Permanent and Functional Male-to-Female Sex Reversal in d-rR Strain Medaka (Oryzias latipes) Following Egg Microinjection of o, p'-DDT Environmental Health Perspectives v.108, n.3, Mar00

J. Stewart G. Edmunds,^1,2 Robert A. McCarthy,² and John S. Ramsdell^1,2

¹Marine Biotoxins Program, Center for Coastal Environmental Health and Biomolecular Research, NOAA National Ocean Service, Charleston, South Carolina, USA
²Marine Biomedical and Environmental Sciences and Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston, South Carolina, USA

Abstract
Complete sex reversal of fish is accomplished routinely in aquaculture practices by exposing fish to exogenous sex steroids during gonadal differentiation. A variety of environmental chemicals are also active at sex steroid receptors and theoretically possess the potential to alter normal sexual differentiation in fish. However, in controlled environmental chemical exposures to date, only partial alterations of fish sexual phenotype have been observed. Here we report complete, permanent, and functional male-to-female sex reversal in the Japanese medaka (Oryzias latipes, d-rR strain) after a onetime embryonic exposure to the xenoestrogen o,p'-DDT. d-rR strain medaka are strict gonochorists that possesses both sex-linked pigmentation, which distinguishes genotypic sex, and sexually dimorphic external secondary sexual characteristics, which distinguish phenotypic sex. We directly microinjected the xenoestrogen o, p'-DDT into the egg yolks of medaka at fertilization to parallel the maternal transfer of lipophilic contaminants to the embryo. At 10 weeks of age, microinjected medaka were examined for mortality and sex reversal. A calculated embryonic dose of 511 ± 22 ng/egg o, p'-DDT (mean ± standard error) resulted in 50% mortality. An embryonic exposure of 227 ± 22 ng/egg o, p'-DDT resulted in 86% (6 of 7) sex reversal of genetic males to a female phenotype (XY females). XY females were distinguished by sex-linked male pigmentation accompanying female secondary sexual characteristics. Histologic examination of the gonads confirmed active ovaries in 100% of the XY females. In 10-day breeding trials in which XY females were paired with normal XY males, 50% of the XY females produced fertilized embryos; this represents a comparable breeding success rate to normal XX females. Fertilized eggs produced from XY females hatched to viable larvae. These results clearly indicate that a weakly estrogenic pesticide, o, p'-DDT, when presented during the critical period of gonadal development, can profoundly alter sexual differentiation. Key words: endocrine disruptors, medaka, o, p' -DDT, sex reversal, xenoestrogen. Environ Health Perspect 108:219-224 (2000). [Online 21 January 2000]

http://ehpnet1.niehs.nih.gov/docs/2000/108p219-224edmunds/abstract.html

Address correspondence to J.S. Ramsdell, Chief, Coastal Research Branch, Center for Coastal Environmental Health and Biomolecular Research, NOAA National Ocean Service, 219 Fort Johnson Road, Charleston, SC 29439 USA. Telephone: (843) 762-8510. Fax: (843) 762-8700. E-mail: john.ramsdell@noaa.gov

We thank Y. Wakamatsu, Nagoya University, Nagoya, Japan, for providing the d-rR strain medaka. We also thank B. Roumilat, South Carolina Marine Resources Research Institute, for assistance with histopathology and J. Kucklick, National Institute for Standards and Technology, for assistance with gas chromatography. The National Ocean Service (NOS) does not approve, recommend, or endorse any proprietary product or material mentioned in this publication. No reference shall be made to NOS, or to this publication furnished by NOS, in any advertised or sales promotion that would indicate or imply that NOS approves, recommends, or endorses any proprietary product or propriety material mentioned herein or that has as its purpose any intent to cause directly or indirectly the advertised product to be used or purchased because of NOS publication.

Received 28 July 1999; accepted 21 September 1999.