Abstract
Synthesis of the hypothalamic peptide, gonadotropin releasing hormone (GnRH), is paramount for reproductive function. GnRH neurons originate in the olfactory region and migrate into the forebrain during development. We recently implicated adhesion related kinase (Ark) in GnRH neuron development based on its differential expression in two GnRH producing cell lines, GT1-7 and Gn10. The Ark membrane receptor encodes an extracellular domain resembling cell adhesion molecules and an intracellular tyrosine kinase. Ark is expressed in Gn10 cells derived from migrating GnRH neurons but not GT1-7 cells of the post-migratory phenotype. Here, we show that Ark and GnRH transcripts are colocalized in the cribriform plate at midgestation, suggesting that Ark is expressed in migrating GnRH neurons in vivo. Furthermore, we have identified the GnRH gene as a downstream target of Ark signaling. Ark inhibits GnRH gene expression in GnRH neuronal cells via the coordinated binding of myocyte enhancer factor-2B and -2C (MEF-2B and -2C) and a putative homeoprotein within the proximal rat GnRH promoter. Given that MEF-2 proteins are widely expressed in the brain, these studies provide further evidence for MEF-2 action during neuronal development. Moreover, our studies elucidate a potential role for Ark in regulating GnRH gene expression during GnRH neuronal migration.
Highlights
The precisely orchestrated synthesis and pulsatile release of gonadotropin releasing hormone (GnRH)1 from neurons of the hypothalamus is essential for reproductive competence
adhesion related kinase (Ark) Expression in Neuronal Cell Lines and in Vivo—Since Gn10 and GT1-7 cells were derived during two windows of GnRH neuronal development, we performed differential display on the cell lines to identify novel factors potentially involved in the migratory process and GnRH gene expression [11]
We demonstrated that Ark is expressed in the Gn10 cells derived during GnRH neuron migration but not the GT1-7 cells of the post-migratory phenotype (Fig. 1, A and B)
Summary
The precisely orchestrated synthesis and pulsatile release of gonadotropin releasing hormone (GnRH) from neurons of the hypothalamus is essential for reproductive competence. The GnRH neuronal pathway has been well characterized during development, the factors regulating GnRH gene expression along the migratory route remain to be identified. The Gn10 GnRH neuronal line was developed by SV40 T-antigen immortalization of GnRH neurons at the time of migration and expresses low levels of GnRH [5]. We performed differential display on the two GnRH producing cell lines to identify novel factors regulating GnRH neuron migration and gene expression [11]. Our studies have shown that Gn10 GnRH neuronal cells are protected from serum withdrawal induced apoptosis by Gas6-Ark signaling pathways [33]. Gas6-Ark signaling does not stimulate Gn10 cell proliferation These data suggest that Ark may play a role in GnRH neuronal survival during development. Preliminary studies in our laboratory suggest that Gas6-Ark
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