PEA3 is the founding member of a subfamily of closely related Ets transcriptional regulatory proteins that includes ERM and ER81. The PEA3 subfamily members share greater than 95% identity in their ETS DNA binding domain and 500/o sequence similarity overall, suggesting these genes may serve redundant functions. The overexpression of each member is positively correlated with HER2 mediated breast tumorigenesis in humans and mice, suggesting a role for this subfamily in mammary development and oncogenesis. This study first addresses the role of PEA3 in cellular transformation mediated by oncogenic Ras and Neu. Wildtype and PEA3-null mouse embryo fibroblast cell lines were infected and tested for focus formation. PEA3-null fibroblasts are refractory to transformation as compared to their wildtype counterparts. Ras and Neu transformed foci show elevated PEA3 subfamily mRNA transcripts and PEA3 protein. ERM and ER81 are expressed in PEA3-null fibroblasts and do not appear to compensate for loss of function mutations in the PEA3 gene resulting in the transformation-defective phenotype. Expression of candidate PEA3 target genes (MMP-3 and MMP-9, which have known roles in transformation) is compromised in PEA3-null fibroblasts. Re-expression of PEA3 in these cells rescues the transformation-deficient phenotype and restores expression of MMP-3 and MMP-9. Hence, PEA3 appears to be a crucial effector in Ras and Neu mediated transformation, in addition to serving an important regulatory role of genes involved in cell motility and invasive tumor behaviour. This study also addresses the role of ER81 in normal mammary gland development. PEA3 is required for normal mammary gland development, as displayed by the reduced branching phenotype in PEA3-null female mice. Mice lacking functional ER81 were generated to determine if ER81 serves a similar role in mammary gland development. ER81 is expressed in the epithelial cells of mammary buds at E 1 0.5, when these structures first appear during mouse embryogenesis. ER81 is then differentially expressed during postnatal mammary gland development, with highest expression occurring at times of extensive epithelial branching. During puberty, expression is observed in undifferentiated cap and body cells of terminal end buds, in differentiated luminal and myoepithelial cells of ducts. During pregnancy, expression in luminal epithelial cells is lost, but persists in the myoepithelial cells within the ducts and alveoli. Targeted disruption of both ERSt alleles result in severely runted mice that die by 4 weeks of age, thereby precluding study of mammary gland development in these mice beyond this developmental stage. However, loss of a single ER81 allele results in healthy looking mice, comparable in size and lifespan to wildtype littermates. Studies employing ER81 heterozygous mice reveal a 50% allelic dose is sufficient for normal mammary gland development. Loss of a single ER81 allele did not result in any overt phenotypes in ductal branching, lobulo-alveolar development, or morphology of the surrounding fat pad. / Thesis / Master of Science (MSc)

La sensation du toucher permet de détecter des stimuli mécaniques via des neurones mécanosensitifs dont les corps cellulaires sont localisés dans le ganglion rachidien dorsal. Ces neurones projettent vers la peau en périphérie et font leurs synapses avec les interneurones dorsaux de la moelle épinière. L'étude de ces neurones était difficile à cause du manque de marqueurs spécifiques pour ces neurones, jusqu'à la découverte du gène MafA dans le ganglion rachidien dorsal. En effet, mon équipe a montré que MafA est un marqueur spécifique des neurones mécanosensitifs à bas seuil de type Rapidly adapting. Le gène c-Maf, de la même famille que MafA, est aussi exprimé dans ces neurones et il est l'acteur principal de leur développement et de leur fonction. Afin de comprendre comment c-Maf contrôle le développement des neurones somatosensoriels, la première partie de mon travail visait à identifier de nouveaux gènes cibles du facteur de transcription c-Maf et à savoir comment l'expression de ce dernier est régulée dans les neurones du ganglion rachidien dorsal. Concernant la recherche des gènes cibles de c-Maf, j'ai réalisé l'étude de l'expression de gènes candidats dans le contexte de perte de fonction de c-Maf chez la souris. J'ai pu identifier deux cibles : p-cadhérine et mab21/L2, parmi une liste de gènes candidats. J'ai par la suite analysé l'expression de P-cadhérine au cours du développement et j'ai observé qu'elle est exprimée dans la sous-population de neurones sensoriels myélinisés exprimant c-Maf ainsi que dans certains interneurones des laminae III/IV de la moelle épinière. Une expression particulière de P-cadherine est observée dans les cellules des capsules frontières dans les zones d'entrée et de sortie des racines rachidiennes. Suite à ces observations, nous avons émis l'hypothèse suivante : l'expression de la p-cadhérine est régulée par c-Maf dans les neurones sensoriels ainsi que dans les interneurones pour assurer la connexion synaptique entre eux. Concernant, la régulation du gène c-maf, la question reste ouverte. La deuxième partie de mon étude concernait l'analyse du rôle de facteurs de transcription MafA, c-Maf, Runx3 et Er81 dans la plasticité neuronale induite chez la souris adulte après axotomie du nerf sciatique. Ces facteurs sont impliqués dans le développement des neurones somatosensoriels. Cette analyse a montré que l'expression de MafA et Er81 diminue trois jours après axotomie du nerf périphérique, alors que celle de Runx3 et de c-Maf n'est pas affectée. On peut suggérer que chez l'adulte, la régulation de l'expression de MafA et Er81 dépend des facteurs neurotrophiques libérés par les cibles de ces neurones tandis que celle de c-Maf et Runx3 en est indépendante. / The sense of touch relies on the detection of mechanical stimuli by specialized cutaneous mechanosensory neurons whose cell bodies are located in the dorsal root ganglia. These neurons project peripherally to the skin and synapse on target interneurons in the spinal cord. Until the discovery of MafA expression in the dorsal root ganglion, the lack of molecular markers of mechanoreceptor neurons has made it difficult to analyze the development of these neurons. My team showed that MafA is a specific molecular marker for low-threshold mechanoreceptor neurons RAM. C-Maf gene is a member of the Maf family and it is expressed in the MafA sensory neurons. The transcription factor c-Maf controls touch receptor development and function.In order to understand how c-Maf controls somatosensory neurons development, the first objective of my study was to find new targets for c-Maf transcription factor and to know how c-Maf expression is regulated in the dorsal root ganglion. Therefore, I have analysed the expression of different candidate genes in a loss of function context of c-Maf in the mice. I identified two targets: p-cadherin and Mab21/L2 among a list of candidates. Then, I analysed the p-cadherin expression during development and found that this target of c-Maf is expressed in a sub-population of c-Maf sensory neurons and interneurons of the laminae III/IV of the spinal cord. A particular expression of p-cadherin was noticed in the boundary cap cells at the dorsal root entry zone and the motor exit point of the spinal cord. These observations let us put the following hypothesis: c-Maf regulates p-cadherin expression in the sensory neurons and the interneurons to enable specific connections between these neurons. No identified factors were found to regulate c-Maf expression. In the second part of my study, I focused my efforts on the analysis of the role of MafA, c-MAf, Runx3 and Er81 transcription factors in neuronal plasticity induced in the adult mice three days after sciatic nerve axotomy. These factors are involved in the development of somatosensory neurons. The analysis showed that MafA and Er81 expression are down-regulated after peripheral nerve axotomy but the c-Maf and Runx3 expression did not change. We suggest that at adult stage the regulation of MafA and Er81 expression depend on neurotrophic factors released by the targets of these neurons but it's not the case for c-Maf and Runx3 expression.