The estrogen-binding region of the cDNA for chicken ER reveals a mRNA of 3.5 kilobases (kb) in rainbow trout liver. The level of this messenger, which is very low in the liver of naive male animals, can be increased by estrogen stimulation. With this chicken probe, we have isolated a clone from a lambda gt10 trout liver cDNA library. The partial cDNA sequence, which encompasses most of the coding region, shows two domains of striking amino acid homology with human, avian, and Xenopus estrogen receptors (ERs) (DNA binding region: 90%, Hormone binding region: 60%). With this specific probe rainbow trout ER, we detected another messenger (4.5 kb) that is less expressed than the 3.5 kb messenger. The kinetics of stimulation of the two messengers is compared with the kinetics of accumulation of vitellogenin mRNA after E2 administration. This report constitutes the first identification of ER mRNA from a fish.

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The northern part of the Bay of Biscaye consists of muddy areas which were the subject of many surveys conducted from the early sixties revealing important modifications. Communities living in these muddy areas are very rich in quality as well as quantity and with high interactions between the different species. With their trophic ethology, their biogenic actions, these species modify largely the sediment quality, its compactness for example is related to the tubicolous species presence. The disappearance of certain dominant species is due to some climatic anomalies causing an important disturbance of the ecosystem. In the infralittoral muddy areas, Zostera beds had been replaced momently by the abundant populations of Melinna. In the coastal muddy sites the recent disappearance of the Maldane cause a momentary imbalance, and for many long years, an equilibrium based on a new dominant species may appear. The intervention of an allogenic factor may in this case, opposite autogenic succession of the community or call the equilibrium which seems established in question again.

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Agarose-gel electrophoresis of polyadenylated RNA from livers of oestrogen-treated male rainbow trout revealed a major high-Mr species (7200 nucleotides), which is absent from the polyadenylated RNA isolated from hormonally unstimulated male trout liver. Translation in vitro of the RNA from oestrogen-treated males in a mRNA-dependent rabbit reticulocyte lysate produced a protein (Mr 200 000) that could be immunoprecipitated with antibodies against trout serum vitellogenin, but no immunoprecipitable protein was synthesized with RNA from control animals. DNA complementary to the RNA from oestrogen-stimulated and control male trout liver was synthesized and back-hybridized, with R0t1/2 of 3.8 X 10(-2) and 1 X 10(-1) mol X litre-1 X s for RNA from hormone-treated and control animals respectively. The 9% increase in the abundant mRNA after oestrogen stimulation is due to the induction of vitellogenin mRNA.

The study of the seasonal regulation of vitellogenesis in rainbow trout (Salmo gairdneri) is hampered by two features of the system which are not seen in species such as Xenopus. First, it is impossible to sex immature trout by external appearance and, secondly, the quantitation of the very low levels of vitellogenin in previtellogenic serum is technically difficult and tedious. We describe the preparation of a specific, sensitive anti-vitellogenin antibody and the use of this antibody in a rocket immunoelectrophoresis system to measure serum vitellogenin. The sensitivity of the assay is such that, using only 2 μL of serum, it is possible to detect vitellogenin at levels of 10 μg/mL, making this assay extremely useful for selecting immature female trout for further studies on the basis of the presence of vitellogenin. Using this system we have also measured the response of individual male trout to stimulation with different levels of estradiol, and we have shown that it is possible to measure the stimulation of vitellogenin by estradiol levels equivalent to those seen during the previtellogenic phase of the reproductive cycle in females. This simple assay system thus alleviates two of the major hurdles in studying vitellogenesis in trout.

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