Oestrogen receptor mRNA and a related RNA transcript in mouse ovaries

Oestrogen receptor mRNA expression in mouse ovaries was analysed by Northern blotting of total RNA using 32P-labelled RNA probes complementary to different functional domains of the oestrogen receptor. The approximately 6.5 kb mouse oestrogen receptor mRNA transcript was present in immature and adult ovaries at extremely low abundance compared with uterus and oviduct. Using a probe complementary to the steroid-binding domain of the oestrogen receptor (probe EF), a novel RNA transcript of approximately 1.5 kb was also found in the ovaries but was absent from uterus and oviduct. The melting temperature of the hybrid produced by the approximately 1.5 kb transcript with probe EF was approximately 10 degrees C lower than that produced by authentic oestrogen receptor mRNA, which demonstrates incomplete sequence homology between the two transcripts and indicates that the approximately 1.5 kb RNA is not a truncated form of oestrogen receptor mRNA. Furthermore, the approximately 1.5 kb RNA lacks the DNA-binding domain found in the oestrogen receptor. The approximately 1.5 kb RNA, but not oestrogen receptor mRNA, was enriched in total RNA from isolated granulosa cells compared with residual ovarian tissue. The encoded product of this novel oestrogen receptor-related RNA could be a steroid-binding protein involved in oestrogen action in the ovaries.