Transgenics identify distal 5 '- and 3 '-sequences specifying gonadotropin-releasing hormone expression in adult mice

GnRH neurons play a critical role in regulating gonadotropin secretion, but their scattered distribution has prevented detailed understanding of their molecular and cellular properties in vivo. Using GnRH promoter-driven tran sgenics we have examined here the role of 5'- and 3'-murine GnRH sequences in specifying GnRH expression in the adult mouse. Transgenic mice bearing a lacZ construct incorporating 5.5 kb of 5'-, all the introns and exons, and 3.5 kb of 3'-murine GnRH sequence were found to express beta-galactosidase (beta gal) immunoreactivity in approximately 85% of all GnRH neurons. Dele tion of GnRH sequence 3' to exon II had no effect upon transgene expression in the GnRH population (89%) but resulted in the appearance of ectopic bet a gal immunoreactivity in several regions of the brain. The production of a dditional mice in which 5'-elements were deleted to leave only -2.1 kb of s equence resulted in an approximately 40% reduction in the number of GnRH ne urons expressing beta gal. Mice in which further deletion of 400 bp allowed only -1.7 kb of 5'-sequence to remain exhibited a complete absence of beta gal immunoreactivity within GnRH and other neurons. These results suggest that elements 3' to exon II of the GnRH gene have little role in enabling G nRH expression within the GnRH phenotype but, instead, are particularly imp ortant in repressing the GnRH gene in non-GnRH neurons. In contrast, elemen ts located between -2.1 and -1.7 kb of distal 5'-sequence appear to be crit ical for the in vivo activation of GnRH expression within GnRH neurons in t he adult brain.