The Effect Of Sex Steroid On The Sex Differentiation In Silurus Meridionalis Chen

The author used aromatase (enzyme for estrogen synthesis) inhibitor (fadrozole), estrogen receptor antagonist (tamoxifen) and methylteslosterone(MT) to administrate the artificial fertilized all female Southern Catfish(Silurus meridionalis Chen) from 5 day after hatching(dah) to 48 dah by oral administration. The corresponding dosage of the above drugs were: 1) fadrozole 10mg/kg, 150mg/kg; 2) tamoxifen 25mg/ kg; 3) MT 10 mg/kg, 50mg/kg; Anymore, we also used MT (50 mg/kg) to administrate the Southern catfish baby fish during different period including 5dah-15dah, 5dah-25dah and 5dah-75 dah. After all these drug administrations were completed, we tried to analyze the results by different ways from naked eyes observation, histology dissection and the change of mRNA in pertinent tissues. The results are as below:The fadrozole group: The lower dosage group had 50% male fish by naked eyes observation of gonads after 5 months past hatching, which was proved by histological dissection. At 48dah, the gonads of some Southern catfish developed relatively slower than control group fish under the effect of fadrozole by the hislological dissection. Meanwhile, the gonads of female fish had already appeared ovary cavity and oocyte. We also found that the mRNA expression of aromatase brain and ovary type in gonad tissue were much lower than control all-female group in 48dah. while the aromatase brain type in brain tissue was not affected. Anyhow, what we unexpected was that we did not get any male fish in the higher dosage fadrozole group, which was confirmed by naked eyes observation , histological dissection and aromatase mRNA expression in the corresponding tissues.The tamoxifen group had 40% male fish by naked eyes observation of gonads after 5 months past hatching, which was proved by histological dissection. The gonads of some Southern catfish developed relatively slower than normal fish under the effect oftamoxifen after the histological dissection of 48 dah fish. Very similar to the results of fadrozole, the expression of aromatase brain and ovary type mRNA in gonad was much lower than control group, while in brain tissue aromaiase brain type was not affected.MT groups: No matter using lower dosage or higher dosage to administrate Southern catfish all female baby fish, we could not observe their effects of gonad on the histology level except gonadal abnormality by the naked eye observation after 5 month hatching. At 48 dah, the histology structure had no changes compared to control group. However, We watched some aggressive behavior such as worry and scattering in the tank compared with the normal gathering phenomenon. What's more, we also found the fork-like tail of these fish under the effect of MT. When drugs administration on the baby fish stopped, the effect on behavior and morphology disappeared.Aromatase is the key enzyme for estrogen synthesis. In order to study the effect of estrogen during the process of sex differentiation in the level of molecular, we designed degenerated primers according to the conservative parts of many published aromatase cDNA sequences. By means of reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification cDNA ends (RACE), we successfully cloned Southern catfish aromatase brain type cDNA. The cDNA consists of 2337 nucleotides, which includes!92 and 624 non-coding nucleotides in the 5' and 3' ends respectively. The coding region of the cDNA consist of 1521 nucleotides which encodes 507 amino acids as the aromatase P450 pre-protein. The deduced amino acid based on cDNA is very similar to Channel catfish (Ictaluruspunctatus), which is as high as.83%. Using semi-quantification PCR to study the relative mRNA expression in different tissues, we found the results ranked as brain>gonad>muscle>spleen, while there were no expression in gill, liver or heart. Compared with much high expression between brain and gonad in the kidney of female fish, the male fish had no expression of aromatase brain type. At the same time, we also studied its expression in go...