Characterization of the ovine LHβ-subunit gene: The promoter is regulated by GnRH and gonadal steroids in transgenic mice

We have previously demonstrated that 1.9 kb of ovine LHβ promoter fused to bacterial chloramphenicol transferase (CAT) coding sequence is sufficient to target expression of the transgene specifically to the gonadotroph cells of the anterior pituitary in mice with no expression being observed ill other tissues. However, it is not known if this region of the ovine LHβ promoter contains the necessary elements that confer transcriptional regulation by gonadal steroids and GnRH. Following gonadectomy, both endogenous pituitary LHβ and CAT activity significantly (P > 0.001) increased as did plasma LH. This post-gonadectomy increase in CAT, pituitary and plasma LH could be suppressed in females by treatment with oestradiol alone or oestradiol and progesterone, with an additional significant (P < 0.05) reduction in CAT activity being observed in one line following the combined steroid treatment. In castrated males, testosterone suppressed CAT activity in one line. Treatment of transgenic ovariectomized females with oestradiol alone significantly suppressed plasma LH (P < 0.01) with no change in pituitary LH content. There was no difference in pituitary LH between oestradiol-treated ovariectomized transgenic and non-transgenic females. Treatment of intact females from both lines with either GnRH antiserum or agonist demonstrated a decrease in pituitary CAT activity whereas similar treatment in intact males had no effect. While endogenous pituitary LH concentrations were variable, plasma LH was lower in all treated animals irrespective of line, sex or expression of the transgene. In conclusion, these results indicate that (1) the presence of CAT protein is not toxic and does not compromise either endogenous LH synthesis, storage and secretion and (2) the ovine LHβ-CAT gene is regulated in a similar but more variable manner to the endogenous LHβ gene. This may relate to the use of CAT as a reporter where its release is not necessarily related to that of the endogenous hormone whose synthesis, storage and release may differ.