| Tributyltin is one kind of organo-tin compounds with androgenic oranti-estrogenic properties. Imposex of gastropods and masculinization of femalefishes were induced by tributyltin exposure. There were also a series of reproductivedamage phenomena in fish caused by tributyltin treatment, such as decreased spermcount and significantly dropped fertilization success rate, but the mechanism remainsunknown. Gender dichroism of guppy (Poecilia reticulata) and reproductive behaviorof male guppy are considered to be sensitive and visual indicators to evaluateendocrine disrupting effects of environmental chemicals. In this study, adult RedAlbino guppy was chosen for the experiments, and a series of effect biomarkers whichare directly related to individual reproduction were adopted to evaluate potential harmof tributyltin on sexual characteristics and reproductive behavior. The effects oftributyltin on population reproduction were determined by number and deformity rateof newborn offsprings. The mRNA expression of P450aromatase (P450arom)isoforms and T (testosterone) and E2(17β-estradiol) levels were investigated todiscuss the underlying endocrine disruption mechanisms of tributyltin exertingreproductive toxicities.(1) Color index was calculated by measuring the orange area and the total area ofskin in guppy following a28-day exposure to5,50and500ng/L TBTCl (tributyltinchloride). There is a significantly increase or no obvious change in females’ or males’skin color index respectively after exposed to50and500ng/L TBTCl, indicating theandrogenic or anti-estrogenic activities of tributyltin on female guppy.(2) Sex steroid levels were examined by radioimmunoassay (RIA), andP450arom mRNA expression levels in ovary were examined by real-time PCR infemale guppy following a28-day exposure to5,50and500ng/L TBTCl. Theexpression of cyp19a mRNA expression in the ovary were downregulated after500ng/L TBTCl treatment, which might inhibite the process of T converted into E2, andthus E2level of females were decreased significantly.(3) Following a28-day exposure of male guppy to5,50and500ng/L TBTCl, gonopodial index was calculated by measuring the gonopodial length and the totalbody length, and T levels were examined by RIA. The results indicated that T levelswere increased after50ng/L TBTCl treatment, along with increase of gonopodialindex, indicating the androgenic activities of tributyltin on male guppy.(4) E2levels were examined by RIA and P450arom mRNA expression levels inbrain were examined by real-time PCR in male guppy following a28-day exposure to5,50and500ng/L TBTCl. With the reduction of cyp19a and cyp19b mRNA in brainof males after TBTCl treatment, there was a dose-related decrease in E2levels, andthese appeared to suppress reproductive behavior of male guppy, including sigmoiddisplay, chase and posturing.(5) Inhibition of reproductive behavior in male guppy eventually led tosignificantly increase of the F1generation deformity rate, expressed as scoliosis andyolk cyst, while offsrings production was unaffected.In conclusion, reproductive toxicities and endocrine disrupting activities oftributyltin on male and female guppy were investigated in different biological levels,such as molecular level (cyp19a and cyp19b mRNA expression and sex hormonelevels), tissue/organ level (gonadosomatic index, gonopodial index and colorationindex), the individual level (reproductive behavior of male guppy, including sigmoiddisplay, chase and posturing) and population level (number and deformity rate ofnewborn offsprings). It was proposed that tributyltin plays its reproductive toxicitiesin male and female guppy by inhibiting aromatase gene expression and theninterfering sex hormone balance. |
