Androgen inhibition of vitellogenin gene expression in tilapia (Oreochromis niloticus).
Treatment of mature female tilapia (Oreochromis niloticus) with high levels of androgen (17 alpha-methyltestosterone, 17 alpha MT) results in a pronounced decline in plasma vitellogenin levels as determined by gel electrophoresis. Total RNA extracted from livers of treated fish and vehicle-injected controls was analyzed by Northern and slot blot hybridization using an oligonucleotide complementary to a sequence in the 3' end of tilapia vitellogenin mRNA. The probe revealed an mRNA of 6.5 kb in liver from the control mature female fish which was decreased by 85% by androgen treatment. As expected, estradiol (E2) treatment induced the 6.5-kb mRNA in mature male tilapia. The antiestrogen, tamoxifen, strongly decreased vitellogenin mRNA levels in mature females. Radioimmunoassay of serum from control and 17 alpha MT-treated female tilapia showed a marked reduction in serum E2 levels, from 11.4 +/- 2.6 ng/ml in controls to 2.2 +/- 0.13 ng/ml in treated fish. Tamoxifen, however, resulted in increased serum E2 levels, probably by blocking E2 negative feedback. The serum E2-lowering effect of 17 alpha MT suggests an inhibitory site of action on gonadotropin production at the hypothalamic-pituitary axis, possibly through an androgen receptor or through an estrogen receptor after local aromatization of 17 alpha MT.
Lazier
C B
CB
Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia, Canada. CBLAZIE@AC.DAL.CA
Langley
S
S
Ramsey
N B
NB
Wright
J M
JM
D000818:Animals; D001667:Binding, Competitive; D001798:Blood Proteins / Q000032:analysis; D015152:Blotting, Northern; D004591:Electrophoresis, Polyacrylamide Gel; D004958:Estradiol / Q000097:blood / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000187:drug effects*; D008099:Liver / Q000378:metabolism; D008297:Male; D008777:Methyltestosterone / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology; D017210:Tilapia / Q000378:metabolism*; D014819:Vitellogenins / Q000097:blood / Q000235:genetics*
D001798:Blood Proteins; D004965:Estrogen Antagonists; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D014819:Vitellogenins; D013629:Tamoxifen; D004958:Estradiol; D008777:Methyltestosterone