DIFFERENTIAL REGULATION OF 2 GENES IMPLICATED IN FISH REPRODUCTION - VITELLOGENIN AND ESTROGEN-RECEPTOR GENES

In rainbow trout as well as in other species, variability of estrogen receptor (ER) gene expression according to the cell type and the physi ological state reflects a differential cell and gene sensitivity to es trogen. We previously demonstrated that expression of the rainbow trou t estrogen receptor (rtER) and vitellogenin (Vg) genes were induced di fferently by estrogens in rainbow trout liver. Therefore, these two ge nes offered a suitable model to study the influence of ER concentratio n on gene transcriptional activities. In the present study we show tha t the transcription rate of rtER and Vg genes during an estrogenic tre atment ave affected differently by variation of cellular ER concentrat ion. We demonstrate that rtER gene exhibits a low threshold response t o loaded estrogen receptor, and increasing ER amounts do not affect th e transcriptional response of this gene during an estrogenic stimulati on. On the contrary, Vg gene expression requires the presence of a hig her loaded estrogen receptor level to be induced, and its transcriptio nal response is directly proportional to the amount of synthesised ER. (C) 1997 Wiley-Liss, Inc.