The Endocrine Regulation of Sex Change Phenomenon in Marin Fish

The Endocrine Regulation of Sex Change Phenomenon in Marin Fish

Content
1. Introduction
2. Endocrine disruptors
3. Sex changes related to endocrine function
4. Conclusion
5. Bibliography

Introduction
Nowadays, it is a well-known fact that endocrine systems are found in most varieties of animal life. At the same time, the recent researches have revealed the fact that changes of the endocrine system can have quite unexpected consequences. For instance, some marine fish under the impact of endocrine disruptors and changes of endocrine system can change their sex during the course of their life cycle.
Endocrine disruptors
Basically, it is endocrine disruptors that are responsible for such a dramatic change of the organisms of marine fish. It should be pointed out that the disruption of the endocrine system can occur in different ways. In this respect, it is worthy of mention that some chemicals mimic natural hormones, fooling the body in over-responding to the stimulus, or responding at inappropriate time. Other endocrine disruptors block the effects of a hormone from certain receptors by blocking the receptor site of the cell. At the same time, others directly stimulate or inhibit the endocrine system and cause overproduction or underproduction of hormones.
In recent years some scientists have proposed that chemicals may inadvertently be disrupting the endocrine system of human and animals, as well as marine fish. In the case of the latter, there is strong evidence that a chemical exposure has been associated with adverse developmental and reproductive effect on the fish.
Sex changes related to endocrine function
The recent researches and experiments revealed the basic sex changes that are related to the functioning and changes of endocrine system. In this respect, it is worthy of mention one of the experiment which aimed at the identification of alterations in gene expression associated with MeHg exposure, specifically those associated with previously observed changes in reproduction and reproductive biomarkers. Fathead minnows were special diets which contained the similar concentration of MeHg in the diets of the wild invertivorous and piscivorous fish. In that research the commercial macro array in conjunction with quantitative polymerase chain reaction was used to examine gene expression in fish in relation to exposure to these environmentally relevant doses of MeHg.
In the result of the research, it was found out that the expression of genes commonly associated with endocrine disruption was altered with Hg exposure. To put it more precisely, the researchers observed a marked up-regulation in vitellogenin mRNA in individual Hg-exposed males and a significant decline of vitellogenin gene expression in female fish with increasing Hg concentrations. Other genes identified by the macro array experiment included those associated with egg fertilization and development, sugar metabolism, apoptosis, and electron transport. The researchers also revealed the fact that there were differences in expression patterns between male and female fish not related to genes specifically associated with reproduction, indicating a potential physiological difference in the reaction of the females and males to MeHg.
Conclusion
Thus, taking into account all above mentioned, it is possible to conclude that the endocrine system plays an important role in the functioning of marine fishes and the changes in its functioning can affect dramatically the sex of the fish. The experiments revealed the facts that such changes can occur under the impact of endocrine disruptors which lead to the changes of the functioning of the endocrine system of fish affecting their sex to the extent that it can be changed. In this respect, the experiment with the use of MeHg is particularly noteworthy since it provides practical evidence of such changes. Consequently it is possible to estimate that the effect of endocrine disruptors on organisms, including marine fish, can lead to serious changes of their functioning.


Bibliography:
1. Armstrong, F. Effects of mercury compounds on fish. In: Biogeochemistry of Mercury in the Environment (Nriagu JO, ed). New York:Elsevier/North Holland Biomedical Press, 1979, 657–670.
2. Arnold B.S., et al. « Effects of methyl mercury on plasma estrogen and 11-keto testosterone in Nile tilapia (Oreochromis niloticus)” [Abstract]. In: Abstracts of 19th Annual Meeting of the Society of Environmental Toxicology and Chemistry, 13–19, November 1998. Charlotte, NC. Pensacola, FL:SETAC Press, 145.
3. Beisswenger P.J., et al. “Glyceraldehyde-3-phosphate dehydrogenase activity as an independent modifier of methylglyoxal levels in diabetes”. Biochim Biophys Acta, 2003, 1637:98–106.
4. Bjornberg, K.A. et al. “Methylmercury exposure in Swedish women with high fish consumption”. Sci Total Environ, 2005, 341:45–52.
5. Bloom, N.S. “On the chemical form of mercury in edible fish and marine invertebrate tissue”. Can J Fish Aquat Sci, 1992, 49:1010–1017.
6. Byrne B.M, Gruber M. “The evolution of egg yolk proteins”. Prog Biophys Mol Biol, 1989, 53: 33–69.
7. Chuang D.M, Hough C, Senatorov V.V. “Glyceradlehyde-3-phophate dehydrogenase, apoptosis, and neurodegenerative diseases”. Annu Rev Pharmacol Toxicol, 2005. 45: 269–290.
8. Colborn, T. “Developmental effects of endocrine disrupting chemicals in wildlife and humans”. Environ Health Perspect, 1993, 101:378–384.
9. Cole, D.C. et al. “Blood mercury levels among Ontario anglers and sport-fish eaters”. Environ Res, 2004, 95:305–314.
10. Drevnick, P.E. and Sandheinrich M.B. “Effects of dietary methylmercury on reproductive endocrinology of fathead minnows”. Environ Sci Technol, 2003, 37:4390–4396.
11. Elliot J. Effects of estradiol-17? on serum calcium and vitellogenin levels in rainbow trout. J Endocrinol, 1979, 83:54–55.
12. “Endocrine Disruptor Screening and Testing Advisory Committee”. EDSTAC Final Report. Washington, DC: U.S. Environmental Protection Agency, 1998.
13. Friedmann, A. “Low levels of dietary methylmercury inhibit growth and gonadal development in juvenile walleye (Stizostedion vitreum)”. Aquat Toxicol, 1996, 35:265–278.
14. Fynn-Aikins, K. “An evaluation of methyl mercury as an endocrine disruptor in largemouth bass”. In 19th Annual Meeting of the Society of Environmental Toxicology and Chemistry, 13–19 November 1998, Charlotte, NC. Pensacola, FL:SETAC Press, 146.
15. Garcia-Morales, P. et al. “Effect of cadmium on estrogen receptor levels and estrogen-induced responses in human breast cancer cells”. J Biol Chem, 2004, 269:16896–16901.