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Rudolf Wu Centre for Coastal Pollution & Conservation City University of Hong Kong

Hypoxia affects sex differentiation and development, leading to a male dominated population in fish. Rudolf Wu Centre for Coastal Pollution & Conservation City University of Hong Kong. What is “ Hypoxia ” ?. Shortage of oxygen < 2 ml /L <2.8 mg/L. Diaz & Rosenberg, 1995. Hypoxia is

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Rudolf Wu Centre for Coastal Pollution & Conservation City University of Hong Kong

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  1. Hypoxia affects sex differentiation and development, leading to a male dominated population in fish Rudolf Wu Centre for Coastal Pollution & Conservation City University of Hong Kong

  2. What is “Hypoxia”? • Shortage of oxygen • < 2 ml /L • <2.8 mg/L Diaz & Rosenberg, 1995

  3. Hypoxia is A Pressing Global Problem

  4. <2.8 mgO2/L Hypoxic area> 1 million Km2 Diaz & Rosenberg 1995

  5. 150 “Dead Zones” all over the world UNEP, 2004

  6. Anthropogenic activities Organic matters & nutrients (EUTROPHICATION) Runoff Sewage effluent Vessel waste discharge Oxygen blocked Low density (Low salinity or high temperature) ALGAL BLOOM Pycnocline Oxygen High density (High salinity or low temperature) Dead algae shrink & decomposers use upoxygen  COD / BOD / SOD Mortality Organisms escape

  7. Decrease in DO in many coastal areas in USA, China, Norway, UK, Sweden, Germany, Denmark, the Black Sea, Adriatic Seas in the last 30-80 years Hypoxia: Some Trend Diaz & Rosenberg, 1995; Rabalais, 2001

  8. Increases in nutrient concentration, algal blooms, large scale hypoxia, and change of species composition, mass mortality of fish and decline in fisheries production are found in large coastal areas all over the world Current situation Diaz & Rosenberg, 1995; Gray & Wu, 2002

  9. Experimental set up 5.8 mg/L • Eggs of zebrafish exposed to 0.8 and 5.8 mg O2/L for 3 months • Studied growth, gonad wt. gametogenesis, malformation, sex hormones, sex ratio and various genes controlling synthesis of sex hormone and apoptosis over time 0.8 mg/L Oxygen controller

  10. Endocrine disruption occurs as early as 48hpf **p<0.01 Shang & Wu, 2004

  11. Endocrine disruption occurs as early as 48hpf ***p<0.005 Shang & Wu, 2004

  12. Under hypoxia, apoptosis concentrates in the head but not the tail Control Hypoxia

  13. Hypoxia alters normal pattern of apoptosis

  14. ♂ Male Zebrafish ♀ Female Zebrafish 1 cm 1 cm Testis Ovary 2 mm 2 mm 200 µm 200 µm

  15. ♀ ♀ ♀ ♂ ♂ ♂ ♂ ♂ ♂ ♂ Hypoxia tips sex balance & favors a male biased population *** Hypoxia Shang, Yu & Wu, 2006 *** p < 0.001

  16. Where the girl are?

  17. Expression of selected genesunder hypoxia

  18. 3-HSD (-) CYP11A (-) CYP19A (ND) CYP19B (-) 3-HSD (-) CYP11A (-) CYP19A (-) CYP19B (-) Aromatase (-) Gonads differentiate into ovaries Sex differentiation begins Sex differentiation/ reversal is completed Final maturation of the gonads Spawning Male 3-HSD (-) CYP11A (-) CYP19A (+) CYP19B (+) T/E2 (NC) Male 3-HSD (-) CYP11A (-) CYP19A (-) CYP19B (NC) T/E2 (NC) Female 3-HSD (+) CYP11A (-) CYP19A (+) CYP19B (+) T/E2 (+) Aromatase (-) Female 3-HSD (-) CYP11A (-) CYP19A (+) CYP19B (NC) T/E2 (+) Aromatase (-) (A) 10 dpf (B) 40 dpf (C) 60 dpf (D) 120 dpf 10-12 dpf 23-25 dpf 42 dpf 60 dpf 120 dpf Larval Juvenile Adult 3 dpf 30 dpf 90 dpf

  19. In vitro evidence • In vitro studies using H295R cell line

  20. Hypoxia affects very large areas and has caused major changes in aquatic ecosystems, as well as decline in fisheries production all over the world For the first time, we found that hypoxia is an endocrine disruptor, and impairs reproduction of fish Overall Conclusions

  21. For the first time in science, we found that : Hypoxia alters various genes controlling synthesis of sex hormones Alternation of sex hormones affects sex differentiation and sex development, and favors a male-biased population in fish A higher male to female ratio will greatly reduce the chance of fish reproduction Overall Conclusions

  22. Since the genes and hormones controlling sex differentiation and reproduction are highly conserved, the endocrine disrupting effects and biased sex ratio observed in fish may also occur in other vertebrates. These are likely to be the major factors leading to decline of natural populations in hypoxic waters The problem of hypoxia is likely to get worse in the coming years Overall Conclusions

  23. Sex ratio in human depends on level of sex hormones of father and mother during conception, and high hormone level during conception favors subsequent birth of sons (James, 2004) Patients suffering from sleeping apnea have lower sex drive and testosterone level (Saaresranta & Polo, 2003) Epilogue

  24. Acknowledgments • This research was supported by the Area of Excellence Grant (AoE/P-04/04) from the University Grants Council, HK SAR government Dr. Eva Shang

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