RESUMO
Müller glia are normally mitotically quiescent cells, but in certain pathological states they can re-enter the mitotic cell cycle. While several cell cycle regulators have been shown to be important in this process, a role for the tumor suppressor, p53, has not been demonstrated. Here, we investigated a role for p53 in limiting the ability of Müller glia to proliferate in the mature mouse retina. Our data demonstrate that Müller glia undergo a developmental restriction in their potential to proliferate. Retinal explants or dissociated cultures treated with EGF become mitotically quiescent by the end of the second postnatal week. In contrast, Müller glia from adult trp53-/+ or trp53-/- mice displayed a greater ability to proliferate in response to EGF stimulation in vitro. The enhanced proliferative ability of trp53 deficient mice correlates with a decreased expression of the mitotic inhibitor Cdkn1a/p21(cip) and an increase in c-myc, a transcription factor that promotes cell cycle progression. These data show that p53 plays an essential role in limiting the potential of Müller glia to re-enter the mitotic cycle as the retina matures during postnatal development.
Assuntos
Proliferação de Células , Regulação da Expressão Gênica no Desenvolvimento/genética , Neuroglia/fisiologia , Retina/citologia , Retina/crescimento & desenvolvimento , Proteína Supressora de Tumor p53/metabolismo , Fator 3 Ativador da Transcrição/genética , Fator 3 Ativador da Transcrição/metabolismo , Fatores Etários , Animais , Animais Recém-Nascidos , Fatores de Transcrição Hélice-Alça-Hélice Básicos/genética , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Inibidor de Quinase Dependente de Ciclina p21/genética , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Fator de Crescimento Epidérmico/farmacologia , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Proteína Glial Fibrilar Ácida/metabolismo , Proteínas de Fluorescência Verde/genética , Proteínas Imediatamente Precoces/genética , Proteínas Imediatamente Precoces/metabolismo , Proteína 1 Inibidora de Diferenciação/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Neuroglia/efeitos dos fármacos , Técnicas de Cultura de Órgãos , RNA Mensageiro/metabolismo , Proteínas Repressoras/genética , Fatores de Tempo , Proteína Supressora de Tumor p53/deficiência , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismoRESUMO
The thymic medulla is generally held to be a specialized environment for negative selection. However, many self-reactive thymocytes first encounter ubiquitous self-antigens in the cortex. Cortical epithelial cells are vital for positive selection, but whether such cells can also promote negative selection is controversial. We used the HY(cd4) model, where T cell receptor for antigen (TCR) expression is appropriately timed and a ubiquitous self-antigen drives clonal deletion in male mice. We demonstrated unambiguously that this deletion event occurs in the thymic cortex. However, the kinetics in vivo indicated that apoptosis was activated asynchronously relative to TCR activation. We found that radioresistant antigen-presenting cells and, specifically, cortical epithelial cells do not efficiently induce apoptosis, although they do cause TCR activation. Rather, thymocytes undergoing clonal deletion were preferentially associated with rare CD11c(+) cortical dendritic cells, and elimination of such cells impaired deletion.