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Developmental Dependence on NurRE and Ebox_Neuro for Expression of Pituitary Proopiomelanocortin

Laboratoire de Génétique Moléculaire, Institut de Recherches Cliniques de Montréal, Montréal, Québec, Canada H2W 1R7

Address all correspondence and requests for reprints to: Jacques Drouin or Aurélio Balsalobre, Laboratoire de Génétique Moléculaire, Institut de Recherches Cliniques de Montréal 110, Avenue des Pins Ouest, Montréal, Québec, Canada H2W 1R7. E-mail: jacques.drouin{at}ircm.qc.ca; or aurelio.balsalobre{at}ircm.qc.ca.

Cell-specific expression of the pituitary proopiomelanocortin (POMC) gene depends on the combinatorial action of a large number of DNA-binding transcription factors (TFs). These include general and cell-restricted factors, as well as factors that act as effectors of signaling pathways. We have previously defined in the distal POMC promoter a composite regulatory element that contains targets for basic helix-loop-helix TFs conferring cell specificity and for NGFI-B orphan nuclear receptors that are responsive to CRH signaling and to glucocorticoid negative feedback. These factors act on neighboring regulatory elements, the Ebox_Neuro and NurRE, respectively. Currently, the Ebox_Neuro is thought to be the target of NeuroD1 during fetal development, but this factor may not account for activity in the adult pituitary; it is also unknown whether the NurRE and NGFI-B-related factors are active before establishment of the hypothalamic-pituitary portal system. In order to assess the importance of these regulatory elements and their cognate TFs throughout pituitary organogenesis and in the adult, we have assessed the activity of mutant POMC promoters in transgenic mice throughout development. These experiments indicate that the Ebox_Neuro and cognate basic helix-loop-helix factors are required throughout development and in the adult gland, beyond expression of NeuroD1. Similarly, the data reveal sustained importance of the NurRE and its cognate factors throughout pituitary development. These data contrast the sustained dependence throughout development on the same regulatory elements with the highly dynamic patterns of TF expression and the modulation of their activity in response to signaling pathways.

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Nuclear Receptors:   NGFIB  |  NURR1  |  NOR1