The LIM-homeodomain proteins Isl-1 and Lhx3 act with steroidogenic factor 1 to enhance gonadotrope-specific activity of the gonadotropin-releasing hormone receptor gene promoter.
The GnRH receptor (GnRH-R) plays a central role in mammalian reproductive function throughout adulthood. It also appears as an early marker gene of the presumptive gonadotrope lineage in developing pituitary. Here, using transient transfections combined with DNA/protein interaction assays, we have delineated cis-acting elements within the rat GnRH-R gene promoter that represent targets for the LIM-homeodomain (LIM-HD) proteins, Isl-1 and Lhx3. These factors, critical in early pituitary development, are thus also crucial for gonadotrope-specific expression of the GnRH-R gene. In heterologous cells, the expression of Isl-1 and Lhx3, together with steroidogenic factor 1 (SF-1), culminates in the activation of both the rat as well as human GnRH-R promoter, suggesting that this combination is evolutionarily conserved among mammals. The specificity of these LIM-HD factors is attested by the inefficiency of related proteins, including Lhx5 and Lhx9, to activate the GnRH-R gene promoter, as well as by the repressive capacity of a dominant-negative derivative of Lhx3. Accordingly, targeted deletion of the LIM response element decreases promoter activity. In addition, experiments with Gal4-SF-1 fusion proteins suggest that LIM-HD protein activity in gonadotrope cells is dependent upon SF-1 binding. Finally, using a transgenic model that allows monitoring of in vivo promoter activity, we show that the overlapping expression of Isl-1 and Lhx3 in the developing pituitary correlates with promoter activity. Collectively, these data suggest the occurrence of a specific LIM-HD pituitary code and designate the GnRH-R gene as the first identified transcriptional target of Isl-1 in the anterior pituitary.
Granger
Anne
A
Physiologie de l'Axe Gonadotrope, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7079, Physiologie et Physiopathologie, Université Pierre et Marie Curie-Paris6, 4 place Jussieu, 75252 Paris cedex 05, France.
Bleux
Christian
C
Kottler
Marie-Laure
ML
Rhodes
Simon J
SJ
Counis
Raymond
R
Laverrière
Jean-Noël
JN
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D006224:Cricetinae; D004247:DNA / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D009928:Organ Specificity; D010902:Pituitary Gland / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D011966:Receptors, LHRH / Q000235:genetics*; D020218:Response Elements / Q000235:genetics; D054339:Steroidogenic Factor 1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D018398:Homeodomain Proteins; C515057:NR5A1 protein, human; D018160:Receptors, Cytoplasmic and Nuclear; D011966:Receptors, LHRH; D054339:Steroidogenic Factor 1; D014157:Transcription Factors; C515058:steroidogenic factor 1, mouse; C515060:steroidogenic factor 1, rat; D004247:DNA