Projet ANR-06-BLAN-0322 – Pit-Net : In vivo functioning of pituitary-scale endocrine cell networks
Programme : Programme blanc (BLANC) 2006
Année de financement : 2006
Coordinateur du projet : CNRS DELEGATION REGIONALE LANGUEDOC ROUSSILLON (CNRS DELEGATION REGIONALE LANGUEDOC ROUSSILLON)
Partenaires : Centre national de la recherche scientifique; Centre national de la recherche scientifique
Montant : 420000.0 euros
Date de début : 2006
Durée : 48 mois
Résumé : Objectifs et contexte : Traditionally the anterior pituitary is viewed as a master endocrine gland in higher organisms with a complex and heterogeneous distribution of cells throughout its parenchyma. At present, functional assessment of these apparently dispersed cells is usually based on cell numbers and activities. However, each endocrine pituitary population needs to mount highly ordered hormone pulses (up to 1,000-fold rise in growth hormone [GH] levels in vivo) in response to physiological demands, whereas the hormone pulses are much smaller when endocrine cells are studied out of the context of the tissue. How the coherence and the integrity of the pituitary are prerequisites for its proper functioning remains, therefore, puzzling. Our recent data has completely changed the view of GH cells, the major population of endocrine cells in the pituitary, from a collection of dispersed cells to a geometrically connected homotypic network of cells. Local cell positioning and connectivity can vary to alter the timing of cellular responses and promote more coordinated pulsatile secretion (Bonnefont et al., PNAS 102:16880-16885, 2005). This was achieved through the synergistic collaborative efforts (development of transgenic GFP-tagged mice, large-scale 2-photon excitation microscopy, multicellular screening of signalling molecules...) of both French and English teams. Together with a third team who will bring further complementary expertise (electrophysiology, maths...), this group of teams will continue to share resources and to mutually stimulate their research efforts to address the proposal of how the anterior pituitary functions as a 3D assembly of intermingled endocrine cell networks. Our working hypothesis is that pituitary-scale cell positioning and associated cell-cell connection mechanisms will be critical parameters that determine how well each endocrine cell population can deliver a coordinated secretory pulse to their target tissues. We have chosen to focus our research activities on both pituitary GH and PRL (prolactin) cells for two major reasons. First, we have already got promising preliminary data showing a network-like organization of PRL cells that is topographically organized with regards to the GH cell network. Secondly, it would offer us the unique opportunity to solve a long-standing question of how such two endocrine cell populations with distinct hormonal outputs seem so closely related during both development and massive plastic changes that can occur throughout adulthood (for example during gestation and lactation). To achieve this goal, the group of teams will develop five sub-projects with significant overlap and interrelationship throughout the project (see B2 for details). Of significant importance will be the use of techniques and tools either recently developed by the teams (new in vivo fluorescence imaging with cellular resolution, new models for targeting/manipulating specific endocrine cell types) or under development (microRNAs for RNA interference under the control of hormone gene-specific promoters, transgenic mice with target-specific expression of an avian retroviral receptor). Perspectives  benefits for health care This project will provide the basis of understanding how a population of individual endocrine cell population (GH and PRL) generates a massive burst of hormone release into the systemic circulation, to deliver the appropriate pulsatile signal for decoding by peripheral tissues. We expect that our combination of transgenic, selective gene deletion/cell ablation strategies with functional in vivo imaging approaches can be applied to other cell types currently thought of as "heterogeneously distributed", not least to other endocrine cell types in the pituitary, and to examine their relationships with the extracellular matrix and non-endocrine cell types, such as the folliculostellate cell network that we described a few years ago (Fauquier et al., PNAS, 98, 8891-8896, 2001). Mor.