Otx2 Induction of the Gonadotropin-releasing Hormone Promoter Is Modulated by Direct Interactions with Grg Co-repressors

doi:10.1074/jbc.M109.002485

Otx2 Induction of the Gonadotropin-releasing Hormone Promoter Is Modulated by Direct Interactions with Grg Co-repressors*

Rachel Larder and
Pamela L. Mellon,¹

From the Department of Reproductive Medicine and Center for Reproductive Science and Medicine, University of California, San Diego, La Jolla, California 92093-0674

¹To whom correspondence should be addressed:
9500 Gilman Dr., La Jolla, CA 92093-0674.
Tel.: 858-534-1312; Fax: 1-858-534-1438; E-mail: pmellon{at}ucsd.edu.

Abstract

Hormonal communication between the hypothalamus, pituitary, and gonads orchestrates the development and regulation of mammalian reproductive function. In mice, gonadotropin-releasing hormone (GnRH) expression is limited to ∼1000 neurons that originate in the olfactory placode then migrate to specific positions scattered throughout the hypothalamus. Coordination of the hypothalamic-pituitary-gonadal axis is dependent upon correct migration of GnRH neurons into the hypothalamus followed by the appropriate synthesis and pulsatile secretion of GnRH. Defects in any one of these processes can cause infertility. Recently, substantial progress has been made in identifying transcription factors, and their cofactors, that regulate not only adult expression of GnRH, but also the maturation of GnRH neurons. Here, we show that expression of Otx2, a homeodomain protein required for the formation of the forebrain, is dramatically up-regulated during GnRH neuronal maturation and that overexpression of Otx2 increases GnRH promoter activity in GnRH neuronal cell lines. Furthermore, Otx2 transcriptional activity is modulated by Grg4, a member of the Groucho-related-gene (Grg) family. Using mutational analysis, we show that a WRPW peptide motif within the Otx2 protein is required for physical interaction between Otx2 and Grg4. Without this physical interaction, Grg4 cannot repress Otx2-dependent activation of GnRH gene transcription. Taken together, these data show that Otx2 is important for GnRH expression and that direct interaction between Otx2 and Grg co-repressors regulates GnRH gene expression in hypothalamic neurons.

Footnotes

↵* This work was supported, in whole or in part, by National Institutes of Health Grants R01 DK044838 and HD020377 (to P. L. M.). This work was also supported by NICHD/NIH through a cooperative agreement (U54 HD012303) as part of the Specialized Cooperative Centers Program in Reproduction and Infertility Research (to P. L. M.).
↵ The on-line version of this article (available at http://www.jbc.org) contains supplemental Fig. S1.
↵3 A. Iyer, N. Miller, and P. Mellon, submitted for publication.
↵2 The abbreviations used are:

GnRH

gonadotropin-releasing hormone

Grg

Groucho-related-gene

EMSA

electrophoretic mobility shift assay

HDAC

histone deacetylase

IVT

in vitro translated

GAPDH

glyceraldehyde-3-phosphate dehydrogenase

GFP

green fluorescent protein

ANOVA

analysis of variance

RT

reverse transcription

TK

thymidine kinase.
- Received April 1, 2009.