RESUMEN
Brain-derived neurotrophic factor (BDNF) was shown to play a role in Schwann cell myelination by recruiting Par3 to the axon-glial interface, but the underlying mechanism has remained unclear. Here we report that Par3 regulates Rac1 activation by BDNF but not by NRG1-Type III in Schwann cells, although both ligands activate Rac1 in vivo. During development, active Rac1 signaling is localized to the axon-glial interface in Schwann cells by a Par3-dependent polarization mechanism. Knockdown of p75 and Par3 individually inhibits Rac1 activation, whereas constitutive activation of Rac1 disturbs the polarized activation of Rac1 in vivo. Polarized Rac1 activation is necessary for myelination as Par3 knockdown attenuates myelination in mouse sciatic nerves as well as in zebrafish. Specifically, Par3 knockdown in zebrafish disrupts proper alignment between the axon and Schwann cells without perturbing Schwann cell migration, suggesting that localized Rac1 activation at the axon-glial interface helps identify the initial wrapping sites. We therefore conclude that polarization of Rac1 activation is critical for myelination.
Asunto(s)
Factor Neurotrófico Derivado del Encéfalo/metabolismo , Proteínas Portadoras/metabolismo , Moléculas de Adhesión Celular/metabolismo , Vaina de Mielina/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Neuropéptidos/metabolismo , Células de Schwann/metabolismo , Transducción de Señal/fisiología , Proteínas de Pez Cebra/metabolismo , Pez Cebra/embriología , Proteínas de Unión al GTP rac/metabolismo , Proteína de Unión al GTP rac1/metabolismo , Proteínas Adaptadoras Transductoras de Señales , Animales , Axones/metabolismo , Factor Neurotrófico Derivado del Encéfalo/genética , Proteínas Portadoras/genética , Moléculas de Adhesión Celular/genética , Proteínas de Ciclo Celular , Movimiento Celular/fisiología , Células Cultivadas , Ratones , Proteínas del Tejido Nervioso/genética , Neuroglía/citología , Neuroglía/metabolismo , Neuropéptidos/genética , Ratas , Células de Schwann/citología , Pez Cebra/genética , Proteínas de Pez Cebra/genética , Proteínas de Unión al GTP rac/genética , Proteína de Unión al GTP rac1/genéticaRESUMEN
Squamous cell carcinoma (SCC) and premalignant endobronchial lesions have been difficult to study in murine models. In this study, we evaluate the topical N-nitroso-tris-chloroethylurea (NTCU) murine SCC model, determine the extent to which resulting premalignant airway dysplasia develops, discuss clinicopathologic grading criteria in lesion progression, and confirm that immunohistochemical (IHC) staining patterns are consistent with those observed in human endobronchial dysplasia and SCC. Male and female FVB mice were treated biweekly with topical NTCU (4, 8, or 40 mmol/L) or vehicle for 32 weeks. Following sacrifice, squamous cell lesions were enumerated and categorized into the following groups: flat atypia, low-grade dysplasia, high-grade dysplasia, and invasive SCC. The 40 mmol/L NTCU concentration produced the entire spectrum of premalignant dysplasias and squamous cell carcinomas, but was associated with poor survival. Concentrations of 4 and 8 mmol/L NTCU were better tolerated and produced only significant levels of flat atypia. Squamous origin of the range of observed lesions was confirmed with IHC staining for cytokeratin 5/6, p63, thyroid transcription factor-1 (TTF-1), and Napsin-A. This study shows that topical application of high-dose NTCU produces endobronchial premalignant lesions with classic squamous characteristics and should allow for improved preclinical evaluation of potential chemopreventive agents.