RESUMEN
The E2f7 and E2f8 family members are thought to function as transcriptional repressors important for the control of cell proliferation. Here, we have analyzed the consequences of inactivating E2f7 and E2f8 in mice and show that their individual loss had no significant effect on development. Their combined ablation, however, resulted in massive apoptosis and dilation of blood vessels, culminating in lethality by embryonic day E11.5. A deficiency in E2f7 and E2f8 led to an increase in E2f1 and p53, as well as in many stress-related genes. Homo- and heterodimers of E2F7 and E2F8 were found on target promoters, including E2f1. Importantly, loss of either E2f1 or p53 suppressed the massive apoptosis in double-mutant embryos. These results identify E2F7 and E2F8 as a unique repressive arm of the E2F transcriptional network that is critical for embryonic development and control of the E2F1-p53 apoptotic axis.
Asunto(s)
Supervivencia Celular/fisiología , Proteínas de Unión al ADN/fisiología , Factor de Transcripción E2F7/fisiología , Desarrollo Embrionario/fisiología , Proteínas Represoras/fisiología , Animales , Apoptosis/efectos de los fármacos , Camptotecina/farmacología , Supervivencia Celular/efectos de los fármacos , Supervivencia Celular/genética , Daño del ADN , Proteínas de Unión al ADN/deficiencia , Proteínas de Unión al ADN/genética , Dimerización , Factor de Transcripción E2F7/deficiencia , Factor de Transcripción E2F7/genética , Desarrollo Embrionario/efectos de los fármacos , Desarrollo Embrionario/genética , Ratones , Ratones Noqueados , Proteínas Represoras/genética , Transcripción Genética/efectos de los fármacosRESUMEN
Salt-dependent oligomerization of nucleosomal arrays is related to fiber-fiber interactions and global chromosome structure. Previous studies have shown that the H2A/H2B and H3/H4 N-terminal domain (NTD) pairs are able to mediate array oligomerization. However, because of technical barriers, the function(s) of the individual core histone NTDs have not been investigated. To address this question, all possible combinations of "tailless" nucleosomal arrays were assembled from native and NTD-deleted recombinant Xenopus core histones and tandemly repeated 5 S rDNA. The recombinant arrays were characterized by differential centrifugation over the range of 0-50 mm MgCl2 to determine how each NTD affects salt-dependent oligomerization. Results indicate that all core histone NTDs participate in the oligomerization process and that the NTDs function additively and independently. These observations provide direct biochemical evidence linking all four core histone NTDs to the assembly and maintenance of global chromatin structures.
Asunto(s)
Cromatina/química , Histonas/química , Nucleosomas/química , Animales , Centrifugación , Cromatina/genética , ADN/metabolismo , Proteínas Recombinantes , Cloruro de Sodio/farmacología , XenopusRESUMEN
The E2F transcription factor family plays a crucial and well established role in cell cycle progression. Deregulation of E2F activities in vivo leads to developmental defects and cancer. Based on current evidence in the field, mammalian E2Fs can be functionally categorized into either transcriptional activators (E2F1, E2F2, and E2F3a) or repressors (E2F3b, E2F4, E2F5, E2F6, and E2F7). We have identified a novel E2F family member, E2F8, which is conserved in mice and humans and has its counterpart in Arabidopsis thaliana (E2Ls). Interestingly, E2F7 and E2F8 share unique structural features that distinguish them from other mammalian E2F repressor members, including the presence of two distinct DNA-binding domains and the absence of DP-dimerization, retinoblastoma-binding, and transcriptional activation domains. Similar to E2F7, overexpression of E2F8 significantly slows down the proliferation of primary mouse embryonic fibroblasts. These observations, together with the fact that E2F7 and E2F8 can homodimerize and are expressed in the same adult tissues, suggest that they may have overlapping and perhaps synergistic roles in the control of cellular proliferation.
Asunto(s)
Proteínas de Ciclo Celular/química , Proteínas de Ciclo Celular/genética , Proliferación Celular , Clonación Molecular/métodos , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/genética , Factores de Transcripción/química , Factores de Transcripción/genética , Secuencia de Aminoácidos , Animales , Proteínas de Ciclo Celular/metabolismo , Proteínas de Ciclo Celular/fisiología , Células Cultivadas , Proteínas de Unión al ADN/metabolismo , Proteínas de Unión al ADN/fisiología , Dimerización , Factores de Transcripción E2F , Factor de Transcripción E2F1 , Factor de Transcripción E2F2 , Factor de Transcripción E2F4 , Factor de Transcripción E2F5 , Factor de Transcripción E2F6 , Factor de Transcripción E2F7 , Fibroblastos/citología , Fibroblastos/fisiología , Biblioteca de Genes , Humanos , Masculino , Ratones , Datos de Secuencia Molecular , Factores de Transcripción/metabolismo , Factores de Transcripción/fisiologíaRESUMEN
Explaining the determinants involved in regulating the equilibrium between different chromatin structural states is fundamental to understanding differential gene expression. Histone variant H2A.Z is essential to chromatin architecture in higher eukaryotes but its role has not yet been explained. We show here that H2A.Z facilitates the intramolecular folding of nucleosomal arrays while simultaneously inhibiting the formation of highly condensed structures that result from intermolecular association. This makes a case for H2A.Z playing a fundamental role in creating unique chromatin domains poised for transcriptional activation. These results provide new insights into understanding how chromatin fiber dynamics can be altered by core histone variants to potentially regulate genomic function.