradiol
17β-estradiol; Estrogen receptor; Eyed embryo; Gene expression; Rainbow trout; Vitellogenin