STEROIDOGENIC FACTOR-I (SF-1) AND THE REGULATION OF EXPRESSION OF LUTEINIZING-HORMONE AND FOLLICLE-STIMULATING-HORMONE B-SUBUNITS IN THE SHEEP ANTERIOR-PITUITARY IN-VIVO

Luteinising hormone (LH) and follicle stimulating hormone (FSH) compri se a common alpha-subunit and hormone-specific beta-subunit, are expre ssed in gonadotroph cells of the anterior pituitary and during the she ep oestrous cycle, are regulated by gonadotrophin releasing hormone (G nRH), ovarian peptides and steroids, Transcription factor steroidogeni c factor-1 (SF-1) transactivates the common alpha-subunit and LH beta subunit in other species, We investigated whether SF-1 regulates beta- subunit expression and the regulation of SF-1 expression in vivo in sh eep, Immunocytochemistry co-localised SF-I, LH and FSH to sheep pituit ary gonadotrophs and electrophoretic mobility shift assays (EMSA) demo nstrated that SF-1 bound to the LH beta promoter in vitro. NO SF-1 DNA binding site was found in the FSH beta promoter, No difference in mea n levels of SF-I, FSH beta, LH beta and GnRHr mRNA was measured betwee n the luteal and follicular phases of the oestrous cycle, However SF-1 mRNA levels were correlated to those of LH beta in individual luteal phase animals (r = 0.88, p < 0.05), when the transcription rate of LH beta was significantly higher (p < 0.01), GnRH antagonist treatment of luteal animals did not produce a significant reduction in mRNA levels of LH beta, SF-1 and FSH beta, Administering oestradiol benzoate with GnRH antagonist reduced levels of SF-1 and FSH beta mRNA from luteal values (p < 0.005), We conclude that: (1) expression of SF-1 is not so lely dependent on GnRH and is downregulated by oestradiol; (2) the LH beta transcription rate is increased during the luteal phase but is no t related to levels of LH beta or SF-1 mRNA; and (3) SF-1 does not app ear to directly regulate expression of FSH beta, but may regulate expr ession indirectly, (C) 1997 Elsevier Science Ltd, All rights reserved.