Differential expression of neural and gonadal aromatase enzymatic activities in relation to gonadal development in Japanese eel, Anguilla japonica.
The objectives of the present study were to investigate the enzymatic characteristics of brain aromatase in Japanese eel, Anguilla japonica, as well as the correlations between aromatase activities in various tissues (brain regions, pituitary, and gonads) and ovarian development. Eel brain aromatase exhibited a K(m) of 75 nM and a V(max) of 1.14 fmol/min mg protein (91.5 fmol/h mg protein), indicating an enzymatic activity much lower than in other teleosts but similar to that in mammals. This supports the hypothesis of the occurrence of a single aromatase gene in eels (representative of an ancient group of teleosts, Elopomorphs), as in mammals, but unlike what is observed in more recent teleosts. Aromatase inhibitors could significantly suppress brain and pituitary aromatase activity. There was no significant sex difference in aromatase activity in the forebrain, midbrain, hindbrain, or pituitary, but there was in the gonads, where aromatase could be detected in the ovaries but not in the testes, in accordance with the role of this enzyme in ovarian differentiation. Comparison with another teleost, black porgy (Percomorph), under the same experimental conditions, further confirmed the low activity of aromatase in the eel. We investigated variations in brain, pituitary, and gonad aromatase activity in relation to ovarian development in control female eels (gonadosomatic index, GSI, 0.1-1.6%) as well as in eels treated with pituitary extract (experimental ovarian maturation; GSI up to 25%). Differential expression of neural and gonadal aromatase was observed in relation to the course of gonadal development. Pituitary aromatase activity increased with GSI at all stages. Brain (specially forebrain) aromatase activity significantly increased in early vitellogenic control eels (GSI>0.8%) and in treated eels. The low activity of eel aromatase may be related to the characteristic life cycle of the eel, in which there is a long delay of the onset of puberty before oceanic reproductive migration.
Jeng
Shan-Ru
SR
Department of Aquaculture, National Taiwan Ocean University, Keelung 202, Taiwan.
Dufour
Sylvie
S
Chang
Ching-Fong
CF
D000735:Androstenedione / Q000378:metabolism; D000811:Anguilla / Q000254:growth & development / Q000378:metabolism*; D000818:Animals; D001141:Aromatase / Q000378:metabolism*; D001921:Brain / Q000201:enzymology*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D008297:Male; D009865:Oocytes / Q000187:drug effects / Q000254:growth & development; D010053:Ovary / Q000201:enzymology*; D010473:Perciformes / Q000378:metabolism; D010902:Pituitary Gland / Q000201:enzymology; D012727:Sex Characteristics; D013737:Testis / Q000201:enzymology*
D000735:Androstenedione; D001141:Aromatase