A tumor necrosis factor decoy receptor homologue is up-regulated in the brook trout (Salvelinus fontinalis) ovary at the completion of ovulation

An up-regulated cDNA fragment was obtained from differential-display polyme rase chain reaction of brook trout ovarian tissue stimulated by phorbol-12- myristate-13-acetate (PMA) and calcium ionophore A23187. Using this cDNA as a probe, a full-length cDNA of 2267 base pairs was obtained by screening a library of PMA/A23187-stimulated ovarian cDNA. The mRNA obtained presumabl y encodes for a 302-amino acid protein showing similarities with several me mbers of the tumor necrosis factor (TNF) receptor superfamily, The protein contains several cysteine-rich domains characteristic of mammalian TNF rece ptor members and is most similar to human decoy receptor 3 and osteoprotege rin, two soluble decoy TNF receptors. Consequently, this TNF receptor homol ogue was tentatively named a trout decoy receptor (TDcR). On Northern blots of ovarian tissue, TDcR hybridized with a 2.2-kilobase transcript that was strongly up-regulated under phorbol ester stimulation. TDcR mRNA was local ized in granulosa cells and was detected in the ovary during and after natu ral ovulation. Its expression was up-regulated at the end of ovulation and progressively down-regulated after 48 h postovulation. Among of her trout t issues tested, the transcript was present only in the testis. To our knowle dge this is the first description of a member of the TNF receptor family fr om a lower vertebrate and the first report of a decoy-like TNF receptor in the vertebrate ovary.