La transició epiteli-mesènquima (TEM) és un procés en què cèl lules epitelials, immòbils i amb polaritat apico-basal transiten cap un fenotip mesenquimal o fibroblàstic. L'expressió del factor de transcripció snail1 és suficient per induir TEM en cèl lules en cultiu i és necessari per la majoria de les TEM fisiològiques descrites. Snail1 és un membre de la família de proteïnes amb dits de Zinc que reprimeix gens epitelials (com l'E-cadherina) a través de la unió directa a seqüències especifiques dels promotors anomenades caixes E i posterior reclutament de corepressors. La TEM també es caracteritza per l'activació de gens mesenquimals, però el mecanisme pel qual snail1 indueix l'expressió d'aquests és poc conegut. En aquest treball demostrem que snail1 actua a nivell transcripcional per incrementar els nivells dels marcadors mesenquimals FN1 (fibronectina) i LEF1 (de l'anglès, lymphoid enhancer-binding factor 1) a través d'un mecanisme nou per aquesta proteïna de dits de Zn que no requereix ni caixes E ni unió directa a l'ADN. A més a més, mostrem que, per a dur a terme l'activació, snail1 coopera amb dos factors de transcripció ja descrits en relació a la TEM: beta-catenina i NF-kappa-B. Els nostres resultats també proven que l'expressió forçada de la E-cadherina evita aquesta cooperació i conseqüent activació gènica. A banda d'aquest mecanisme, també hem descrit que el factor de transcripció TFCP2c, que no havia estat prèviament relacionat amb TEM, és necessari per l'activació del gen FN1 induïda per snail1. / Epithelial-mesenchymal transition (EMT) is a cellular process by which no motile epithelial, apico-basal-polarized cells transit towards a motile mesenchymal front-backpolarized phenotype. Expression of the transcription factor snail1 is sufficient to induce EMT in cultured cells and it is required for most of the physiological EMTs described. Snail1 is a member of the Zn finger protein family that represses epithelial genes (such as E-cadherin) by directly binding to specific promoter sequences called E-boxes and subsequent recruitment of corepressors. EMT is also accompanied by activation of mesenchymal genes, however, little is known of how snail1 induces their expression.In this work we provide evidence that snail1 acts at the transcriptional level to increase the levels of the mesenchymal FN1 (fibronectin) and LEF1 (lymphoid enhancer-binding factor 1) genes through a novel mechanism for this Zn finger protein that does not require neither E-boxes nor direct binding to DNA. Furthermore, we describe a cooperative action in such mechanism between snail1 and two transcription factors previously related to EMT: beta-catenin and NF-kappaB. Our results also show that restoration of E-cadherin levels prevents such cooperation and subsequent activation. In addition, we also demonstrate that TFCP2c, which had not been previously linked to EMT, is also required for snail1-induced transcriptional activation of the FN1 gene.

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Retinoic acid (RA) is a well-known neurodevelopmental signaling molecule. It is reported to induce effects on neurite formation in differentiating neurons and to interfere with the actin cytoskeleton. Therefore, this project aimed to investigate the mechanisms behind effects of RA on the actin cytoskeleton of developing neurons using the C17.2 neural progenitor cells (NPCs) in vitro model. The goal was to evaluate the morphological effects the growth cone had upon exposure to RA agonist and antagonist, and to analyze the expression of three genes: Coronin actin-binding protein 1C(Coro1c), Cdc42 effector protein 4 gene (Cdc42), and Fibronectin (Fn1). These genes were selected because of their relation to actin dynamics and/or their regulation by the Wnt pathway, which regulates/affects actin reorganization. Since the Wnt pathway was also shown to be affected by RA, this study aimed to investigate the relationship between RA and actin through the Wnt pathway. Cdc42 and Fn1 are related to both the Wnt pathway and actin dynamics, whereas Coro1cis a known actin-related protein. The expressions showed significant increase with Coro1c, while Cdc42 and Fn1 had a similar overall trend increase with the RA agonist. The RA antagonist showed no significant effect, except a trend decrease in all the genetic expressions. All genetic expression effects subside with the increase of RA agonist and antagonist concentrations. The results suggest the changes in actin filaments are related to a low dose effect of RA. The findings indicate a possibility of a regulation mechanism that controls actin-related gene expression in response to RA. This mechanism is possibly not restricted to the Wnt pathway seeing that a non-Wnt related gene was affected as well.