An octamer-binding site is crucial for the activity of an enhancer active at the embryonic met-/mesencephalic junction

An enhancer sequence found in the Protease Nexin-1 (PN-1) gene was shown to drive lacZ expression specifically at the met-/mesencephalic junction in t ransgenic mouse embryos. A functional study of this enhancer has been perfo rmed to better understand the mechanisms regulating isthmic gene expression . An octamer-binding site for POU domain factors was found to be crucial fo r the activity of the enhancer in vivo. Comparative expression studies of P OU domain factors, electrophoretic mobility shift assays and transient tran sfection experiments, strongly suggest that Brn-1/-2 regulate the enhancer activity in vivo. In addition, in vitro experiments indicated that FGF-8 wa s required for the maintenance of the enhancer activity, but not for the sy nthesis of Brn-1/-2. The data represents the first functional evidence for a role of POU factors in the regulation of met-/mesencephalic gene expressi on. It also implies that at least two regulatory pathways, namely the FGF-8 signaling and the octamer-binding site pathway, synergistically interact t o control the PN-1 enhancer activity in vivo. (C) 1999 Elsevier Science Ire land Ltd. All rights reserved.